Transition Metal Complexes of Heavier Vinylidenes: Allylic Coordination vs Vinylidene-Alkyne Rearrangement at Nickel

Paresh Kumar Majhi; Michael Zimmer; Bernd Morgenstern; Volker Huch; David Scheschkewitz

doi:10.1021/jacs.1c06453

Transition Metal Complexes of Heavier Vinylidenes: Allylic Coordination vs Vinylidene-Alkyne Rearrangement at Nickel

J Am Chem Soc. 2021 Aug 25;143(33):13350-13357. doi: 10.1021/jacs.1c06453. Epub 2021 Aug 11.

Authors

Paresh Kumar Majhi¹, Michael Zimmer¹, Bernd Morgenstern², Volker Huch², David Scheschkewitz¹

Affiliations

¹ Krupp-Chair of General and Inorganic Chemistry, Saarland University, 66123 Saarbrücken, Germany.
² Service Center X-ray Diffraction, Saarland University, 66123 Saarbrücken, Germany.

PMID: 34380307
DOI: 10.1021/jacs.1c06453

Abstract

Transition metal π-allyl complexes are key reagents/intermediates of various catalytic and stoichiometric allylation reactions. We now report the first transition metal complex of a heavier allylic π-system. The η³-Si₂Ge allyl nickel complex is formally obtained by the oxidative addition of the Si-Cl bond of the heavier vinylidene [R₂(Cl)Si-(R)Si═(NHC)Ge:] to [Ni(COD)₂] (R = 2,4,6-triisopropylphenyl; NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; COD = 1,5-cyclooctadiene). Due to geometric constraints, the coordination to the Ni(II) center occurs through the formal Si═Ge double bond instead of the residual lone pair of electrons at germanium. In contrast, the Si-N bond of the analogous vinylidene [R₂(Me₂N)Si-(R)Si═(NHC)Ge:] (obtained by nucleophilic substitution of Cl by NMe₂) does not oxidatively add to Ni(0), and a hydridosilagermene-η²-nickel complex is obtained instead. The formation of this complex necessarily implies the isomerization of the heavier vinylidene to the corresponding heteroalkyne with the Si≡Ge triple bond in the coordination sphere of nickel followed by the activation of a C-H bond of one of the isopropyl groups of an N-heterocyclic carbene (NHC) ligand.