Transition metal–carbon bonds. Part XVI. Cationic allylic complexes of palladium(II). A cationic allylic complex of platinum(II)

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Abstract
In aqueous acetone [Pd2Cl2(2-methylallyl)2] reacts with PPh3 to give the colourless cation [Pd(2-methylallyl)(PPh3)2]+, isolated as its tetraphenylborate salt. Similar complexes with PMe2Ph and AsMe2Ph were prepared. Treatment of [PdCl2(PPh3)2] with 2-methylallylmagnesium chloride followed by hydrolysis gave the hydrated chloride [Pd(2-methylallyl)(PPh3)2]Cl·2H2O. Attempts to prepare analogous complexes with other allylic ligands were unsuccessful. N.m.r. data show the 2-methylallyl ligands in these cations to be symmetrically π-bonded to the palladium. Conductimetric studies on systems of the type [Pd2X2 all2]+x mol. of L have shown that the tendency to form ionic species decreases (1) for different ligands L in the order PMe2Ph PEt2Ph PEt3 > PPh3 > AsPh3 > SbPh3 > pyridine; (2) for different allyl ligands ‘all’ in the order 2-methylallyl > allyl > 1-methylallyl > 1,3-dimethylallyl > 1,1-dimethylallyl; and (3) for different halogens X in the order Cl > Br > I. Compounds of the type [Pd2Cl2 all2] react rapidly with an excess of PPh3 in aqueous acetone to give [Pd(PPh3)4] and [all PPh3]+ Cl–. Treatment of [Pd(PPh3)4] with an excess of the allylic chloride gives [PdCl all PPh3]. Treatment of [PtCl2(AsMe2Ph)2] with 2-methylallylmagnesium chloride followed by water and NaBPh4 gave the salt [Pt(2-methylallyl)(AsMe2Ph)2]+ BPh4 –.

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