STRUCTURE AND STEREODYNAMICS OF [M(CO)5(P(C6H4ME-O)3)] (M = CR, MO ORW) AND [CR(CO)3(P(C6H4ME-O)3)]

The crystal structure of [Cr(CO)5{P(C6H4Me-o)3}] has been determined. It reveals an exo2 conformation for the phosphine ligand, in agreement with molecular mechanics calculations. Barriers to P-C rotation in th e series [M(CO)5{P(C6H4Me-o)3}] (M = Cr, Mo or W) are in the range 36- 42 kJ mol-1; restricted M-P rotation is also evident in the low-temper ature (CO)-C-13 NMR spectrum of [Cr(CO)5{P(CH4Me-o)3}]. The crystal st ructure of the pi complex [Cr(CO)3{P(C6H4Me-o)}3] is most consistent w ith an electron-acceptor character for the P(C6H4Me-o)2 substituent. C rystal data: [Cr(CO)5{P(CH4Me-o)3}], monoclinic, space group P2(1)/n, a = 10.774(2), b = 14.951 (5), c = 14.687(7) angstrom, beta = 91.45(2) -degrees, Z = 4, R' = 0.0980 for 209 variable parameters and 2326 obse rved reflections; [Cr(CO)3{P(C6H4Me-o)3}], monoclinic, space group P2( 1)/a, a = 16.725(2), b = 7.340(1), c = 17.675(4), beta = 92.66(2)-degr ees, Z = 4, R' = 0.1187 for 263 variable parameters and 1848 observed reflections.