NMRNMR NNuclear M Magnetic RResonance

NMR for Organometallic compoundsNMR for Organometallic compounds

Index NMR-basicsNMR-basics H-NMRH-NMR NMR-SymmetryNMR-Symmetry Heteronuclear-NMRHeteronuclear-NMR

Dynamic-NMRDynamic-NMR NMR and Organometallic compoundsNMR and Organometallic compounds

NMR in Organometallic compoundsNMR in Organometallic compoundsspins 1/2 nucleispins 1/2 nuclei

For small molecules having nuclei I=1/2nuclei I=1/2 : Sharp lines are expectedSharp lines are expected

W1/2 (line width at half height) = 0-10 Hz

If the nuclei has very weak interactions with the environment,

Long relaxation timeLong relaxation time occur (109109Ag => TAg => T11 up to 1000 s !!! up to 1000 s !!!)

This makes the detection quite difficult!

Isotope Nat. Abun-dance %

() 107 rad T-1 s-1

Frequency (MHz)

Rel. Receptivity

1H 99.985 26.7519 100.0 1.003H - 28.535 106.7 --

3He 0.00013 -20.380 76.2 5.8 * 10-7

13C 1.11 6.7283 25.1 1.8 * 10-4

15N 0.37 -2.712 10.1 3.9 * 10-6

19F 100.0 25.181 94.1 8.3 * 10-1

29Si 4.7 -5.3188 19.9 3.7 * 10-4

31P 100.0 10.841 40.5 6.6 * 10-2

57Fe 2.2 0.8661 3.2 7.4 * 10-7

77Se 7.6 5.12 19.1 5.3 * 10-4

89Y 100.0 -1.3155 4.9 1.2 * 10-4

103Rh 100.0 -0.846 3.2 3.2 * 10-5

107Ag 51.8 -1.087 4.0 3.5 * 10-5

109Ag 48.2 -1.250 4.7 4.9 * 10-5

111Cd 12.8 -5.6926 21.2 1.2 * 10-3

113Cd 12.3 -5.9550 22.2 1.3 * 10-3

NMR in Organometallic compoundsNMR in Organometallic compoundsNMR properties of some spins 1/2 nucleiNMR properties of some spins 1/2 nuclei

Index

Isotope Nat. Abundance

%

Magnetogyric ratio ()

107 rad T-1 s-1

Relative NMR

frequency (MHz)

Rel. Receptivity

117Sn 7.6 -9.578 35.6 3.5 * 10-3

119Sn 8.6 -10.021 37.3 4.5 * 10-3

125Te 7.0 -8.498 31.5 2.2 * 10-3

129Xe 26.4 -7.441 27.8 5.7 * 10-3

169Tm 100.0 -2.21 8.3 5.7 * 10-4

171Yb 14.3 4.712 17.6 7.8 * 10-4

183W 14.4 1.120 4.2 1.1 * 10-5

187Os 1.6 0.616 2.3 2.0 * 10-7

195Pt 33.8 5.768 21.4 3.4 * 10-3

199Hg 16.8 4.8154 17.9 9.8 * 10-4

203Tl 29.5 15.436 57.1 5.7 * 10-2

205Tl 70.5 15.589 57.6 1.4 * 10-1

207Pb 22.6 5.540 20.9 2.0 * 10-3

Spin Spin 1/21/2

Multinuclear NMR

• There are at least four other factors we must consider• Isotopic AbundanceIsotopic Abundance. Some nuclei such as 19F and 31P are 100% abundant

(1H is 99.985%), but others such as 17O have such a low abundance (0.037%). Consider: 13C is only 1.1% abundant (need more scans than proton).

• Sensitivity goes with the cube of the frequencySensitivity goes with the cube of the frequency. 103Rh (100% abundant but only 0.000031 sensitivity): obtaining a spectrum for the nucleus is generally impractical. However, the nucleus can still couple to other spin-the nucleus can still couple to other spin-active nucleiactive nuclei and provide useful information. In the case of rhodium, 103Rh coupling is easily observed in the 1H and 13C spectra and the JJRhXRhX can often can often be used to assign structuresbe used to assign structures

• Nuclear quadrupoleNuclear quadrupole. For spins greater than 1/2, the nuclear quadrupole moment is usually larger and the line widths may become excessively line widths may become excessively large.large.

