Peripheral electrophilic properties of dichloro[NN′-ethylenebis(salicylideneiminato)]titanium(IV) : a route leading to a stable Ti–H–B unit

Abstract

The title complex [Ti(salen)Cl₂](1)[salen =NN′-ethylenebis(salicylideneiminate)] reacts with a thf solution of LiBH₄ to give [{Ti(salen)(BH₄)₂}₂]·2thf (2) as an orange crystalline solid. Complex (2) is formed by the substitution of Cl^– by BH₄^– followed by addition of BH₄^– to the imino-groups of the salen ligand. The i.r. spectrum shows the disappearance of bands due to –CN– and the presence of strong bands due to Ti–H and B–H vibrations, which are shifted to lower values in the deuteriated derivative [{Ti(salen)(BD₄)₂}₂]·thf (3). Crystals of (2) are formed in dimeric units having crystallographic C_i() symmetry. Each metal atom surrounded by the sexidentate ligand (salen)(BH₄)₂ having a H₂N₂O₂ set of donor atoms achieves seven-co-ordination by sharing one of the salen oxygens with the other titanium of the dimeric unit. Other relevant structural features of complex (2) are the presence of BNH₂ groups bonded to titanium through a bridging hydrogen, and the consequent existence of two electron-deficient four-membered rings, [graphic omitted]. The Ti(salen)(BH₄)₂ unit is supposed to form from a titanium-promoted activation of the CN– bond in [Ti(salen)Cl₂]. [{Ti(salen)(BH₄)₂}₂]·2thf (2) crystallises in the space group P2₁/c with a= 11.802(9), b= 20.039(15), c= 9.272(6)Å, β= 90.00(5)°, and Z= 2. The final R factor was 0.068 for 1 028 observed reflections.