Bis-ortho-chelated arylcopper compounds. Synthesis and X-ray crystal structure of Cu4Br2[C6H3(CH2NMe 2)2-o,o′2

Article abstract of DOI:10.1021/om00103a012

A novel arylcopper(I) compound has been prepared from the reaction of lithiated C₆H₄(CH₂NMe₂)₂-o,o′ with CuBr. An X-ray crystal structure determination on this new compound revealed it not to be [Cu{C₆H₃(CH₂NMe₂) ₂-o,o′}] but its 1:1 CuBr adduct (Cu₄Br₂C₂₄H₃₈N₄; orthorhombic; Pcab; a = 18.167 (3), b = 19.462 (3), c = 17.036 (2) ?; Z = 8). The determined molecular structure shows a highly asymmetric [Cu₄{C₆H₃(CH₂NMe₂) ₂-o,o′}₂Br₂] 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) ? (mean)] and two bridging bromine atoms [Cu-Br distance 2.397 (1) ? (mean)]. The Cu-Cu distances for the two adjacent C-bridged bonds are 2.412 (2) and 2.406 (2) ? and for the Br-bridged bonds are 2.429 (2) and 2.737 (2) ?. 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) ? (mean)], thus making them all three-coordinate. Variable-temperature ¹H 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 [Li₂{C₆H₃(CH₂NMe₂) ₂-o,o′}₂] with CuBr{P(OMe)₃} afforded an arylcopper compound whose formulation based on elemental analysis and ¹H NMR data is [Cu₂{C₆H₃(CH₂NMe₂) ₂-o,o′}Br{P(OMe)₃}₂].