Tetraalkylcuprates(III): Formation, Association, and Intrinsic Reactivity

• DOI: 10.1021/ja209433j
• Publication Date: 2011-11-30T22:08:10Z
• Authors: Aliaksei Putau; Harald Brand; Konrad Koszinowski
• Keywords: Fragmentation

Tetraalkylcuprates are prototypical examples of organocopper(III) species, which remained elusive until their recent detection by NMR spectroscopy. In agreement with the studies, present electrospray ionization mass spectrometric experiments, as well supporting electrical conductivity measurements, indicate that LiCuMe(2)·LiCN reacts a series alkyl halides RX. The resulting Li(+)Me(2)CuR(CN)(-) intermediates then afford observable Me(3)CuR(-) tetraalkylcuprate anions upon Me/CN exchanges added MeLi. contrast, reactions neopentyl iodide and various aryl give rise to halogen-copper exchanges. Concentration- solvent-dependent studies suggest lithium tetraalkylcuprates not fully dissociated in ethereal solvents, but partly form Li(+)Me(3)CuR(-) contact ion pairs presumably also triple ions LiMe(6)Cu(2)R(2)(-). According theoretical calculations, these consist two square-planar subunits binding central Li(+) ion. Upon fragmentation gas phase, mass-selected undergo reductive elimination, yielding both cross-coupling products MeR homocoupling product Me(2). branching between channels markedly depends on nature substituent R. LiMe(6)Cu(2)R(2)(-) (as mixed analogues LiMe(6)Cu(2)R(R')(-)) fragmentation, strongly favor former. On basis we rationalize this prevalence preferential interaction Me groups each subunit, thereby effectively blocks channel. Our results thus show how counterion can alter reactivity an organocopper species at molecular level.