Open Access Repository

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

Downloads

Downloads per month over past year

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

[img] PDF (Whole thesis)
whole_PeacockEv...pdf | Request a copy
Full text restricted
Available under University of Tasmania Standard License.

Abstract

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.

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

Copyright 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).

Additional Information:

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

Item Statistics: View statistics for this item

Actions (login required)

Item Control Page Item Control Page
TOP