Effect of ancillary ligation on the relative bond disruption enthalpies of Ru-H and Ru-Cl bonds in Cp(PR3)(2)RuX (PR3 = PMe3, PMe2Ph, PMePh2, PPh3; X = H, Cl)

The ruthenium chloride and hydride complexes Cp(PR3)(2)RuH {X = Cl; PR3 = PMe3 (1), PMe2Ph (2), PMePh2 (3), PPh3 (4); X = H; PR3 = PMe3 (5), PMe2Ph (6), PMePh2 (7), PPh3 (8)} were studied by spectroscopy and solution calorimetry. The structures of 2 and 3 are reported and complete the structural characterization of the series 1-4. In this series, the Ru-Cl distance (2.449 +/- 0.007 Angstrom) remains constant, while the Ru-PR3 distance increases in the order 1 < 2 < 3 < 4. The ruthenium hydrides 5-8 were prepared from the reaction of the corresponding ruthenium chloride with KOMe in methanol. Spectroscopic data on hydrides 5-8 indicated that the ruthenium hydride interaction decreases in the order 5 > 6 > 7 > 8. Enthalpies of reaction for the hydride/chloride metatheses of 5-8 with chlorocarbons (CHCl3 or CCl4) were studied by solution calorimetry and allowed for the determination of Ru-Cl bond disruption enthalpies (BDEs) relative to the corresponding Ru-H BDEs. [BDE(Ru-Cl) - BDE(Ru-H)] values covered a 6 kcal/mol range with an average of 21.4 +/- 2.5 kcal/mol. The magnitude of [BDE(Ru-Cl) - BDE(Ru-H)] correlated with the number of methyl groups on the phosphine and was dependent on the electronic and steric properties of the phosphine.