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Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki–Heck catalysis mediated by complexes of N,S-donor ligands

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Jones, Roderick C and Canty, AJ and Gardiner, MG and Skelton, BW and Tolhurst, V and White, AH (2010) Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki–Heck catalysis mediated by complexes of N,S-donor ligands. Inorganica Chimica Acta, 363 (1). pp. 77-87. ISSN 0020-1693

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Abstract

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the four or six position of the pyridyl ring, R4,R6-pyCH2ER1 [R4 = R6 = H, ER1 = SMe (1), SeMe (2), SPh (6), SePh (7); R4 = Me, R6 = H, ER1 = SMe (3), SPh (8), SePh (9); R4 = H, R6 = Me, ER1 = SMe (4), SPh (10), SePh (11); R4 = H, R6 = Ph, ER1 = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R4,R6-pyMe with butyl lithium followed by R1EER1. On reaction with PdCl2(NCMe)2, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C6H4)pyCH2ER1-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER1 = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl2(R4,R6-pyCH2ER1). Complexes with R6 = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R4 = Me, ER1 = SMe), 7a (R4 = H, ER1 = SePh) and 9a (R4 = Me, ER1 = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl2(N,E) motifs and bridging ligands, trimeric [PdCl2(l-6-MepyCH2SPh-N,S)]3 (10a) and dimeric [PdCl2(l-6-MepyCH2SePh-N,Se)]2 (11a). This behaviour is attributed to avoidance of the Me...Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)–16.8(2)]. When examined as precatalysts for the Mizoroki–Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC6H4Br and 4-RC6H4Cl). The most active precatalysts are PdCl2(R4-pyCH2SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl2(pyCH2SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Bun 4NCl at 120 C as a solvent under non-aqueous ionic liquid (NAIL) conditions.

Item Type: Article
Keywords: palladium, thiomethylpyridine, Heck, Mizoroki-Heck, Non-aqueous ionic liquid catalysis, NAILs, dimeric complexes, trimeric complexes, Nitrogen-sulfur ligands, Heteroleptic ligands
Journal or Publication Title: Inorganica Chimica Acta
Page Range: pp. 77-87
ISSN: 0020-1693
Identification Number - DOI: 10.1016/j.ica.2009.10.002
Additional Information: The definitive version is available at http://www.sciencedirect.com
Date Deposited: 21 Dec 2009 00:33
Last Modified: 18 Nov 2014 04:08
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