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.