CONFORMATIONAL PREFERENCES IN MOLYBDENUM(II) PI-ALLYL COMPLEXES - ROLE OF CH/PI INTERACTION

A series of isostructural complexes 1a-g of general formula LMo(CO)2(eta3-R1R3C=CHCHR2), where L = bis(3,5-dimethyl-1-pyrazolyl)phosphinate, R1, R3 = CH3, H, and R2 = CH3, C6H5, p-OCH3C6H4, p-NO2C6H4, were prepared and their solution conformations were studied. The close proximity of phenyl and methyl groups in certain conformations was shown to result from a CH/pi attractive interaction. The structure of the complex 1a (R2 = C6H5, R1, R3 = H) was determined by X-ray crystallography. The compound C21H23MoN4O4P crystallized in monoclinic space group P2(1)/n with a = 7.592(1) angstrom, b = 11.134(3) angstrom, c = 26.464(2) angstrom, beta = 95.02(1)-degrees, V = 2228.4(6) angstrom3, Z = 4, and mu(calc) = 1.56 g cm-3. Using Mo Kalpha radiation for 2480 observed reflections (omega/2theta scan mode, maximum theta = 23.5-degrees), the structure was refined to R = 0.038.