Striking features of an acyclic silylene-nickel(0) complex in the activation of small molecules

  Since the first isolable N-heterocyclic carbene (NHC) from Arduengo in 1991,1 carbenes have seen numerous applications, most notably so as both ligands in transition metal catalysis and as catalysts in their own right.... [ view full abstract ]

  Since the first isolable N-heterocyclic carbene (NHC) from Arduengo in 1991,¹ carbenes have seen numerous applications, most notably so as both ligands in transition metal catalysis and as catalysts in their own right. Despite the first N-heterocyclic silylene (NHSi) being reported in 1994, only recently have NHSis seen effective use as steering ligands in metal-mediated catalysis.² Further, acyclic silylenes, which have been shown to be extremely reactive species, eluded chemists as isolable compounds until very recently.³ We have now learned that the easily accessible NHC-supported chloro silylene (^TMSL)Cl(NHC)Si: (^TMSL = N(SiMe₃)(Dipp); Dipp = 2,6-Prⁱ₂C₆H₃; NHC = :C[N(Prⁱ)C(Me)]₂) first reported by Cui et al. can act as a facile acyclic (amido)(chloro)silylene transfer reagent in the synthesis of the 16 valence electron (VE) Ni⁰ complex, [(^TMSL)ClSi:→Ni(NHC)₂] 1.⁴ Importantly, the synthesis of 1 can be achieved in high yields through low temperature mixing of equimolar quantities of NHC, (^TMSL)Cl(NHC)Si:, and Ni(cod)₂ (cod = 1,5-cyclooctadiene). Complex 1 displays a striking reactivity towards small molecules, including the facile cleavage of H₂ under ambient conditions, and the cleavage of both B-O bonds in catechol borane (HBcat) to form a terminal hydroborylene Ni^II complex. This suite of reactions largely relies upon the synergistic interaction between the acyclic silylene and the 16 VE nickel centres in 1, which has been highlighted by DFT calculations. These and other remarkable features of 1 will be discussed in my contribution.

1. A. J. Arduengo, R. L. Harlow, M. Kline, J. Am. Chem. Soc. 1991, 113, 361-363.
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3. (a) A. V. Protchenko, K. H. Birjkumar, D. Dange, A. D. Schwarz, D. Vidovic, C. Jones, N. Kaltsoyannis, P. Mountford, S. Aldridge, J. Am. Chem. Soc., 2012, 134, 6500–6503; (b) T. J. Hadlington, J. A. B. Abdalla, R. Tirfoin, S. Aldridge, C. Jones, Chem. Commun. 2016,  52, 1717-1720.
4. T. J. Hadlington, T. Szilvasi, M. Driess, 2017, accepted for publication in Angewandte Chemie.