The effect of ligand basicity on the unconventional hydrogen-bond in H(mu-H)Os-3(CO)(10)L (L = amine) derivatives

The reaction of amine ligands with the unsaturated 46e(-) cluster Os-3(mu-H-2)(CO)(10) yields a series of complexes of formula Os3H(mu-H)(CO)(10)(amine). In these derivatives the presence of an unconventional hydrogen-bond M-H...H-N is detected by the evaluation of proton spin-lattice relaxation times. In order to elucidate the relationship between pK(b) and H...H length. the M-H...H-N distances were quantified for amines of known pK(b). In practice, this was achieved by comparing the T-1 values of the terminal hydride resonances of the protonated isotopomer with the T-1 values of the corresponding derivative containing selectively deuterated amine. A nice correlation between the M-H...H-N distances and the pK(b) of the amine ligands was found. DFT calculations were carried out for the cluster on Os3H(mu-H)(CO)(10)(Benzylamine) to gain a fuller understanding of the possible coordination geometries of an amine ligand on the surface of a tri-osmium cluster.