Cobalt PCP pincer complexes via an unexpected sequence of ortho metalations

Mark A. Kent, Christopher H. Woodall, Mairi F. Haddow, Claire L. McMullin, Paul G. Pringle*, Duncan F. Wass

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

15 Citations (Scopus)

Abstract

The cobalt PCP pincer complexes [Co{2,6-(CH2PPh2-κP)2C6H3-κC1}(L)2], where L = PMe3 (1), CO (2), have been prepared. Complex 1 is obtained by a transmetalation reaction between 1-lithio-2,6-bis((diphenylphosphino)methyl)benzene and [CoCl(PMe3)3]. Subsequent exposure of 1 to CO gave complex 2. Complexes 1 and 2 can also be obtained from 1,3-bis((diphenylphosphino)methyl)benzene and [CoMe(PMe3)4]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co{2-(CH2PPh2-κP)-4-(CH2PPh2)-C6H3-κC1}(PMe3)3] (4). After reflux of the reaction mixture for 24 h, a rearrangement of 4 occurs to give pincer complex 1 with loss of PMe3 in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of 4 to 1 has been probed using 1-deuterio-2,6-bis((diphenylphosphino)methyl)benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh2 group in the product complex 1, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate.

Original languageEnglish
Pages (from-to)5686-5692
Number of pages7
JournalOrganometallics
Volume33
Issue number20
DOIs
Publication statusPublished - 27 Oct 2014

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