Stepwise reactions of TiCl4 and Ti((OPr)-Pr-i)Cl-3 with 2-propanol. Variable-temperature NMR studies and crystal structures of [TiCl2((OPr)-Pr-i)((HOPr)-Pr-i)(mu-Cl)](2) and [TiCl2((OPr)-Pr-i)((HOPr)-Pr-i)(mu-(OPr)-Pr-i)](2)

The reactions of TiCl4 and Ti((OPr)-Pr-i)Cl-3 with 1-3 molar equiv of 2-propanol give the dimeric complexes [TiCl3((HOPr)-Pr-i)(mu-Cl)](2) (1), [TiCl2((OPr)-Pr-i)((HOPr)-Pr-i)(mu-Cl)](2) (2), and [TiCl2((OPr)-Pr-i)((HOPr)-Pr-i)(mu-(OPr)-Pr-i)](2) (3). The reactions are shown to proceed stepwise with the consecutive addition of 2-propanol. Complexes 2 and 3 are dynamic in solution. However, the proton VT NMR studies show that they are static and remain the dimeric features in solution at low temperatures. Two inequivalent methyl environments are observed for the 2-propanol ligand of complex 3, probably due to the intramolecular hydrogen bonding from the isopropanolic hydrogen to the chloride on the second titanium metal center. 2 crystallizes in the orthorhombic space group Pbca with cell parameters of a = 12.605(3) Angstrom, b = 12.841(4) Angstrom, c = 15.414(4) Angstrom, Z = 4, D-calcd = 1.456 g/cm(3), R = 0.049, R(w) = 0.062, and G(OF) = 1.38. 3 crystallizes in the monoclinic space group P2(1)/c with cell parameters of a = 9.457(2) Angstrom, b = 15.277(2) Angstrom, c = 11.354(4), beta = 112.76(2)degrees, Z = 2, D-calcd = 1.305 g/cm(3), R = 0.032, R(w) = 0.048, and G(OF) = 1.29. Through the analysis of the bonding features of the solid-state structures 2 and 3, the relative bonding sequence of (OPr)-O---Pr-i > Cl- > (HOPr)-Pr-i > mu-(OPr)-Pr-i > mu-Cl- is established. This bonding order is useful for the prediction of the geometries of six-coordinate titanium complexes containing those ligands with the rule ''the strong ligand prefers a position trans to the weak ligand in the complexes''. Besides, the reaction features demonstrated in this study may apply to the reaction of TiCl4 or Ti((OPr)-Pr-i)Cl-3 with diols, especially for chiral diols used as ligands in titanium complexes for various asymmetric syntheses of organic compounds.