A coordination chemistry dichotomy foricosahedral carborane-based ligandsAlexander M. Spokoyny, Charles W. Machan, Daniel J. Clingerman, Mari S. Rosen,

Michael J. Wiester, Robert D. Kennedy, Charlotte L. Stern, Amy A. Sarjeant and Chad A. Mirkin*

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune thesterics and electronics of coordinating moieties, we describe here how icosahedral carboranes—boron-rich clusters—caninfluence metal–ligand interactions. Using a series of phosphine–thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum–sulfur interaction of platinum(II)–thioether complexes. Experimental observations, supported by computational work, show that icosahedral carboranes canact either as strong electron-withdrawing ligands or electron-donating moieties (similar to aryl- or alkyl-based groups,respectively), depending on which atom of the carborane cage is attached to the thioether moiety. These and similarresults with carborane-selenol derivatives suggest that, in contrast to carbon-based ligands, icosahedral carboranes exhibita significant dichotomy in their coordination chemistry, and can be used as a versatile class of electronically tunablebuilding blocks for various ligand platforms.

Ligand design can be used to influence the chemical properties ofsmall molecules1, catalysts2, supramolecular assemblies3, sur-faces4 and nanomaterials5. Typically, the properties of ligands

are adjusted by the covalent attachment of electron-donating or-withdrawing groups to the heteroatom involved in metal bondingor through the use of groups that can influence reactivity basedupon relative degrees of steric bulk6. The majority of such prop-erty-adjusting groups have been carbon-based6,7, with a fewnotable exceptions in the area of silicon chemistry8–11. As ageneral rule, alkyl-based moieties are electron-donating6,7,11–14,and aryl-based ligands are considered more electron-withdraw-ing6,7,15. Often, aryl and alkyl moieties are used to change thesteric constraints or electronic properties of a ligand, but it is diffi-cult to do so without simultaneously affecting both the sterics andelectronics of a given ligand11–17. This is especially true if dramaticchanges in electronics are required (for example in converting aligand from very electron-donating to the other extreme). Ideally,one would like a moiety with the ability to adjust electron-donatingor -withdrawing properties without significantly affecting the stericproperties of the substituent.

Icosahedral carboranes are an interesting class of exceptionallystable boron-rich clusters that can be easily modified at differentvertices via straightforward chemical reactions18. Although thecoordination chemistry of carboranes has been extensively studiedover the past several decades18–31, no group has systematicallystudied how direct positional attachment of heteroatoms to carbor-anes affects the electronics of such substituents in the context oftheir corresponding metal-coordinating abilities. This is surprising,considering that the orthogonal chemical reactivity of CH and BHvertices of these clusters has been recognized for a long time18.These properties are best exemplified by the work of Hawthorneand co-workers, in which the Lewis acidic character of Hg(II)centres in mercurocarborand complexes was shown to be signifi-cantly altered depending on whether the Hg(II) was attached toboron (B9/10) or carbon vertices of m-carborane (SupplementaryFig. SI-1)20,21. This difference can be attributed to the three-

dimensional (3D) aromatic character of the C2B10H12 carboranecluster and the fact that the more electronegative carbon atoms con-tribute more electrons to cluster bonding than the boron atoms,which results in the carbon atoms effectively being electron-deficient (hence their electron-withdrawing character)18. These fea-tures can be experimentally observed from dipole measurements; inortho-carborane, for example, there is a net dipole moment of 4.45,which points away from two carbon vertices18. In this Article, wereport the discovery that icosahedral carboranes can be used as sub-stituents in phosphino–thioether hemilabile ligands where the pointof attachment of the sulfur to the carborane dictates the electronicproperties of the thioether without significantly affecting the stericproperties of the ligand.

We and others have been exploring the metal-binding propertiesof polydentate hemilabile ligands for the past two decades16,32–38.Specifically, we have shown how large supramolecular constructs,which mimic the properties of allosteric enzymes, can be assembledvia a novel coordination chemistry strategy, termed the ‘weak-linkapproach’ (WLA)32,36–38. By virtue of the hemilabile ligands usedto construct WLA complexes, small molecules can be used tochemically toggle them between flexible open and rigid closed archi-tectures32,36–38. This is achieved by reversible cleavage of weak M–Xbonds, while the stronger M–P bonds remain unchanged32,36–38. It istherefore crucial to be able to control the electronic nature of themetal-binding heteroatoms, and often it is desirable to do sowithout affecting steric considerations. In this Article, we showthat in the context of a hemilabile ligand, the coordination strengthof a carborane-functionalized thioether to Pt(II) can be significantlyaltered by means of the positional attachment of the heteroatom(specifically, sulfur) at different vertices of the boron-richcluster. From our experimental observations, which are supportedby computational work, we conclude that icosahedral carboranes,depending on the positional attachment of the sulfur moiety, canact either as strong electron-withdrawing (similar to fluorinatedaryl) or electron-donating moieties (alkyl-based, for example,1-adamantyl or tert-butyl). Additional work on carborane selenols

Department of Chemistry and the International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, lllinois 60208, USA.

