Bulky Acyclic Aminooxycarbene Ligands

A series of sterically demanding acyclic aminooxycarbenes (AAOCs) were prepared in good yields from chloroiminium salts and alkoxysilanes via the TMS-Cl elimination pathway. The steric profiles of bulky AAOCs were determined by X-ray crystallographic studies of the Au(I) complexes. The percent buried volume values (%VBur) of the AAOC ligands range from 35.8% to 47.9%. Acyclic aminooxycarbenes maintain coplanarity around the carbene center, in sharp contrast to the similarly bulky acyclic diaminocarbenes that show significant distortion from the coplanarity. The Au(I) complexes of AAOCs exhibited high efficiency in the hydroamination of alkenyl ureas. Bulkier AAOC–Au(I) complexes displayed faster reaction rates and higher conversions. The reaction rate, yield, and stereoselectivity observed with the AAOC–Au(I) catalyst were better than those with acyclic diaminocarbene Au catalysts and comparable to the best results reported to date.