J . Phys. Chem. 1990, 94,6255-6263
6255
Stereodynamics of trans-[ (t-Bu),PPh],MCI, [M = Pt( II)and Pd( II)]and trans-[ ( t -Bu),PPh],M(CO)CI [M = Rh( I)and I r ( I)]. Dynamic NMR and X-ray Crystallographic Studies Christine M. DiMeglio,* Linda A. Luck, Christopher D. Rithner, Arnold L. Rheingold,+ Wendy L. Elcesser, John L. Hubbard, and C. Hackett Bushweller* Departments of Chemistry, University of Vermont, Burlington, Vermont 05405, and University of Delaware, Newark, Delaware I971 6 (Received: November 28, 1989)
Single-crystal X-ray analysis of trans-[(t-B~)~PPh]~MCl~ for which M = Pt(I1) or Pd(I1) reveals a molecular conformation (C,) in which both phenyl groups are mutually anti. In both cases, the metal atom lies on a crystallographic inversion center and the overall geometry at the metal template is essentially square planar. The 31PllH}dynamic NMR (DNMR) spectra and trans-[(r-B~)~PPh],PtCI, show a decoalescence at low temperature into four singlets of both rrans-[(r-B~)~PPh]~PdCl~ (four diastereomeric conformations). One singlet resonance is strongly dominant in both complexes. Two singlets correspond to the two diastereomeric conformations in which the phenyl groups are anti to each other and oriented on the same side or opposite sides of the coordinationplane (Ci and C2molecular symmetry). The other two singlets are assigned to diastereomeric conformations in which the phenyl groups are mutually syn and on the same side or opposite sides of the coordination plane (C,and C2molecular symmetry). On the basis of 31PNMR chemical shift correlations with molecular geometry and circumstantial arguments, the dominant conformation is assigned to the molecular geometry present in the crystal (C, molecular in which M = Rh(1) or Ir(1) show a decoalescence symmetry). The 31P(’HJDNMR spectra for trans-[(t-B~)~PPh]~M(CO)Cl into four subspectra (four diastereomeric conformations). The dominant subspectra are assigned to the two diastereomeric conformations in which the phenyl groups are mutually anti and oriented on the same side or opposite sides of the coordination plane (C,symmetry). The other two subspectra are assigned to those conformations in which the two phenyl groups are syn to the carbon monoxide ligand (C, and C, symmetry). There is no evidence in the 3’P{1H)DNMR spectra for those conformations in which both phenyl groups are syn to CI.
Introduction Tetracoordinate, square-planar complexes of Pt(II), Pd(II), Rh(I), and Ir(1) are ubiquitous in the chemical literature and constitute an important class of compounds. They are used in a variety of chemical applications.’ For example, Rh(C0)CI[ PPh312is used in the hydroformylation reactions of alkenes and alkynes.* Wilkinson’s catalyst, RhC1[PPh3ls, is widely used in the selective hydrogenation of a wide range of unsaturated organic molecule^.^ Bulky phosphine ligands stabilize the trans versus cis isomers in bis(phosphine) complexes and are known to enhance certain reactions, including intramolecular metallati~n.