A Series of Dinuclear Copper Complexes Bridged by Phosphanylbipyridine Ligands: Synthesis, Structural Characterization and Electrochemistry

The phosphanylbipyridine ligands 6‐(diphenylphosphanyl)‐4,4′‐dimethyl‐2,2′‐bipyridine (PPh 2 ‐Me 2 ‐bipy, a ), 4,4′‐di‐ tert ‐butyl‐6‐(diphenylphosphanyl)‐2,2′‐bipyridine (PPh 2 ‐ t Bu 2 ‐bipy, b ), and 6‐(diisopropylphosphanyl)‐2,2′‐bipyridine (P i Pr 2 bipy, c ) and the corresponding dinuclear copper complexes [Cu 2 (μ‐PPh 2 ‐Me 2 ‐bipy) 2 (NCCH 3 ) 2 ](PF 6 ) 2 ( 1 ), [Cu 2 (μ‐PPh 2 ‐ t Bu 2 ‐bipy) 2 (NCCH 3 ) 2 ](PF 6 ) 2 ( 2 ), [Cu 2 (μ‐P i Pr 2 bipy) 2 (μ‐NCCH 3 )](PF 6 ) 2 ( 3 ), and [Cu 2 (μ‐P i Pr 2 bipy) 2 {μ‐CNCH(CH 3 ) 2 }](PF 6 ) 2 ( 4 ) were synthesized. The X‐ray structures of 1 – 4 show that the complexes are dinuclear with the bidentate bipyridine coordinating to one copper atom and the phosphane moiety coordinating the other copper center. Complexes 3 and 4 possess short Cu–Cu distances with bridging acetonitrile and isocyanide ligands. The cyclic voltammograms of 1 – 4 were examined under N 2 and CO 2 . Under N 2 , 1 – 3 show four quasi‐reversible 1e – reductions, and under CO 2 , they show current enhancement at the second reduction. In comparison, complex 4 shows four irreversible reductions under N 2 and no current enhancement under CO 2 .