Some New Dicationic Dihydrogen Complexes of Ruthenium

A series of new dicationic dihydrogen complexes of ruthenium of the type $trans-[(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2$ $[dppe = Ph_2PCH_2CH_2PPh_2; R = CH_3, CH_3CH_2, CH_3CH_2CH_2, CH_2=CH, p-CH_3-C_6H_4-CH_2, C_6H_5, and (CH_3)_2N]$ have been prepared by the protonation reaction of the precursor hydrides, trans- $[(dppe)_2Ru(H)(RCN)][BF_4]$ using $HBF_4·OEt_2$. The variable temperature spin-lattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2$ -HD isotopomers indicate the intact nature of the H-H bond in these complexes. It was found that the spectroscopic and chemical properties of these derivatives are not very sensitive to the change in the trans nitrile ligand. The $pK_a$ values of the dihydrogen complexes have been determined using the equilibrium: trans- $[(dppe)_2Ru(H)(RCN)][BF_4] + HBF_4\cdot OEt_2 \rightleftharpoons trans- [(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2 + Et_2O$ by $^1H\hspace{2mm}NMR$ spectroscopy.