CORRELATIONS BETWEEN STRUCTURE, MAGNETISM, AND POLYMERIZATION ACTIVITY OF PARAMAGNETIC BENZYLCHROMIUM COMPLEXES

Reaction of [{Cp*Cr(mu-Cl)}(2)] with benzyllithium yielded [{Cp*Cr(mu-Bz)}(2)] (1), a Cr-II alkyl complex with bridging benzyl groups and a Cr-Cr bond, which rearranged at room temperature to [Cp*Cr(eta(1)-Bz)(mu-eta(3):eta(6)-Bz)CrCp*] (2), a mixed valent (Cr-I/Cr-II) complex with a benzyl ligand coordinating as an eta(6)-arene ligand to one chromium and as an eta(3)-allyl ligand to the other one. Upon heating, 2 reductively eliminated bibenzyl and yielded [(Cp*Cr)(2)(mu-eta(6):eta(6)-Bz-Bz)] (3), in which two 17-electron sandwich complexes are linked by an ethano bridge. The crystal structures of 2 and 3 have been determined. Magnetic susceptibility and saturation magnetization measurements showed 2 to be ferromagnetically coupled (ground state S = 2, J = + 23(1) cm(-1)). Of the three isomers, only 2 catalyzed the polymerization of ethylene, presumably because it contains a Cr-III alkyl.