SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF RUTHENIUM(II) ETA-2-DIHYDROGEN COMPLEXES OF THE TYPE [RUH(ETA-2-H2)(L) (TRIPHOS)]+ (L = CO, P(OCH2)3CET, PME2PH - TRIPHOS = PPH(CH2CH2PPH2)2)

The dihydride complexes RuH2(L)(triphos) (L = CO (4), P(OCH2)3CEt (5), PMe2Ph (6); triphos = PPh(CH2-CH2PPh2)2) CH2PPh2)2) are prepared by reaction of RuCl2(L)(triphos) with NaBH4 in refluxing ethanol. Protonation of 4-6 in CD2Cl2 at 193 K with HBF4.OEt2 affords the eta2-dihydrogen complexes [RuH(eta2-H2)(L)(triphos)]+ (L = CO (7),P(OCH2)3CEt(8),PMe2Ph(9)). Deprotonation of 7-9 with NEt3 regenerates 4-6. The monohydride complexes [RuH(CH3CN)(L)(triphos)]BF4 (L = P(OCH2)3CEt (10), PMe2Ph (11)) are prepared from 8 and 9, respectively, by substitution of the eta2-dihydrogen ligand with CH3CN. The eta2-dihydrogen coordination in 7-9 is established by variable-temperature H-1 NMR T1 measurements and 1J(HD) coupling constants. Complex 7 is fluxional and gives a broad resonance in the hydride region of the H-1 NMR spectrum at all accessible temperatures, but the low T1(min) value of 8 ms suggests the presence of one eta2-dihydrogen ligand. The hydride region of the H-1 NMR spectrum of each of complexes 8 and 9 consists of a broad resonance for the eta2-dihydrogen ligand and a binomial pseudoquintet for the terminal hydride ligand. The T1(min) values of the eta2-dihydrogen resonance are 13 and 9 ms for 8 and 9, respectively. The chemical shifts of the eta2-HD resonances for the isotopomers [RuH(eta2-HD)(L)(triphos)]+ and [RuD(eta2-HD)(L)(triphos)]+ are different by 0.080 ppm for L = P(OCH2)3CEt and 0.067 ppm for L = PMe2Ph due to the higher trans influence of deuteride compared to that of hydride. These two isotopomers show a 1J(HD) coupling constant of 32.8 Hz for L = P(OCH2)3CEt and 32.2 Hz for L = PMe2Ph.