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Combined DFT and experimental studies of C–C and C–X elimination reactions promoted by a chelating phosphine–alkene ligand: the key role of penta-coordinate PdII

Estévez, Laura; Tuxworth, Luke W.; Sotiropoulos, Jean-Marc; Dyer, Philip W. Dyer; Miqueu, Karinne

Combined DFT and experimental studies of C–C and C–X elimination reactions promoted by a chelating phosphine–alkene ligand: the key role of penta-coordinate PdII Thumbnail


Authors

Laura Estévez

Luke W. Tuxworth

Jean-Marc Sotiropoulos

Karinne Miqueu



Abstract

A combined computational and experimental study of the coordination chemistry of phosphine–alkene ligand L1 (N-diphenylphosphino-7-aza-benzobicyclo[2.2.1]hept-2-ene) with Pd0 and PdII is presented. Experimentally it is established that ligand L1 promotes direct alkyl–alkyl and indirect alkyl–halide reductive elimination from PdII species, affording the palladium(0) complex [Pd(κ2-P,C-L1)2] (2) in each case. The effectiveness of L1 in promoting these reactions is attributed to the initial formation of a penta-coordinate intermediate [PdMe(X)(κ1-P-L1)(κ2-P,C-L1)] (X = Me, Cl) coupled with the ease with which it transforms to 2. From computation, a lower activation barrier for C(sp3)–C(sp3) coupling and subsequent elimination has been computed for a stepwise associative pathway involving the initial formation of [PdMe2(κ1-P-L1)(κ2-P,C-L1)], compared to that computed for direct elimination from its parent, cis-[PdMe2(κ2-P,C-L1)]. Moreover, the C(sp3)–C(sp3) coupling reaction has been found to be primarily under thermodynamic control. It has also been demonstrated computationally that the methyl group of penta-coordinate [PdCl(Me)(κ1-P-L1)(κ2-P,C-L1)] is susceptible to nucleophilic attack by the phosphorus lone pair of a further equivalent of ligand L1, which proceeds through an SN2-like transition state. This initiates an unusual, indirect intermolecular reductive elimination process, resulting in the formation of equimolar quantities of the methyl phosphonium chloride salt of L1 and complex 2, in agreement with experimental observations. In contrast to the C(sp3)–C(sp3) coupling, computation shows that this indirect C(sp3)–Cl reductive elimination process is essentially under kinetic control.

Citation

Estévez, L., Tuxworth, L. W., Sotiropoulos, J., Dyer, P. W. D., & Miqueu, K. (2014). Combined DFT and experimental studies of C–C and C–X elimination reactions promoted by a chelating phosphine–alkene ligand: the key role of penta-coordinate PdII. Dalton Transactions, 43(29), 11165-11179. https://doi.org/10.1039/c4dt00340c

Journal Article Type Article
Acceptance Date Mar 11, 2014
Online Publication Date Mar 11, 2014
Publication Date Aug 7, 2014
Deposit Date Jul 10, 2014
Publicly Available Date Mar 29, 2024
Journal Dalton Transactions
Print ISSN 1477-9226
Electronic ISSN 1477-9234
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 43
Issue 29
Pages 11165-11179
DOI https://doi.org/10.1039/c4dt00340c

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