Diimino(NHC)-Stabilized Stannylone: Synthesis and Reversible Coupling with Isocyanates

Reduction of cationic stannylene [(dim(NHC))SnCl]+ (dim(NHC) = diimino N-heterocyclic carbene) by potassium graphite affords the Sn(0) compound (stannylone) (dim(NHC))Sn (14). SC-XRD study of 14 revealed a shortened C–Sn bond, indicating a multiple bond character. Stannylone 14 undergoes a [2 + 2] cycloaddition with isocyanates RNCO (R = 4-tolyl or 2,6-xylyl) to furnish novel alkyl carboxamido stannylenes 21 (R = 4-tolyl) and 22 (R = 2,6-xylyl), featuring a C–C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of 22 with 4-tolyl isocyanate to 100 °C results in isocyanate metathesis, demonstrating reversible C–C bond formation in the coordination sphere of the tin atom.