Group IB organometallic chemistry : XIX. Synthesis and characterization of mixed-organocopper cluster compounds R4R′2Cu6 containing aryl and acetylide ligands

Abstract Mixed-organocopper cluster compounds Ar 4 Cu 6 (CCR) 2 (Ar = 2-Me 2 NC 6 H 4 , R = phenyl, 4-tolyl, 2,4-xylyl or mesityl) have been prepared in high yield by the ligand-substitution reaction of Ar 4 Cu 6 Br 2 with two equivalents of LiCCR. Ar 4 Cu 6 (CCC 6 H 4 CH 3 -4) 2 has also been prepared via the aryl—arylacetylide exchange reaction of Ar n Cu n with HCCC 6 H 4 CH 3 -4 as well as via the reaction of Ar n Cu n with polymeric CuCCC 6 H 4 CH 3 -4. IR and NMR spectroscopy reveal that Ar 4 Cu 6 (CCR) 2 and Ar 4 Cu 6 Br 2 have the Ar 4 Cu 6 skeleton as a common structural feature. Dynamic NMR spectroscopy provides information about the occurrence of intra-cluster CuN coordination. The position of the ν(CC) band (≈ 2040 cm −1 ) and considerations concerning the number of cluster electrons in Ar 4 Cu 6 X 2 clusters (84 e ) suggest that the CCR ligand acts as a three electron ligand bridging two equatorial Cu atoms of the Cu 6 core. In solution the Cu 2 CCR interaction is probably fluxional (σ,π σ(2 e –3 c ) π,σ).