*e-mail: chadnano@northwestern.edu

ARTICLESPUBLISHED ONLINE: 22 JULY 2011 | DOI: 10.1038/NCHEM.1088

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry590

© 2011 Macmillan Publishers Limited. All rights reserved.

mailto:chadnano@northwestern.eduhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

shows that this is probably a general characteristic of carboranes asheteroatom substituents. This dichotomous behaviour in coordi-nation chemistry is extremely unusual and may become a versatiletool for regulating the electronic properties of ligands withoutaltering sterics.

Results and discussionPhosphine–thioether (P,S) hemilabile ligands can be used to syn-thesize a wide variety of monoligated and bisligated Pt(II) complexesin high yield (Fig. 1a)38. These structures are ideal for studying thecoordination strength of the thioether moieties as a function of sub-stituents on the sulfur atom. Indeed, strongly electron-donatinggroups such as 2CH3 result in thioethers capable of displacing aCl2 ligand from the inner coordination sphere, while strongly elec-tron-withdrawing groups such as 2C6F4H yield structures in whichthe thioethers remain uncoordinated to the Pt(II) centre undersimilar reaction conditions38. In principle, therefore, one can useanalogues of these complexes in the context of hemilabile ligandscontaining icosahedral carboranes to probe their relative bindingstrengths. To test this hypothesis, we designed and synthesized aseries of new carborane-based (P,S) hemilabile ligands (1a–d) inwhich the point of attachment of the carborane cage to the thioetheris systematically varied (1a, 1c and 1b) (Fig, 1b). Ligand 1d, whichhas two methyl groups attached to the carbon atoms of the ortho-carborane cage, was used as a negative control to study the conse-quence of cage functionalization (because it provides a direct

comparison with 1c). These (P,S) chelate ligands 1a–d were syn-thesized from carborane thiols (I, II, III and V; Fig. 2 andSupplementary Information pp. 3–8) in good yields.

Plešek et al. made the original observation that ortho- and meta-carboranes (compounds I and III, respectively, Fig. 2) functionalizedwith thiols at the B9 position have an acidity that is �1 × 105 to 1 ×106 times lower than the corresponding carboranes functionalized onthe C1 atom (compound II, Fig. 2).39 Such differences in pKa are alsoobserved in the case of alkyl- and aryl-based thiols, with thelatter being more acidic39. This observation raises the question ofwhether or not one can construct ligands from icosahedral carboranesthat exhibit vastly different coordination chemistry simply basedupon the position of the heteroatom (S in this case) on thecarborane cage.

Others have studied the adsorption properties of I and II (Fig. 2)in the context of self-assembled monolayers (SAMs) on gold, butthese studies did not address ligating strength as a function ofheteroatom attachment to the carborane40,41. Additionally, Lyubimovet al. studied the catalytic properties of Rh(I) complexes of 2,2′-bis-(diphenylphosphino)-1,1′-bi-2-naphthol (BINOL)-based thiopho-sphite ligands, which are derivatives of I–III42. Although the het-eroatoms attached to the carborane moieties are not involved inmetal–ligand coordination in that work (the thiophosphites coordi-nate via phosphorus atoms), an enantioselectivity difference ofhydrogenated products was observed and proposed by the authorsto be the result of different electronic environments imposed bythe different carborane ligands. Finally, in contrast with some ofthese early observations about the electronic consequences of func-tionalization of the carborane cage, there have been several reportsin the recent literature that generalize icosahedral carboranes aselectron-withdrawing species43,44.

When one equivalent of ligand 1a is added to one equivalent ofPt(II) precursor (in all cases Pt(cod)Cl2; cod¼ 1,5-cyclooctadiene)in dichloromethane (CH2Cl2), the monochelate species 2a formsinstantaneously and quantitatively as determined by 31P{1H} NMRspectroscopy (Figs 3 and 4a). The spectrum of complex 2a exhibitsa singlet at d 41, which is diagnostic of ligand 1a chelating to thePt(II) centre (1JP-Pt¼ 3,625 Hz)38. Coordinatively similar structures2e–h are observed when 1-phosphinoethyl-2-thioalkyl (1e, 1f; seeSupplementary Information, pp. 7–8) and -aryl (1g, 1h; seeSupplementary Information, pp. 10–11) ligands are used instead of1a. 11B/11B{1H} NMR spectroscopy is a very useful technique withwhich to characterize carborane-based complexes such as 2a insolution, because upon metal coordination of the thioether moietyto the Pt(II) centre, the resonance corresponding to the B9 atomshifts approximately 4 ppm upfield (Fig. 4c).