• Relaxation timeRelaxation time

NMR in Organometallic compoundsNMR in Organometallic compoundsspins > 1/2 nucleispins > 1/2 nuclei

These nuclei possess a quadrupole momentquadrupole moment (deviation from spherical charge distribution) which cause extremely short relaxation timeextremely short relaxation time and extremely large linewidth Wextremely large linewidth W1/21/2 (up to 50 KHz)

WW1/2 1/2 ~ ~ (2I + 3) Q2 q2

zz c

I2 (2I -1)

Q = quadrupole momentqzz = electric field gradientc = correlation timeI = spin quantum number

Narrow linesNarrow lines can be obtained for low molecular weightlow molecular weight (small small cc)and if nuclei are embedded in ligand field of cubiccubic (tetrahedral, octahedral) symmetrysymmetry (qzz blocked)

NMR properties of some spins quadrupolar nucleiNMR properties of some spins quadrupolar nuclei Isotope Spin Abun-

dance %

() 107 rad T-1 s-1

Freq. (MHz)

Rel. Recep-tivity

Quadrupole moment10-28

m2

2H 1 0.015 4.1066 15.4 1.5 * 10-6 2.8 * 10-3

6Li 1 7.4 3.9371 14.7 6.3 * 10-4 -8 * 10-4

7Li 3/2 92.6 10.3975 38.9 2.7 * 10-1 -4 * 10-2

9Be 3/2 100.0 -3.7596 14.1 1.4 * 10-2 5 * 10-2

10B 3 19.6 2.8746 10.7 3.9 * 10-3 8.5 * 10-2

11B 3/2 80.4 8.5843 32.1 1.3 * 10-1 4.1 * 10-2

14N 1 99.6 1.9338 7.2 1.0 * 10-3 1 * 10-2

17O 5/2 0.037 -3.6279 13.6 1.1 * 10-5 -2.6 * 10-2

23Na 3/2 100.0 7.0801 26.5 9.3 * 10-2 1 * 10-1

25Mg 5/2 10.1 -1.639 6.1 2.7 * 10-4 2.2 * 10-1

27Al 5/2 100.0 6.9760 26.1 2.1 * 10-1 1.5 * 10-1

33S 3/2 0.76 2.055 7.7 1.7 * 10-5 -5.5 * 10-2

35Cl 3/2 75.5 2.6240 9.8 3.6 * 10-3 -1 * 10-1

37Cl 3/2 24.5 2.1842 8.2 6.7 * 10-4 -7.9 * 10-2

39K 3/2 93.1 1.2498 4.7 4.8 * 10-4 4.9 * 10-2

47Ti 5/2 7.3 -1.5105 5.6 1.5 * 10-4 2.9 * 10-1

49Ti 7/2 5.5 -1.5109 5.6 2.1 * 10-4 2.4 * 10-1

51V 7/2 99.8 7.0453 26.3 3.8 * 10-1 -5 * 10-2

55Mn 5/2 100.0 6.608 24.7 1.8 * 10-1 4 * 10-1

Quadrupolar nuclei: Oxygen-17

NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-VerlagTerence N. Mitchellm Burkhard Costisella

Notable nuclei• 1919FF: spin ½, abundance 100%, sensitivity (H=1.0) : 0.83

2JH-F = 45 Hz, 3JH-F trans = 17 Hz, 3JH-F Cis = 6 Hz 2JF-F = 300 Hz, 3JF-F = - 27 Hz

• 2929SiSi: spin ½, abundance 4.7%, sensitivity (H=1.0) : 0.0078The inductive effect of Si typically moves 1H NMR aliphatic resonances upfield to approximately 0 to 0.5 ppm, making assignment of Si-containing groups rather easy. In addition, both carbon and proton spectra display Si satellites comprising 4.7% of the signal intensity.

• 3131PP: spin ½, abundance 100%, sensitivity (H=1.0) : 0.07 1JH-P = 200 Hz, 2JH-P ~2-20 Hz, 1JP-P = 110 Hz, 2JF-P ~ 1200-1400 Hz, 3JP-P = 1-27 Hzthe chemical shift range is not as diagnostic as with other nuclei, the magnitude of the X-P coupling constants is terrific for the assignment of structuresKarplus angle relationship works quite well

Notable nuclei• 3131PP: spin ½, abundance 100%, sensitivity (H=1.0) : 0.07

1JH-P = 200 Hz, 2JH-P ~2-20 Hz, 1JP-P = 110 Hz, 2JF-P ~ 1200-1400 Hz, 3JP-P = 1-27 Hzthe chemical shift range is not as diagnostic as with other nuclei, the magnitude of the X-P coupling constants is terrific for the assignment of structuresKarplus angle relationship works quite well

22JJH-PH-P is 153.5 Hz for the phosphine trans 153.5 Hz for the phosphine trans to the hydridehydride, but only 19.8 Hz to the 19.8 Hz to the (chemically equivalent) cis phosphines(chemically equivalent) cis phosphines.

