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Synthesis and structural characterisation of group 10 metal(ii) gallyl complexes: analogies with platinum diboration catalysts?

Dalton Transactions
The Royal Society of Chemistry
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Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)]2}]- (Ar = C6H3Pri2-2,6), with a variety of mono- and bidentate phosphine, tmeda and 1,5-cyclooctadiene (COD) complexes of group 10 metal dichlorides are reported. In most cases, salt elimination occurs, affording either mono(gallyl) complexes, trans-[MCl{Ga{[N(Ar)C(H)]2}}(PEt3)2] (M = Ni or Pd) and cis-[PtCl{Ga{[N(Ar)C(H)]2}}(L)] (L = R2PCH2CH2PR2, R = Ph (dppe) or cyclohexyl (dcpe)), or bis(gallyl) complexes, trans-[M{Ga{[N(Ar)C(H)]2}}2(PEt3)2] (M = Ni, Pd or Pt), cis-[Pt{Ga{[N(Ar)C(H)]2}}2(PEt3)2], cis-[M{Ga{[N(Ar)C(H)]2}}2(L)] (M = Ni, Pd or Pt; L = dppe, Ph2CH2PPh2 (dppm), tmeda or COD). The crystallographic and spectroscopic data for the complexes show that the trans-influence of the gallium(i) heterocycle lies in the series, B(OR)2 > H- > PR3 [similar] [:Ga{[N(Ar)C(H)]2}]- > Cl-. Comparisons between the reactivity of one complex, [Pt{Ga{[N(Ar)C(H)]2}}2(dppe)], with that of closely related platinum bis(boryl) complexes indicate that the gallyl complex is not effective for the catalytic or stoichiometric gallylation of alkenes or alkynes. The phosphaalkyne, ButC[triple bond, length as m-dash]P, does, however, insert into one gallyl ligand of the complex, leading to the novel, crystallographically characterised P,N-gallyl complex, [Pt{Ga{[N(Ar)C(H)]2}}{Ga{PC(But)C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.

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