When one equivalent of ligand 1b was added to the same Pt(II)precursor under conditions identical to those used for ligand 1a, thebis-phosphine adduct 2b was formed instead of a structure analo-gous to 2a with one equivalent of a chelating hemilabile ligand(Fig. 3). The 31P{1H} NMR spectrum of 2b shows a single resonanceat d 7 (1JP-Pt¼ 3,638 Hz), which is highly diagnostic of a complexwith two monodentate phosphine ligands bound in a cis

1e 1f 1h 1i

1c 1d 1a 1b

S0.184

Ph2P

S

Me

Me

0.188

Ph2P

S0.192

Ph2P

S0.385

Ph2P

S

Ph2P

0.248

Ph2P

S 0.262

1g

Ph2P

S

CH3

CH30.282

Ph2P

S 0.305

Ph2P

S

F

F

F

F0.335

b

a

Bisligatedopen

Bisligatedsemi-open

Bisligatedclosed

2+2X–

Ph2P S

Ph2P S

R

RPt

+X–

Ph2P

Ph2P

S

Cl

S R

RPt

Ph2P

Ph2P

Cl

Cl

S R

S R

Pt

Monoligated

Ph2P S

Cl Cl

RPt

Thioether–platinum interaction strength

BHCHCB

Figure 1 | Coordination chemistry and electronic characteristics of

phosphine–thioether (P,S) ligands. a, Coordination-based motifs derived

from various possible interactions of hemilabile (P,S) ligands with Pt(II).

b, Comparison of carbon-based and carborane-based ligands and

corresponding Mulliken charge densities on sulfur atoms associated with the

thioether moieties of the ligands.

SHSHSH SH

Me

Me

BHCHCB

I II III V

Figure 2 | Structures of the carborane thiols (I, II, III and V) used to

synthesize the (P,S) chelate ligands investigated in this study. The point of

attachment of the carborane to the sulfur atom is systematically altered.

NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088 ARTICLES

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry 591

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1chttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1chttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compVhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1fhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ghttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1hhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compIIIhttp://www.nature.com/compfinder/10.1038/nchem.1088_compVhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

configuration38,45. Consistent with this assignment, only half of thePt(cod)Cl2 precursor was consumed, which was confirmed by195Pt NMR spectroscopy (see Supplementary Information, p. 22).For 2b, a triplet at d 24,389 (1JPt-P¼ 3,638 Hz) is observed in the195Pt NMR spectrum46. A similar reactivity is observed when thefluorinated ligand 1i (Fig. 1b) is used with the Pt(II) precursorunder nearly identical reaction conditions38, which suggests thatthe S-functionalized carboranyl moiety in 1b acts as a strongly elec-tron-withdrawing substituent. This conclusion is reinforced bystudying the product of the reactions between 2a and 2b with anadditional equivalent of hemilabile ligand (1a and 1b), respectively.In particular, the addition of a second equivalent of ligand 1a tocomplex 2a (obtained in situ from Pt(cod)Cl2 and one equivalentof 1a) results in the formation of 3a (Fig. 3). Complex 3a has onehemilabile ligand chelating to the Pt(II) centre and another boundin monodentate fashion through the phosphine moiety. A Cl2

ligand that was originally bound to the Pt(II) centre in 2a hasbeen displaced to the outer coordination sphere to accommodatethe additional phosphine ligand. 31P{1H} NMR spectroscopy

shows that the hemilabile ligands in 3a are undergoing rapidexchange in a ‘windshield wiper’ motion involving the thioethersreplacing one another at room temperature in CD2Cl2 solution(Fig. 3 and Supplementary Information, p. 22)38. Consistent withthis conclusion, when the sample is cooled below 25 8C(Supplementary Information, p. 22), two sharp 31P{1H} NMR reso-nances at d 45 (1JP-Pt¼ 3,525 Hz) and d 10 (1JP-Pt¼ 3,255 Hz) areobserved for 3a, indicative of the semi-open complex. The downfieldresonance is assigned to the fully chelating (k2) (P,S) ligand and theupfield resonance is assigned to the k1-phosphine bound ligand andagrees well with literature analogues of isostructural complexes38,45.At temperatures below coalescence, one can also clearly observeresolved 2JP-P coupling: 13 Hz for the phosphine moiety of the(P,S) ligand chelated to Pt(II) and 14 Hz for the ligand bound ink1 fashion through the phosphine (Supplementary Information,p. 22). Bulky alkyl-based ligands (1e and 1f ) react with the Pt(II)precursor under nearly identical reaction conditions to yield com-plexes with coordination environments and fluxional behavioursimilar to compound 3a (Supplementary Information, pp. 11–13).

a +Cl–

S

Cl

Pt

S

Ph2P

Ph2PS

Cl ClPt

Ph2P

+Cl–

S

Cl

Pt

S

Ph2P

Ph2P

1aPt(cod)Cl2, 1 eq.

CD2Cl2, r.t.

2a

1a, 1 eq.

CD2Cl2, r.t.

3a

AgBF4, 2 eq.

CD2Cl2, r.t.

NaBArF, 1 eq.

CD2Cl2, r.t.

4a3a'

Ph2P

Ph2P

S

Cl

Pt

S

+BArF–

S

Cl

Pt

S

Ph2P

Ph2P

+BArF–

Ph2P

Ph2P

S

S

Pt

2+2BF4

–

b

Ph2P

Ph2P

Cl

ClPt

S

S

Ph2P

Ph2P

Ph2P

Ph2P

Ph2P

Cl

ClPt

S

S

S

Ph2P S

Pt

2+2BF4

–

4bNaBArF, 1 eq.

CD2Cl2, r.t.

S

Cl

Pt

S

+BArF–

3b

Pt(cod)Cl2, 1 eq.CD2Cl2, r.t.

1b

0.5 eq.

0.5 eq. Pt(cod)Cl2

0.5 eq. cod

+

+

1b, 1 eq.

