Studies of amidino-complexes of copper(I) and (II). Carboxylate analogues

Lithioamidines &;{;R′N(Li)C(R)NR′; R = H, CH₃, C₆H₅; R′ = C₆H₅, $\text{p}$-CH₃C₆H₄&;}; react with anhydrous copper(II) chloride to form Cu&;{;R′NC(R)NR′&;};₂]_n complexes, and with anhydrous copper(I) chloride to form Cu&;{;R′NC(R)NR′&;};]_m. The copper(II) complexes are diamagnetic, purple solids, which are air stable in the solid state but very air reactive in solution. Experimental data are consistent with a dimeric or more highly associated structure, and an X-ray structural determination shows Cu&;{;C₆H₅NC(C₆H₅)NC₆H₅&;};₂]₂ to be dimeric with four bridging amidino-groups and a short CuCu distance (2.46Å). The copper(I) complexes are pale yellow solids, which in solution are subject to rapid aerial oxidation, especially in the presence of free amidines, and disproportionation to Cu&;{;R′NC(R)HR′&;};₂]_n and copper metal. Differences in properties are noted between acetamidino-, benzamidino- and formamidino-complexes, the last complexes of copper(I) being most stable towards disproportionation. Cu&;{;C₆H₅NC(CH₃)NC₆H₅&;};₂ reacts with pyridine (Py) to form the copper(I) derivative Cu&;{;C₆H₅NC(CH₃)NC₆H₅&;};. 2Py and with carbon disulphide to form Cu&;{;C₆H₅NC(CH₃)NC₆H₅&;};₂.CS₂ which is reduced to form Cu&;{;C₆H₅NC(CH₃)NC₆H₅&;};.CS₃.