Properties and reactions of tetranuclear copper(I) complexes [LCuX]₄ (L=N,N-dimethylaminomethylferrocene; X=Cl and Br). Crystal and molecular structure of (μ₄-O)L₄Cu₄Cl₆

Copper(I) chloride and bromide react with equimolar L=N,N-dimethylaminomethylferrocene in methylene chloride or nitrobenzene at room temperature under N₂ to give soluble tetranuclear copper(I) complexes [LCuX]₄ (VII). The room temperature electronic spectra of L and VII are very similar, indicating little, if any, electronic coupling of copper(I) with the ferrocene moiety. Products [CuX]₄ completely reduce O₂ to coordinated oxide in the tetranuclear oxocopper(II) products [LCuX]₄O₂ (VIII) that are converted by excess CO₂ to tetranuclear dicarbonatocopper (II) complexes [LCuX]₄(CO₃)₂ (IX). VII are oxidized by O₂ to VIII in a second-order reaction whose rate-determining step is insertion of O₂ through the halo core of VII. The properties of VIII are consistent with a (μ-O)₂[LCuX]₄ molecular core structure. The electrochemistry of L is not much affected by coordination to copper(I) or copper(II). Attempted crystallization of VIII and IX (XCl) gives (μ₄-O)L₄Cu₄Cl₆ (Xa), which crystallizes in the tetragonal space group P42₁c, with a=16.930(6), c=13.084(7) Å, V=3750 ų and Z=2. The crystallographic data from 1744 reflections at 233 K were refined to give R=0.047 and R_w=0.052. The core molecular structure of Xa consists of a central oxo group that is tetrahedrally coordinated to four copper(II) centers. Each copper(II) carries a monodentate ligand L and is bridged to three other copper(II) centers by chlorine ligands. This core structure is very similar to those of the N,N-diethylnicotinamide and pyridine analogues. Complexes VIII-X are not transmetalated at practical rates by Co(NS)₂ and Ni(NS)₂ (NS is monoanionic S- methyl isopropylidenecarbodithioate). Likely reasons are that steric effects interfere with reaction precursor formation and that VIII-X contain very strong copper-L bonds.