RESTRICTED METAL ARENE AND PHOSPHORUS CARBON BOND ROTATION IN (ARENE)CR(CO)2L COMPLEXES (L = PPH3, P(O-TOLYL)3)

(1,4-Di-tert-butylbenzene)Cr(CO)2PPh3 exhibits restricted arene-Cr bond rotation in solution (DELTAG(double dagger)203 = 31.6 kJ mol-1). A series of (arene)Cr(CO)2P(o-tolyl)3 complexes have been prepared which exhibit restricted P-C rotation in solution; in cases where planar chirality is present, diastereoisomers may be observed which differ in the helicity of the exo2 phosphine conformation. Diastereoisomer interconversion and o-tolyl ring exchange occur with very similar activation energies. Crystal structure data: (1,4-di-tert-butylbenzene)Cr(CO)2PPh3, monoclinic, space group P2(1)/n, a = 10.137(1) angstrom, b = 13.992(2) angstrom, c = 20.882(3) angstrom, beta = 96.16(2)-degrees, Z = 4, R(w) = 9.18% for 345 refined parameters and 3643 observed reflections; (p-xylene)Cr(CO)2P(o-tolyl)3, monoclinic, space group P2(1)/n, a = 8.552(1) angstrom, b = 17.410(2) angstrom, c = 17.558(2) angstrom, beta = 91.95(2)-degrees, Z = 4, R(w) = 9.96% for 317 defined parameters and 3392 observed reflections; (benzene)Cr-(CO)2P(M-tolyl)3, monoclinic, space group P2(1)/n, a = 11.120(3) angstrom, b = 11.227(1) angstrom, c = 20.289(4) angstrom, beta = 100.63(2)-degrees, Z = 4, R(w) = 6.49% for 299 defined parameters and 3127 observed reflections.