See Selnau, H. E.; Merola, J. S. Organometallics, 1993, 5, 1583-1591.

Notable nuclei• 103103RhRh: spin ½, abundance 100%, sensitivity (H=1.0) : 0.000031

11JJRh-CRh-C = 40-100 Hz, = 40-100 Hz, 11JJRh-C(Cp)Rh-C(Cp) = 4 Hz, = 4 Hz,

For example, in the 13C NMR spectrum of this linked Cp, tricarbonyl Rh dimer at 240K (the dimer undergoes fluxional bridge-terminal exchange at higher temperatures),

the bridging carbonyl bridging carbonyl is observed at at 232.53 232.53 and is a triplet with triplet with 11JJRh-CRh-C = 46 Hz = 46 Hz. The equivalent terminal carbonyls equivalent terminal carbonyls occur as a doubletdoublet at 190.18190.18 with 11JJRh-CRh-C = 84 Hz = 84 Hz:

See Bitterwolf, T. E., Gambaro, A., Gottardi, F., Valle G Organometallics, 1991, 6, 1416-1420.

Chemical shift for organometallicChemical shift for organometallic

In molecules, the nuclei are screened by the electrons. So the effective field at the nucleus is:

BBeffeff = B = B00(1-(1-))

Where is the shielding constant.

The shielding constant has 2 terms: dd (diamagnetic) (diamagnetic) and pp (paramagnetic) (paramagnetic)

dd - depends on electron distribution in the ground stateelectron distribution in the ground state

pp - depends on excited stateexcited state as well. It is zero for electrons in s-orbital.

This is why the proton shift is dominated by the diamagnetic termproton shift is dominated by the diamagnetic term. But heavier nuclei are dominated by the paramagnetic term.heavier nuclei are dominated by the paramagnetic term.

Index

SymmetrySymmetry

Si

ClBr

H H

Cl

PtBr

PPh3

PPh3 PtBr

PPh3

Cl

PPh3

P31 P31H are equivalents are non-equivalent are equivalent

Non-equivalent nuclei could "by accident" have the same shift and this could cause confusion.

Some Non-equivalent groupNon-equivalent group might also become equivalentbecome equivalent due to some averaging processaveraging process that is fast on NMR time scale. (rate of exchange is greater than the chemical shift difference)

e.g. PFPF55 : Fluorine are equivalent at room temperatureFluorine are equivalent at room temperature (equatorial

and axial positions are exchanging by pseudorotation)

Index

Symmetry in Boron compoundsSymmetry in Boron compounds

Proton - NMRProton - NMR Increasing the 1 s orbital density increases the shieldingIncreasing the 1 s orbital density increases the shielding

  M = CM = C M = SiM = Si M = GeM = Ge

MH4 0.10.1 3.23.2 3.13.1

MH3I 2.02.0 3.43.4 3.53.5

MH3Br 2.52.5 4.24.2 4.54.5

MH3Cl 2.82.8 4.64.6 5.15.1

(MH3)2O 3.23.2 4.64.6 5.35.3

MH3F 4.14.1 4.84.8 5.75.7

Shift to low field when the metal is heavier (Shift to low field when the metal is heavier (SnHSnH44 - - = 3.9 ppm = 3.9 ppm))

Index

Proton – NMR : Chemical shiftProton – NMR : Chemical shift

• Further contribution to shielding / deshieldingshielding / deshielding is the anisotropicanisotropic magnetic susceptibility from neighboring groups (e.g. AlkenesAlkenes, Aromatic ringsAromatic rings -> deshielding in the plane of the bound)

• In transition metal complexes there are often low-lying excited electronic states. When magnetic field is applied, it has the effect of mixing these to some extent with the ground state.

• Therefore the paramagnetic term is important for those nuclei Therefore the paramagnetic term is important for those nuclei themselves => large high frequency shifts (low field).themselves => large high frequency shifts (low field). The protons protons bound to these will be shielded (bound to these will be shielded ( => 0 to -40 ppm) => 0 to -40 ppm) (these resonances are good diagnostic. )

• For transition metal hydride this range should be extended to 70 For transition metal hydride this range should be extended to 70 ppm!ppm!

• If paramagnetic species are to be included, the range can go to 1000 If paramagnetic species are to be included, the range can go to 1000 ppm!!ppm!!

Index

Proton NMR and other nucleiProton NMR and other nuclei

• The usual range for proton NMR is quite small if we The usual range for proton NMR is quite small if we compare to other nuclei:compare to other nuclei:

• 1313C => 400 ppmC => 400 ppm• 1919F => 900 ppmF => 900 ppm• 195195Pt => 13,000 ppm !!!Pt => 13,000 ppm !!!