CD2Cl2, r.t.

2b 2b

AgBF4, 2 eq.

CD2Cl2, r.t.

BHCHCB

Figure 3 | Synthetic scheme outlining the synthesis of Pt(II) complexes. a,b, Reactions involving ligands 1a (a) and 1b (b). All transformations are quantitative

as observed by in situ 31P and 31P{1H} NMR spectroscopy. Full details on synthesis and characterization can be found in the Supplementary Information.

ARTICLES NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry592

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1fhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

In contrast, when two equivalents of 1b are added to Pt(cod)Cl2,one observes the exclusive formation of the fully open non-chelatedcomplex 2b, with concomitant consumption of the Pt(II) precursor(no Pt(cod)Cl2 was observed in the

195Pt NMR spectrum). Thisobservation is consistent with the conclusion that ligand 1a is aweaker chelating ligand than 1b.

Additional evidence in support of the proposed dichotomy incoordination-based chemistry for this novel class of carborane-based

hemilabile ligands comes from studying the fluxional behaviour of3b (Fig. 3), the product formed from abstracting a single Cl2

ligand from 2b with one equivalent of NaBArF (BArF¼ tetra-kis[(3,5-trifluoromethyl)phenyl]borate) and comparing it to theBArF2 salt of 3a, 3a′, formed by metathesis with NaBArF(Fig. 3). Although 3a′ still exhibits the fluxionality of 3a, as observedby 31P{1H} NMR spectroscopy (Fig. 4a and SupplementaryInformation, p. 14), semi-open complex 3b (measured from

a b c

80 60 40 20 0 –20

42.5 ppm 10.0 ppm31P

31P

31P

31P{1H} 31P{1H}

31P{1H}

4b

3b

2b

1b

ppm

1:1

10 5 0 –5 –10 –15 –20 –25 ppm

11BF4–

11B{1H}

11B{1H}

11B

11B

11B

11B

11BArF–

11B9-S1a

1a

2a

2a

3a'

4a

020 –20 ppm406080

4546

4a31P

31P

31P

31P{1H}

31P{1H}31P{1H}

3a'

2a

1a

ppm 1011 ppm

Figure 4 | Characterization of the ligands. a–c, Representative 31P/31P{1H} NMR spectra of complexes with ligand 1a (a), ligand 1b (b) and 11B/11B{1H} NMRdata highlighting changes associated with the transformations involving ligand 1a (c). As B9 is the only substituted boron atom in the carborane cluster,

it does not exhibit B–H coupling and can therefore be easily distinguished from other resonances assigned to other boron atoms of the carborane cage.

4a 4b

4c

PtP1

S1

S2P2

PtP1

S1

S2P2

PtP1

S1

S2P2

PtP1 S1

S2P2

4d

Figure 5 | Crystallographically derived X-ray structure representations of closed carborane-based Pt(II) complexes 4a–4d. Solvent molecules and anions

are omitted for clarity. Atom colour code: pale red, B; grey, C; blue, P; black, Pt; white, H. Full details on crystallographic refinement can be found in

Supplementary Section 3. (CCDC no. 824088–824091.)

NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088 ARTICLES

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry 593

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4dhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

250 8C to 30 8C) is locked into a more static state. Indeed, its31P{1H} NMR spectrum exhibits two well-resolved resonances at d42 (1JP-Pt¼ 3,452 Hz; 2JP-P¼ 14 Hz) and d 10 (1JP-Pt¼ 3,365 Hz;2JP-P¼ 14 Hz), assigned to the two magnetically inequivalent Patoms (Fig. 4b). Thus, the behaviour of 3a′ clearly resembles thebehaviour of complexes formed from bulky alkyl-based ligand 3e′,while the behaviour of 3b tracks the behaviour of the fluorinatedligand 1i in the analogous complex 3i (SupplementaryInformation, pp. 15–16).

It is also well established that 1JP-Pt values for square planar Pt(II)complexes are sensitive to the influence of the trans substituent (thatis, the stronger the trans influence, the lower the observed corre-sponding coupling value)45,47. Indeed, the value of 1JP-Pt for thenon-chelated phosphine ligand (trans to the coordinated thioether)in 3a′ is �140 Hz greater than for the analogous non-chelated phos-phine in 3b. These phosphines are trans to the sulfur atom with thecovalently attached carborane, and their 1JP-Pt values reflect the rela-tive electron-donating or -withdrawing characteristics of the carbor-anyl moiety on the sulfur atom. The magnitude of this differencein the value of 1JP-Pt splitting (�180 Hz) is comparable to thesemi-open complexes with ligands 1e and 1i, respectively(Supplementary Information, pp. 15–16).

Complete abstraction of both chlorides from complexes 3a and2b can be accomplished by adding two equivalents of AgBF4. Thisleads to the formation of 4a and 4b, respectively, as can be observedby 11B{1H} and 31P{1H} NMR spectroscopies as well as othercharacterization methods (Figs 3, 4 and SupplementaryInformation, pp. 16–17). Both of these complexes exhibit a well-

resolved 31P{1H} NMR spectrum with a singlet at d 48 (1JP-Pt¼3,135 Hz) and d 43 (1JP-Pt¼ 3,207 Hz) for 4a and 4b, respectively.Similarly to the above-mentioned correlation between the transeffect of the thioether and the 1JP-Pt value, we observed a 70 Hzdifference, indicating that the thioether moiety in 4a exhibits asmaller trans effect than in 4b. Single-crystal X-ray diffractionstudies of 4a and 4b further corroborate the effect of the thioethertrans influence (Fig. 5), where the S–Pt bond length in 4a is0.04 Å shorter than in 4b.

