Synthesis, Characterization and Reactivity of a Series of Ruthenium Acetylide Complexes

Jason F. Hill Jason F. Hill and Cliff J. Timpsonand Cliff J. TimpsonRoger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809Roger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809

AbstractMetal complexes based on ruthenium have enjoyed considerable attention due to the ability to extensively manipulate both the electrochemical and the photophysical properties of the complexes by varying substituents on the ligands. Recently, we have become interested in producing metal complexes of the type trans-[ClRu(dppm)2CCPh-4-Y] where Y is -NO2, -H, and -OCH3 in order to quantify the influence the Y substituent has on the metal-based redox potential and it’s ability to labilize the trans- chloride ligand in the presence of Tl+ ion. Following modified procedures of McDonagh et al. for the synthesis of acetylide complexes, we have been able to synthesis trans-[ClRu(dppm)2CCPh-4-H] and trans-[ClRu(dppm)2CCPh-4-OCH3] in good yield. Our efforts to synthesis, purify, and characterize these complexes, along with preliminary kinetic studies of the chloride abstraction reactions will be presented.

Methods and MaterialsRuthenium acetylide complexes were prepared following modified procedures of McDonagh et al.5 Spectroscopic grade solvents (Aldrich) and reagents (Aldrich) were obtained commercially and used as supplied. All synthetic reactions were conducted under argon atmosphere and products purified by column chromatography using basic alumina (Aldrich) and eluting with dichloromethane. Rate reactions were carried out in a 100:1 molar ratio thallium ion to ruthenium acetylide complex and monitored via cyclic voltammetry using a Bio-Analytical Systems (BAS) CV-50W equipped with 2mm Pt disk working electrode and Pt wire auxiliary electrode. All cyclic voltammetric measurements were obtained in 0.1M TBAH/CH3CN at a scan rate of 200mV/s and reported verses a Ag+/AgCl reference electrode. UV-Vis spectra were collected on a Hewlett-Packard HP-8453 Diode Array spectrophotometer. Infrared data was collected on a Perkin-Elmer 1600 series FT-IR.

AcknowledgmentsFinancial support for travel form RWU Provost-Sponsored Student Scholarship Research AwardFinancial supports for chemical and lab supplies from RWU Committee for Undergraduate ResearchMr. David Futoma (RWU adjunct faculty) for his time and help in labDr. Stephen O’Shea for his time and help running NMR dataMrs. Lyndsey Medeiros (RWU ‘06) for her assistance in labRWU Facilities and Stockroom Personnel

References1. Balzani, V; Scandola, F. Supermolecular Photochemistry; Wiley, Chinchester, UK, 1991.2. Fischetti, L; Gordon, M; Reardon, M; Timpson, C.J. “Impact of Substituents on the Metal-based Redox Potential for a Series of Complexes Based on trans-[Cl(pyridine)4Ru-L]+ where L is a Para-substituted Derivative of Cyanobenzene” Poster at ACS Meeting Anaheim Spring 2004. 3. Kuber, A; Nandor, H; Hira, S; Petricko, R; Von Riesen, D; Timpson, C. J. “In-Situ Generation of Trans- [Ru(pyridine)4(L)(Solvent)]2+ Obtained by Cl- Abstraction from trans-[Ru(pyridine)4(L)Cl]+” Poster at ACS Meeting San Diego Spring 2001. 4. McGrady, J.E.; Lovell. T.; Stranger, R.;Humphrey, M.G. Organometallics 1997, 16, 4004. 5. McDonagh, A.M.; Deeble, G.J.; Hurst, S.; Cifuentes, M.P.; Humphrey, M.G. J Chem. Ed. 2001, 78, 232.6. Carol, F.A. Perspectives on Structure and Mechanism in Organic Chemistry. First ed. Brooks Cole: 1997: 384.

IntroductionOur group has been interested in exploring metal complexes of ruthenium where a halide ligand is formally trans to a ligand which may be synthetically altered to prepare oligomeric metal complexes.1-3 Previous efforts in our group have explored the possibility of removing the halide in the complex [Ru(pyridine)4(L)Cl]+ (where L is cyano benzene, n-cyano alkanes, and substituted pyridine derivatives.) via Tl+ or Ag+ assisted loss of the chloride ligand.2,3 These attempts generally resulted in either no-reaction of the complexes on reasonable timescales or in decomposition of the complexes when the reactions were heated. Qualitative attempts to model these complexes with HyperChem® supported significant charge on the metal center hindering loss of the chloride ligand.2-4 In contrast however, we report here our successful attempts to remove the chloride ligand with Tl+ ion in complexes of the type trans- [ClRu(dppm)2(CCPh-4-Y)] where dppm = diphenylphosphinomethane and CCPh is a phenylacetylide derivative substituted in the 4-position with Y = H, NO2 and OCH3 .

Spectroscopic and Electrochemical Data

Synthetic Scheme

OHNH2

Cl

CH3

H

BrCHO

NH2 OH l

CH3

H

BrCHO

Reaction of trans-[ClRu(dppm)2CCPh]with Tl+ followed via Cyclic Voltammetry

Electron Withdrawing Effects of Acetylide Substituent

Substituent IR UV-Vis E ½ V

. -Y (KBr) v/cm-1 ( acetonitrile nm) V Ag-AgCl

OCH3 (C≡C) 2075 273 0.32

288

H (C≡C) 2072 309 0.41

268

NO2 (C≡C) 2045 471 0.60

267

Dependence of Relative Rate Constant on E1/2

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RuCl3

DMSO

RuDMSO

DMSO Cl

Cl

DMSO

DMSO

Ph2P PPh2

PPh2

PPh2Ph2P

CClHC Y

Ph2P

Ru

NEt3

PPh2

PPh2Ph2P

CCl C Y

Ph2P

Ru

PF6-

Ru

Ph2P

Ph2P Cl

Cl

PPh2

PPh2

CH2Cl2, reflux 35 min

Ph2P

Ru

PPH2

PPh2Ph2P

CCl C YTlPF6

CH3CN

Ph2P

Ru

PPH2

PPh2Ph2P

CH3CCN C YPF6

-

Heat-30minArgon gas

Excess acetoneFreeze 24 hrs.

toluene,reflux,35 min.

HCCPh-4-Y / NH4PF6

+

CH2Cl2, 5 min

Y = OCH3

H

NO2

Abstraction of Chloride Reaction

+

+ TlCl

cis-

trans-

trans-

NO2

H

OCH3

0.25

0.35

0.45

0.55

0.65

-0.4 -0.2 0 0.2 0.4 0.6 0.8 1

σρ

E 1/2

V v

Ag

/Ag

Cl

.

OCH3

H

NO2

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

0.2 0.3 0.4 0.5 0.6 0.7

E1/2 V v Ag/AgCl

k rel

s-1