Organometallics 1995,14, 3527—3530
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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 -31 and -130 coupling constants across the central metal atom 12«/ —Rh—h) were measured in a series of octahedral rhodium hydrido phosphine detected, complexes [Rh(PMe3)2(CO)(Cl)(X)H; X = Cl, phenyl (2 isomers)] using a frequency-selective, two-dimensional NMR experiment. The relative and absolute signs of 2«/i3c-Rh-H, 2e/I3c-Rh-p> and Vp-Rh-H were determined, and in the case of 2Ji3C_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. Organometallics 1995.14:3527-3530. Downloaded from pubs.acs.org by MIAMI UNIV on 10/30/18. For personal use only.
(*
Introduction
coupling constants is characteristic of the relative position of the phosphorus nuclei around the iron center, with Vp-M-Pf irons/ > 2Jp-U-P(cis) and 2Jp-U-P(trans) of 2 opposite sign to 5Jp_m-pí«s)·7 Early studies6 suggested that similar trends were apparent in the heteronuclear 31 - coupling constants (2Jp-m-h) in transition metal 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 to facilitate the measurement of coupling constants,9·10 and these include homonuclear 2D experiments such as ECOSY,1011 selective excitation methods,12 and heteronuclear 2D and 3D experiments.1314 We recently reported8 the application of a proton-detected, frequencyselective 2D NMR experiment for measuring the detailed structure of phosphorus-coupled multiplets in the 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.15 The relative magnitudes of 2Ji3C-m-h (cis/trans) 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 2J^c~ri¡-h, 2Ji3C_Rh_P, and Vp-Rh-H couplings for the complexes
The photoactive rhodium(I) complex trans-Rh(PMe3)2(CO)Cl (1) is one of the most efficient reagents for the catalytic activation and functionalization of hydrocarbons. írons-Rh(PMe3)2(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.1 Recent studies of the mechanism of carbonylation of arenes have indicated that the reaction proceeds via six-coordinate rhodium hydrido species, and 1H, 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 to the electronic structure of bonded atoms and molecular geometry in terms of dihedral angles.3-5 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 atom.6’7 In six-coordinate iron(II) phosphine complexes the relative magnitude of 31P-31P
(6) (a) Moore, D. S.; Robinson, S. D. Chem. Soc. Rev. 1983,12, 415. (b) Kaesz, H. D.; Saillant, R. B. Chem. Rev. 1972, 72, 231. (7) Field, L. D.; Baker, . 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, O. W.; Ernst, R. R. J. Am. Chem. Soc. 1985, 107, 6394. (1Í) Griesinger, C.; Sorensen, O. W.; Ernst, R. R. J. Magn. Reson. 1987, 75, 474. (12) (a) Brueschweiler, R.; Madsen, J. C.; Griesinger, C.; Sorensen, O. 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.
Abstract published in Advance ACS Abstracts, May 15, 1995. (1) See for example: (a) Tanaka, M.; Sakakura, T. PureAppl. Chem. 1990, 62, 1147. (b) Sakakura, T.; Sodeyama, T.; Tanaka, M. Nouv. 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.; Sai to, 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, (f) Maguire, J. A.; Boese, W. T.; Goldman, A. S. J. Am. Chem. Soc. 1989, 111, 7088. (g) Maguire, J. A.; Boese, W. T.; Goldman, . 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) Güntert, P.; Braun, W.; Billeter, M.; Wüthrich, 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. ®
0276-7333/95/2314-3527$09.00/0
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1995 American Chemical Society
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RhCPMesMCOXClhH (2) and RhíPMesJaíCOXCIXCeHe)!! (2 isomers 3 and 4). PMeg |
„
PMea
PMeg
ci
Cl— Rh—H
Cl—
OC^
OC
|
PMe3
(2)
H
Rh—
Cl—
OC^
Rh13—H I
PMes
PMe3
(3)
(4)
Results and Discussion The activation of hydrocarbons has been achieved a number of transition metal complexes.17 Where 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 irtms-Rh(PMe3)2(CO)Cl (1) in benzene/THF at 230 K generates 2 isomers of Rh(PMe3)2(COXClXC6H5)H (3 and 4).2 The 13COlabeled complexes (2-13CO, 3-13CO, and 4-13CO) required for this study were generated from irans-Rh(PMe3)2(13CO)Cl (l-13CO). The assignment of the relative disposition of substituents about the metal center was achieved using NMR spectroscopy and described elsewhere.2
with
