Synthesis and characterization of a novel class of dicopper(I) bis(carboxylate)-bridged complexes

The syntheses, spectroscopic properties, crystal and molecular structures, and bonding of several dicopper(I) bis-(carboxylate)-bridged complexes are described in which the bridging dicarboxylate ligand is the dianion of m-xylylenediamine bis(Kemp's triacid imide) (H2XDK, 1). A sterically demanding benzyl derivative of H2XDK was prepared, H2BXDK (6). Reaction of these two ligands as well as the propyl analog, H2PXDK (2), with thallium ethoxide provided dithallium salts Tl2L (L = XDK, 7; PXDK, 8; and BXDK, 9). :Reaction of 7, 8, or 9 with excess CuBr(Me2S) in CH2Cl2/MeCN afforded dinuclear acetonitrile adducts [Cu2L(MeCN)I (L = XDK, 10; PXDK, 11; and BXDK, 12) in high yield and multigram quantities. The coordination chemistry of the Cu-2-(XDK) platform was explored with a range of ancillary ligands. Treatment of 10, 11, or 12 with an excess of the specified neutral donor ligand provided complexes [Cu-2(XDK)(PPh3)(2)] (13), [Cu-2(XDK)(2,6-Me2C6H3NC)(3)] (14a), [Cu-2(XDK)(mu-2,6-Me2C6H3NC)(2,6-Me2C6H3NC)(2)] (14b), [Cu-2(XDK)(NB)(2)] (15), [Cu-2(XDK)(tmeda)] (17), [Cu-2-(PXDK)(tmeda)] (18), [Cu-2(BXDK)(tmeda)] (19), and [Cu(4,4'-Me(2)bpy)(2)][Cu(XDK)] (20). Reaction of 10 with an excess of cyclohexene resulted in the loss of the acetonitrile ligand, affording the parent unsubstituted complex [Cu-2(XDK)] (16). Attempts to prepare anionic carbon-bridged dicopper(I) complexes with alkyl-or aryllithium compounds or cyanide reagents resulted instead in extraction of one of the Cu(I) ions, affording (Et4N)[Cu(PXDK)] (21) and [CuLi(XDK)(THF)(2)] (22). Crystallographic chemical analysis of the complexes revealed linear two-coordinate, trigonal three-coordinate, and pseudotetrahedral four-coordinate copper(I), depending upon the composition, and variable degrees of Cu-Cu bonding (d(Cu-Cu) range, 2.5697(8)-3.4211(6) Angstrom).