Organometallics 1996,14, 3527-3530
3527
Signs and Magnitudes of Heteronuclear Coupling Constants in Octahedral Rhodium Complexes by High-Resolution 2D NMR Martin G. Partridge, Barbara A. Messerle,* and Leslie D. Field* Department of Organic Chemistry, University of Sydney, Sydney 2006, NSW, Australia Received November 23, 1994@ The magnitude and sign of 1H-31P and 'H-13C coupling constants across the central metal atom ( 2 J x - ~ h - ~were ) measured in a series of octahedral rhodium hydrido phosphine complexes [Rh(PMe3)2(CO)(Cl)(X)H;X = C1, phenyl (2 isomers)] using a 'H detected, frequency-selective, two-dimensional NMR experiment. The relative and absolute signs of 2Ji3C-Rh-H, 2Ji3C-Rh-p, and 'JP-Rh-H were determined, and in the case of 2J13C-Rh-H both the magnitude and sign of the coupling constant were found to depend on the relative disposition of the coupled nuclei about the central metal atom.
Introduction The photoactive rhodium(1)complex truns-Rh(PMe3)~(C0)Cl (1) is one of the most efficient reagents for the catalytic activation and functionalization of hydrocarbons. trans-Rh(PMea)z(CO)Cl(1) reacts with both linear and branched alkanes to give organorhodium complexes which eventually form organic products e.g. by carbonylation or dehydrogenation.' Recent studies of the mechanism of carbonylation of arenes have indicated that the reaction proceeds via six-coordinate rhodium hydrido species, and 'H, 31P, and 13C NMR spectroscopy was used to determine the stereochemistry of the unstable intermediates.2 The measurement of coupling constants between NMR-active atoms in ligands and the metal center (where the metal is itself NMR-active) and also between the NMR-active atoms in different ligands has developed into an important tool for the characterization of organometallic compounds by NMR spectroscopy. In organic and organometallic compounds, both homonuclear and heteronuclear coupling constants are sensitive t o the electronic structure of bonded atoms and molecular geometry in terms of dihedral angle^.^-^ In organometallic compounds, the magnitude of homo- and heteronuclear coupling constants can provide information about the stereochemistry of metal complexes as well as the oxidation state and coordination geometry of the central metal In six-coordinate iron(I1) phosphine complexes the relative magnitude of 31P-31P @Abstractpublished in Aduance ACS Abstracts, May 15, 1995. (1)See for example: (a) Tanaka, M.; Sakakura, T. Pure Appl. Chem. 1990,62,1147. (b) Sakakura, T.; Sodeyama, T.; Tanaka, M. Nouu. J . Chim. 1989,13,737. (c) Sakakura, T.; Sodeyama, T.; Sasaki, K.; Wada, K.; Tanaka, M. J.Am. Chem. SOC.1990, 112, 7221. (d) Nomura, K.; Saito, Y. J . Chem. Soc., Chem. Commun. 1988, 161. (e) Tanaka, M.; Sakakura, T. In Homogeneous Transition Metal Catalysed Reactions; Moser, R., Slocum, D. W., Eds.; American Chemical Society: Washington, DC, 1992; Vol. 230, p 181 and references therein. (0 Maguire, J. A.; Boese, W. T.; Goldman, A. S. J.Am. Chem. Soc. 1989,111,7088. (g) Maguire, J. A,; Boese, W. T.; Goldman, M. E.; Goldman, A. S. Coord. Chem. Rev. 1990, 97, 179. (h) Boese, W. T.; Goldman, A. S. J. Am. Chem. SOC.1992, 114, 350. (2)Boyd, S. E.; Field, L. D.; Partridge, M. G. J. Am. Chem. SOC. 1994,116, 9492. (3) Guntert, P.; Braun, W.; Billeter, M.; Wuthrich, K. J . Am. Chem. SOC.1989,111, 3997. (4) Karplus, M. J. Am. Chem. SOC.1963,85, 2870. (5) Bystrov, V. F. Prog. NMR Spectrosc. 1976, 10, 41.
