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Nickel [II] complexes of thio-B-diketonates as olefin conversion catalysts
thesisposted on 2023-05-27, 17:43 authored by Peacock, Evan John
The work in this thesis details the synthesis and catalytic behaviour of new nickel(II) coordination and organometallic complexes containing a chelating monothio-fl-diketonate ligand [Ni(Ri(CS)CH(CO)R2)(PL3)X] (1, X=halide or hydrocarbyl). Concurrent with the nickel studies, palladium(II) mono- and di-thiofl-diketonate model systems for olefin oligomerisation catalysis were developed. The synthesis of the monothio-13-diketonate (sacac) ligands by the thiolation of 13- diketonate compounds was thoroughly investigated with a view to more efficient procedures. Existing methods gave the best yields. An alternative procedure involving a Claisen condensation did however offer synthetic flexibility. The mixed ligand nickel coordination complexes (1, X= halide) could not be formed by previously published means. Alternative synthetic techniques (using a metathesis reaction) have been developed, including one of the first applications of ultrasound to the production of homogeneous metal complexes from homogeneous reactants. A selenium analogue [Ni(CH3(CSe)CH(CO)CH3XPnBu3)C1] was also synthesised. The monothio-P-diketonate complexes are extremely labile and readily disproportionate in solution by reverse reaction to equilibrium concentrations. This made isolation difficult. Only [Ni(CH3(CS)CH(CO)C6H6)(PnBu3)CI] and Ni(CH3(CS)CH(CO)C6H6)(P(C6F111)3)C1] were isolable as the pure mixed ligand product. The formation of 1 was greatest in selected polar solvents and appears to be catalysed by a Bronsted acid. A mechanism is discussed. New cationic complexes containing a chelating phosphine ligand [Ni(R1 (CS)CH(CO)R2)(Ph2P(CH2),Ph2)][BP14] (2, n=1,2) were prepared by an existing method. New and previously described palladium(II) di- and mono-thio-f3- diketonate complexes based on 1 were prepared. Catalysts generated from the complexes 1 and an alkylaluminium cocatalyst (Ziegler-type catalyst) oligomerise and isomerise a range of olefins and diolefins. Activities are consistently higher than for P-diketonate or dithio-13-diketonate based systems. In several cases enzyme-like rates were exhibited. The catalyst generated from [Ni(CH3(CS)CH(CO)C6H6)(P(C6I-Iii)3)C1] + Et2A1C1 is particulary efficient at dimerising 1-butene. Interestingly several catalysts display a duality of behaviour that arises from at least two independent catalytic species and can be initiated by trace amounts of additives. Catalysts generated from 2 display similar behaviour to, but are not as efficient as, those derived from 1. Oligomerisation catalysts can be formed from bis-ligand com concentration dependent. Substituents R1and R2influence activity; electron withdrawing ligands (eg R1= CF3) effect higher activities. The effect of ligands and cocatalyst on the catalytic behaviour of 1 has been studied in detail. Variation of the phosphine ligand influences product distribution and activity. Altering the monothio-p-diketonate ligand affects the degree of complex disproportionation prior to activation which influences activity. The lability of 1 has allowed considerable versatility in the design of these catalytic systems. For example a one to one mixture of [Ni(R1 (CS)CH(CO)R2)2] and [Ni(PL3)X2] with cocatalyst exhibits long term activity and product specificity identical to [Ni(R1 (CS)CH(CO)R2)(PL3)X]. Variation of the alkylaluminium cocatalyst has significant influence on catalytic activity and product distribution. A catalyst generated from [Ni(CH3(CS)CH(CO)C6H6)(P(C6H 1)3)Cl] and a weak Lewis acidity cocatalyst dimerises propene to >80% dimethylbutenes. Lewis acidity of the metal centre appears to be required for successful Ziegler based olefin oligomerisation catalysis. An organometallic version of 1 (X= o-toly1) was prepared and found to be a moderately active single component catalyst for the oligomerisation of ethene at high pressure. This is the first example of a well defined single component nickel catalyst containing an SAO chelate ligand. A study of this complex and the less active palladium analogues permitted the identification of products from multiple ethene insertions into the nickel-hydrocarbyl bond, yielding useful mechanistic information. The nickel complex can also be reversibly carbonylated at low CO pressure. Palladium(II) based catalysts isomerise 1-octene; in agreement with the nickel systems, monothio-P-diketonates are far more active than the dithio-p-diketonates. The palladium monothio-13-diketonate derived catalysts oligomerise propene with remarkable activity. Analysis of products gave important insights into the catalytic cycle. In situ VT-NMR studies of catalysts generated from 1 (and palladium analogues) allowed the observation of intermediates, yielding important mechanistic information and indicating intricate cocatalyst/metal complex interactions. Palladium dithio-I3-diketonate derived systems were shown for the first time to act as oligomerisation catalysts.
Rights statementCopyright the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from copyright owner(s). Includes bibliographical references. Thesis (Ph.D.)--University of Tasmania, 1996.