Zweikernige Bisphosphankupfer(I)-Komplexe mit dem 2,2′-Bipyrimidin-Brückenliganden: Strukturelle Analogie zu „Blauen“ Kupferzentren und Reduktion zu paramagnetischen Spezies / Dinuclear Bis(phosphane)copper(I) Complexes with 2,2′-Bipyrimidine as Bridging Ligand: Structural Analogy to “Blue” Copper Centers and Reduction to Paramagnetic Species

Dinuclear complexes [(PR3)2Cu(μ: η4-bpym)Cu(PR3)2](BF4)2 with the bis-chelating bridging ligand 2,2′-bipyrimidine (bpym) and various monodentate and bidentate phosphanes were synthesized via a four component “self assembly” reaction. The reversible electrochemical reduction to monocationic radical complexes was studied by cyclic voltammetry and electron spin resonance (ESR). Highly resolved ESR spectra revealed the presence of the bpym anion radical ligand via resolved hyperfine coupling with 1H, 14N, 31P, 63Cu and 65Cu nuclei. The variation of phosphane ligands was accompanied by significant changes of electrochemical potentials which were rationalized considering electronic and structural effects. The configurational flexibility of Cu(I) in this environment is evident from the X-ray crystal structure analysis of [(PPh3)2Cu(μ: η4-bpym)Cu(PPh3)2](BF4)2 - H2O• CH3OH for which the coordination at the metal can be described as 3 + 1 (NN′P + P′), qualitatively similar to the (NN′S + S′) arrangement around the type 1 Cu centers of “blue” copper proteins. Intramolecular cooperative π donor/π acceptor/π donor “sandwich” interactions provide parts of the driving force for this highly distorted coordination geometry which illustrates the proclivity of Cu(I) towards such an “entatic state” arrangement.