1102
Inorg. Chem. 1991, 30, 1102-1 107
symmetric ring-breathing mode should split into four components (a, b, a, b,) under C, unit cell symmetry, the g and u modes being Raman and IR active, respectively. This splitting was not observed at ambient pressure, however, indicating that the intermolecular coupling between the molecules in the unit cell is weak but may be increased by applying pressure, eventually resulting in the observed peak broadening. The origin of the coupling may arise from the ring-ring interaction, which has been calculated to be the largest contributor to the intermolecular interaction at ambient pressure.6 Very recently, Coffer and coworkersi9 have examined the high-pressure IR spectra of a series of C2 hydrocarbon ligands coordinated to a triosmium framework and found that the values of dv/dP follow the order: C-H stretching > C-C stretching > C-H bending. In our study of CpRe(CO)’, no such conclusion could be drawn owing to the complex spectrum of the Cp ligand. The pressure dependence of the ring tilt a t 349 cm-l is twice that of the antisymmetric ring tilt in ferr0cene.l’ High-pressure IR studies of some metal-sandwich compounds by Nakamoto and co-workers20 have indicated that the metal-ring stretching vibration is more pressure sensitive than is the ring tilt vibration. However, these two vibrations have almost same du/dP value in CpRe(C0)’. All values of the relative pressure sensitivity, d In v/dP, are typical of those found for internal vibrational modes except for
+ + +
Coffer, J. L.; Drickamer, H. G.; Park, J. T.; Roginski, R. T.; Shapley, J. R. J. Phys. Chem. 1990, 94, 1981. Nakamoto, K.; Udovich, C.; Ferraro, J. R.; Quattrcchi, A. Appl. Spectrosc. 1970, 24, 606.
three bands initially at 129 cm-’ ( C p R t ( C O ) , bending (e)), 114 cm-I (C-ReC bending (e)), and 100 cm-l (C-ReC bending (al)). These three internal modes shift with increasing pressure at rates much faster than normal. The large d In v/dP value of some low-frequency internal modes may result from the coupling with external modes. However, according to Chhor and Lucazeau,Iothis does not occur for CpRe(C0)’. The C-ReC bending vibrations are expected to be less sensitive than the corresponding stretching vibrations because they are less affected by the volume change of crystal. But the reverse is observed in our work. It is possible that the larger d In v/dP values for the C-Re42 bending modes may result from slight changes in the C - R e C angles upon application of pressure from its average value of 90’: because a pressure-induced angle change will certainly increase the restoring potential and at the same time the energy of the bending mode. As pointed out by Elian and cO-workers,2l the (0)C-MC ( 0 ) angle in such a system is extremely sensitive to the extent of mixing between the carbonyl molecular orbitals and to the nature of the other ligands present. If it is again considered that pressure facilitates electron density transfer from the Cp ring to the Re metal, then the C - R d angle should become larger with increasing pressure. Acknowledgment. This research work was generously supported by grants from the NSERC and CANMET (Canada) and the FCAR (Quebec). Y.H.acknowledges the award of a graduate fellowship from McGill University. (21)
Elian, M.; Chen, M. M. L.; Mingos, D. M. P.;Hoffmann, R. Inorg. Chem. 1976, 15, 1148.
Contribution from the Institut fur Anorganische Chemie der Universitlt, Auf der Morgenstelle 18, D-7400Tubingen 1, West Germany
Phosphorus-31 Solid-state NMR Studies of Cyclic and Acyclic PhosphineMetal (M = Complexes. Determination of Chemical Shift Anisotropy, Scalar Coupling lJM-p SSMn9 9s/97Mo,183W), and SSMnQuadrupolar Coupling Constants Ekkehard Lindner,* Riad Fawzi, Hermann August Mayer, Klaus Eichele, and Klaus Pohmer Received June 28, 1990 The I’P chemical shift tensors of cyclic and acyclic metal phosphine complexes of the type [M]PPh2R([MI = (OC),BrMn (l), Cp(OC)2CIW (2), CP(OC)~M~W (3);R = Et (a), Pr (b), Bu (e), Pe = Pentyl (a)) and [M]PPh2(CH2),([MI = (OC),Mn (4), Cp(OC)2W !S), CP(OC)~MO (6); n = 3 (a), 4 (c); [MI = (OC),MnS02 (7);n = 2 (b), 3 (c), 4 (a)) are determined by solid-state NMR techniques and correlated to structural features of the compounds. In general the isotropic chemical shift in the solid-state was found to be. of the same order as the chemical shift in solution. There are differences in the tensor components due to structural changes for the manganese complexes 1. Different bond weakening abilities of a ligand (trans influence) in complexes 2 and 3 cause a large change of only one tensor component, while the other components remain constant. A Ycrossover”of the center shielding tensor component and the low-field component is observed for the five- and six-membered rings 4b-7b and &7c, respectively. 55Mn- and 95/97Md1P coupling constants have k e n observed that are not obtainable in solution. The different spacings within the multiplets of the ”P CP/MAS spectrum of the manganese complex Id allows us to estimate the quadrupolar coupling constant x and the asymmetry parameter 7 of the electric field gradient at manganese.
