Activation of 7‑Silanorbornadienes by N‑Heterocyclic Carbenes: A Selective Way to N‑Heterocyclic-Carbene-Stabilized Silylenes

The synthesis of
hydridosilylenes Ter­(H)­Si: 3a (Ter:
2,6-bis­(2,4,6-trimethylphenyl)­phenyl) and Ter*­(H)­Si: 3b (Ter*: 2,6-bis­(2,4,6-triiso-propylphenyl)­phenyl)
stabilized by the N-heterocyclic carbene (NHC) ImMe4 is
reported. The synthesis of stabilized hydridosilylenes 3 was accomplished by a previously unknown NHC-induced fragmentation
of silanorbornadiene derivatives. Structural studies of the stabilized
silylenes 3 and of its Fe­(CO)4 complex 12 accompanied by a theoretical analysis of their bonding
situation indicate that stabilized silylenes such as 3 can be regarded as neutral silyl anion equivalents. A computational
investigation of the reaction course indicate a virtual one-step reaction
between the NHC and the silanorbornadiene. A theoretical assessment
of the scope and limitations of this reaction suggests that it is
general and can be used also for the synthesis of other carbene analogues
such as germylenes and phosphinidenes.