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Issue 29, 2010
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Low-coordinate rare-earth complexes of the asymmetric 2,4-di-tert-butylphenolate ligand prepared by redoxtransmetallation/protolysis reactions, and their reactivity towards ring-opening polymerisation

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Abstract

New trivalent lanthanoid aryloxide complexes have been prepared by redoxtransmetallation/protolysis (rtp) reactions using 2,4-di-tert-butylphenol (dbpH). Mononuclear octahedral complexes from tetrahydrofuran (thf) were of the type [Ln(dbp)3(thf)3] (Ln = La (1), Pr (2), Nd (3), Gd (4), Er (5)). The lanthanoid contraction results in the rather subtle change in stereochemistry from meridional (La, Pr, Nd, Gd) to facial (Er). An analogous reaction with neodymium in dimethoxyethane (dme), resulted in the isolation of the seven coordinate [Nd(dbp)3(dme)2] (6), and this is comparable with the thf complexes in terms of steric crowding. Dinuclear complexes of the type [Ln2(dbp)6(thf)2], (Ln = Nd (7), Er (8)) were obtained when 1 and 5 were recrystallised from toluene. These dimeric complexes contain two bridging and four terminal phenolates, as well as a single coordinated molecule of thf at each metal. A similar structural motif was observed for the products when the reaction was performed in diethyl ether, and in the absence of a solvent, yielding [Nd2(dbp)6(Et2O)2] (9) and [Nd2(dbp)6(dbpH)2] (10) respectively. Complexes 3 and 4 alone were efficient but poorly-controlled initiators for the ROP of rac-lactide, but with an excess of BnOH as a co-initiator they showed features consistent with immortal polymerisation. Use of BnNH2 led to well-controlled, amine-initiated immortal ROP of rac-lactide, only the second report of this type of process for a group 3 or lanthanoid system.

Graphical abstract: Low-coordinate rare-earth complexes of the asymmetric 2,4-di-tert-butylphenolate ligand prepared by redoxtransmetallation/protolysis reactions, and their reactivity towards ring-opening polymerisation

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Publication details

The article was received on 25 Feb 2010, accepted on 19 May 2010 and first published on 10 Jun 2010


Article type: Paper
DOI: 10.1039/C0DT00023J
Citation: Dalton Trans., 2010,39, 6693-6704
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    Low-coordinate rare-earth complexes of the asymmetric 2,4-di-tert-butylphenolate ligand prepared by redoxtransmetallation/protolysis reactions, and their reactivity towards ring-opening polymerisation

    L. Clark, G. B. Deacon, C. M. Forsyth, P. C. Junk, P. Mountford and J. P. Townley, Dalton Trans., 2010, 39, 6693
    DOI: 10.1039/C0DT00023J

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