• Advantage of proton NMR : Solvent effects are Advantage of proton NMR : Solvent effects are relatively smallrelatively small

• Disadvantage: peak overlapDisadvantage: peak overlap

Index

Chemical shifts of other elementChemical shifts of other element

There is no room to discuss all chemical shifts for all elements in the periodical table. The discussion will be discussion will be limited to limited to 1313C, C, 1919F, F, 3131PP *as these are so widely used.

 Alkali Organometallics (lithiumlithium) will be briefly discuss

For heavier non-metal element we will discuss For heavier non-metal element we will discuss 7777Se and Se and 125125TeTe.

 For transition metal, we will discuss For transition metal, we will discuss 5555Mn and Mn and 195195PtPt

Index

Alkali organometallics: Alkali organometallics: OrganolithiumOrganolithium

For Lithium: we have the choice between 2 nuclei:

66Li : Q=8.0*10Li : Q=8.0*10-4-4 a=7.4%a=7.4% I=1I=177Li : Q=4.5*10Li : Q=4.5*10-2-2 a=92.6%a=92.6% I=3/2I=3/2

66Li : Higher resolutionLi : Higher resolution 77Li : Higher sensitivityLi : Higher sensitivity

7Li NMR : larger diversity of bonding compare to Na-Cs (ionic)

• Solvent effects are important (solvating power affects the Solvent effects are important (solvating power affects the polarity of Li-C bond and govern degree of association polarity of Li-C bond and govern degree of association• covers a small range: 10 ppmcovers a small range: 10 ppm• Covalent compound appear at low field (2 ppm range)Covalent compound appear at low field (2 ppm range)• Coupling 11JJC-LiC-Li between carbon and Lithium indicate covalent bond

OrganolithiumOrganolithium

Boron NMRBoron NMR

For Boron: we have the choice between 2 nuclei:

1010B : Q= B : Q= 8.5 * 108.5 * 10-2-2 a=19.6%a=19.6% I=3I=31111B : Q= B : Q= 4.1 * 104.1 * 10-2-2 a=80.4%a=80.4% I=3/2I=3/2

1111B : Higher sensitivityB : Higher sensitivity

Boron NMRBoron NMR

Boron Boron NMRNMR

1111B coupling with Fluorine: B coupling with Fluorine: 1919F-NMRF-NMR

1010B : Q= B : Q= 8.5 * 108.5 * 10-2-2 a=19.6%a=19.6% =10.7=10.7 I=3 I=3

NaBBFF44 / D2O

1919F-NMRF-NMR

2nI+1 = 72nI+1 = 7

2nI+1 = 42nI+1 = 4

1111BBFF44

1010BBFF44

Isotopic shiftIsotopic shift

1111B : Q= B : Q= 4.1 * 104.1 * 10-2-2 a=80.4%a=80.4% =32.1 I=3/2=32.1 I=3/2

BoronBoron can couple to other nuclei as shown here on 1919F-NMRF-NMR

JJF-10BF-10B

JJF-11BF-11B

= 10B10B

11B11B

JJBFBF=0.5 Hz=0.5 Hz JJBFBF=1.4 Hz=1.4 Hz

C13 shifts C13 shifts

Saturated Carbon appear between 0-100 ppm with electronegative substituents increasing the shifts.electronegative substituents increasing the shifts. CHCH33-X : directly related to the electronegativity of X.-X : directly related to the electronegativity of X.

The effects are non-additive: CHThe effects are non-additive: CH22XY cannot be easily predictedXY cannot be easily predicted

Shifts for aromatic compounds appear between 110-170 ppmShifts for aromatic compounds appear between 110-170 ppm -bonded metal alkene may be shifted up to 100 ppm: shift -bonded metal alkene may be shifted up to 100 ppm: shift

depends on the mode of coordinationdepends on the mode of coordination one extreme shift is CIone extreme shift is CI44 = -293 ppm !!! = -293 ppm !!! Metal carbonyls are found between 170-290 ppm. (very long Metal carbonyls are found between 170-290 ppm. (very long

relaxation time make their detection very difficult)relaxation time make their detection very difficult) Metal carbene have resonances between 250-370 ppmMetal carbene have resonances between 250-370 ppm

Index

F-19 shiftsF-19 shifts

• electronegativity• Oxidation state of neighbor• Stereochemistry• Effect of more distant group

Wide range: 900 ppmWide range: 900 ppm! And are not easy to interpretnot easy to interpret. The accepted referencereference is now: CClCCl

