Palladium complexes of multidentate pyrazolylmethyl pyridine ligands: Synthesis,structures and phenylacetylene polymerization |
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| Authors: | Stephen O. Ojwach Ilia A. Guzei James Darkwa Selwyn F. Mapolie |
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| Affiliation: | 1. Department of Chemistry, University of Johannesburg, Auckland Park Kingsway Campus, Auckland Park 2006, South Africa;2. Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA;3. Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa |
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| Abstract: | The compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (MeNˆNˆN) (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (tBuNˆNˆN) (L2), react with either [Pd(NCMe)2Cl2] or [Pd(COD)ClMe] to form the mononuclear palladium complexes [Pd(MeNˆNˆN)Cl2] (1), [Pd(MeNˆNˆN)ClMe] (2), [Pd(tBuNˆNˆN)Cl2] (3) and [Pd(tBuNˆNˆN)ClMe] (4). Reactions of 1, 2 and 4 with the halide abstractor, NaBAr4 (Ar = 3,5-(CF3)2C6H3), led to the formation of stable tridentate cationic species [Pd(MeNˆNˆN)Cl]+(5), [Pd(MeNˆNˆN)Me]+ (6) and [Pd(tBuNˆNˆN)Cl]+ (7) respectively. The analogous carbonyl linker cationic species [Pd{(3,5-Me2pz-CO)2-py}Cl]+ (9) and [Pd{(3,5-tBu2pz-CO)2-py}Cl]+ (10), prepared by halide abstraction of the neutral complexes [Pd{(3,5-Me2pz-CO)2-py}Cl2] and [Pd{(3,5-tBu2pz-CO)2-py}Cl2] by NaBAr4, were however less stable with t1/2 of 14 and 2 days respectively. Attempts to crystallize 1 and 3 from the mother liquor resulted in the isolation of the salts [Pd(MeNˆNˆN)Cl]2[Pd2Cl6] (11) and [Pd(tBuNˆNˆN)Cl]2[Pd2Cl6] (12). Although when complexes 1–4 were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerization or polymerization were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerized and polymerized phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. |
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| Keywords: | (Pyrazolylmethyl)pyridine Bidentate palladium complexes Tridentate ligand coordination Cationic palladium complexes Phenylacetylene Polymerization |
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