Density functional theory (DFT) calculations on the geometry-optimized structures of ligands 1a–i provide a clear account of theobserved coordination behaviour. Mulliken charge density distri-butions at the sulfur atoms of these ligands (Fig. 1 andSupplementary Section 4) show that the sulfur atoms in B9-functio-nalized carboranes are significantly more electron-rich than those ofthe C1-functionalized analogue 1b. Moreover, these values suggestthat the thioether in 1b is more electron-poor than in the fluori-nated analogue 1i, whereas the same moieties in 1a, 1c and 1d aremore electron-rich than in the bulky alkyl-based ligands 1e and1f. For all of the ligands 1a–i, calculated Mulliken charges on thephosphorus atoms remain nearly identical, signifying that theethyl spacer between the thioether and phosphine moietiesscreens any potential electronic influence. According to these calcu-lations, ligands 1c and 1d should exhibit a qualitatively similarcoordination strength at their thioether moieties to ligand 1a.This was confirmed through a series of experiments under identicalconditions to that of 1a shown in Fig. 3 (Supplementary Sections 1–2).The introduction of two methyl groups on the o-carborane (ligand1d, Fig. 1) had minimal effect on the coordination chemistryobserved, suggesting that functionalization via this route canretain both the steric and electronic parameters of this system andprovide a strategy for orthogonal ligand functionalization.Furthermore, our studies indicate that 1a acts as an electron-donat-ing ligand in the halide-induced ligand rearrangement reaction(HILR) when paired with an electron-withdrawing ligand 1i(Supplementary Information, pp. 19–20)38.

Driven by the temptation to suggest that the observed phenom-ena are general with respect to other heteroatoms, we synthesizedtwo carborane selenol derivatives (5a and 5b), which allowed usto probe directly the electronic environment of the heteroatomnuclei (selenium) via 77Se/77Se{1H} NMR spectroscopy(Supplementary Information, pp. 20–21). Strikingly, the 77Se{1H}NMR spectrum of the C-functionalized m-carborane selenol 5b(Fig. 6) exhibits a resonance very far downfield at d 347 inCD2Cl2. As a point of reference, the

77Se NMR spectrum ofCF3SeH, perhaps the most electron-withdrawing carbon-basedselenol derivative, exhibits a resonance at d 287 (ref. 48). In contrast,the B9-functionalized m-carborane selenol 5a exhibits an extremelyupfield resonance at d 2280, which appears as a quartet due tocoupling to the adjacent 11B nuclei (S¼ 3/2). Thisresonance indicates that the electron-donating B9-functionalizedm-carborane cage is far more shielding than any known alkyl-based substituent. Indeed, theoretical calculations of Mullikencharges (0.038 for Se in 5a and 0.270 in 5b) and 77Se NMR shieldingconstants support these experimental observations (SupplementarySection 4). Although a shift difference of �625 ppm is virtuallyunattainable with the same carbon-based substituent, one singlecarborane-based moiety (m-carborane) can successfully serve asan extremely electron-withdrawing or extremely electron-donating moiety.

ConclusionsOur work suggests that a thioether moiety attached to different ver-tices of icosahedral carboranes can experience either a strongly elec-tron-withdrawing (similar to fluorinated aryls) or strongly electron-donating (similar to electron-donating bulky alkyls) influence. This

a

b

c

m-Carborane

SeH

SeH

5a

5b

i

ii

200 –200 –400 ppm

ppm–278

0

77Se{1H} NMRof 5a

5aB9

Se

348

77SeNMRof 5b

400 200 0

5b C1

Seppm

347 ppm

Figure 6 | Studies of carborane-selenol derivatives. a, Synthetic scheme

and conditions: (i) Se2Cl2, CH2Cl2, AlCl3, aqueous work-up followed by

reduction w. NaBH4 in EtOH; (ii) n-BuLi, diethyl ether, 0 8C to roomtemperature, then elemental Se. b,c, Representative 77Se/77Se{1H} NMRspectra of meta-carborane selenol derivatives 5a and 5b and their

computational models, respectively.