33FF. With literature chemical shift,

care must be taken to ensure they referenced their shifts properly. Sensitive toSensitive to::

Index

F-19 shiftsF-19 shiftsThe wide shift scale allow to observe all the products in the reaction

of : WF6 + WCl6 --> WFnCln-6 (n=1-6)

WF

F

FF

F

FW

FF

FCl

F

FW

FCl

FCl

F

F

WF

F

FCl

F

Cl

WCl

Cl

FCl

F

FW

ClF

FCl

F

ClW

ClCl

ClCl

F

FW

ClCl

FCl

F

ClW

ClCl

FCl

Cl

Cl

Index

Sn shiftsSn shifts

H-NMR of Sn compoundH-NMR of Sn compound

3 isotopes with spin ½ :

Sn-115 a=0.35%

Sn-117 a=7.61%

Sn-119 a=8.58%

2JSN117-H

2JSN119-H = 54.3 Hz

2JSN119-H = 1.046 * 2JSN117-H

(ratio of of the 2 isotopes)

NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-VerlagTerence N. Mitchellm Burkhard Costisella

Sn-119Sn-1193 isotopes with spin ½ :

Sn-115 a=0.35%

Sn-117 a=7.61%

Sn-119 a=8.58%

NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-VerlagTerence N. Mitchellm Burkhard Costisella

Sn-119 coupling

Sn-117 a=7.61%Sn-119 a=8.58%

1- molecule containing 1 Sn-119

2- molecule containing Sn119, Sn117 J between Sn-119 and Sn-1173- molecule containing two Sn119 Form an AB spectra (J=684 Hz)4- molecule containing Sn119 and C13 J between Sn119 and C13

Dynamic NMR

p261

C13

CycloheptatrieneCycloheptatriene

Dynamic Dynamic NMRNMR

11H-NMRH-NMR

P-31 ShiftsP-31 Shifts

• - 460 ppm for P- 460 ppm for P44

• +1,362 ppm phosphinidene complexe: tBuP[Cr(CO)+1,362 ppm phosphinidene complexe: tBuP[Cr(CO)55]]22

• Interpretation of the shifts is not easy : there seems to be many contributing factors

• PPIIIIII covers the whole normal rangewhole normal range: strongly substituent dependant

• PPVV narrower range: - 50 to - 50 to + 100 + 100.• Unknown can be predicted by extrapolation or interpolationUnknown can be predicted by extrapolation or interpolation• PXPX22YY or PYPY33 can be predicted from those for PXpredicted from those for PX33 and PXY and PXY22

• The best is to compare with literature values.

The range of shifts is ± 250 ppm from HThe range of shifts is ± 250 ppm from H33POPO

44 Extremes: Extremes:

Index

P-31 ShiftsP-31 Shifts

Index

There are many analogies between PhosphorusPhosphorus and SeleniumSelenium chemistry.

There are also analogies between the chemical shifts of 3131PP and 7777SeSe but the effect are much larger in SeleniumSelenium!

For example:Se(SiHSe(SiH

33))22 and P(SiHP(SiH

33))33 are very close to the low frequency limit (high fieldhigh field)

The shifts in the series SeRSeR22 and PRPR

33 increase in the order R= Me < Et < PrR= Me < Et < Prii < Bu < Butt

There is also a remarkable correlation between 7777SeSe and 125125TeTe. (see picture next slide)

Other nuclei: Selenium, TeluriumOther nuclei: Selenium, Telurium

Index

Correlation between Tellurium and Selenium ShiftsCorrelation between Tellurium and Selenium Shifts

Index

Manganese-55Manganese-55

Manganese-55Manganese-55 can be easily observed in NMR but due to it’s large large quadrupole momentquadrupole moment it produces broad linesbroad lines • 10 Hz for symmetrical environment e.g. MnO4

-

• 10,000 Hz for some carbonyl compounds. •It’s shift range is => 3,000 ppm3,000 ppm

•As with other metals, there is a relationshiprelationship between the oxidation state and chemical shielding •Reference: MnMnVIIVII : : = 0 ppm (MnO = 0 ppm (MnO44

--))• MnMnII : : –1000 to –1500 –1000 to –1500• MnMn-I-I : : –1500 to -3000 –1500 to -3000

5555Mn chemical shifts seems to reflect the total electron density on Mn chemical shifts seems to reflect the total electron density on the metal atomthe metal atom

Index

Pt-195 ShiftsPt-195 Shifts

PlatinumPlatinum is a heavy transition element. It has wide chemical shift scale: 13,000 wide chemical shift scale: 13,000 ppm!ppm!

