DEUTERIUM QUADRUPOLE COUPLING-CONSTANTS AND IONIC BOND CHARACTER IN TRANSITION-METAL HYDRIDE COMPLEXES FROM H-2 NMR T1 RELAXATION DATA IN SOLUTION

H-2 T1 NMR relaxation times have been measured in solution for the D l igands of some transition metal hydride complexes and used for the cal culation of deuterium quadrupole coupling constants (DQCC) and of the ionic contribution to the M-D bond. The DQCC values for the terminal h ydride complexes WD(CO)2(NO)(PR3)2 (R = CH3, Ph), MnD(NO)2(PEt3)2, MnD (CO)3(PEt3)2, ReD2(CO)(NO)(PR3)2 (R = CH3, Cy, Pr(i), OPr(i)), cis- an d trans-ReD(CO)(PMe3)4, cis,mer-ReD(CO)2(PMe3)3, trans,mer-ReD(CO)3(PM e3)2,fac-Red(CO)3(PMe3)2, OsD4(PTol3)3, RhDCl2(PPri3)2, and RhD2Cl(PPr i3)2 cover a range from 55 to 158 kHz. Values of 148 and greater-than- or-equal-to 120 kHz have been obtained for two nonclassical dihydrogen ligands of the complexes ReD(D2)(CO)(NO)(PMe3)2+ and Re(D2)(CO)-(PMe3 )4+ assuming their rapid rotation. The DQCC as well as the ionicity of the M-D bond is discussed in terms of structural parameters and subst itution patterns of these complexes.