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Studies in alkylpalladium chemistry, including development of the new oxidation state +IV

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Byers, Peter Kenneth (1988) Studies in alkylpalladium chemistry, including development of the new oxidation state +IV. PhD thesis, University of Tasmania.

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Abstract

This thesis describes the development of convenient and systematic routes to a
wide range of monomethylpalladium(II) and dimethylpalladium(II) complexes of
nitrogen donor ligands, and the first development of an extensive chemistry of
alkylpalladium(IV) complexes. The work reported here has important implications for
catalytic processes employing palladium, and for the future development of the new
oxidation state, +Iv, in organopalladium chemistry.
The synthesis and characterisation of (PdMe2(Ln )) and PdMeX(Ln) }
complexes is described, with 2,2'-bipyridyl (bipy), 1,10-phenanthroline (phen), and
alkane bridged bidentate ligands as L2 and tridentate ligands as L3, where L2 and L3
contain combinations of the N-donor heterocycles N-methylimidazol-2-yl, pyridin-2-y1
and pyrazol- 1-yl. Tridentate ligands were initially employed to assess the ability of
palladium(H) to adopt coordination numbers greater than four. The reaction of
(PdMe2(Ln)) with various organohalides (RX) has been studied, and has led to the
detection, isolation and characterisation of the first hydrocarbylpalladium(IV)
complexes.
The complexes (PdMe2(Ln)) and (PdMeI(Ln)) have been synthesised using
methyllithium. During development of these routes, the complexes (PdMe2(11-
PYridazine)) n and [PdMe(-1-X)(SMe2))2 (X=C1,Br,I) were also isolated, and reaction
of these complexes with ligands (La ) give dimethylpalladium(ii) and
methylpalladium(ii) complexes, respectively. The iodo-bridged dimer (PdMe(gI)(SMe2))
2 has also been used to prepare cationic complexes by reaction with AgBF4
followed by addition of bipy, or by direct reaction with 2,2':6',2"-terpyridyl (terpy).
The halogeno-dimers (PdMe(1.1-x)(SMe2))2, with square planar geometry for
Pd(i1), have been characterised by near and far infrared and 1H NMR spectroscopy,
molecular weight determinations, and an X-ray structure analysis for (PdMe4tC1)(SMe2))
2. The dimethylpalladium00 complex (PdMe2(g-pyridazine)) n is unstable
at ambient temperature, and was characterised only by 1H NMR spectroscopy. The neutral complexes, (PdMeX(Ln)) (X=Me, halide), and cationic
complexes, [PdMe(S)(hiPY)]BF4 (S=SMe2, CH3CN, y-pic) and [PdMe(terpy)]I,
were characterised by microanalysis, 1 H NMR spectroscopy, and, for square planar
[PdMe(y-Pic)(biPY)]BF4, an X-ray structure analysis. 1H NMR spectra for the alkane
bridged bidentate ligand complexes, (PdMeX(1,2)) (X=Me, halide), at ambient
temperature were consistent with rapid boat to boat inversion of the chelate ring, while
spectra for the tridentate ligand complexes (PdMeX(L3)) (X=Me, halide) were
consistent with rapid exchange between free and bound donor groups. Both processes
could be resolved upon cooling, and low temperature solution state conformations
determined. 1H NMR spectra of the cationic complexes [PdMe(S)(hiPY)JBF4 also
displayed variable temperature behaviour, consistent with site exchange of the Pd-S
and Pd-Me groups.
Synthesis of the complexes (PdMeI(L2)) was also accomplished by reaction of
Mel with the corresponding dimethylpalladium(II) complex (PdMe2(1-2)), and led to
the in situ detection of palladium(IV) intermediates, and to the subsequent isolation and
characterisation of the first hydrocarbylpalladium(IV) complexes.
Reaction of Mel with (PdMe2(L2)) gave the isolable complexes
(pdivme3I(L2)) for L2=bipy and phen only, although neutral, and in some instances,
cationic complexes, were spectroscopically detected for most of the other bidentate
ligand complexes studied. The reaction of Mel with the tridentate ligand complexes
(PdMe2(L3)), on the other hand, produced the cations (PdIvMe3(L3))I, which could
be isolated for all tridentate ligands studied. The reaction of organohalides (RX) with
(PdMe2((pyridin-2-yl)bis(N-methylimidazol-2-yOmethane)) to give the stable cations
[Pd1 vMe2R(pymim2CH)]X was also studied, and the reaction of PhCH2Br with
(PdMe2(bipy)) produced the neutral complex (PdIvMe2(CH2Ph)Br(bipy)).
The neutral complexes (PdMe2RX(L2)) were characterised by microanalysis,
1H NMR spectroscopy, molecular weight determinations, and for (PdMe3I(bipy)) by
an X-ray structure determination. The kinetics of oxidative addition of Mel to
(PdMe2(hiPY)) and reductive elimination of ethane from (PdMe3I(bipY)) have been
studied, and in both cases reaction proceeds via a polar intermediate, and an estimate
of the Pd(IV)-Me bond strength has been determined. The cationic complexes
[PdMe2R(L3)]X were characterised by microanalysis, 1H NMR spectroscopy, and by
an X-ray crystallographic study of the isostructural cations [MMe3(pz3CH)]I (M=Pd,
Pt). For both isolated and in situ detected neutral and cationic complexes a facial
arrangement of the organogroups is proposed.

Item Type: Thesis (PhD)
Keywords: Palladium catalysts, Oxidation, Electrolytic
Copyright Holders: The Author
Copyright Information:

Copyright 1998 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 the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1989. Includes bibliography

Date Deposited: 25 Nov 2014 00:44
Last Modified: 21 Jun 2016 03:06
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