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 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 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 pK_b 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.