Synthesis of di-, tri- and penta-nuclear titanium(IV) species from reactions of titanium(IV) alkoxides with 2,2'-biphenol (H(2)L(1)) and 1,1'-binaphthol (H(2)L(2)); crystal structures of [Ti(3)(mu(2)-OPr(i))(2)(OPr(i))(8)L(1)], [Ti(3)(OPr(i))(6)L(1)(3)], [Ti(5)mu(3)-O)(2)(mu(2)-OR)(2)(OR)(6)L(1)(4)](R = OPr(i), OBu(n)) and [Ti(2)(OPr(i))(4)L(2)(2)].

Reaction of titanium(iv) alkoxides [Ti(OR)(4)](R = OPr(i), OBu(n)) with 2,2[prime or minute]-biphenol [C(12)H(8)(OH)(2), H(2)L(1)] affords two trinuclear species [Ti(3)(OPr(i))(10)L(1)] and [Ti(3)(OPr(i))(6)L(1)(3)] each possessing an open-chain V-shaped arrangement of three titanium atoms with the former having both bridging alkoxide and biphenylate groups and the latter having only biphenylate as bridging groups. Variations in reaction conditions yield the pentanuclear species [Ti(5)([micro sign](3)-O)(2)(OR)(8)L(1)(4)](R = OPr(i), OBu(n)) which have two central bridging oxygen atoms in the Ti(5) framework and bridging alkoxide and biphenylate groups. In contrast 1,1[prime or minute]-binaphthol [C(24)H(12)(OH)(2), H(2)L(2)] yields the dinuclear [Ti(2)(OPr(i))(4)L(2)(2)] where only the binaphthylate ligands act as bridging groups. Some of the compounds show catalytic activity in esterification reactions.

Ruthenium dihydride complexes: NMR studies of intramolecular isomerization and fluxionality including the detection of minor isomers by parahydrogen-induced polarization.

NMR studies reveal that complexes Ru(CO)(2)(H)(2)L(2) (L = PMe(3), PMe(2)Ph, and AsMe(2)Ph) can have three geometries, ccc, cct-L, and cct-CO, with equilibrium ratios that are highly dependent on the electronic properties of L; the cct-L form is favored, because the sigma-only hydride donor is located trans to CO rather than L. When L = PMe(3), the ccc form is only visible when p-H(2) is used to amplify its spectral features. In contrast, when L = AsMe(2)Ph, the ccc and cct-L forms are present in similar quantities and, hence, must have similar free energies; for this complex, however, the cct-CO isomer is also detectable. These complexes undergo a number of dynamic processes. For L(2) = dppe, an interchange of the hydride positions within the ccc form is shown to be accompanied by synchronized CO exchange and interchange of the two phosphorus atoms. This process is believed to involve the formation of a trigonal bipyramidal transition state containing an eta(2)-H(2) ligand; in view of the fact that k(HH)/k(DD) is 1.04 and the synchronized rotation when L(2) = dppe, this transition state must contain little H-H bonding character. Pathways leading to isomer interconversion are suggested to involve related structures containing eta(2)-H(2) ligands. The inverse kinetic isotope effect, k(HH)/k(DD) = 0.5, observed for the reductive elimination of dihydrogen from Ru(CO)(2)(H)(2)dppe suggests that substantial H-H bond formation occurs before the H(2) is actually released from the complex. Evidence for a substantial steric influence on the entropy of activation explains why Ru(CO)(2)(H)(2)dppe undergoes the most rapid hydride exchange. Our studies also indicate that the species [Ru(CO)(2)L(2)], involved in the addition of H(2) to form Ru(CO)(2)(H)(2)L(2), must have singlet electron configurations.