.
Introduction Today high-resolution 31PN M R spectroscopy in solution is a widely used method with manifold applications in the observation of changes in bonding and stereochemistry of phosphorus compounds.’ In these studies the diagnostic manner in which the spectra reflect the local environments of the nuclei is a key feature. Generally, a “elation of spectral information to structural details is difficult. Within a series of mutually related compounds, the problems are reduced in a first approximation to one structural parameter as the major contributor that determines the spectrum. In this way it is possible to correlate 6(’’P) empirically with various
parameters. Examples are the definition of group contributions to the chemical shift of phosphines: the coordination shift A6 on complexation of phosphines to metal fragments,’ the dependence of 6(3’P)in complexes on the cone angle of the ligand! and the ring contribution AR for phosphorus atoms involved in chelate rings.5 The last effect, in particular, has been well-known since one of the first publications about ’lP NMR studies on organometallic compounds.6 Later investigations showed a clear dependence of ( 2 ) Grim, S. 0.;McFarlane, W.; Davidoff, E. F. J. Org. Chem. 1967, 32, 181.
( 1 ) Phosphorus-31
NMR Spectroscopy in Stereochemical Analysis: Or-
ganic Compounds and Metal Complexes; Verkade, J. G., Quin, L. D., Eds.;VCH Publishers: Deerfield Beach, FL, 1987.
0020-1669/91/1330-1102$02.50/0
(3) Mann, B. E.; Masters, C.; Shaw, B. L.; Slade, R. M.; Inorg. Nucl. Chem. Lett. 1971, 7, 881. (4) Tolman, C . A. Chem. Reo. 1977, 77, 313. ( 5 ) Garrou, P.E. Chem. Rev. 1981, 81, 229.
0 1991 American Chemical Society
Stainbank, R.E.
31PNMR Studies of Phosphine-Metal Complexes
Inorganic Chemistry, Vol. 30, No.5, 1991 1103
Table 1. Solid-state and Solution 3'P NMR Isotropic Chemical Shifts (ppm)O and Coupling Constants (Hz)of Compounds 1-7b compd no. bi,(solid) IJM-p(solid) d b(soln) lJM-p(soln) Bh(solid) - b(soln) (OC)4BrMnPPh2Et la 42.4 44 (9) 38.7 3.7 197 (9)
(OC)4BrMnPPh2Pr (OC)4DrMnPPh2Bu (OC)4BrMnPPh2Pe cis-Cp(OC)zC1WPPh2Bu rr~ns-Cp(0C)~MeWPPh~Et tr~ns-Cp(0C)~MeWPPh~Pr fr~ns-Cp(0C)~MeWPPh~Bu
lb le Id 2c 3s 3b
trans-Cp(OC),Me W PPh2Pe (OC)4MnPPh2(CH2),
3d
36.2 35.9 38.9 13.3 33.8 30.8 29.2 26.1 28.5
4b 4c
84.2
82.2
2.0
41.4
43.2
-1.8
-
Cp(OC)2MoPPh2(CH2)4 I (OC)4MnPPh2(CH2)2S02 (OC)4MnPPh2(CH2)3S02 , I (OC),MIIPP~~(CH~)~SO~
3c
6c
51.3
207 (5) 203 (9) 210 (3) 259 (9) 236 (6) 231 (11) 246 (1 4)
50.5
209 (2)
35.8 37.0 36.8 12.7 30.3 26.6 27.0 27.0 27.0
0.8 -1.1 2.1 0.6 3.5 4.2 2.2 -0.9 1 .5
264.4 247.8 247.4 247.8 247.8 247.8
64.9
311.0
9.1
11.6
285.3
4.8
91.8 47.3
4.0
-12 (4)
72.6
-0.6
-5 (1)
28.8
-4.4
-1 (2)
45.8
4.7
159 (7)
7b 72.0 (3) -.214 7c 24.4 206 ( I ) 7d
41 (9) 36 (14) 41 (4)
8.5
'Relative to external 85% H,P04. bAbbreviations: Me = methyl, Et = ethyl, Pr = propyl, Bu = butyl, Pe = pentyl, Ph = phenyl, Cp = q5-cyclopentadienyl.CCf.eq 1.
