Electrocatalytic reductive dimerization of the 2,2′-bipyridyl tungsten alkylidyne complex [W( [tbnd]CC 6H 4NMe 2-4)(NCMe)(CO) 2{κ 2-2,2′-(NC 5H 4) 2}] +

Abstract

Potentiometric measurements have shown that the cationic 2,2′-bipyridyl tungsten alkylidyne complex [W( CC 6H 4NMe 2-4)(NCMe)(CO) 2{κ 2-2,2′-(NC 5H 4) 2}][PF 6] ( 2) is electroactive in MeCN solution with a reduction ( E pc ≈ −1.0 V vs. ferrocene) leading to complex dimerization, identified by a number of electrochemical markers. Multiple redox cycles have led to the partial deposition of the dimerized product on the electrode surface, which appears to electrocatalyze subsequent coupling cycles. Comparison with electrochemical measurements of related alkylidyne complexes, including the precursor complex [W( CC 6H 4NMe 2-4)(O 2CCF 3)(CO) 2{κ 2-2,2′- (NC 5H 4) 2}] ( 1), has provided indirect evidence of intermolecular bond formation between κ 2-2,2′-bipyridyl ligands. The cationic complex 2 has additionally been the subject of gamess computational analysis, revealing calculated ν max(CO) stretching absorptions in good agreement with measured parameters. This study has also permitted a molecular orbital analysis, which has indicated an energy-accessible LUMO almost entirely located on the 2,2′-bipyridyl ligand of complex 2, the purported site for dimerization. It is believed that occupation of this orbital upon reduction of compound 2 leads to a short-lived metastable precursor to 2,2′-bipyridyl ring coupling. Furthermore, a very weak π-antibonding interaction of the metal–alkylidyne π-framework with the MeCN ligand in the occupied frontier molecular orbitals of complex 2 has been noted and compared with a surprisingly significant π interaction with the CF 3 CO 2 - carboxylate group in complex 1.