0276-733319512314-3527$09.00/0
coupling constants is characteristic of the relative position of the phosphorus nuclei around the iron center, with 2Jp-M-p(transi > 2 J ~ - ~ - ~ ( c i sand i 'Jp-M-p(trans) of opposite sign t o 2Jp-M-p(cis).7 Early studies6 suggested that similar trends were apparent in the heteronuclear ) metal 31P-1H coupling constants ( 2 J p - ~ -in~transition complexes containing both phosphine and hydride ligands, and this was confirmed recently for a series of octahedral Fe and Ru hydrido phosphine complexes.8 A number of NMR techniques are available t o facilitate the measurement of coupling c o n s t a n t ~ , ~and J~ these include homonuclear 2D experiments such as ECOSY,l0J' selective excitation methods,12and heteronuclear 2D and 3D experiment^.^^,'^ We recently reported8the application of a proton-detected, frequencyselective 2D NMR experiment for measuring the detailed structure of phosphorus-coupled multiplets in the 'H NMR spectra of metal hydrides. The method allowed the measurement of both the magnitude and the relative signs of the P-H, P-P, and C-H coupling constants in a series of iron and ruthenium hydrides. The relative signs of homonuclear and heteronuclear coupling constants have been established only for a limited number of organometallic complexes.l5 The relative magnitudes of 2 h C - M - H (cisltruns) couplings in octahedral Rh compounds have been measured in earlier work.16 In this paper we report the measurement of both the magnitudes and signs of 2 J 1 3 ~ - ~ h - ~ , 2 J 1 3 ~ - ~ h and - ~ , 'Jp-Rh-H couplings for the complexes (6)(a)Moore, D. S.; Robinson, S. D. Chem. SOC.Rev. 1983,22,415. (b) Kaesz, H. D.; Saillant, R. B. Chem. Rev. 1972, 72, 231. (7) Field, L. D.; Baker, M. V. Inorg. Chem. 1987,26, 2011. (8)Field, L. D.; Bampos, N.; Messerle, B. A. Organometallics 1993, 12, 2529. ( 9 ) ( a ) Bax, A.; Freeman, R. J. Magn. Reson. 1981, 44, 542. (b) Oschkinat, H.; Pastore, A,; Pfaendler, P.; Bodenhausen, G. J. Magn. Reson. 1986, 69, 559. (c) Mueller, L. J. Magn. Reson. 1987, 71, 191. (10)Griesinger, C.; Sorensen, 0. W.; Ernst, R. R. J . Am. Chem. SOC.
1985,107, 6394. (11) Griesinger, C.; Sorensen, 0. W.; Ernst, R. R. J. Magn. Reson. 1987, 75, 474. (12) (a) Brueschweiler, R.; Madsen, J. C.; Griesinger, C.; Sorensen, 0. W.; Ernst, R. R. J. Magn. Reson. 1987, 73, 380. (b) Emsley, L.; Bodenhasuen, G. J.Am. Chem. SOC.1991,113,3309. (c) Bodenhausen, G.; Freeman, R.; Morris, G. A. J. Magn. Reson. 1976,23, 171. (13) Titman, J. J.; Neuhaus, D.; Keeler, J. J. Magn. Reson. 1989, 85, 111. (14) (a) Kessler, H.; Mronga, S.; Gemmecker, G. Magn. Reson. Chem. 1991, 29, 527. (b) Kessler, H.; Anders, U.; Gemmecker, G. J. Magn. Reson. 1988, 78, 382.
0 1995 American Chemical Society
Partridge et al.
3528 Organometallics, VoE. 14, No. 7, 1995
Rh(PMe3)dCOXClhH(2) and Rh(PMesh(COXCl)(C6H5)H (2 isomers 3 and 4).
2
Results and Discussion
JP-C
The activation of hydrocarbons has been achieved Where with a number of transition metal ~omp1exes.l~ the product metal complexes are thermally unstable or short lived, it is necessary to obtain as much structural information as possible on the products in situ in solution before isolation or derivatization. Previously we have shown that irradiation of truns-Rh(PMe3)z(CO)C1(1)in benzenePTHF at 230 K generates 2 isomers of Rh(PMe3)2(CO)(Cl)(C6Hs)H(3 and 4h2 The I3COlabeled complexes (W3C0, S-13C0, and 4J3CO) reIH -8.00 -8.10 ppm quired for this study were generated from trans-RhFigure 1. Two-dimensional, frequency-selective, proton(PMe3)#3CO)C1 (lJ3CO). The assignment of the relative detected 1H-31P correlation spectrum of 3-13C0.The slopes disposition of substituents about the metal center was of the two solid lines shown indicate the signs of the achieved using NMR spectroscopy and described elseproduct ('Jc-H) x ('JP-C) and the product ( ' J R h - d x where.2 (IJRh-p). 'H spectrum of 3-l3CO showing only the metalMagnitudes and Relative Signs of Coupling bound hydride. The resonance from unlabeled 3 is indicated Constants. A selective two-dimensional heteronuclear by an asterisk. correlation experiment (analogous to a homonuclear COSY-45 experimentga) was used to determine the expressed in splittings arising from the passive rather relative signs of the couplings 2J13C-Rh-H, Z J ~ l s c - ~ h - p ,and than active couplings in each cross-peak. 