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Synthetic and computational studies of the palladium(IV) system Pd(alkyl)-(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination

Citation

Sharma, M and Ariafard, A and Canty, AJ and Yates, BF and Gardiner, MG and Jones, RC, Synthetic and computational studies of the palladium(IV) system Pd(alkyl)-(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination, Dalton Transactions, 41, (38) pp. 11820-11828. ISSN 1477-9226 (2012) [Refereed Article]

Copyright Statement

Copyright The Royal Society of Chemistry 2012

DOI: doi:10.1039/c2dt31086d

Abstract

Synthetic routes to methyl(aryl)alkynylpalladium(IV) motifs are presented, together with studies of selectivity in carboncarbon coupling by reductive elimination from PdIV centres. The iodonium reagents IPh(C[triple bond, length as m-dash]CR)(OTf) (R = SiMe3, But, OTf = O3SCF3) oxidise PdIIMe(p-Tol)(L2) (13) [L2 = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2′-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d6 or toluene-d9 at −80 C to form complexes PdIV(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CR)(L2) [R = SiMe3, L2 = dmpe (4), bpy (5), phen (6); R = But, L2 = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C[triple bond, length as m-dash]CR above [similar]−50 C. NMR spectra show that isomeric mixtures are present for the PdIV complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between −80 C and −60 C observed for the dmpe complex 4 in toluene-d8. Kinetic data for reductive elimination from PdIV(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CSiMe3)(dmpe) (4) yield similar activation parameters in acetone-d6 (66 2 kJ mol−1, ΔH 64 2 kJ mol−1, ΔS −67 2 J K−1 mol−1) and toluene-d8 (Ea 68 3 kJ mol−1, ΔH 66 3 kJ mol−1, ΔS −74 3 J K−1 mol−1). The reaction rate in acetone-d6 is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol−1), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible CC coupling products (13.0 kJ mol−1). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC[triple bond, length as m-dash]CSiMe3 and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp2 for p-Tol, sp for C[triple bond, length as m-dash]CSiMe3) to form the product with the strongest CC bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me3SiC[triple bond, length as m-dash]C trans to OTf. Crystal structure analyses are presented for PdIIMe(p-Tol)(dmpe) (1), PdIIMe(p-Tol)(bpy) (2), and the acetonyl complex PdIIMe(CH2COMe)(bpy) (11).

Graphical abstract: Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in CC reductive elimination

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Inorganic Chemistry
Research Field:Transition Metal Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Sharma, M (Dr Manab Sharma)
Author:Ariafard, A (Associate Professor Alireza Ariafard)
Author:Canty, AJ (Professor Allan Canty)
Author:Yates, BF (Professor Brian Yates)
Author:Gardiner, MG (Associate Professor Michael Gardiner)
Author:Jones, RC (Dr Roderick Jones)
ID Code:78553
Year Published:2012
Web of Science® Times Cited:9
Deposited By:Chemistry
Deposited On:2012-07-07
Last Modified:2015-07-10
Downloads:0

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