C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE PROPERTIES OF THE UNSATURATED ANION {[RE3(MU-H)4(CO)9(NCME)]- AT LOW-TEMPERATURE}

The carbonyl resonances of [Re3(μ-H)4(CO)9(NCMe)]- have been assigned and the 13C spin-lattice relaxation times measured at different field strengths (20.15,50.31, and 75.43 MHz) at 238 K. The results indicate that scalar coupling of the second kind with rhenium isotopes is the dominant relaxation mechanism at this temperature. Values of T1Q (Re) and 1J(187Re-C) were calculated. The presence on the H2Re(CO)3(NCMe) moiety of a poor π-acceptor ligand doubles 1J(187Re-C) with respect to the unsubstituted H2Re(CO)4 moiety in the precursor [Re3(μ-H)4(CO)10]-.