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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. Synthesis, structures and catalytic activity in ring-opening polymerization of rac-lactide.

Abstract

Lithium silylamides 1,8-C10H6[N(SiMe3)Li(L)]2 (L = Et2O (1Et2O); L = TMEDA (1TMEDA)) when treated with PhC≡N form the adducts 1,8-C10H6[N(SiMe3)Li(N≡CPh)(OEt2)][N(SiMe3)Li(OEt2)] (2Et2O) 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 one retained coordinated L ligand. The salt metathesis reactions of LnCl3 (Ln = Y, Sm) with equimolar amounts of 2Et2O and 2TMEDA (THF, 4 h, 40 °C) result in benzonitrile insertion and formation of new dianionic amido-amidinate ligand. The reactions of 2Et2O with LnCl3 afford 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 for 2TMEDA and YCl3 it leads to the formation of neutral salt free yttrium chloro complex {1,8-C10H6[NSiMe3][NC(Ph)NSiMe3)]}YCl(TMEDA) (4). The treatment of 3Y and 4 with tBuOK allow for 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 initiatiors for ring opening polymerization of rac-lactide. Neutral tert-butoxide complex 8 demonstrated significantly higher activity compared to that of ionic 7.

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Publication details

The article was received on 10 Oct 2017, accepted on 14 Nov 2017 and first published on 14 Nov 2017


Article type: Paper
DOI: 10.1039/C7DT03809G
Citation: Dalton Trans., 2017, Accepted Manuscript
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    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. Synthesis, structures and catalytic activity in ring-opening polymerization of rac-lactide.

    A. Trifonov, D. Lyubov, A. Cherkasov, G. K. Fukin, K. A. Lyssenko, E. A. Rychagova and S. Yu. Ketkov, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT03809G

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