The effect of ligand basicity on the unconventional hydrogen-bond in H(μ-H)Os3(CO)10L (L=amine) derivatives

The reaction of amine ligands with the unsaturated 46 e− cluster Os3(μ-H2)(CO)10 yields a series of complexes of formula Os3H(μ-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 pKb and H⋯H length, the MH⋯HN distances were quantified for amines of known pKb. In practice, this was achieved by comparing the T1 values of the terminal hydride resonances of the protonated isotopomer with the T1 values of the corresponding derivative containing selectively deuterated amine. A nice correlation between the MH⋯HN distances and the pKb of the amine ligands was found. DFT calculations were carried out for the cluster on Os3H(μ-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.