SYNTHESIS AND STRUCTURE OF NEW MOLYBDENUM PI-ALLYL COMPLEXES - UNEXPECTED HYDROLYSIS OF TRIS(3,5-DIMETHYL-1-PYRAZOLYL)PHOSPHINE OXIDE

The reaction of tris(3,5-dimethyl-l-pyrazolyl)phosphine oxide (1) with (CH3CN)2(CO)2MoX(eta-3CH2CHRCH2) (3a-d; R = H, CH3, Ph; X = Cl, Br) gave products 4a-c (R = H, CH3, Ph) in which the ligand 1 was partially hydrolyzed. The proton NMR spectra of complexes 4a-c were dynamic due to [GRAPHICS] nonrigidity of these molecules. The structure of the complex 4c (R = Ph) was established by X-ray diffraction. The compound C21H23MoPO4N4 crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 10.013 (1) angstrom, b = 14.154 (2) angstrom, c = 15.951 (2) angstrom, V = 2260.7 (5) angstrom 3, Z = 4, and rho-(calcd) = 1.77 g cm-3. With use of Cu K-alpha radiation, for 1842 observed reflections (omega-2-theta mode, maximum theta = 60-degrees), the structure was refined to R = 0.0817; the largest shift/esd was 0.08. The crystal structure showed that one pyrazole group was replaced by oxygen; the oxygen was placed cis to the allyl group. EHMO calculations indicated that such a conformation was more stable than the one where oxygen was trans to the allyl group.