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

Reactions of the anionic gallium( I) heterocycle, [:Ga{[N(Ar)C(H)](2)}]- (Ar = C6H3Pr2i-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-infuence of the gallium(I) heterocycle lies in the series, B(OR)(2) > H- > PR3 similar to [: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, (BuC)-C-t 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(Bu-t)C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.