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

Abstract

Dinuclear complexes [(PR3)2C u(//:/74-bpym )Cu(PR3)2](BF4)2 with the bis-chelating bridging ligand 2,2'-bipyrimidine (bpym) and various m onodentate and bidentate phosphanes were synthesized via a four com ponent "self assembly" reaction. The reversible electrochemical reduction to m onocationic radical complexes was studied by cyclic voltammetry and electron spin resonance (ESR). Highly resolved ESR spectra revealed the presence o f the bpym anion radical ligand via resolved hyperfine coupling with 'H, 14N , 31P, 63Cu and 65Cu nuclei. The variation o f phosphane ligands was accompanied by significant changes o f electrochemical potentials which were rationalized considering electronic and structural effects. The configura tional flexibility o f Cu(I) in this environment is evident from the X-ray crystal structure ana lysis o f [(PPh3)2C u(//:^4-bpym )Cu(PPh3)2](BF4)2 H2O C H 3OH for which the coordination at the metal can be described as 3 + 1 (N N'P + P'), qualitatively similar to the (NN'S + S') arrange ment around the type 1 Cu centers o f "blue" copper proteins. Intramolecular cooperative n donor/;: acceptor/^ donor "Sandwich" interactions provide parts o f the driving force for this highly distorted coordination geometry which illustrates the proclivity o f Cu(I) towards such an "entatic state" arrangement.