[2 + 2] Cross Coupling of Benzene and Tropylium Ligands in Reductively Activated Piano Stool Complexes of Mn, Cr, and W

We have established cation/anion coupling reactions between the tropylium ligand in [M(η7-C7H7)(CO)3]+ (M = Cr, W) and the reductively activated η4-benzene ligand in [Mn(η4-C6H6)(CO)3]- (3-) to form [M(CO)3(μ2-η6:η5-C7H7−C6H6)Mn(CO)3]; [Cr(CO)3(μ2-η6:η5-C7H7−C6H6)Mn(CO)3] can be further reduced to [Cr(CO)3(μ2-η5:η4-C7H7−C6H6)Mn(CO)3]2-, in which the tropylium and benzene ligands have undergone a [2 + 2] cross coupling reaction.