Aryl imido complexes of the group 4 metals: Structural aspects and mechanistic study of formation
The addition of aniline (PhNH 2 ≥ 2 equivalents) to the organometallic compounds [Ti(OC 6 H 3 Pr i 2 -2,6) 2 (η 2 -Bu t NCCH 2 Ph)(CH 2 Ph)], [Ti(OC 6 H 3 Ph 2 -2,6) 2 (C 4 Et 4 )] and [Zr(OC 6 H 3 Bu t 2 -2,6) 2 (CH 3 ) 2 ] in hydrocarbon solvents leads to the formation of the mononuclear bis(phenylamido) derivatives [M(OAr) 2 (NHPh) 2 ] [M = Ti, OAr = OC 6 H 3 Pr i 2 -2,6 (1); M = Ti, OAr = OC 6 H 3 Ph 2 -2,6 (2); M = Zr, OAr = OC 6 H 3 Bu t 2 -2,6 (3)]. Treatment of [Hf(CH 2 Ph) 4 ] first with PhNH 2 (4 equivalents), followed by HOC 6 H 3 Bu t 2 -2,6 (2 equivalents), leads to the related bis(phenylamido) compound 4 (M = Hf; OAr = OC 6 H 3 Bu t 2 -2,6). The two homoleptic aryl amido compounds [M(NHC 6 H 3 Pr i 2 -2,6) 4 ] [M = Zr (5); Hf (6)] have also been obtained by addition of 2,6-diisopropylaniline to the tetra-benzyl compounds [M(CH 2 Ph) 4 ] (M = Zr, Hf). The addition of 4-pyrrolidinopyridine (py') to all of the aryl amido compounds except 4 leads to elimination of 1 equivalent of aryl amine and the formation of a series of five-coordinate aryl amido derivatives of the general formula [M(OAr) 2 (@?NPh)(py') 2 ] [M = Ti, OAr = OC 6 H 3 Pr i 2 -2,6 (7); M = Ti, OAr = OC 6 H 3 Ph 2 -2,6 (8); M = Zr, OAr = OC 6 H 3 Bu t 2 -2,6 (9); and [M(NHAr) 2 (@?NAr)(py') 2 ]; M = Zr, Ar = C 6 H 3 Pr i 2 -2,6 (10); M = Hf, Ar = C 6 H 3 Pr i 2 -2,6 (11)]. In the case of the hafnium bis(phenylamido) complex 4, addition of 4-pyrrolidinopyridine resulted in the formation of a simple adduct. [Hf(OC 6 H 3 Bu t 2 -2,6) 2 (NHPh) 2 (py')], [4.py']. (A similar adduct, [4.py'], was detected in the conversion of 3-9.) No elimination of aniline from [4.py'] and formation of a phenylimido derivative were observed. Both 2,2'-bipyridine and 1,10-phenanthroline were found to eliminate aniline from compounds 1-3 to produce insoluble products. Addition of 3,4,7,8-tetramethyl-1,10-phenanthroline to 2, however, yielded a soluble phenylimido derivative (12). The four-coordinate aryl amido compounds 2, 3 and 5 were found to be pseudo-tetrahedral in the solid state, while the five-coordinate aryl imido compounds 7, 9, 10 and 11 are best described as distorted trigonal-bipyramidal with trans-axial pyridine ligands. In the phenanthroline derivative 12 a distorted trigonal-bipyramidal geometry exists about the titanium atom with an aryloxide oxygen atom trans to a phenanthroline nitrogen. The bonding of the aryl imido, aryl amido and pyridine groups is described. A detailed study of the reaction of a series of bis(aryl amido) complexes, [Zr(OAr) 2 (NHC 6 H 4 -4X) 2 ] (3) X (X = H, F, CH 3 , OMe, Br), with a variety of pyridine ligands was undertaken. The mono-pyridine adduct [3 X .py] is rapidly formed, followed by the slow formation of the corresponding aryl imido complex [Zr(OAr) 2 (@?NHC 6 H 4 -4X)(py) 2 ] [9 X ] and an equivalent of substituted aniline. Equilibrium constants for the reaction [3 X py] + py = [9 X ] + ArNH 2 were measured. Formation of the aryl imido ligand was found to be favoured by a more basic pyridine ligand and by electron-withdrawing substituents o
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