Intermolecular proton-hydride bonding in ion pairs:: Synthesis and structural properties of [K(Q)][MH5(PiPr3)2] (M = Os, Ru; Q=18-crown-6, 1-aza-18-crown-6, 1,10-diaza-18-crown-6)

The salts [K(Q)]MH5((PPr3)-Pr-i)(2)] (1Os, 1Ru, Q = 18-crown-6; 2Os, 2Ru, Q = 1-aza-18-crown-6; 3Os, 3Ru, Q = 1,10-diaza-18-crown-6) were prepared by the reaction of OsH2Cl2(PiPr(3))(2) or RuCl3/2.5PiPr(3) with KH in the presence of one of these crown ethers under an atmosphere of H-2 and were characterized by NMR and infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The X-ray structures of 3Os and 3Ru indicate that short intermolecular proton-hydride interactions between the hydrides of the anion and the NH moieties of the cation cause the self-assembly of one-dimensional networks of pentagonal bipyramidal [MH5((PPr3)-Pr-i)(2)](-) anions and [K(diaza-18-crown-6)](+) cations. The X-ray structures of 2Os and 2Ru indicate that these also form one-dimensional chains due to MH ... HN and weak MH ... HC interactions between the hydrides of the anions and the NH and methylene CH of the [K(aza-18-crown-6)](+) cation. The MH ... HN distance is 1.7 Angstrom for both 2Os and 2Ru and 1.9 and 1.8 Angstrom for 3Os and 3Ru, respectively. These distances were calculated by assigning a value of 1.0 Angstrom to the N-H bond length and using the refined average Os-H and Ru-H distances of 1.56(4) and 1.58(3) Angstrom observed in 1Os and 1Ru. Values of 2.2 and 2.1 Angstrom were similarly obtained for the MH ... HC distances in 2Os and 2Ru, respectively, using a value of 1.09 Angstrom for the C-H bond length. The solid-state infrared spectra of 2Os, 3Os, 2Ru, and 3Ru show shifts in the NH, OsH, and RuH bands to lower frequencies relative to the free NH bands in [K(1-aza-18-crown-6)][BPh4] and [K(1,10-diaza-18-crown-6)][BPh4] and unperturbed OsH and RuH bands in 1Os and 1Ru. Solution NMR and infrared spectra and T-1, NOE, and NOESY experiments demonstrate that the MH ... HN interactions persist in solutions of these complexes. The THF solutions of the salts containing proton -hydride bonds undergo efficient H/D exchange with D-2 gas, resulting in deuteration of the hydrides of the [MH5((PPr3)-Pr-i)(2)](-) anion and the NH hydrogens of the [K(1,10-diaza-18-crown-6)](+) cation. On the other hand, complexes 1Os and 1Ru that do not have MH ... HN bonding do not undergo H/D exchange with D-2 gas. The relative strength of the proton-hydride bonds in the osmium and ruthenium complexes, as evidenced by their NMR and infrared spectral characteristics, is related to the magnitude of the acid dissociation constants of the respective conjugate acids of the anions.