Synthesis, stereochemistry, and reactivity of group 4 metal complexes that contain a chiral tetradentate diamine-diamide ligand

Ti and Zr complexes of the new chiral tetradentate diamine-diamide ligand (Me2PMEN)(2-) are described (H-2(Me2PMEN), 1 = N,N'-dimethyl-N,N'-bis[(S)-2-methylpyrrolidine]ethylenediamine). The reaction of 1 with Zr(NMe2)(4) affords (Me2PMEN)Zr(NMe2)(2) (C-2-2) which is shown by NMR to have effective C-2-symmetry in solution. Addition of excess ClSiMe3 to C-2-2 gives (Me2PMEN)ZrCl2 (3) as a mixture of two isomers, C-2-3 (kinetic product) and C-1-3 (thermodynamic product). An X-ray diffraction study of C-1-3 revealed a distorted octahedral structure with a cis-amide/cis-chloride arrangement of ligands. Reaction Of C-1/C-2-3 with MeLi yields (Me2PMEN)ZrMe2 (C(2)4), which exists as a single C-2-symmetric isomer in solution. The reaction of 1 and Zr(CH2Ph)(4) affords (Me2PMEN)Zr(CH2Ph)(2) (5), which can be isolated as a mixture of two isomers, C-1-5 (kinetic product) and C-2-5 (thermodynamic product). The Ti derivative (Me2PMEN)Ti(CH2Ph)(2) (C-2-6) was prepared similarly from 1 and Ti(CH2Ph)(4). Compound 6 shows effective C-2-symmetry in solution. An X-ray study of 6 revealed a C-2-symmetric distorted octahedral structure with a trans-amide/cis-benzyl arrangement of ligands. Iodinolysis Of C-2-6 followed by alkylation. with MeMgCl leads to the unstable dimethyl derivative (Me2PMEN)TiMe2 (C-2-7). Alkyl abstraction from C(2)4, C-1/C-2-5, and C-2-6 using [Ph3C][B(C6F5)(4)], [HNMe2Ph][B(C6F5)(4)], [HNMePh2][B(C6F5)(4)], or B(C6F5)(3) affords cationic alkyl complexes, of which [(Me2PMEN)M(CH2Ph)][B(C6F5)(4)] (M = Ti, 8; M = Zr, 9) were isolated. In situ-generated 8 and 9 are moderately active ethylene polymerization catalysts.