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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| Title: | 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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| Authors: | Jones, Roderick C.1, Canty, Allan J.1 Allan.Canty@utas.edu.au, Gardiner, Michael G.1, Skelton, Brian W.2, Tolhurst, Vicki-Anne1, White, Allan H.2 |
| Source: | Inorganica Chimica Acta. Jan2010, Vol. 363 Issue 1, p77-87. 11p. |
| Subjects: | Organopalladium compounds, Molecular structure, Complex compounds synthesis, Metal complexes, Ligands (Chemistry), Pyridine, Heck reaction, Catalysts |
| Abstract: | Abstract: Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-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 LiBu n 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(μ-6-MepyCH2SPh-N,S)]3 (10a) and dimeric [PdCl2(μ-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 Bu n 4NCl at 120°C as a solvent under non-aqueous ionic liquid (NAIL) conditions. [Copyright &y& Elsevier] |
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| Database: | Engineering Source |
| Abstract: | Abstract: Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-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 LiBu n 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(μ-6-MepyCH2SPh-N,S)]3 (10a) and dimeric [PdCl2(μ-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 Bu n 4NCl at 120°C as a solvent under non-aqueous ionic liquid (NAIL) conditions. [Copyright &y& Elsevier] |
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| ISSN: | 00201693 |
| DOI: | 10.1016/j.ica.2009.10.002 |