The shifts depends strongly on the donor atomshifts depends strongly on the donor atom but vary little with long range. For example: PtClPtCl

22(PR(PR33))22

have very similar shifts with different Rsimilar shifts with different R

Many platinum complexes have been studied by 1H, 13C and 31P NMR. But products not involving those nuclei can be missed : PtClPtCl

442-2-

Major part of Pt NMRPt NMR studies deals with phosphine ligands as these can be easily studied with P-31 NMRP-31 NMR.

Index

Lines are broad (large CSA) large temperature dependence (1 ppm per degree)Lines are broad (large CSA) large temperature dependence (1 ppm per degree)

I = ½ a=33.8% K2PtCl6 ref set to 0. Scale: -6000 to + 7000 ppm !!

Pt-195 : coupling with protonsPt-195 : coupling with protonsCSA relaxation on CSA relaxation on 195195PtPt can have unexpected influence on proton proton satellitessatellites. CSA relaxation increases with the square of the fieldCSA relaxation increases with the square of the field. If the relaxation (time necessary for the spins to changes their spin state) is fast compare to the coupling, the coupling can even disapear!

N+

CO2-

Pt

Cl

Cl

H

H

H

H

CHCH22=CH=CH22

11H-NMRH-NMR

a=33.8%

Pt-195 I = ½ a=33.8%

H6 : dd

J5-6 = 6.2 HzJ4-6 = 1.3 Hz

JH6-Pt195 = 26 Hz

NMR – From Spectra to Structures An Experimental approachSecond edition (2007) Springler-VerlagTerence N. Mitchellm Burkhard Costisella

Pople NotationPople Notation

Si Si

H

H

HH

ClCl

A B3

P

HF

F

A M 2 X

I

FF

FF

F

A B4

Spin > ½ are generally omitted.

Index

Effect of Coupling with exotic nuclei in NMR Effect of Coupling with exotic nuclei in NMR Natural abundance 100%Natural abundance 100%

11H, H, 1919F, F, 3131P, P, 103103RhRh : all have 100% natural abundance.

When these nuclei are present in a molecule, scalar coupling must be present. Giving rise to multiplets of n+1 linesmultiplets of n+1 lines.

 

One bond coupling can have hundreds or thousands of HzOne bond coupling can have hundreds or thousands of Hz.

They are an order of magnitude smaller per extra bound between the nuclei involved. Usually coupling occur up to 3-4 bounds.

Example:Example:

P(SiHP(SiH33))33

+ LiMeLiMe -> ProductProduct : P-31 NMRP-31 NMR shows septetshows septet ===>

product is then P(SiHproduct is then P(SiH33))22

--Index

P-31 Spectrum of P-31 Spectrum of PFPF22H(NHH(NH22))22 labeled with labeled with 1515NN

coupling with H (largest coupling : Doublet) coupling with H (largest coupling : Doublet) then we see triplet with large coupling with fluorinethen we see triplet with large coupling with fluorine

With further Coupling to 2 N produce triplets, Coupling to 2 N produce triplets, further coupled to 4protons => quintetsfurther coupled to 4protons => quintets

2 x 3 x 3 x 5 = 90 lines2 x 3 x 3 x 5 = 90 lines ! !

tt

11JJP-FP-F

11JJP-FP-F

tt11JJP-HP-HTripletTriplet 11JJP-NP-N

Quintet Quintet 22JJP-HP-H

Effect of Coupling with exotic nuclei in NMREffect of Coupling with exotic nuclei in NMR

• For example: WFWF66 as 183183W has 14% abundanceW has 14% abundance, the fluorinefluorine spectra should show satellite signals separated by the coupling constant between fluorine and tungsten. The central signal has 86%central signal has 86% intensity and the satellites have 14%.satellites have 14%. This will produce 1:12:1 1:12:1 patternpattern

Low abundance nuclei of spin 1/2Low abundance nuclei of spin 1/2

1313C, C, 2929Si, Si, 117117Sn, Sn, 119119Sn, Sn, 183183WW : should show scalar coupling

=> satellite signals around the major isotope.

Index

Si-29 couplingSi-29 coupling• 29Si has 5% abundance.

• For HH33Si-SiHSi-SiH33 , the chance of finding

• HH33--2828SiSi----2929SiSi-H-H33 is 10%.10%. Interestingly we can see that the two kind of protons are no longer equivalent so homonuclear coupling homonuclear coupling become observablebecome observable! The molecule with 2 Si-29 is present with 0.25% intensity and is difficult to observe.

• The second group gives smaller coupling

Index

Coupling with PlatinumCoupling with Platinum 195195Pt the abundance is 33%.Pt the abundance is 33%.

