REACTIVITY OF RUTHENIUM TRIHYDRIDES WITH BRONSTED AND LEWIS-ACIDS - X-RAY CRYSTAL-STRUCTURES OF (CP-STAR-RU[C6H9P(C6H11)2])BF4 AND ((CP-STAR-RUH[P(C6H11)3])(MU-H)2CU(MU-CL))2 - EVIDENCE FOR EXCHANGE COUPLING BETWEEN 2 HYDROGEN-ATOMS

The reaction of Cp*RuH3(PPh3) (1a; Cp* = C5Me5) with P(OMe)3 produces Cp*RuH(PPh3)[P(OMe)3] (2), whereas no reaction occurs between 1a and pyridine. The protonation of 1a by HBF4/Et2O yields [Cp*RuH2(PPh3)2]BF4 (3), but the same reaction with Cp*RuH3[P(c-C6H11)3] (1b) leads to the evolution of 3 mol of H-2 and formation of {Cp*Ru[C6H9P(c-C6H11)2]}BF4 (4). Complex 4 contains a cyclohexenyl group coordinated through the C = C double bond and a strong agostic interaction, as demonstrated by both an X-ray crystal structure determination and H-1 and C-13 NMR studies. The protonation of 1b with CF3COOH produces Cp*Ru(OCOCF3[P(c-C6H11)3] (5), in which the trifluoroacetato group is bidentate. The reactions of 1b with the Lewis acids [CuCl]n and [Cu(MeCN)4]BF6 lead to {[Cp*Ru[P(c-C6H11)3]H-(mu-H)2]Cu(mu-Cl)}2 (6), which was characterized by X-ray crystallography, and to {[Cp*Ru[P(c-C6H11)3]H-(mu-H)2]2Cu}PF6 (7), respectively. The anomalous H-1 NMR behavior of 1 is retained in 6 (viz. a single signal for the hydrides at room temperature and AB2 spectra showing large temperature-dependent coupling constants at lower temperature). However, three distinct signals are observed for the hydrides of 7 at low temperature, two of which are coupled with large temperature-dependent coupling constants. These phenomena are discussed in light of the new findings on exchange coupling in trihydride complexes. This is the first observation of exchange coupling between two hydrogen atoms only. Finally, 1b also reacts with AlCl3 to yield Cp*RuCl[P(c-C6H11)3] but not with BF3/Et2O. 4 crystallizes in the monoclinic space group P2(1), with a = 9.305 (1) angstrom, b = 16.101 (2) angstrom, c = 10.621 (1) angstrom, beta = 97.92 (1)degrees, V = 1576.1 (3) angstrom 3, and Z = 2. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R = 0.043 for 4052 reflections. In addition to the Cp* ligand and the phosphorus atom of the phosphine, the coordination around the ruthenium atom involves a cyclohexenyl group with three carbon atoms at bond distances from the metal center. Crystals of 6 are monoclinic, space group P2(1)/c, with a = 12.2131 (8) angstrom, b = 10.7975 (8) angstrom, c = 22.7072 (17) angstrom, beta = 104.16 (1)degrees, V = 2903.4 (4) angstrom 3, and Z = 2. The structure was solved by Patterson methods and refined to R = 0.040 for 3916 observed reflections. The molecule is centrosymmetric, with two {Cp*RuH[P(C6H11)3]}(mu-H)2Cu moieties bridged by two chlorine atoms. The Ru-Cu distance is short (2.651 (2) angstrom) and is bridged by two mu-2-hydride ligands.