'JP-R~-H.' The pulse sequence [ ( n / ~ ) { X-zo-C' ) /z){X), An example of a typical multiplet observed from the C7/2){ lH-selective}-detect{ lH}], was applied with the 'H spectrum of complex Rh(PMe3)2(l3C0)(C1)(CsHs)H(3selective proton excitation envelope centered on the 13CO) is given in Figure 1. In the normal (1D) NMR resonance of the metal-bound hydride. Selective 'H spectrum of 3-l3CO, the lH NMR spectrum shows a excitation was achieved using an E-BURP p u l ~ e , ~ ~ J ~ single complex multiplet in the high field (metal hywhich maintains the pure in-phase character and dride) region at 6 -8.05 ppm and a single multiplet in detailed multiplet structure of the resonance. The the 31P spectrum at 6 -6.55 ppm. The spin system magnitudes of all coupling constants were measured contains the NMR observable nuclei 'H, 13C, 31P,and from the high-resolution 2D NMR spectra. lo3Rh,and in the proton-detected 1H-31P correlation The fine structure observed in each cross peak of the experiment, the observed multiplet has only one active two-dimensional spectrum is not symmetrical, but the as well as passive heteronuclear coucoupling (JP-H) pattern of resonances in the multiplet is skewed due to plings ( J I Q - H , J R h - H in F2 and J w - ~J ~~h P -3, 1in ~ F1).20 systematic peak absences. As in the COSY-45 experiIn Figure 1,the active coupling defines four quadrants ment, the relative signs of coupling constants are of antiphase transitions-each quadrant is displaced from another by a passive coupling in F1 (Jp-y) and a (15) See for example: (a) Pregosin, P. S.; Kunz, R. W. NMR Basic passive coupling in F2 (JH-Y).In this type of experiPrinc. Prog. 1979,15,28-34,86and references therein. (b) Verkade, J. G. Coord Chem. Rev. 1972/73,9,1. (c) Goodfellow, R. J.; Taylor, B. ment, the number of quadrants observed depends on the F. J. Chem. Soc., Dalton Trans. 1974, 1676. (d) Pankowski, M.; number of passive couplings to 'H and 31P and only Chodkiewicz,W.; Simonnin, M.-P. Inorg. Chem. 1985,24,533. (e) Hyde, transitions which are connected in F1 and F2, i.e. where E. M.; Kennedy, J. D.; Shaw, B. L.; McFarlane, W. J. Chem. Soc., Dalton Trans. 1977,1571. the coupled 31Pand lH nuclei have a common coupling (16)(a) Whitesides, G. M.; Maglio, G. J. Am. Chem. SOC. 1969,91, partner Y, are visible. The slope of the line joining any 4980. (b) Brown, J. M.; Kent, A. G. J . Chem. Soc., Perkin Trans. 2 1987,1597. two quadrants depends on the product of the passive (17)See for example: (a)Hoyano, J . K.; McMaster, A. D.; Graham, couplings ( J p - y ) x (JH-y) by which they are separated. W. A. G. J . Am. Chem. SOC.1983,105,7190.(b) Jones, W. D.; Feher, If the signs of J p - Y and JH-Yare different, the slope of F. J. Organometallics 1983,2,562.(c) Wenzel, T. T.; Bergman, R. G. J.Am. Chem. Soc. 1986,108,4856.(d) Graham, W. A. G. J . Organomet. the line will be opposite t o that where J p - y and JH-Y Chem. 1988,300,81.(e) Baker, M.V.; Field, L. D. J.Am. Chem. SOC. have the same sign. In Figure 1,the multiplets joined 1987,109,2825.(0 Field, L.D.; George, A. V.; Messerle, B. A. J . Chem. by the solid line (a) are separated by the passive Soc., Chem. Commun. 1991, 19, 1339. (g) Selective Hydrocarbon Activation; Principles and Progress; Davies, J. A., Watson, P. L., in F2 and the passive coupling 'Jp-c in coupling 'Jc-H Liebman, J. F., Greenberg, A,, Eds; VCH Publishers, Inc.: New York, 1990;and references therein. (h)Activation and Functionalisation of Alkanes; Hill, C. L., Ed.; Wiley Interscience: New York, 1989;and references therein. (18)Geen, H.; Wimperis, S.; Freeman, R. J . Magn. Reson. 1989,85, 620. (19)Geen, H.; Freeman, R. J.Magn. Reson. 1991,93, 93.
(20) ( a ) Ernst, R. R.; Bodenhausen, G.; Wokaun, A. Principles of Nuclear Magnetic Resonance in One and Two Dimensions; Oxford University Press: Oxford, U.K., 1987;pp 414-22. (b) Bax, A. Two Dimensional NMR in Liquids; Delft University Press, D. Reidel Publishing Co.: Dordrecht, Holland, 1982; pp 78-84.
Octahedral Rhodium Complexes
Organometallics,
Table 1 . Relative Magnitudes (Hz) and Signs of Heteronuclear Coupling Constants for the Hydride Resonances of Complexes 2-4O COmpleX
no.