Platinum specie will give rise to satellite signal with a relative ratio ofsatellite signal with a relative ratio of 1 : 4 : 11 : 4 : 1. This intensity pattern is diagnostic for the presence of platinum.

If the atom is coupled to If the atom is coupled to 2 Pt2 Pt, the situation is more complex:, the situation is more complex:

2/3 x 2/3 => no Pt2/3 x 2/3 => no Pt spin (central resonancecentral resonance)

1/3 x 1/3 => two Pt1/3 x 1/3 => two Pt with spin 1/2 => triplettriplet

remaining molecule has 2x (1/3 x 2/3) = 4/9 => one Pt2x (1/3 x 2/3) = 4/9 => one Pt with spin 1/2 => doubletdoublet

 Adding the various components together we now have 1:8:18:8:11:8:18:8:1 pattern. The weak outer lines are often missed, leaving what appear weak outer lines are often missed, leaving what appear to be a triplet to be a triplet 1:2:1 !!!1:2:1 !!!

Index

Carbon-13 in organometallic NMRCarbon-13 in organometallic NMR

13C is extremely useful to organometallic NMR

For example:For example:

Palladium complexe has:

• 4 non-equivalent Methyls4 non-equivalent Methyls

• 2 methylenes2 methylenes

• Allyl :Allyl : 11 methylene, 2 methynylmethylene, 2 methynyl

•Phenyl: 4 C: mono-subst.Phenyl: 4 C: mono-subst.

Index

2929Si-NMRSi-NMR

Polymeric siloxanes are easily studied by NMR: These have • terminal Rterminal R33SiO-SiO-• Chain RChain R22Si (O-)Si (O-)22

• Branch R-Si(O-)Branch R-Si(O-)33

• Quaternary Si(O-)Quaternary Si(O-)44

All these Silicon have different shifts making it possible to study All these Silicon have different shifts making it possible to study the degree of polymerization and cross-linkingthe degree of polymerization and cross-linking

Index

Coupling with Quadrupolar Nuclei (I>1/2)Coupling with Quadrupolar Nuclei (I>1/2)

• 2n2nII + 1+ 1 lines• The observation

of such coupling depends on the relaxation rate of the quadrupolar nuclei (respect to coupling constant)

Index

Coupling with Quadrupolar Nuclei (I>1/2)Coupling with Quadrupolar Nuclei (I>1/2)

Factors contributing to Coupling constantFactors contributing to Coupling constant

• Magnetic Moment of one nuclei interact Magnetic Moment of one nuclei interact with the field produced by with the field produced by orbital motion orbital motion of the electronsof the electrons – which in turn interact – which in turn interact with the second nuclei.with the second nuclei.

• There is a dipole interaction involving the dipole interaction involving the electron spin magnetic momentelectron spin magnetic moment

• There is also a contribution from spins of contribution from spins of electrons which have non-zero probability electrons which have non-zero probability of being at the nucleusof being at the nucleus => => Fermi contactFermi contact

Index

1-bound coupling1-bound coupling• Depends onDepends on s-orbital character of the bound s-orbital character of the bound

– HybridizationHybridization of the nuclei involved11JJCHCH => 125 (sp => 125 (sp33), 160 (sp), 160 (sp22), 250 (sp)), 250 (sp)

• ElectronegativityElectronegativity is another factor: increase the couplingincrease the coupling– CClCCl33H => H => 11JJCHCH = 209 Hz = 209 Hz

• Coupling can be used to determine coordinationcoordination number of PFPF , PHPH compounds, and to distinguish axialaxial, equatorialequatorial orientation of Fluorines.– 1JPH = 180 (3 coordinate) , 1JPH = 400 (4 coordinate)

• Coupling can also be used to distinguish single double bond– E.g.

P

RR

Se

R

P

Se

RR

R

Index

2-bound coupling2-bound coupling

• 22JJ can give structural informationstructural information: There is a relationship between 22JJ and Bond angleBond angle

• => coupling range passes through zero. Therefore the sign of the coupling must be determined

Pt2-

P

P

XX Pt2-

P

X

PX

Trans Cis

J (trans) > J (cis)

Index

3-bound coupling3-bound coupling

• Depends on Dihedral angleDihedral angle

33JJXYXY = A cos 2 = A cos 2 + B cos + B cos + C + C

A, B, C : empirical constantsA, B, C : empirical constants

Index

Complicated proton spectra : CHComplicated proton spectra : CH33-CH-CH22-S-PF-S-PF22

