Structural Snapshots of a Flexible Cu_2P_2 Core that Accommodates the Oxidation States Cu^ICu^I, Cu^(1.5)Cu^(1.5), and Cu^(II)Cu^(II)

Abstract

The phosphido-bridged dicopper(I) complex {(PPP)Cu}_2 has been synthesized and structurally characterized ([PPP]^- = bis(2-di-iso-propylphosphinophenyl)phosphide). Cyclic voltammetry of {(PPP)Cu}_2 in THF shows fully reversible oxidations at −1.02 V (Cu^(1.5)Cu^(1.5)/Cu^ICu^I) and −0.423 V (Cu^(II)Cu^(II)/Cu^(1.5)Cu^(1.5)). Chemical oxidation of {(PPP)Cu}_2 by one electron yields the class III mixed-valence species [{(PPP)Cu}_2]^+ (EPR, UV−vis). Structural data establish an unexpectedly large change (0.538 Å) in the Cu•••Cu distance upon oxidation state. Oxidation of {(PPP)Cu}_2 by two electrons yields the dication [{(PPP)Cu}_2]^(2+), an antiferromagnetically coupled dicopper(II) complex. Maintenance of a pseudotetrahedral geometry that is midway between a square plane and an ideal tetrahedron at the copper centers, along with a high degree of flexibility at the phosphide hinges, allows for efficient access to Cu^ICu^I, Cu^(1.5)Cu^(1.5), and Cu^(II)Cu^(II) redox states without the need for ligand exchange, substitution, or redistribution processes.

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