| Abstract |
Two complete series of titanium complexes of the type [Ti(pyrrolyl)(NMe2)xCl(3-x)] (pyrrolyl = 2,3,4,5-tetramethylpyrrolyl (TMP), x = 3 (1), 2 (2), 1 (3), 0 (4); pyrrolyl = 2,5-dimethylpyrrolyl (DMP), x = 3 (5), 2 (6), 1 (7), 0 (8)) were prepared by reaction of equimolar amounts of either [Ti(NMe2)(x)Cl4-x] (x = 4, 3 and 2) with the corresponding pyrrole (1-3 and 5-7) or TiCl4 with Li(pyrrolyl) (4 and 8). A study on the effect on the pyrrolyl coordination mode of the number of strong pi-donor amido ligands present in the Ti coordination sphere was carried out by C-13 NMR spectroscopy and by X-ray diffraction, when possible. For both pyrrolyl ligands, the eta(5)-coordination to the metal is favoured when there are two or less coordinated amido ligands. However, the presence of a third amido ligand inhibits this type of coordination, shifting the pyrrolyl ring to a sigma N binding mode (eta(1)), due to an increase of the electron density at the metal centre. For these two complete series of Ti monopyrrolyl complexes we have observed that C-13 NMR deshielding parameters (in relation to the parent pyrrole molecules), in the absence of detectable eta(5)-eta(1) dynamic behaviour, could be used as an assignment criterion for the N-heterocyclic ring type of coordination in Ti pyrrolyl complexes. (C) 2010 Elsevier B.V. All rights reserved. |
