Nickel [II] complexes of thio-B-diketonates as olefin conversion catalysts
Creators: name: Peacock, Evan John
Publisher: name: University Of Tasmania
Year: 2023

description: 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 &gt;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.