Bis ortho chelated arylcopper compounds; Synthesis and X-ray crystal structure of Cu4Br2[C6H3(CH2NMe2)2-o,o']2

A novel arylcopper(1) compound has been prepared from the reaction of lithiated C8H4!CHzNMe2)z-o,o’ with CuBr. An X-ray crystal structure determination on this new compound revealed it not to be [Cu(C6H3(CHzNMe2)2-o,oq] but its 1:l CuBr adduct ( C U , B ~ ~ C ~ ~ H ~ ~ N , ; orthorhombic; Pcab; a = 18.167 (3), b = 19.462 (3), c = 17.036 (2) 8; 2 = 8). The determined molecular structure shows a highly asymmetric [ C U ~ ( C ~ H ~ ( C H ~ N M ~ ~ ) ~ O , O j2Br2] molecule containing four differently coordinated copper atoms. The copper atoms, which are all three-coordinate, are in a butterfly arrangement which is kept together by two bridging C ipso atoms of the aryl ligands [Cu-C distance 2.074 (5) 8, (mean)] and two bridging bromine atoms [Cu-Br distance 2.397 (1) 8 (mean)]. The Cu-Cu distances for the two adjacent C-bridged bonds are 2.412 (2) and 2.406 (2) A and for the Br-bridged bonds are 2.429 (2) and 2.737 (2) A. The coordination pattern of the CH2NMe2 side arms is such that each of the copper atoms is N-coordinated [Cu-N distance 2.176 (4) A (mean)], thus making them all three-coordinate. Variable-temperature ‘H NMR measurements in the temperature range 233-373 K show that this asymmetric structure is not retained in solution and that a more symmetric molecule is formed. These spectra also show the existence of complex fluxional processes. Reaction of [Liz(CBH3(CHzNMez)z-o,o q2]with C U B ~ { P ( O M ~ ) ~ ) afforded an arylcopper compound whose formulation based on elemental analysis and ‘H NMR data is [CU~(C~H~(CH,NM~~)~-O,O~B~{P(OM~)~]~].