~Complexes of bulky chiral phosphines show useful asymmetric inductionSs In many cases, the bulky phosphine possesses one or more phenyl substituents, and assessing the conformational behavior of the phenyl group is important. While X-ray crystallographic studies have defined the molecular geometry of many complexes in the solid state: there have been few definitive systematic studies of the molecular stereodynamics in solution.’ Elucidating conformational behavior in solution is important if one is to have an incisive understanding of chemical reactions in solution. One ligand of interest is di-tert-butylphenylph~sphine.~~~ In the free phosphine, dynamic N M R (DNMR) studies and molecular mechanics calculations show that the phenyl group is strongly buttressed by the two tert-butyl groups in the most stable equilibrium g e ~ m e t r y . The ~ phenyl plane essentially bisects the (t-Bu)-P-(t-Bu) moiety (1). Molecular mechanics calculations indicate that there is a 7 O twist about the Ph-P bond away from C, symmetry as a result of the tert-butyl groups twisting to minimize 1S-dimethyl nonbonded repulsions. There is a high barrier to 2-fold phenyl rotation (AG*= 10.5 kcal/mol) due to repulsive nonbonded interactions between the phenyl group and proximate tert-butyl methyl groups in the transition state (2). *Towhom correspondence should be addressed at the University of Vermont. ‘University of Delaware. 0022-3654/90/2094-6255$02.50/0
1
2 These studies also reveal a lower barrier to tert-butyl rotation (AG* = 6.3 kcal/mol). As a ligand bound to the squareplanar templates
( I ) Alyea, E. C., Meek, D. W., Eds. Catalytic Aspects of Meral Phosphine Complexes; Adv. Chem. Ser. No. 196; American Chemical Society: Washington, DC, 1982. (2) Livingstone, S.E. Compr. Inorg. Chem. 1973, 3, 1237. (3) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J . Chem. SOC.A 1966, 1711. Motelatici, S.;Osborn, J. A.; Wilkinson, G.; Van de Ent, A. J. Chem. Soc. A 1968, 1054. (4) Cheney, A. J.; Mann, B. E.; Shaw, B. L.; Slade, R. M. J. Chem. Soc. A 1971, 3833.
(5) (a) Morrison, J. D.; Masler, W. F.; Newburg, M. K. Adu. Caral. 1976, 25, 81. (b) Bosnich, B.; Fryzuk, M. D. Top. Stereochem. 1981, 12, 119.
0 1990 American Chemical Society
6256
The Journal of Physical Chemistry, Vol. 94, No. 16, 1990
TABLE I: Selected Bond Angles and Distances for Structures 7 and 8 structure 7 angles CI( I)-Pt-P( I ) CI( I)-Pt-Cla P-Pt-P Pt-P-C( 1 ) Pt-P-C( 1 1 ) Pt-P-C(7) P-C( I)-C(6) P-C( I)-C(2) structure 7 distances Pt-CI(I) Pt-P( I ) P-C(1) P-C(7) P-C(11)
A 2.309 (2) 2.368 (2) 1.840 (7) 1.904 (8) 1.900 (7)
Pd(l)-CI(I) Pd(1)-P(1) P(l)-C(II) P( I)-C(S) P(I)-C(I)
bond angles of 180.0'. The Cla-Pt-P( 1) bond angle in 7 is 92.0' ( 1 ) and the CI(1)-Pd-P(l) bond angle in 8 is 92.1' (1) (Table 1).
structure 8 angles CI(1)-Pd-P( 1 ) CI( I)-Pd-Cla P-Pd-P Pd-P-C( 1 1) Pd-P-C( 1) Pd-P-C( 5) P-C( 1 1)-C( 12) P-C(I 1)-C(16) structure 8 distances
deg 88.0 180.0 180.0 111.9 117.5 108.0 117.5 123.7
DiMeglio et al.
