SYNTHESIS AND NMR T(1) RELAXATION STUDY OF RHENIUM AND MANGANESE HYDRIDE COMPLEXES

Some new and known hydride complexes of manganese (MnH(NO)2(PEt3)2, Mn H(CO)3(PEt3)2) and rhenium (ReH(CO)n(PMe3)5-n, n = 1, 2, 3;ReH2(CO)(NO )(PR3)2) were prepared. H-1 selective and nonselective relaxation time s were determined as a function of temperature for each compound. From the measurements, the contributions of the M-H dipole-dipole interact ion to the relaxation times of the H ligands were isolated, and the M- H bond lengths were calculated using the model of an isotropic motion. In all cases reasonable M-H bond distances from 1.60 (Mn-H) to 1.77 a ngstrom (Re-H) have been obtained in spite of clear evidence for an an isotropic rotation of the investigated hydrides. Possible errors in su ch calculations (<4%) have been examined by an analysis of anisotropic effects using Woessner's equation and an approach based on a distribu tion of molecular correlation times. Thus the isotropic motion approac h, even though not strictly correct, is of high potential value in the elucidation of structural features of mononuclear hydride complexes i n solution.