A mechanistic investigation of carbon–hydrogen bond stannylation: synthesis and characterization of nickel catalysts?

Dalton Transactions Pub Date: 2012-04-11 DOI: 10.1039/C2DT30310H

Abstract

The complex (iPr3P)Ni(η2-Bu3SnCH[double bond, length as m-dash]CH2)2 (1a) was characterized by NMR spectroscopy and was identified as the active species for catalytic C–H bond stannylation of partially fluorinated aromatics, for example in the reaction between pentafluorobenzene and Bu3SnCH[double bond, length as m-dash]CH2, which generates C6F5SnBu3 and ethylene. The crystalline complex (iPr3P)Ni(η2-Ph3SnCH[double bond, length as m-dash]CH2)2 (1b) provides a more easily handled analogue, and is also capable of catalytic stannylation with added Ph3SnCH[double bond, length as m-dash]CH2 and C6F5H. Mechanistic studies on 1b show that the catalytically active species remains mononuclear. The rate of catalytic stannylation is proportional to [C6F5H] and inversely proportional to [Ph3SnCH[double bond, length as m-dash]CH2]. This is consistent with a mechanism where reversible Ph3SnCH[double bond, length as m-dash]CH2 dissociation provides (iPr3P)Ni(η2-Ph3SnCH[double bond, length as m-dash]CH2), followed by a rate-determining reaction with C6F5H to generate the stannylation products. Kinetic competition reactions between the fluorinated aromatics pentafluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene and 1,3-difluorobenzene all suggest significant Ni–aryl bond formation in the rate-determining step under catalytic conditions. Labelling studies are consistent with an insertion of the hydrogen of the arene into the vinyl group, followed by β-elimination or β-abstraction of the SnPh3 moiety.

Graphical abstract: A mechanistic investigation of carbon–hydrogen bond stannylation: synthesis and characterization of nickel catalysts
Recommended Literature