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Metalation of trimethylphosphine-borane. Unexpected reactivity of a simple phosphine-borane-stabilized carbanion toward siloxanes

Lookup NU author(s): Dr Keith Izod, Dr Corinne Wills, Emeritus Professor Bill Clegg, Dr Ross Harrington

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Abstract

The reaction between trimethylphosphine-borane (3) and 1 equiv of MeNa in diethyl ether gives the polymeric complex [{Me2P(BH 3)CH2}Na(THF)]∞ (5a) in good yield after recrystallization from THF. In contrast, the reaction between 3 and 1 equiv of n-BuLi in diethyl ether gives the unusual complex {Me2P(BH 3)CHSiMe2OLi}4Li4(Et 2O)2.75(THF)1.25 (6), which crystallizes as a cluster containing [Me2P(BH3)CHSiMe2O] 2- siloxy-functionalized carbanions formed via the reaction between the α-lithiated intermediate {Me2P(BH3)CH 2}Li (4) and silicone grease. Although the intermediate 4 could not be isolated, reactions between in situ-generated 4 and sources of Me 2SiO (Dow Corning silicone grease, silicone oil, hexamethylcyclotrisiloxane (8)) proceed cleanly to give good yields of 6; no reaction was observed between 4 and hexamethyldisiloxane. Reactions between 4 and 8 generate half an equivalent of 3 per equivalent of 4 consumed, and the cluster 6 reacts with excess siloxane to give 3 and unidentified products that contain silicon, but not phosphorus; thus, the optimum ratio of 4 to 8 in these reactions is 6:1. Variable-temperature 1H, 7Li, 11B{1H}, and 31P{1H} NMR spectroscopy suggests that 6 is subject to dynamic equilibria in solution that involve deaggregation of the cluster. © 2007 American Chemical Society.


Publication metadata

Author(s): Izod K, Wills C, Clegg W, Harrington RW

Publication type: Article

Publication status: Published

Journal: Organometallics

Year: 2007

Volume: 26

Issue: 11

Pages: 2861-2866

ISSN (print): 0276-7333

ISSN (electronic): 1520-6041

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/om070150j

DOI: 10.1021/om070150j


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