'JRh-Pb
'JRh-Hb
'JC-Rh-H
'JP-Rh-Hlas)
+ 9.0 Hz
2
81.1
17.3
+3.8
f12.7
13.2
-65.0
+13.2
,,.o
RhLH 'Me3)
+9.0
2 J H-Rh-C (trans) - 65.0 Hz
Conclusions
I ,,> I JW-Rh-H(cisll 2JC-Rh-H couplings were measured for compounds 2-4, and the values of the coupling constants are listed in Experimental Section Table 1. Syntheses and manipulations of chemicals were carried out The relative magnitudes of heteronuclear 'JC-Rh-H under nitrogen with standard Schlenk and high-vacuum couplings have previously been reported and it was techniques. found that typically 2J13C-Rh-HftrQns) > 2J13C-Rh-H(cis).16 In The samples for study were prepared in 5 mm NMR tubes complexes 2 and 4 it was found that 2J'3C-Rh-Hfci~) is with concentric Youngs PTFE valves connected. Low-temperphotolyses were carried out using a 125 W mediumrelatively small and has a positive sign, and 2 J ~ - ~ - ~ t m n sature ) pressure vapor lamp with the NMR tube being suspended in in 3 is relatively large and negative in sign. It should a double-walled Pyrex dewar containing ethanol cooled with be possible to use the magnitude and signs of coupling a refrigeration coil. constants t o assign stereochemistry in closely related Benzene and THF were dried by refluxing over sodium/ complexes without the need for full structural analysis. benzophenone and distilled under nitrogen prior to use. However, it should be noted that coupling constants are NMR Spectroscopy. Spectra were recorded on Bruker dependent on the specific aspects of the metal complex AMX400 and AMX600 spectrometers. Spectra of the rhodium including the metal center in the complex, the metal complexes (2-4) were acquired at 230 K i n THF-da. 31PNMR oxidation state, the geometry of the complex, ligand spectra were referenced to external, neat trimethyl phosphite, types, etc., and extrapolation beyond closely related taken as 140.85 ppm at the temperature quoted; 'H and 13C NMR spectra were referenced to residual solvent resonances. complexes is not possible.16a The selective lH-X correlation spectra were acquired using The relative magnitudes Of 2JP-Rh-H and 2JC-Rh-P are a previously described pulse sequence:8[(n/2){X}-~~-(~/2){X}, unchanged for all the complexes studied, as would be (n/2){'H-selective}-detect{ 'H}], where TO is the variable delay. expected since the relative stereochemistry of the metalSelective E-BURP p u l ~ e s ' ~were J ~ applied using Bruker soft bound hydride and phosphine and metal-bound phospulse hardware. Shaped pulses were defined by 256 points, phine and carbonyl is the same for all the complexes. centered on the resonanceb) of the metal-bound hydrides in The signs of 2Jp-Rh-Hfeis) and 2JC-Rh-pfcis) are positive. the 'H spectrum. Selective pulses were typically between 5
'
(21)Jameson, C. J. J.Am. Chem. SOC.1969,91, 6232. (22) The 13Csatellites of the methyl proton resonance of PMe3 were observed, and the slope of the line connecting the quadrants of the passively coupled 13C satellites corresponds to a negative value 0 f J I J C - H (F2) x J13c-p (Fl).
and 15 ms in duration giving excitation widths of approximately 200-1200 Hz. In 2D acquisitions, typically, 1024 data points were acquired over a sweep width of 1500 Hz in the 'H spectrum, with 256 increments and 64 scans per increment. A relaxation delay of 2.5 s was left between acquisitions.
Partridge et al.
3530 Organometallics, Vol. 14, No. 7, 1995 Spectra were zero-filled to 512 points in F1 and 2048 points in Fz. Sine-bell weightings were applied to the data in both dimensions (shifted by n/2 in Fz and n/4 in F1) prior to Fourier transformation. Metal Complexes. FWPMe3)z(CO)Cl(l),?73 Rh(PMedz(C0)C1 (l-1sCO),24 Rh(PMe3)2(CO)(Cl)zH(2hZ4 and Rh(PMedz(C0)(Cl)(CeH5)H(2 isomers 3 and 4)* were prepared by literature methods.
Acknowledgment. We gratefully acknowledge financial support from the Australian Research Council, the University of Sydney for the award of a H. B. and F. M. Gritton Research Fellowship (M.G.P.),and also Johnson-Matthey PLC for the generous loan of rhodium salts.
(23) Synthesis adapted from: Dunbar, K. R.; Haefner, S. C. Inorg. Chem. 1992,31,3676.
(24) Boyd, S. E.: Field, L. D.; Hambley T. W.; Partridge, M. G. Organometallics 1993,12, 1720.
OM940894U