ARTICLES NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry594

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3eprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3eprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3aprimehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp3ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp2bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp4bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1chttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ehttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1fhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1chttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1dhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp1ihttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5bhttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5ahttp://www.nature.com/compfinder/10.1038/nchem.1088_comp5bhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

dichotomy is an intrinsic property of the carborane moiety, and thusone can envision that many heteroatoms attached in a fashionsimilar to sulfur can be tuned in such a manner. This conclusionis supported by the unprecedented difference in the 77Se NMRchemical shifts obtained for B9 and C1-functionalized meta-carbor-ane selenols. This also suggests that referring to a carborane (or car-boranyl) moiety solely as electron-withdrawing, without specifyingits point of attachment, is not rigorously correct43,44. Nevertheless,applications of this concept may not be limited only to the tuningof hemilability detailed here. For example, C-functionalized carbor-ane-based phosphines are known, and their coordination chemistryqualitatively resembles the properties of aryl-based analogues49. Ifsynthetic routes towards B-functionalized carborane phosphinescan be established, one may obtain electron-rich phosphines withsignificant steric bulk, which may be non-flammable and chemicallyinert13,17. Very recently, Hawthorne and co-workers reported apromising route for accessing B-functionalized carboraneamines50, which, if used as ligands, can potentially provide a stra-tegic avenue towards many interesting low-coordinate transition-and lanthanide-metal complexes.11,12 Moreover, B9-functionalizedselenols may serve as interesting model ligands for SAMs on goldand other metals4, because selenols have been predicted to havehigher binding affinities for noble metal surfaces4. Overall, giventhat icosahedral carboranes are extremely robust and relativelyinexpensive (Supplementary Information, p. 1), these and manyother features associated with using them as building blocks tomodulate heteroatom–metal interactions can complement existingapproaches in ligand design via conventional carbon-based substituents.

Received 17 March 2011; accepted 10 June 2011;published online 22 July 2011

References1. Zhao, H. & Gabbaı̈, F. P. A bidentate Lewis acid with a telluronium ion as an

anion-binding site. Nature Chem. 2, 984–990 (2010).2. Trnka, T. M. & Grubbs, R. H. The development of L2X2Ru¼CHR olefin

metathesis catalysts: an organometallic success story. Acc. Chem. Res. 34,18–29 (2001).

3. Olenyuk, B., Whiteford, J. A., Fechtenkötter, A. & Stang, P. J. Self-assemblyof nanoscale cuboctahedra by coordination chemistry. Nature 398,796–799 (1999).

4. Yaliraki, S. N., Kemp, M. & Ratner, M. A. Conductance of molecular wires:influence of molecule–electrode binding. J. Am. Chem. Soc. 121,3428–3434 (1999).

5. Park, S. Y. et al. DNA-programmable nanoparticle crystallization. Nature 451,553–556 (2008).

6. Crabtree, R. H. The Organometallic Chemistry of the Transition Metals 3rd edn(Wiley, 2001).

7. Tolman, C. A. Steric effects of phosphorus ligands in organometallic chemistryand homogeneous catalysis. Chem. Rev. 77, 313–348 (1977).

8. Bonasia, P. J., Christou, V. & Arnold, J. Alkyl-, silyl-, and germyl-substitutedthiolate, selenolate, and tellurolate derivatives and interconversion of silyl speciesby chalcogen metathesis. J. Am. Chem. Soc. 115, 6777–6781 (1993).

9. Duchateau, R. Incompletely condensed silsesquioxanes: versatile tools indeveloping silica-supported olefin polymerization catalysts. Chem. Rev. 102,3525–3542 (2002).

10. Mintcheva, N., Tanabe, M. & Osakada, K. Synthesis and characterization ofplatinasilsesquioxane complexes and their reaction with arylboronic acid.Organometallics 30, 187–190 (2011).

11. Wolczanski, P. T. Structure and reactivity studies of transition metals ligated bytBuSi3X (X¼O, NH, N, S, and CC). Chem. Commun. 740–757 (2009).

12. Diaconescu, P. L. Reactions of aromatic N-heterocycles with d0fn-metal alkylcomplexes supported by chelating diamide ligands. Acc. Chem. Res. 43,1352–1363 (2010).

13. Surry, D. S. & Buchwald, S. L. Biaryl phosphane ligands in palladium-catalyzedamination. Angew. Chem. Int. Ed. 47, 6338–6361 (2008).

14. Back, O., Donnadieu, B., Parameswaran, P., Frenking, G. & Bertrand, G.Isolation of crystalline carbene-stabilized P2-radical cations and P2-dications.Nature Chem. 2, 369–373 (2010).

15. Casey, C. P. et al. Electron withdrawing substituents on equatorial and apicalphosphines have opposite effects on the regioselectivity of rhodium catalyzedhydroformylation. J. Am. Chem. Soc. 119, 11817–11825 (1997).

16. Gunanathan, C., Ben-David, Y. & Milstein, D. Direct synthesis of amides fromalcohols and amines with liberation of H2. Science 317, 790–792 (2007).

17. Welch, G. C., San Juan, R. R., Masuda, J. D. & Stephan, D. W. Reversible,metal-free hydrogen activation. Science 314, 1124–1126 (2006).

18. Grimes, R. N. Carboranes 2nd edn (Elsevier, 2011).19. Hawthorne, M. F. et al. Electrical or photocontrol of the rotary motion of a

metallacarborane. Science 303, 1849–1851 (2004).20. Zheng, Z., Diaz, M., Knobler, C. B. & Hawthorne, M. F. A mercuraborand

characterized by B–Hg–B bonds: synthesis and structure of cyclo-[(t-BuMe2Si)2C2B10H8Hg]3. J. Am. Chem. Soc. 117, 12338–12339 (1995).

