Formation of [(CO)(HCCH)Tp'W=NCH(CH3)CH(CH3)N=WTp'(HCCH)(CO)][I3]2 by oxidation of Tp'W(CO)(HCCH)(NCHCH3) and radical dimerization

By treating Tp'W(CO)(HCCH)(NCHCH3) with iodine, a 1 e− oxidation of the metal complex occurs leading to radical coupling through the β-carbons of two 1-azavinylidene ligands. Formation of the diimido bridged dimer [(Tp'W(CO)(HCCH))2(μ-NCH(CH3)CH(CH3)N)][I3]2 occurs diastereoselectively; only the S,S,R,R diastereomer is isolated. An inversion center is located at the center of the bridge C-C bond, leading to identical spectroscopic signals for each end of the dimer. A second order splitting pattern, A3XA3′X′, characterizes the bridge protons in the 1H NMR spectrum. As a result of one electron oxidation of the monomer followed by ligand coupling, each metal center is oxidized from tungsten (II) to tungsten (IV), d4 to d2, leading to a high carbonyl stretching frequency of 2116 cm−1 in the IR spectrum of the dicationic product.