6("P) on the ring size. Compared to the signals of corresponding acyclic compounds? the signal of the phosphorus in five-membered metallacycles is shifted 20-50 ppm to lower field while the phosphorus signal in six-membered rings resonates 2-1 7 ppm at higher fields. In an earlier paper considering this ring effect on the phosphorus-3 1 shielding, we compared the isotropic chemical shifts in the solid state with structural data derived from single-crystal X-ray diffraction experiments on cyclic and acyclic phosphine complexes of manganese and tungsten.' We were able to show that the acyclic compounds and the six-membered cycles have staggered conformations and similar chemical shifts. The five-membered cycles have eclipsed conformations and were found to be downfield-shifted compared to their homologues. In the solid state, a nucleus undergoes a variety of observable interactions with its environment that often have a characteristic influence on its NMR spectrum. The magnitudes of these influences are strongly dependent on the orientation of the interaction relative to the external magnetic field and are best described as 3 X 3 matrices." In solution, the isotropic tumbling of molecules reduces the interactions to the trace of the matrix, which results in the isotropic value. In the case of dipolar and quadrupolar coupling, the trace becomes zero, leaving the resonance unaffected. However, in the solid state, no such isotropic motion exists; thus a shift, broadening, and/or splitting of the resonances is caused by chemical shift anisotropy and dipolar and quadrupolar interactions. These interactions provide additional structural information that may be extracted from a solid-state NMR spectrum. In the present paper, we wish to report how chemical shift anisotropy (CSA) and quadrupolar coupling influence the solidstate )'P NMR spectra of cyclic and acyclic phosphine-metal complexes and discuss these effects in terms of the geometry of the complexes or the properties of the ligands. Experimental Section A. NMR spectn#lcopy. Cross-polarization*magic-angle-spinning"P CP/MAS NMR spectra were obtained on a Bruker MSL-200 wide-bore spectrometer operating at 4.7 T (31Pat 81 .OOO MHz) in a double-bearing Bruker ,'P CP/MAS probe and using a sweep width up to 62 kHz, a recycle time of 2 s, and a contact time of 5 ms. The isotropic lines were identified via experiments at different spinning rates. Reported tensor (6) Meriwether, L. S.;Leto, J. R. J . Am. Chem. Soc. 1961, 83, 3192. (7) Lindner, E.; Fawzi, R.;Mayer, H. A,; Eichele, K.;Pohmer, K. J . Organomet. Chem. 1990, 386,63. (8) Mehring, M. In High Resoltuion NMR Spectroscopy in Solids; Diehl, P., Ruck, E., Eds.; N M R Basic Principles and Progress 11; Springer Verlag: Berlin, 1976.
components are mean values obtained from different measurements at spinning rates between 1.0 and 3.7 kHz. Numbers for these measurements are given in the last column of Table 11. The standard deviations denote the scattering of these measurements. An absolute error of 5 ppm is estimated; that for the manganese complexes is IO ppm. Between 200and 300-mg samples of compound were spun in Zr02rotors. Chemical shifts were referenced to an external sample of 85% H3P04. The solution 3'P('H)NMR spectra were recorded at 32.392 MHz on a Bruker WP-80 spectrometerat 243 K chemical shifts were referenced to external 85% H3P04in acetone-d,. The high-frequency-positive convention has been used in reporting all chemical shifts. B. Synthesis. Compounds 1,2,3a-c, 4,s: 6b? and 71°were prepared as previously described. Compounds 3d and 6c were prepared in an analogous manner.' ~ ~ s - C ~ ( O C ) ~ M ~ W(3d): P F Iyellow I ~ P ~solid; yield 54% mp 88 O C ; IR (uco in CHCI,) 1923 s, 1831 vs cm-I. Anal. Calcd for C25Hs02PW C, 52.10; H, 5.07. Found: C, 51.79; H 4.98. Cp(OC)2MoPPh2(CH2)4(6c): yellow solid; yield 42%; mp 178 OC; IR (vc0 in CHCI,) 1929 vs, 1845 s cm-I. Anal. Calcd for C23H2302M~P: C, 60.27; H, 5.06. Found: C, 61.01; H, 5.34.
.
