Synthesis of Mixed Silylene–Carbene Chelate Ligands from N‐Heterocyclic Silylcarbenes Mediated by Nickel

Abstract

AbstractThe NiII‐mediated tautomerization of the N‐heterocyclic hydrosilylcarbene L2Si(H)(CH2)NHC 1, where L2=CH(CCH2)(CMe)(NAr)2, Ar=2,6‐iPr2C6H3; NHC=3,4,5‐trimethylimidazol‐2‐yliden‐6‐yl, leads to the first N‐heterocyclic silylene (NHSi)–carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L1Si:(CH2)(NHC)NiBr2] 2 (L1=CH(MeCNAr)2). Reduction of 2 with KC8 in the presence of PMe3 as an auxiliary ligand afforded, depending on the reaction time, the N‐heterocyclic silyl–NHC bromo NiII complex [L2Si(CH2)NHCNiBr(PMe3)] 3 and the unique Ni0 complex [η2(Si‐H){L2Si(H)(CH2)NHC}Ni(PMe3)2] 4 featuring an agostic SiH→Ni bonding interaction. When 1,2‐bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi–NHC chelate‐ligand‐stabilized Ni0 complex [L1Si:(CH2)NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni0 complex 6, [L1Si:(CH2)NHCNi(CO)2], is easily accessible by the reduction of 2 with K(BHEt3) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada–Corriu‐type cross‐coupling reactions.