Unraveling organocuprate complexity : fundamental insights into intrinsic group transfer selectivity in alkylation reactions
Rijs, Nicole J.
O’Hair, Richard A. J.
Date of Issue2014
School of Physical and Mathematical Sciences
The near thermal conditions of an ion-trap mass spectrometer were used to examine the intrinsic gas-phase reactivity and selectivity of nucleophilic substitution reactions. The well-defined organocuprate anions [CH3CuR]– (R = CH3CH2, CH3CH2CH2, (CH3)2CH, PhCH2CH2, PhCH2, Ph, C3H5, and H) were reacted with CH3I. The rates (reaction efficiencies, ϕ) and selectivities (the product ion branching ratios) were compared with those of [CH3CuCH3]– reacting with CH3I. Alkyl R groups yielded similar efficiencies, with selectivity for C–C bond formation at the coordinated R group. Inclusion of unsaturated R groups curbed the overall reactivity (ϕ = 1 to 2 orders of magnitude lower). With the exception of R = PhCH2CH2, these switched their selectivity to C–C bond formation at the CH3 group. Replacing an organyl ligand with R = H significantly enhanced the reactivity (8-fold), resulting in the selective formation of methane. Unique decomposition and side-reactions observed include: (1) spontaneous β-hydride elimination from [RCuI]– byproducts; and (2) homocoupling of the pre-existing organocuprate ligands in [CH3CuC3H5]–, as shown by deuterium labeling. DFT (B3LYP-D/Def2-QZVP//B3LYP/SDD:6-31+G(d)) predicts that the alkylation mechanism for all species is via oxidative addition/reductive elimination (OA/RE). OA is the rate-limiting step, while RE determines selectivity: the effects of R on each were examined.
DRNTU::Science::Chemistry::Organic chemistry::Organometallic compounds
The journal of organic chemistry
© 2014 American Chemical Society. This is the author created version of a work that has been peer reviewed and accepted for publication by The Journal of Organic Chemistry, American Chemical Society. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [Article DOI: http://dx.doi.org/10.1021/jo4027325].