Modular Synthesis of Fischer Biscarbene Complexes of Chromium

Abstract

Aromatic and (hetero)­aromatic chromium aminocarbenes were lithiated on the (hetero)­aromatic ring and transmetalated with ZnBr2. The subsequent Pd­(PPh3)4- or PdCl2(XantPhos)-catalyzed Negishi reaction with dibromoarenes or chromium alkoxy-/aminocarbenes bearing bromine atoms yielded bisaminocarbene or mixed bisalkoxyaminocarbene complexes of chromium. This methodology allows easy access to the biscarbene complexes containing poly­(hetero)­aromatic bridges, such as biphenylene, bithienylene, tetrathienylene, 1,1′-ferrocenylene, and others. In total, 18 new biscarbene complexes, including two containing both chromium and tungsten, were synthesized in this fashion. The electrochemical behavior of the biscarbenes obtained exhibits electronic communication between the metals.