Results and Discussion As a manifestation of the three-dimensional nature of the chemical shielding, the spectrum of a stationary powdered sample will show a chemical shift anisotropy (CSA) pattern." The singularities in this powder pattern correspond to the principal elements of the chemical shift tensor (Figure la). Magic-angle spinning (MAS) at rotating speeds much below the powder line width causes the patterns to break up into a sharp isotropic line &,,(solid) = + bzz + 6,,)/3, flanked by spinning sidebands (Figure Ib,c)." The intensities of the spinning sidebands are related to the CSA and provide an opportunity to recover the chemical shift parameters by graphical analysis.'* The isotropic chemical shifts obtained from the 31PN M R spectra of complexes 1-7 in solution and in the solid state show no significant deviations (Table I), which indicates that there are no substantial structural changes between the solid state and the solution. Exceptions are 5b and 6b,due to different ring conformations in solution and in the solid state, which was established by ' H (400 MHz) N M R spectroscopy in solution and singlecrystal X-ray diffraction in the solid state.' ~~
~
~~
(9) Lindner, E.; Klister, E. U.; Hiller, W.; Fawzi, R.Chem. Ber. 1984. 117, 127.
(IO) Lindncr, E.; Funk, G. J . Organomet. Chem. 1981, 216, 393. (11) Maricq, M. M.; Waugh, J. S.J . Chem. Phys. 1979,70, 3300. (12) Herzfeld, J.; Berger, A. E. J . Chem. Phys. 1980,73,6021.
1104 Inorganic Chemistry, Vol. 30, No. 5, 1991
Lindner et al.
Table 11. Calculated ,IP NMR Chemical Shift Anisotropy Parameters’ for Compounds 1-7b
compd (OC)4BrMnPPh2Et (OC),BrMnPPh2Pr (OC)4BrMnPPh2Bu (OC),BrMnPPh2Pe cis-Cp(OC)2CIWPPh2Bu rr~ns-Cp(0C)~MeWPPh~Et rruns-Cp(OC)lMeWPPh2Pr rruns-Cp(OC)2MeWPPh2Bu
no. la lb IC
Id 2c
4, 86 87 91 94 51
(0)
(0) (7) (1) (2)
3a
1 IO ( I )
3b
rruns-Cp(OC)2MeWPPh2Pe
3d
(OC)&~PP~~(CHZ)~ (OC)IM~PP~Z(CHZ)~ 1 CP(OC)ZWPP~Z(CHZ)~ CP(OC)ZWPP~Z(CHZ)~ CP(OC)zMoPPh2(CH2)3 1 CP(OC)ZMOPP~Z(CHZ)~ (OC)4MnPPh2(CH2)2S02 , (OC),MnPPhz(CH2)3S02 , (OC)4MnPPh2(CH2)4S02
4b
118 ( I ) 116 (2) 120 (3) 117 ( I ) 181
4c Sb SC
121 (2) 169(1) 114(2)
6b
209 (1)
6c 7b 7c 7d
154(1) 156 (3) 85 (1) 99 (1)
.
3c
. .
55 (2) 44 (3) 47 (IO) 41 (1) 16 (1) 18 (1) 7 (2) 6 (IO) -9 (7) 5 (4) 92 38 (1) 99 (1) -15 ( I ) 143 ( I ) 34 78 23 58
215 163 259 188 173 120
131 132 142 133 146 119 143 146 163 154 126 91
39 22 28 7 11 -34 -47 -43 -66 -58 12 -7 35 -58 49 -28 10 -3
no. of spinning rates 2 2 2 2 4 4 4 3 3 4 1 2 4 4 4 4 2 2
-16 -23 -32 -20 -28 -27 -33 -38 -35 -37 -2 1 -34 -46 -49 -50
(1)
(2) (3) (3) (0) (I) (I) (2) (11) (9) (3)
105
73
22
2
102 1 IO
123 1 I4
19 137 151 154 154 202 155
-34 (2) -17 (7)
(4) (2) (2)
115
155
(2) (I) (2) (I)
-35 ( I ) -6 (2)
p: %
Abd 67 77 84 84 57
PC
633
822
a From graphical analysis of sideband intensities’O or from singularities of the powder pattern; standard deviations in parentheses. For abbreviations see Table I. CAnisotropy range p = bj3 - b l l . dAnisotropy parameter Ab = b l l - (bZ2+ 6,,)/2. eAsymmetry parameter p = (bll b33 2622)/(633 - bll).”
+
To separate the effects on the phosphorus-31 shielding by ring closure from other influences, we studied the acyclic compounds 1-3. The manganese complexes 1 differ by up to 15 ppm in their respective tensor components (Table 11, Figure 2) due to changes in the bond angles at phosphorus and variations of the torsional angle Br-Mn-PC(alky1). The structural differences in bond and torsional angles were obtained from singlecrystal X-ray diffraction studies of lW?J3 Le., the bond angles Mn-P
