Reversible Coupling of Germylone with Isocyanates

Ge(0) compound 5 undergoes coupling with isocyanates to afford imine-ligated alkyl carboxamido germylenes 7 and 8. Moreover, this addition is reversible, as evidenced by an exchange reaction of 8 with p-tolyl isocyanate and by DFT calculations.

Abstract

The germylone dimNHCGe (5, dimNHC=diimino N-heterocyclic carbene) undergoes a [2+2] cycloaddition with isocyanates RNCO (R=4-tolyl or 3,5-xylyl) to furnish novel alkyl carboxamido germylenes 7 (R=4-tolyl) and 8 (R=3,5-xylyl), featuring a C−C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of 8 with 4-tolyl isocyanate to 100 °C results in isocyanate metathesis, demonstrating reversible C−C bond formation on the reduced germanium compound. DFT calculations suggest that this process occurs via the reductive dissociation of isocyanate from 8 that regenerates the parent Ge(0) compound 5.