Magnitudes and Relative Signs of Coupling Constants. A selective two-dimensional heteronuclear correlation experiment (analogous to a homonuclear
COSY-45 experiment98) was used to determine the relative signs of the couplings 2J13c-Rh-H, 2J13c-Rh-p> and 2Jp-Rh-H·8 The pulse sequence [(Y2){X}-r0-('7/2){X}, (•V2){ -selective}-detect}1!!}], was applied with the selective proton excitation envelope centered on the of the metal-bound hydride. Selective resonance excitation was achieved using an E-BURP pulse,18-19 which maintains the pure in-phase character and The detailed multiplet structure of the resonance. magnitudes of all coupling constants were measured from the high-resolution 2D NMR spectra. The fine structure observed in each cross peak of the two-dimensional spectrum is not symmetrical, but the pattern of resonances in the multiplet is skewed due to systematic peak absences. As in the COSY-45 experiment, the relative signs of coupling constants are (15) See for example: (a) Pregosin, P. S.; Kunz, R. W. NMR Basic Princ. Prog. 1979,15, 28-34, 86 and references therein, (b) Verkade, J. G. Coord Chem. Rev. 1972/73, 9, 1. (c) Goodfellow, R. J.; Taylor, B. F. J. Chem. Soc., Dalton Trans. 1974, 1676. (d) Pankowski, M.; Chodkiewicz, W.; Simonnin, M.-P. Inorg. Chem. 1985, 24, 533. (e) Hyde, E. M.; Kennedy, J. D.; Shaw, B. L.; McFarlane, W. J. Chem. Soc.,
Dalton Trans. 1977, 1571. (16) (a) Whitesides, G. M.; Maglio, G. J. Am. Chem. Soc. 1969, 91, 4980. (b) Brown, J. M.; Kent, A. G. J. Chem. Soc., Perkin Trans. 2 1987, 1597. (17) See for example: (a) Hoyano, J. K.; McMaster, A. D.; Graham, W. A. G. J. Am. Chem. Soc. 1983,105, 7190. (b) Jones, W. D.; Feher, 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. Chem. 1986, 300, 81. (e) Baker, . V.; Field, L. D. J. Am. Chem. Soc. 1987,109, 2825. (0 Field, L. D.; George, A. V.; Messerle, B. A. J. Chem. Soc., Chem. Commun. 1991, 19, 1339, (g) Selective Hydrocarbon Activation; Principles and Progress; Davies, J. A., Watson, P. L., 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.
Figure
1. Two-dimensional, frequency-selective, protondetected —31P correlation spectrum of 3-13CO. The slopes of the two solid lines shown indicate the signs of the product (Vc-h) x (2Jp-c) and the product (Vrh-h) x I’dRh-p)· spectrum of 3-13CO showing only the metalbound hydride. The resonance from unlabeled 3 is indicated by an asterisk.
expressed in splittings arising from the passive rather than active couplings in each cross-peak. An example of a typical multiplet observed from the spectrum of complex Rh(PMe3)2(13CO)(Cl)(C6Ü5)H (313CO) is given in Figure 1. In the normal (ID) NMR NMR spectrum shows a spectrum of 3-13CO, the single complex multiplet in the high field (metal hydride) region at ó -8.05 ppm and a single multiplet in the 31P spectrum at -6.55 ppm. The spin system contains the NMR observable nuclei , 13C, 31P, and correlation 103Rh, and in the proton-detected -31 experiment, the observed multiplet has only one active coupling (Jp-h) as well as passive heteronuclear couplings (Jisc-h, Jrr-h in F2 and Ji3c-31P, Jrii-31p in FI).20 In Figure 1, the active coupling defines four quadrants of antiphase transitions—each quadrant is displaced from another by a passive coupling in FI (Jp- ) and a passive coupling in F2 (Jh-y). In this type of experiment, the number of quadrants observed depends on the number of passive couplings to and 31P and only transitions which are connected in FI and F2, i.e. where
the coupled 31P and nuclei have a common coupling partner Y, are visible. The slope of the line joining any two quadrants depends on the product of the passive couplings (Jp- ) x (Jh-y) by which they are separated. If the signs of Jp- and Jh-y are different, the slope of the line will be opposite to that where Jp- and Jh-y have the same sign. In Figure 1, the multiplets joined by the solid line (a) are separated by the passive coupling 2Jc-h in F2 and the passive coupling 2Jp-c in (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, Vol. 14, No.
Table 1. Relative Magnitudes (Hz) and Signs of Heteronuclear Coupling Constants for the Hydride Resonances of Complexes 2-4° complex
no.
Vn-p1 Vm-h6 Vc-rr-h Vp-Rh-mtisj Vp-Rh-Omj
PMeg
7,
1995
3529
The absolute signs of the one bond couplings to rhodium could not be determined; however, Vc-rh, Vh-rh, and Vp-rh have the same sign.