21. Hawthorne, M. F. & Zheng, Z. Recognition of electron-donating guests bycarborane-supported multidentate macrocyclic Lewis acid hosts:mercuracarborand chemistry. Acc. Chem. Res. 30, 267–276 (1997).

22. Crowther, D. J., Baenziger, N. C. & Jordan, R. F. Group 4 metal dicarbollidechemistry. Synthesis, structures and reactivity of electrophilic alkylcomplexes (Cp*)(C2B9H11)M(R), M¼Hf, Zr. J. Am. Chem. Soc. 113,1455–1457 (1991).

23. Viñas, C., Núñez, R., Teixidor, F., Kivekäs, R. & Sillanpää R. Versatility of nido-monophosphinocarboranes as ligands. Tricoordination via PPh2 and BH inrhodium(I) complexes. Organometallics 17, 2376–2378 (1998).

24. Olejniczak, A. B., Mucha, P., Grüner, B. & Lesnikowski, Z. J. DNA-dinucleotidesbearing a 3′ ,3′-cobalt- or 3′ ,3′-iron-1,2,1′ ,2′-dicarbollide complex.Organometallics 26, 3272–3274 (2007).

25. Rosair, G. M., Welch, A. J. & Weller, A. S. Sterically encumbered, charge-compensated metallacarboranes. Synthesis and structures of rutheniumpentamethylcyclopentadienyl derivatives. Organometallics 17,3227–3235 (1998).

26. Mueller, J., Base, K., Magnera, T. F. & Michl, J. Rigid-rod oligo-p-carboranes formolecular tinkertoys. An inorganic Langmuir–Blodgett film with afunctionalized outer surface. J. Am. Chem. Soc. 114, 9721–9722 (1992).

27. Batsanov, A. S. et al. Sulfur, tin and gold derivatives of 1-(2′-pyridyl)-ortho-carborane, 1-R-2-X-1,2-C2B10H10 (R¼2′-pyridyl, X¼SH, SnMe3 or AuPPh3).Dalton Trans. 3822–3828 (2004).

28. Saxena, A. K. & Hosmane, N. S. Recent advances in the chemistry of carboranemetal complexes incorporating d- and f-block elements. Chem. Rev. 93,1081–1124 (1993).

29. Jin, G.-X. Advances in the chemistry of organometallic complexes with1,2-dichalcogenolato o-carborane ligands. Coord. Chem. Rev. 248,587–602 (2004).

30. Spokoyny, A. M. et al. Carborane-based pincers: synthesis and structure of SeBSeand SBS Pd(II) complexes. J. Am. Chem. Soc. 131, 9482–9483 (2009).

31. van der Vlugt, J. I. Boryl-based pincer systems: new avenues in boron chemistry.Angew. Chem. Int. Ed. 49, 252–255 (2010).

32. Farrell, J. R., Mirkin, C. A., Guzei, I. A., Liable-Sands, L. M. & Rheingold, A. L.The weak-link approach to the synthesis of inorganic macrocycles. Angew.Chem. Int. Ed. 37, 465–467 (1998).

33. Jeffrey, J. C. & Rauchfuss, T. B. Metal complexes of hemilabile ligands. Reactivityand structure of dichlorobis(o-(diphenilphosphino)anisole)ruthenium(II). Inorg.Chem. 18, 2658–2666 (1979).

34. Moxman, G. L. et al. Second-generation catalyst for intermolecularhydroacylation of alkenes and alkynes using b-S-substituted aldehydes:the role of a hemilabile P–O–P ligand. Angew. Chem. Int. Ed. 45,7618–7622 (2006).

35. Lindner, R., van der Bosch, B., Lutz, M., Reek, J. N. H. & van der Vlugt, J. I.Tunable hemilabile ligands for adaptive transition metal complexes.Organometallics 30, 499–510 (2011).

36. Gianneschi, N. C. et al. A supramolecular approach to an allosteric catalyst.J. Am. Chem. Soc. 125, 10508–10509 (2003).

37. Yoon, H. J., Kuwabara, J., Kim, J.-H., & Mirkin, C. A. Allosteric supramoleculartriple-layer catalysts. Science 330, 66–69 (2010).

38. Rosen, M. S. et al. The chelating effect as a driving force for the selectiveformation of heteroligated Pt(II) complexes with bidentate phosphino-chalcoether ligands. Inorg. Chem. 50, 1411–1419 (2011).

39. Plešek, J., Heřmánek, S. & Štı́br, B. Electron-transfer phenomena in isolatedicosahedral borane units. J. Less Common Met. 67, 225–228 (1979).

40. Baše, T. et al. Carboranethiol-modified gold surfaces. A study and comparison ofmodified cluster and flat surfaces. Langmuir 21, 7776–7785 (2005).

41. Hohman, J. N. et al. Self-assembly of carboranethiol isomers on Au{111}:intermolecular interactions determined by molecular dipole orientations. ACSNano 3, 527–536 (2009).

42. Lyubimov, S. E. et al. Chiral carborane-derived thiophosphites: a new generationof ligands for Rh-catalyzed asymmetric hydrogenation. J. Organomet. Chem.693, 3689–3691 (2008).

43. Tsuboya, N. et al. Nonlinear optical properties of novel carborane-ferroceneconjugated dyads. Electron-withdrawing characteristics of carboranes. J. Mater.Chem. 12, 2701–2705 (2002).

