SYNTHESIS AND REACTIVITY OF HYDRIDOTRIS(PYRAZOLYL) BORATE DIHYDROGEN RUTHENIUM COMPLEXES

The reaction of various hydridotris(pyrazolyl) borate salts with RuHCl(COP)(bpm) (3) (bpm = bispyrazolylmethane; COD = 1,5-cyclooctadiene) produces LRuH(COD) (L = hydridotris(3,5-dimethylpyrazolyl) borate, Tp*, 4a; hydridotris(3-isopropyl-4-bromopyrazoly) borate, Tp',4b). Hydrogenation of 4a,b under 3 bar of dihydrogen in pentane yields LRuH(H-2)(2) in high yield (L = Tp*, 5a; L = Tp', 5b). 5a,b were characterized by classical analytical and spectroscopic methods including T-1 measurements (5a, T-1min = 26 ms at 163 K, 400 MHz; 5b, T-1min = 28 ms at 182 K, 300 MHz) and by partial deuteration leading to the sequential observation of the series of isotopomers LRuH(5-x)D(x) (x = 1-4). The observed J(H-D) coupling constant in these isotopomers of 5a and 5b, respectively 5.4 and 5.2 Hz, allows the calculation of J(H-D) of coordinated hydrogen deuteride, namely 27 and 26 Hz, in agreement with two unstretched dihydrogen ligands. Hydrogenation of 4a or 4b in the presence of a ligand L' or substitution of H-2 by L' in 5a or 5b leads to the new hydrido dihydrogen complexes LRuH(H-2)L' (L' = PCy(3), L = Tp*, 6a; L = Tp', 6b; L' = THT, L = Tp*, 7a; L = Tp', 7b; L' = py, L = Tp*, 8a; L = Tp', 8b; L' = NHEt(2), L = Tp*, 9a). Hydrogenation of 4a in the presence of excess ligand L' leads to the disubstituted complexes Tp*RuH-(L')(2) (L' = py, 10a; L' = THT, 11a). T-1 measurements for 10a and 11a allow the determination of the relaxation for a monohydride in these systems, and thus the calculation of the H-H distance of the coordinated dihydrogen molecules in 5a-9a yields values in each case near 0.9 Angstrom. Substitution of H-2 in 5a occurred with CO to yield Tp*RuH(CO)(2) (12a). Surprisingly, 5a does not react with CH3I, CH3COOH, and CF3COOH but does with HBF4 . Et(2)O and CF3SO3H. The latter reaction leads in the presence of MeCN to [Tp*Ru(MeCN)(3)](CF3SO3) (14a). Finally, both 5a and 5b readily undergo H/D exchange at room temperature between deuterated aromatic solvents (C6D6 or C6D5CD3) and both the ruthenium bound hydrogens and the methyl and pyrazolyl groups of the ligands, thus demonstrating the high reactivity of these compounds for C-H activation.