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

Lithium silylamides 1,8-C10H6[N(SiMe3)Li(L)]2 (L = Et2O (UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/); L = TMEDA (1TMEDA)), when treated with PhC≡N, formed the adducts 1,8-C10H6[N(SiMe3)Li(N≡CPh)(OEt2)][N(SiMe3)Li(OEt2)] (UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/) and 1,8-C10H6[N(SiMe3)Li(N≡CPh)][N(SiMe3)Li(TMEDA)] (2TMEDA) 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 UGRAPHIC DISPLAY="INLINE" ID="UGT3" SRC="UGT3"/ and 2TMEDA (THF, 4 h, 40 °C) resulted in benzonitrile insertion and formation of new dianionic amido-amidinate ligands. The reactions of UGRAPHIC DISPLAY="INLINE" ID="UGT4" SRC="UGT4"/ 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 2TMEDA 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. [ABSTRACT FROM AUTHOR]