Almost quintetAlmost quintet

Index

Complicated Fluorine spectra : PFComplicated Fluorine spectra : PF22-S-PF-S-PF22

Second order spectra: 1919FFChemically equivalentChemically equivalentMagnetically non-equivalentMagnetically non-equivalent11JJPFPF different from different from 33JJPHPH

This type of spectra is frequent in transition metalmetal complex:MMClCl22((PPRR33))22

Index

Equivalence and non-equivalenceEquivalence and non-equivalence

P

O

O

PhO

PF

F P

FF

FF are Non-EquivalentThe 2 phosphorus2 phosphorus are Pro-chiral: non-equivalent

Index

To identify a compound: PFTo identify a compound: PF221515NHSiHNHSiH33

Use as many techniques as possible

Proton nmr spectraProton nmr spectra is difficult to analyze with so many J’sis difficult to analyze with so many J’sBut withBut with 1919F, F, 1515NN andand 3131P P spectra it’s easier (get heteronuclear J)spectra it’s easier (get heteronuclear J)

Index

To identify a compound: PFTo identify a compound: PF221515NHSiHNHSiH33

Use as many techniques as possible

Using decoupler : easier analysisUsing decoupler : easier analysis

Index

Multinuclear ApproachMultinuclear Approach

Proton NMR spectra: 3 groups of peaks integrating for Proton NMR spectra: 3 groups of peaks integrating for 1212::44:1:1

Resonances due to MethylMethyl and CHCH22 have coupling with 3131PPAnd also shows satellites due to mercury coupling (satellites due to mercury coupling (199199Hg 16.8%)Hg 16.8%)

While third resonance is broad

In In 3131P, there is a single signal: Symmetrical compound: that has P, there is a single signal: Symmetrical compound: that has Mercury satellitesMercury satellites

In In 199199Hg NMR (Hg NMR (with proton decouplingwith proton decoupling): quintet demonstrate the ): quintet demonstrate the presence of presence of 4 Phosphorus4 Phosphorus

Index

Heteronuclear NOEHeteronuclear NOE

• NOE enhancement can give useful gain in signal-to-noiseNOE enhancement can give useful gain in signal-to-noise• It is most efficient when the It is most efficient when the heteronucleiheteronuclei is bound to is bound to protonproton

NOENOEMAXMAX = 1 + = 1 + HH/2/2XX

• For nuclei having negative negative , NOENOE is negativenegative (for 2929Si, max=-1.5Si, max=-1.5)

Index

Exchange : DNMR – Dynamic NMRExchange : DNMR – Dynamic NMRNMR is a convenient way to study rate of reactions – provided that the lifetime of participating species are comparable to NMR time scale (1010--

55 s s)H

H

H

H

H

GeMe3

At low temperature, hydrogens form an A2B2XA2B2X spin system

At higher temperature germaniumgermanium hop from one C to the next

Index

Paramagnetic compounds in NMRParamagnetic compounds in NMRUsually paramegnetic compounds are too braod => give ESRIn NMR, Chemical shift is greatlyChemical shift is greatly expandedexpanded

Paramagnetic shifts are made up of 2 component:Paramagnetic shifts are made up of 2 component:

1. Through space Dipolar interaction between the magnetic Dipolar interaction between the magnetic momentmoment of the electronelectron and of the nucleusnucleus

2.2. Contact Shift: Contact Shift: coupling between electron and nucleus. This interaction would give a doublet in NMR but J ~ millions of Hertz!!With such large coupling, intensity of the 2 resonances are With such large coupling, intensity of the 2 resonances are not equal => weighted mean position is not equal => weighted mean position is not midwaynot midwayWith fast relaxation, collapse of the multiplet may fall thousands Hertz away from expected position => Contact Shift Contact Shift

Contact Shift give a measure of unpaired spin density at resonating Nucleus.Contact Shift give a measure of unpaired spin density at resonating Nucleus.Useful for studying spin distribution in organic radical or in ligands in organo Useful for studying spin distribution in organic radical or in ligands in organo metallic complexesmetallic complexes

Paramagnetic compounds in NMRParamagnetic compounds in NMR4 sets of resonances:4 sets of resonances: 1 symmetrical Fac: the 3 ligand are identical 1 symmetrical Fac: the 3 ligand are identical

3 Asymetrical ligand in Mer occur with 3 3 Asymetrical ligand in Mer occur with 3 time the probability.time the probability.

Index

NMR-basicsNMR-basics

H-NMRH-NMR

NMR-SymmetryNMR-Symmetry

Heteronuclear-NMRHeteronuclear-NMR

Dynamic-NMRDynamic-NMR

NMR and Organometallic compoundsNMR and Organometallic compounds

Special 1D-NMRSpecial 1D-NMR