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Phenylpalladium(IV) Chemistry: Selectivity in Reductive Elimination from Palladium(IV) Complexes and Alkyl Halide Transfer from Palladium(IV) to Palladium(II)


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Markies, BA, Canty, AJ, Boersma, J and van Koten, G 1994 , 'Phenylpalladium(IV) Chemistry: Selectivity in Reductive Elimination from Palladium(IV) Complexes and Alkyl Halide Transfer from Palladium(IV) to Palladium(II)' , Organometallics, vol. 13, no. 5 , pp. 2053-2058 , doi: 10.1021/om00017a071.

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Methyl iodide, benzyl bromide, and benzyl iodide react with PdMePh(bpy) (bpy = 2,2'-
bipyridyl) in acetone at 0 °C to form the isolable fuc-triorganopalladium(1V) complexes PdIMez-
Ph(bpy) (3) and PdXMePh(CHzPh)(bpy) [X = Br (4), I (5)l. Complex 3 occurs as a mixture
of isomers in a cu. 1:l ratio, involving the phenyl group in a position trans either to bpy (3a)
or to iodine (3b), while complexes 4 and 5 are obtained as one isomer which, most likely, has
the benzyl group trans to the halogen. The selectivity of reductive elimination from a metal
bonded to three different groups could be studied for the first time. The complexes undergo
facile reductive elimination in (CD3)zCO at 0 °C, in which PdIMezPh(bpy) gives a mixture of
ethane and toluene in a 4:l molar ratio together with PdIR(bpy) (R = Ph, Me), whereas PdXMePh-
(CHzPh)(bpy) (X = Br, I) gives exclusively toluene and PdX(CHZPh)(bpy). The analogous
tmeda complex, PdMePh(tmeda) (tmeda = N,N,N',N'-tetramethylethylenediamine), reacts
more slowly than PdMePh(bpy1 with alkyl halides. Methyl iodide reacts cleanly with PdMePh-
(tmeda) at 0 °C in (CD3)zC0 to form ethane and PdIPh(tmeda), but the expected palladium(1V)
intermediate could not be detected. Benzyl bromide does not react with PdMePh(tmeda)
below the decomposition temperature of the latter under these conditions (50 °C, (CD&CO),
while benzyl iodide reacts at 40 °C to give a complicated mixture of products of which ethane,
diphenylmethane, ethylbenzene, toluene, and PdIR(tmeda) (R = Me, Ph) could be identified.
Benzyl iodide reacts with PdMez(tmeda) at -30 °C in (CD3)zCO to form PdIMez(CHzPh)-
(tmeda), for which lH NMR spectra showed the benzyl group to be trans to one of the N-donor
atoms. However, PdIMez(CHzPh) (tmeda) is unstable and undergoes facile reductive elimination
to form ethane and PdI(CH2Ph)(tmeda). Transfer of alkyl and halide groups from palladium-
(IV) to palladium(I1) complexes occurs in (CD3)zCO at low temperatures for several reaction
systems in which the resulting palladium(1V) complex is known to be more stable than the
palladium(1V) reagent. There is a strong preference for benzyl group transfer from PdXMePh-
(CHZPh)(bpy) to PdMez(L2) (X = Br, I; LZ = bpy, phen). The mechanism of the transfer
reactions is discussed in terms of the mechanism suggested earlier for alkyl halide transfer from
palladium(1V) to platinum(II), palladium(I1) to palladium(O), cobalt(II1) to cobalt(I), and
rhodium(II1) to rhodium(1). These reaction systems involve nucleophilic attack by the lower
oxidation state reagent at an alkyl group attached to the higher oxidation state reagent.

Item Type: Article
Authors/Creators:Markies, BA and Canty, AJ and Boersma, J and van Koten, G
Journal or Publication Title: Organometallics
ISSN: 0276-7333
DOI / ID Number: 10.1021/om00017a071
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