44. Fabre, B., Clark, J. C. & Vicente, M. G. H. Synthesis and electrochemistry ofcarboranylpyrroles. Towards preparation of electrochemically and thermallyresistant conjugated polymers. Macromolecules 39, 112–119 (2006).

NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088 ARTICLES

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry 595

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

45. Garrou, P. E. DR ring contributions to31P NMR parameters of transition-metal–

phosphorus chelate complexes. Chem. Rev. 81, 229–266 (1981).46. Cobley, C. J. & Pringle, P. G. Probing the bonding of phosphines and phosphites

to platinum by NMR. Correlations of 1J(PtP) and Hammett substituentconstants for phosphites and phosphines coordinated to platinum(II) andplatinum(0). Inorg. Chim. Acta 265, 107–115 (1997).

47. Hassan, F. S. M., McEwan, D. M., Pringle, P. G. & Shaw, B. L. Synthetic andnuclear magnetic resonance studies on dialkyl- and diarylplatinum complexescontaining chelating, monodentate, or bridging Ph2PCH2PPh2 ligands. J. Chem.Soc. Dalton Trans. 1501–1506 (1985).

48. Patai, S. & Rappoport, Z. (eds) The Chemistry of Organic Selenium and TelluriumCompounds Vol. 1 (John Wiley & Sons, 1986).

49. Maulana, I., Lonnecke, P. & Hey-Hawkins, E. Platinum(II) and palladium(II)complexes of chiral P–Cl functionalized bis-phosphino ortho-carboranes. Inorg.Chem. 48, 8638–8645 (2009).

50. Sevryugina, Y., Julius, R. L. & Hawthorne, M. F. Novel approach toaminocarboranes by mild amidation of selected iodo-carboranes. Inorg. Chem.49, 10627–10634 (2010).

AcknowledgementsThis research was supported by the National Science Foundation (NSF), the Army ResearchOffice (ARO), the Defense Threat Reduction Agency (DTRA), and the Air Force Office of

Scientific Research (AFOSR) (through a Multidisciplinary University Research Initiative(MURI) award). A.M.S. is grateful to the Department of Education for a GraduateAssistance in Areas of National Need (GAANN) Fellowship, and Northwestern Universityfor a Presidential Fellowship. The authors thank the Northwestern University IntegratedMolecular Structure Education and Research Center (IMSERC) staff for providinginvaluable assistance with analytical instrumentation.

Author contributionsA.M.S. originated and developed the concept with C.A.M., who supervised and guided theresearch. All experiments were designed and performed by A.M.S., C.W.M., D.J.C., M.S.R.,M.J.W. and R.D.K. A.M.S. and C.W.M. performed all computational studies. C.L.S., A.A.S.and R.D.K. performed all crystallographic studies. A.M.S. and C.A.M. co-wrote themanuscript. All authors discussed the results and commented on the manuscript duringits preparation.

Additional informationThe authors declare no competing financial interests. Supplementary informationand chemical compound information accompany this paper at www.nature.com/naturechemistry. Reprints and permission information is available online athttp://www.nature.com/reprints. Correspondence and requests for materials should beaddressed to C.A.M.

ARTICLES NATURE CHEMISTRY DOI: 10.1038/NCHEM.1088

NATURE CHEMISTRY | VOL 3 | AUGUST 2011 | www.nature.com/naturechemistry596

© 2011 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/sifinder/10.1038/nchem.1088http://www.nature.com/cifinder/10.1038/nchem.1088www.nature.com/naturechemistrywww.nature.com/naturechemistryhttp://www.nature.com/reprintsmailto:chadnano@northwestern.eduhttp://www.nature.com/doifinder/10.1038/nchem.1088www.nature.com/naturechemistry

A coordination chemistry dichotomy for icosahedral carborane-based ligandsResults and discussionConclusionsFigure 1 Coordination chemistry and electronic characteristics of phosphine–thioether (P,S) ligands.Figure 2 Structures of the carborane thiols (I, II, III and V) used to synthesize the (P,S) chelate ligands investigated in this study.Figure 3 Synthetic scheme outlining the synthesis of Pt(II) complexes.Figure 4 Characterization of the ligands.Figure 5 Crystallographically derived X-ray structure representations of closed carborane-based Pt(II) complexes 4a–4d.Figure 6 Studies of carborane-selenol derivatives.ReferencesAcknowledgementsAuthor contributionsAdditional information

/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 150 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 450 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.00000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 2400 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.00000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck true /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError false /PDFXTrimBoxToMediaBoxOffset [ 35.29000 35.29000 36.28000 36.28000 ] /PDFXSetBleedBoxToMediaBox false /PDFXBleedBoxToTrimBoxOffset [ 8.50000 8.50000 8.50000 8.50000 ] /PDFXOutputIntentProfile (OFCOM_PO_P1_F60) /PDFXOutputConditionIdentifier () /PDFXOutputCondition (OFCOM_PO_P1_F60) /PDFXRegistryName () /PDFXTrapped /False

/SyntheticBoldness 1.000000 /Description >>> setdistillerparams> setpagedevice