title: Unraveling organocuprate complexity: fundamental insights into intrinsic group transfer selectivity in alkylation reactions.
abstract: 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.
authors.affiliation: School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology and §ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, The University of Melbourne , Victoria 3010, Australia.
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Rijs
authors.forename: Naohiko
authors.initials: N
authors.lastname: Yoshikai
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nakamura
authors.forename: Richard A J
authors.initials: RA
authors.lastname: O'Hair
mesh_terms: D000478:Alkylation; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D056831:Coordination Complexes; D005740:Gases; D007477:Ions; D008024:Ligands; D003300:Copper