Copper formal oxidation states above +1 in organometallic chemistry: The possibility of synthesizing cyclopentadienylcopper chlorides by oxidative addition reactions

Although organometallic compounds of Cu(I) have been known for some time, including cyclopentadienyl derivatives of the type CpCuL (Cp = η⁵-cyclopentadienyl ligand; L = phosphine or CO), organometallic compounds of copper in higher formal oxidation states are essentially unknown except for a few alkylcopper(III) and allylcopper(III) derivatives, only stable at very low temperatures. Theoretical studies on the cyclopentadienyl derivatives Cp₂Cu₂Cl_n (n = 1, 2, 3) indicate a preference for structures with terminal Cp rings and bridging Cl atoms up to a maximum of two of the latter. However, Cp₂Cu₂Cl_n (n = 1, 2, 3) structures with bridging Cp rings are found at only slightly higher energies. The lowest energy doublet mixed Cu(II/III) oxidation state Cp₂Cu₂Cl₃ structure with a single bridging Cl atom can be formally derived from the lowest energy doublet Cu(I/II) mixed oxidation state Cp₂Cu₂Cl structure by oxidative addition of Cl₂.