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

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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 Ci() 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.

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