2J
2J
P-Rh-C (cis)
H-Rh-P (cis)
Cl
a—Rh—H ocr I
2
81.1
17.3
+3.8
+12.7
+12.0
3
100.4
13.2
-65.0
+13.2
+9.0
4
98.4
28.1
+4.7
+13.9
+9.6
PMea PMe3 I
H
CI-Rh'-
cxr
I
PMeg
Cl—Rh^H cxr
|
PMe3
NMR data for 223 (THF-dg, 230 K): lH -13.29 (Rh-H); 13C (Rh-CO); 31P ó -3.34 (Rh-PMe3). NMR data for 32 (C6He/ ó -8.05 (Rh-H); 13C 191.6 (Rh-CO); 31P ó THF-ds, 230 K): ó -6.55 (Rh-PMe3). NMR data for 42 (CsHe/THF-dg, 230 K): -14.62 (Rh-if); 13C 190.9 (Rh-CO); 31P -8.53 (Rh-PMe3). 6 Signs of coupling constants not determined. °
0 and Vc-p < 0.21·22 The magnitudes and signs of the heteronuclear Vc-Rh-H couplings were measured for compounds 2-4, and the values of the coupling constants are listed in Table 1. The relative magnitudes of heteronuclear 2Jc-Rh-H couplings have previously been reported and it was found that typically 2J™c-Bh-wtraw) > 2=713c-Rh-Hrc¿s>·16 In complexes 2 and 4 it was found that 2Ji3C_Rh_Hrds-l is relatively small and has a positive sign, and 2Jc-Rh-wtmns) in 3 is relatively large and negative in sign. It should be possible to use the magnitude and signs of coupling constants to assign stereochemistry in closely related complexes without the need for full structural analysis. However, it should be noted that coupling constants are dependent on the specific aspects of the metal complex including the metal center in the complex, the metal oxidation state, the geometry of the complex, ligand types, etc., and extrapolation beyond closely related complexes is not possible.163 The relative magnitudes ofVp-Rh-H and Vc-Rh-p are unchanged for all the complexes studied, as would be expected since the relative stereochemistry of the metalbound hydride and phosphine and metal-bound phosphine and carbonyl is the same for all the complexes. The signs of 2Jp--Rh-Wcisi and Vc-Rh-p+JSj are positive. (21) Jameson, C. J. J. Am. Chem. Soc. 1969, 91, 6232. (22) The 13C satellites 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 ofji’c h (F2) X e/l3c-P (FI).
A heteronuclear pulse sequence incorporating a bandselective pulse enabled high-resolution two-dimensional -31 and —13C NMR spectra of rhodium hydrides to be obtained. Heteronuclear 31P-1H and —13C coupling constants were assigned and measured from the detailed structure of the complex cross-peak mul-
tiplets. This is the first systematic study which has examined the relative signs and magnitudes of heteronuclear coupling constants in a series of related octahedral rhodium hydride complexes. The stereochemistry of the complexes was determined independently, and the absolute signs of some coupling constants were determined by reference to the C-H and C-P couplings in PMea. In complexes 2 and 4 it was found that V‘3c-Rh-Hfcis) is relatively small and has a positive sign, and Vi3c-Rh-Hrtrans) in 3 is relatively large and negative in sign. In summary, in the octahedral rhodium hydride complexes studied the following is observed: 2(^i3C-Rh-H(cis)
>
0
|2^i3C-Rh-H(frans)l
2«^i3C-Rh-H«rans)< 0 ^
l^isc-Rh-Hteis)!
Experimental Section Syntheses and manipulations of chemicals were carried out under nitrogen with standard Schlenk and high-vacuum techniques. The samples for study were prepared in 5 mm NMR tubes with concentric Youngs PTFE valves connected. Low-temperature photolyses were carried out using a 125 W mediumpressure vapor lamp with the NMR tube being suspended in a double-walled Pyrex dewar containing ethanol cooled with a refrigeration coil. Benzene and THF were dried by refluxing over sodium/ benzophenone and distilled under nitrogen prior to use. NMR Spectroscopy. Spectra were recorded on Bruker AMX400 and AMX600 spectrometers. Spectra of the rhodium complexes (2—4) were acquired at 230 K in THF-da- 31P NMR spectra were referenced to external, neat trimethyl phosphite, and 13C taken as 140.85 ppm at the temperature quoted; NMR spectra were referenced to residual solvent resonances. The selective -X correlation spectra were acquired using a previously described pulse sequence:8 [( /2){ }- -( /2){ >, ( /2){ -selective}-detect! }], where 0 is the variable delay. Selective E-BURP pulses18·19 were applied using Bruker soft pulse hardware. Shaped pulses were defined by 256 points, centered on the resonance(s) of the metal-bound hydrides in the spectrum. Selective pulses were typically between 5 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 spectrum, with 256 increments and 64 scans per increment. A relaxation delay of 2.5 s was left between acquisitions.
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Spectra were zero-filled to 512 points in Fi and 2048 points in Sine-bell weightings were applied to the data in both dimensions (shifted by /2 in F2 and /4 in Fi) prior to Fourier
F2.
transformation. Metal Complexes. Rh(PMe3)2(CO)Cl (l),23 Rh(PMe3)2(CO)C1 (l-13CO),24 Rh(PMe3)2(CO)(Cl)2H (2),24 and Rh(PMe3)2(CO)(ClXCeHslH (2 isomers 3 and 4)2 were prepared by literature methods.
(23) Synthesis adapted from: Dunbar, K. Chem. 1992, 31, 3676.
R; Haefher,
S. C.
Inorg.
Acknowledgment. We gratefully acknowledge financial support from the Australian Research Council, the University of Sydney for the award of a . B. and F. M. Gritton Research Fellowship (M.G.P.), and also Johnson-Matthey PLC for the generous loan of rhodium salts.
OM940894U (24) Boyd, S. E.: Field, L. D.; Hambley T. W.; Partridge, M. G. Organometallics 1993, 12, 1720.
