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Issue 24, 2018
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Reactivity of a dearomatised pincer CoIIBr complex with PNCNHC donors: alkylation and Si–H bond activation via metal–ligand cooperation

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Abstract

The double aminolysis reaction of [Co{N(SiMe3)2}2] by the salt 1-(6-((dicyclohexylphosphaneyl)methyl)pyridin-2-yl)-3-(2,6-diisopropylphenyl)-1H-imidazol-3-ium bromide, which contains one phosphane, one pyridine and one imidazolium groups, of formula [o-Cy2PCH2(C5H3N)(o-C3H3N2DiPP)]Br and abbreviated as (CyPNpyrCim)Br, was previously shown to afford the Co(II) complex [Co(CyP*NaCNHC)Br] (1) containing a dearomatised picolyl moiety in the tridentate, anionic donor ligand CyP*NaCNHC (Na = anionic amido, P* = vinylic P donor). We now report that formation of 1 is preceded by an intermediate tentatively assignable to the 5-coordinate Co(II) complex [Co(CyPNpyrCNHC){N(SiMe3)2}Br] (2). The reaction of 1 with LiCH2SiMe3 afforded the dark purple, paramagnetic [Co(CyP*NaCNHC)CH2SiMe3] (3) with a low spin d7 CoII; the electronic configurations of 1 and 3 were corroborated by EPR spectroscopy. Addition of excess (≥4 equiv.) H2SiPh2 to a solution of 1 gave the diamagnetic [Co(CyP(SiHPh2)NCNHC)Br] (4) following Si–H activation and silylation of the ligand backbone at the α-CHP. Reduction of CoII to CoI by silanes is uncommon.

Graphical abstract: Reactivity of a dearomatised pincer CoIIBr complex with PNCNHC donors: alkylation and Si–H bond activation via metal–ligand cooperation

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Publication details

The article was received on 02 Apr 2018, accepted on 09 May 2018 and first published on 10 May 2018


Article type: Paper
DOI: 10.1039/C8DT01279B
Citation: Dalton Trans., 2018,47, 7888-7895
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    Reactivity of a dearomatised pincer CoIIBr complex with PNCNHC donors: alkylation and Si–H bond activation via metal–ligand cooperation

    T. Simler, S. Choua, A. A. Danopoulos and P. Braunstein, Dalton Trans., 2018, 47, 7888
    DOI: 10.1039/C8DT01279B

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