Stereodynamics of sterically crowded metal-phosphine complexes: trans-[(t-Bu){sub 2}P(l-Pr)]{sub 2}MCl{sub 2} [M = Pt(II) and Pd(II)]. One-dimensional dynamic and two-dimensional chemical exchange NMR studies, X-ray crystallographic studies, molecular conformation trapping, and molecular mechanics calculations
- Univ. of Vermont, Burlington, VT (United States); and others
By using complementary techniques including dynamic NMR (DNMR) spectroscopy, X-ray crystallography, molecular conformation trapping and molecular mechanics calculations, incisive pictures of the stereodynamics of two sterically crowded Pd(II) and Pt(II) complexes have been elucidated. X-ray crystallography shows that the molecular geometry in the only crystalline modification (P2{sub 1}/a space group) of trans-[(t-Bu){sub 2}P(i-Pr)]{sub 2}PdCl{sub 2} (1) has C{sub i} symmetry. The isopropyl groups are mutually anti; the dihedral angle between the two P-CH bonds is 180{degrees}. For the isopropyl group on each phosphine ligand, one methyl group is anti and the other gauche ot the palladium atom. There are significant torsions about Pd-P,P-(i-Pr) and P-(t-Bu) bonds including a dihedral angle between proximate P-CH and Pd-Cl bonds of 21.6{degrees}. On the basis of the hypotheses that (a) when placed in solution, the conformation of each phosphine ligand of 1 will adopt an essentially exclusive preference for that in the crystal and (b) the two phosphines act essentially independently of each other, four stable diastereomeric equilibrium conformations are predicted. In two diastereomeric conformations, the isopropyl groups are mutually syn with dihedral angles between the P-CH bonds of 44{degrees} (C{sub 2} symmetry) and 0{degrees} (C{sub s} symmetry). In the other two diastereomeric forms, the isopropyl groups are mutually anti with dihedral angles between the P-CH bonds of 136{degrees} (C{sub 2} symmetry) and 180{degrees} (C{sub i} symmetry). Two-dimensional {sup 31}P({sup 1}H) NMR chemical exchange spectroscopy in conjunction with theoretical simulations of the one-dimensional {sup 31}P({sup 1}H) and {sup 13}C({sup 1}H)DNMR spectra do reveal the presence of four diastereomeric equilibrium conformations and allow elucidation of the preferred conformational interconversion pathways. 32 refs., 8 figs., 1 tab.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 458789
- Journal Information:
- Journal of Physical Chemistry, Vol. 96, Issue 22; Other Information: PBD: 29 Oct 1992
- Country of Publication:
- United States
- Language:
- English
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