Phosphorus-31 Chemical Shift Anisotropies in Solid, Octahedral Chromium(0) Triphenylphosphine Derivatives

Article abstract of DOI:10.1021/ic960816u

The ³¹P chemical shift anisotropies have been measured at 293 K for the triphenylphosphine ligands in solid pentacarbonyl(triphenylphosphine)chromium(0), Cr(CO)₅(PPh₃) (1), and cis- and trans-tetracarbonyl(triphenylphosphine)(thiocarbonyl)chromium(0), Cr(CO)₄(PPh₃)(CS) (2 and 3). The major changes in the shift tensors occur for the δ₁₁ and δ₂₂ components perpendicular to the Cr-P bond direction. The individual tensor components of the ³¹P chemical shifts are clearly more important than are the isotropic values in providing information on the chromium-phosphorus bonding. The crystal structure of 3 has been determined by single-crystal X-ray diffraction. The complex crystallizes in the monoclinic P2₁/n (No. 14) space group with cell constants (at 293 K) a = 9.558(5) A?, b = 15.275(2) A?, c = 15.341(2) A?, β = 96.66(2)°, V = 2225(1) A?³ and Z = 4; R = 0.069 and R_w = 0.067. The crystal structure of 1 has been reported previously and most of the structural features are quite similar to those for 3. For instance, the Cr-P distances are 2.422(4) A? for 1 and 2.424(4) A? for 3. The P-Cr-C(S) and Cr-C-S linkages in 3 are almost linear with the angles being 178.4(4) and 174.1(9)°, respectively. The most significant difference between 1 and 3 is that Cr-C(X) (X = O, S) distance trans to PPh₃ is appreciably shorter for the thiocarbonyl, viz., 1.79(1) vs 1.845(4) A?. This shortening would be expected if CS is a much better π-acceptor ligand than is CO, as is thought to be the case.