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 (<b>14</b>). SC-XRD study of <b>14</b> revealed a shortened C-Sn bond, indicating a multiple bond character. Stannylone <b>14</b> undergoes a [2 + 2] cycloaddition with isocyanates RNCO (R = 4-tolyl or 2,6-xylyl) to furnish novel alkyl carboxamido stannylenes <b>21</b> (R = 4-tolyl) and <b>22</b> (R = 2,6-xylyl), featuring a C-C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of <b>22</b> 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.