Synthesis and properties of the 16-electron complex [(C5Me5)RuCl(PMeiPr2)] and of half-sandwich ruthenium hydrido complexes containing bulky monodentate phosphine ligands

The 16-electron complex [(C5Me5)RuCl(PMeiPr2)] (1) was obtained by reaction of [{(C5Me5)RuCl}4] with PMeiPr2 in petroleum. This compound appears to be in equilibrium with the dimer [{(C5Me5)Ru(PMeiPr2)}2(μ-Cl)2] as inferred from low-temperature NMR studies. The 18-electron complex [(C5Me5)RuCl(PMeiPr2)2] was formed upon addition of PMeiPr2 to 1. The related species [(C5H5)RuCl(PMeiPr2)2] (2) was obtained by reaction of [(C5H5)RuCl(PMeiPr2)(PPh3)] with PMeiPr2, followed by column chromatography. A range of RuIV dihydrides [(C5R5)RuH2(PR3)2][BPh4] (R=Me, H; PR3=PMeiPr2, PEt3) have been prepared and characterised. The corresponding monohydrido complexes [(C5R5)RuH(PR3)2] were obtained by deprotonation of the cationic dihydrides. Protonation at low temperature of either of these monohydrido complexes yielded back the corresponding dihydrido derivative, except in the case of [(C5Me5)RuH(PEt3)2], for which the metastable cationic dihydrogen complex [(C5Me5)Ru(H2)(PEt3)2]+ was obtained and characterised by NMR spectroscopy. This compound rearranges to its dihydrido tautomer as the temperature is raised, and a kinetic study of such process was accomplished. Interestingly, the only isolable dinitrogen adduct of the type [(C5R5)Ru(N2)(PR3)2][BPh4] among all possible combinations of phosphines and cyclopentadienyl ring substituents was [(C5Me5)Ru(N2)(PEt3)2][BPh4].