Synthesis, Stereochemistry, and Reactivity of Group 4 Metal Complexes That Contain a Chiral Tetradentate Diamine-Diamide Ligand

Abstract

Ti and Zr complexes of the new chiral tetradentate diamine-diamide ligand (Me2PMEN)2- are described (H2(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 (C2-2) which is shown by NMR to have effective C2-symmetry in solution. Addition of excess ClSiMe3 to C2-2 gives (Me2PMEN)ZrCl2 (3) as a mixture of two isomers, C2-3 (kinetic product) and C1-3 (thermodynamic product). An X-ray diffraction study of C1-3 revealed a distorted octahedral structure with a cis-amide/cis-chloride arrangement of ligands. Reaction of C1/C2-3 with MeLi yields (Me2PMEN)ZrMe2 (C2-4), which exists as a single C2-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, C1-5 (kinetic product) and C2-5 (thermodynamic product). The Ti derivative (Me2PMEN)Ti(CH2Ph)2 (C2-6) was prepared similarly from 1 and Ti(CH2Ph)4. Compound 6 shows effective C2-symmetry in solution. An X-ray study of 6 revealed a C2-symmetric distorted octahedral structure with a trans-amide/cis-benzyl arrangement of ligands. Iodinolysis of C2-6 followed by alkylation with MeMgCl leads to the unstable dimethyl derivative (Me2PMEN)TiMe2 (C2-7). Alkyl abstraction from C2-4, C1/C2-5, and C2-6 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.