Synthesis, Structure, Coordination Expansion and Theoretical Modelling of Dichlorobis(phenoxo) Titanium( IV ) Complexes

Thermalisation of TiCl 4 and two equivalents of a phenol in toluene is found to be the best preparative method for quantitative yields of a variety of dichlorobis(phenoxo) complexes. [TiCl 2 (OC 6 H 4 CMe 3 ‐4) 2 ] ( 1 ) is monomeric in benzene, a phenoxo‐bridged dimer in the solid state and undergoes coordination expansion with 4,4 ' ‐dimethyl‐2,2′‐bipyridine (dmbipy) to give [TiCl 2 (OC 6 H 4 CMe 3 ‐4) 2 (dmbipy)] ( 2 ). Also monomeric are [TiCl 2 (OC 6 H 2 Me 3 ‐2,4,6) 2 ] ( 3 ) and [TiCl 2 (OC 6 H 3 i Pr 2 ‐2,6) 2 ] ( 5 ) which expand their coordination with dmbipy to give [TiCl 2 (OC 6 H 2 Me 3 ‐2,4,6) 2 (dmbipy)] ( 4 ) and [TiCl 2 (OC 6 H 3 i Pr 2 ‐2,6) 2 (dmbipy)] ( 6 ). In contrast [TiCl 2 (OC 6 H 2 {CMe 3 } 2 ‐2,6‐Me‐4) 2 ] ( 7 ) is only partially formed by the thermolysis reaction and does not coordinatively expand with dmbipy. [TiCl 2 (OC 6 H 3 Me 2 ‐2,4) 2 ] ( 8 ) is monomeric in benzene and reacts to form [TiCl 2 (OC 6 H 3 Me 2 ‐2,4) 2 (dmbipy)] ( 9 ). [TiCl 2 (OC 6 H 3 {CMe 3 } 2 ‐2,4) 2 ] ( 10 ) forms along with the tri‐phenoxo complex [TiCl{OC 6 H 3 (CMe 3 ) 2 ‐2,4} 3 ]. [TiCl 2 (OC 6 H 3 CMe 3 ‐2‐Me‐6) 2 ] ( 11 ) is monomeric in benzene and forms [TiCl 2 (OC 6 H 3 CMe 3 ‐2‐Me‐6) 2 (dmbipy)] ( 12 ). 2‐Phenylphenol and 1‐napthol form [TiCl 2 (OC 6 H 4 Ph‐2) 2 ] ( 13 ) and [TiCl 2 (OC 10 H 9 ) 2 ] ( 14 ) which are monomeric in benzene. DFT calculations give structural parameters for monomeric [TiCl 2 (OC 6 H 5 ) 2 ] ( 15 ) in good agreement with the X‐ray data for [TiCl 2 (OC 6 H 3 Me 2 ‐2,6) 2 ]. Each oxygen of the phenoxo ligand in 15 acts essentially as a 2π donor to titanium and there is substantial p π (O)‐p π *(C=C) backbonding with the phenyl ring, which is absent in [TiCl 2 (OCH 3 ) 2 ] ( 16 ). The global minimum for the dimer [(TiCl 2 {OC 6 H 5 }{μ‐OC 6 H 5 }) 2 ] is in almost perfect agreement with the crystal structure obtained for [(TiCl 2 {OC 6 H 5 }{μ‐OC 6 H 5 }) 2 ] or [(TiCl 2 {OC 6 H 4 CMe 3 ‐4}{μ‐OC 6 H 4 CMe 3 ‐4}) 2 ] ( 1 ). The dimerisation energy for 15 is–26.2 kJ · mol –1 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)