deg 92. I I80 180.0 112.3 107.8 117.3 118.3 124.7
A 2.301 (2) 2.398 (2) 1.828 (7) 1.921 (8) 1.881 (7)
TABLE 11: Setected Dihedral Angles for Structures 7 and 8 structure 7 structure 8 angle CI( I )-Pt-P-C( 1 ) Cla-Pt-P-C( 11) Cla-Pt-P-C( 7) Cla-Pt-P-C( 1 ) Pt-P-C(l)-C(2) Pt-P-C(I I)-C(12) Pt-P-C(7)-C(IO)
deg -32.4 -92.7 33.8 147.6 142.7 167.8 160.0
angle Cla-Pd-P-C( I 1) Cl(1)-Pd-P-C(I) CI(I)-Pd-P-C(S) Cl(1)-Pd-P-C(ll) Pd-P-C(I l)-C(I6) Pd-P-C(I)-C(4) Pd-P-C(5)-C(6)
deg -32.0 -92.7 33.8 148.0 144.4 166.0 161.2
of Pt(II), Pd(II), Rh(I), and Ir(I), this phosphine provides an opportunity to assess the conformational consequences of a highly constrained phenyl group. In order to shed some insight into the molecular stereodynamics, we report 31P(1HJDNMR studies of complexes 3-6, as well as the single-crystal X-ray structures for 3 and 4. t-Bu
\
x I
Ph-P-M-P 1-BU yI
'
/
t-Bu Ph
FBu
3: M = R(II); X E Y E CI 4: M = Pd(II); X E Y = CI 5: M = Rh(0; X = CI;Y = CO 6 M = Ir(I): X = CI; Y = CO
Results Complexes 3 and 4 were recrystallized several times from 1 :1 CH2C12/CH30Hto yield yellow crystals suitable for single-crystal X-ray analysis. Crystals of 3 and 4 are isomorphous and orthorhombic and belong to the Pbca space group. In both crystal structures 7 and 8, the metal atom resides on a crystallographic inversion center. The overall geometry at the metal template is approximately square planar with P( 1 )-M-P and Cl( 1)-M-Cla (6) Mason, R.; Bailey, N. A. J . Chem. SOC.A 1968, 2594. Otsuka, S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J . Am. Chem. sot. 1976,98,5850. Hoffman, P. R.;Yoshida, T.; Okano, S.;Ibers, J. A. h o r g . Chem. 1976, 15, 2462. Immirizi, A,; Musco, A. J . Chem. Soc. Chem. Ch"n.1974,400. Cardin, C. J.; Muir, K. W. J . Chem. SOC.,Dolton Trans. 1977, 1593. Bailey, N. A.; Jenkins, J. M.; Mason, R. Shaw, B. L. Chem. Commun. 1965, 237. (7) (a) Bushweller, c. H.;Hoogasian, S.; English, A. D.;Miller, J. S.; Lourandos, M. Z. Inorg. Chem. 1981,20,3448. (b) Mann, B. E.; Shaw, B. L.; Stainbank, R. E. J . Chem. SOC.D 1971, 1103. (c) Mann, B. E.;Shaw, B. L.; Slade, R. M. J. Chem. Soc. A 1971,2976. (d) Emphall, H. D.;Hyde, E.M.;Mentzer. E.; Shaw. B. L. J . Chem. SOC.Chem. Commun. 1977,2285. (e) Smith, J. G.;Thompson, D.T.J . Chem. SOC. A 1%7,1694. ( f ) Bennett, M. A.; Tomkins, 1. B. J . Orgammer. Chem. 1973,51, 289. (g) Faller, J. W.; Johnson, B. V. J . Organomer. Chem. 1975, 96,99. (h) Reed, C. A.; Roper, W. R. J. Chem. SOC.,Dalton Trans. 1978, 1365. (8) (a) Bright, A.; Mann, B. E.; Masters, C.; Shaw, B. L.; Slade, R. M.; Stainbank, R. E. J . Chem. SOC.A 1971, 1826. (b) Otsuka, S.; Yoshida, T.; Okano, T.; Ibers, J. A. Inorg. Chem. 1976, 15, 2462. (c) Otsuka, S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J . Am. Chem. Soc. 1974, 96, 3322. (9) Rithner, C. D.;Bushweller, C. H. J . Am. Chem. Soc. 1985, 107,7823.
V
8
In both 7 and 8, the phenyl groups are anti to each other and the molecular symmetry is Ci. The preferred conformation in the free phosphine is essentially maintained by the phosphine ligand in the metal c ~ m p l e x .However, ~ nonbonded interactions between the butressed phenyl group and the chlorine force the phenyl group away from the CI-M-CI axis causing a twist about each M-P bond. In structure 7,the CI(1)-Pt-P( I)
