C–H Bond Activation and Isoprene Polymerization by Rare-Earth-Metal Tetramethylaluminate Complexes Bearing Formamidinato N-Ancillary Ligands

Abstract

The bimetallic formamidinate complexes Ln(Form)(AlMe4)2 (Ln = Y, Form (ArNCHNAr) = EtForm (Ar = 2,6-Et2C6H3), MesForm (Ar = 2,4,6-Me3C6H2), DippForm (Ar = 2,6-iPr2C6H3), tBuForm (Ar = 2-tBuC6H4); Ln = La, Form = DippForm, tBuForm) were obtained in high yield by protonolysis reactions between formamidines (FormH) and homolepticrare-earth-metal tetramethylaluminates Ln(AlMe4)3. Y(Form)(AlMe4)2 (Form = EtForm, DippForm) were also prepared by treatment of Y(Form)[N(SiHMe2)2]2(thf) with trimethylaluminum after the former were prepared by the protonolysis of Y[N(SiHMe2)2]3(thf)2 complexes with EtFormH or DippFormH. The monomeric six-coordinate complexes Ln(Form)(AlMe4)2 (Ln = Y, Form = EtForm, MesForm, DippForm, tBuForm; Ln = La, Form = DippForm, tBuForm) show similar molecular structures with distorted-octahedral geometry and bidentate (N,N′) Form and AlMe4 ligands. The complex [La(EtFormAlMe3)(AlMe4)2](C7H8)1.5 from a protonolysis reaction between La(AlMe4)3 and EtFormH has the EtForm ligand adopting a config...