Monocyclopentadienyl Phenoxido–Amino and Phenoxido–Amido Titanium Complexes: Synthesis, Characterisation, and Reactivity of Asymmetric Metal Centre Derivatives

Abstract

AbstractReduction of phenol–imine derivatives R′N=CH(3,5‐R2C6H2‐2‐OH) (R = tBu; R′ = C6H5 1a, p‐MeC6H4 1b, Cy 1c, tBu 1d, 2,6‐Me2C6H3 1e; R = H; R′ = p‐MeC6H4 1f; Cy = cyclohexyl) with MBH4 (M = Li, Na) or AlLiH4 in ethyl ether or thf at room temperature affords the phenol–amine compounds R′NHCH2(3,5‐R2C6H2‐2‐OH) 2a–c and 2e,f. The N‐R‐[2,4‐di‐tert‐butyl]benzo‐1‐oxa‐3‐azine species (R = tBu 2d1, 2,6‐Me2C6H3 2e1) are obtained by Mannich reaction of 2,4‐di‐tert‐butylphenol with RNH2 in refluxing methanol. Intermediate 2d1 is converted in ethanol at room temperature into N‐tert‐butyl[2‐hydroxy‐3,5‐di‐tert‐butyl]benzylamine (2d), whereas 2e is not obtained from 2e1 by using this procedure.N‐alkyl,N‐tert‐butyl[2‐hydroxy‐3,5‐di‐tert‐butyl]benzylaminecompounds tBuN(R)CH2(3,5‐tBu2C6H2‐2‐OH) (R = Me 2g, Et 2h, nPr 2i, CH2Ph 2j) are also prepared by the appropriate synthetic method. Treatment of 2a–c with 1 equiv. of TiCpCl3 in the presence of 2.5 equiv. of NEt3 in hexane at room temperature gives the monocyclopentadienyl phenoxido–amido monochloride complexes TiCp[R′NCH2(3,5‐tBu2C6H2‐2‐O)]Cl (R′ = C6H5 3a, R′ = p‐MeC6H4 3b, R′ = Cy 3c). The analogous complex Ti(η5‐C5H4SiMe2Cl)[C6H5NCH2(3,5‐tBu2C6H2‐2‐O)]Cl (4a) results from the reaction of 2a with Ti(η5‐C5H4SiMe2Cl)Cl3. Nevertheless, 2d reacts with TiCpCl3 in hexane in the presence of NEt3 at room temperature yielding the monocyclopentadienyl phenoxido dichloride compound TiCp[tBuNHCH2(3,5‐tBu2C6H2‐2‐O)]Cl2 (5), whereas in ethyl ether and in the absence of NEt3 adduct 5·HCl is obtained, which is further converted into TiCp[tBuNCH2(3,5‐tBu2C6H2‐2‐O)]Cl (3d) by addition of a NEt3/ethyl ether solution. The reaction of TiCpCl3 with 2a in the presence of 2.5 equiv. of NEt3 in a polar solvent (thf, CH2Cl2 or toluene) at room temperature affords TiCp[Ph(H)NCH2(3,5‐tBu2C6H2‐2‐O)]Cl (6a) as a mixture of two stereoisomers. All the reported compounds were characterised by the usual analytical and spectroscopic methods and the molecular structures of 2a, 2d, 2e and 3d were determined by X‐ray diffraction analysis from suitable single crystals. Preliminary studies of catalytic activity for ethylene polymerisation by using solid methylaluminoxane as cocatalyst were performed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)