Low-Valent Titanium Species Stabilized with Aluminum/Boron Hydride Fragments

Low-valent titanium species were prepared by reaction of [TiCp*X-3] (Cp*=eta(5)-C5Me5; X=Cl, Br, Me) with LiEH4 (E=Al, B) or BH3(thf), and their structures elucidated by experimental and theoretical methods. The treatment of trihalides [TiCp*X-3] with LiAlH4 in ethereal solvents (L) leads to the hydride-bridged heterometallic complexes [{TiCp*(mu-H)}(2){(mu-H)(2)AlX(L)}(2)] (L=thf, X=Cl, Br; L=OEt2, X=Cl). Density functional theory (DFT) calculations for those compounds reveal an open-shell singlet ground state with a Ti-Ti bond and can be described as titanium(II) species. The theoretical analyses also show strong interactions between the Ti-Ti bond and the empty s orbitals of the Al atom of the AlH2XL fragments, which behave as sigma-accepting (Z-type) ligands. Analogous reactions of [TiCp*X-3] with LiBH4 (2 and 3 equiv.) in tetrahydrofuran at room temperature and at 85 degrees C lead to the titanium(III) compounds [{TiCp*(BH4)(mu-X)}(2)] (X=Cl, Br) and [{TiCp*(BH4)(mu-BH4)}(2)], respectively. The treatment of [TiCp*Me-3] with 4 and 5 equiv. of BH3(thf) produces the diamagnetic [{TiCp*(BH3Me)}(2)(mu-B2H6)] and paramagnetic [{TiCp*(mu-B2H6)}(2)] complexes, respectively.

Automated summary

Low-valent titanium species were prepared by reacting [TiCp*X-3] with LiEH4 or BH3(thf), and their structures were elucidated using experimental and theoretical methods. The compounds can be described as either titanium(II) or titanium(III) species, with specific molecular structures and interactions between the Ti-Ti bond and the Al atoms.