Rare-earth metal-mediated PhCN insertion into N,N-bis(trimethylsilyl)naphthalene-1,8-diamido dianion – a synthetic approach to complexes coordinated by ansa-bridged amido-amidinato ligand

Abstract

Lithium silylamides 1,8-C₁₀H₆[N(SiMe₃)Li(L)]₂ (L = Et₂O (); L = TMEDA (1^TMEDA)), when treated with PhCN, formed the adducts 1,8-C₁₀H₆[N(SiMe₃)Li(NCPh)(OEt₂)][N(SiMe₃)Li(OEt₂)] () and 1,8-C₁₀H₆[N(SiMe₃)Li(NCPh)][N(SiMe₃)Li(TMEDA)] (2^TMEDA) containing one benzonitrile molecule coordinated to Li ion while the second molecule retains a coordinated L ligand. The salt metathesis reactions of LnCl₃ (Ln = Y, Sm) with equimolar amounts of and 2^TMEDA (THF, 4 h, 40 °C) resulted in benzonitrile insertion and formation of new dianionic amido-amidinate ligands. The reactions of with LnCl₃ afforded ionic chloro complexes [{1,8-C₁₀H₆[NSiMe₃][NC(Ph)NSiMe₃]}{1,8-C₁₀H₆[N(H)SiMe₃][NC(Ph)NSiMe₃]}LnCl][Li(L)_n] (Ln = Y, L = THF, n = 4 (3Y), Ln = Sm, L = DME, n = 3 (3Sm)), while the reaction of 2^TMEDA and YCl₃ leds to the formation of the neutral salt-free yttrium chloro complex {1,8-C₁₀H₆[NSiMe₃][NC(Ph)NSiMe₃]}YCl(TMEDA) (4). The treatment of 3Y and 4 with tBuOK enabled the synthesis of tert-butoxides [{1,8-C₁₀H₆[NSiMe₃][NC(Ph)NSiMe₃]}{1,8-C₁₀H₆[N(H)SiMe₃][NC(Ph)NSiMe₃]}YOtBu][Li(THF)₄] (7) and {1,8-C₁₀H₆[NSiMe₃][NC(Ph)NSiMe₃]}YOtBu(TMEDA) (8). Complexes 7 and 8 were evaluated as initiators for the ring opening polymerization of rac-lactide. Neutral tert-butoxide complex 8 demonstrated significantly higher activity compared to that of ionic 7.