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Nickel [II] complexes of thio-B-diketonates as olefin conversion catalysts


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Peacock, Evan John 1996 , 'Nickel [II] complexes of thio-B-diketonates as olefin conversion catalysts', PhD thesis, University of Tasmania.

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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
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
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
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.

Item Type: Thesis - PhD
Authors/Creators:Peacock, Evan John
Keywords: Nickel compounds, Organometallic compounds, Chelates, Nickel catalysts, Ligands
Copyright Holders: The Author
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Additional Information:

Includes bibliographical references. Thesis (Ph.D.)--University of Tasmania, 1996.

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