Synthesis, Characterization, and Electrochemical Relationships of Dinuclear Complexes of Platinum(II) and Platinum(III) Containing Ortho-Metalated Tertiary Arsine Ligands

Reaction of 2-Li-4-MeC6H3AsPh2 with [PtCl2(SEt2)2] gives two isomeric dinuclear platinum(II) complexes, one containing
a half-lantern structure with two chelating and two bridging C6H3-5-Me-2-AsPh2 ligands, [Pt2(κ2As,C-C6H3-5-Me-2-AsPh2)2(μ-κAs,κC-C6H3-5-Me-2-AsPh2)2], and the other, a full-lantern with four bridging C6H3-5-Me-2-AsPh2 ligands,
[Pt2(μ-κAs,κC-C6H3-5-Me-2-AsPh2)4]. The lantern structure of the latter is retained in the dihalodiplatinum(III) complexes
that are formed by oxidative addition of chlorine, bromine, or iodine to the isomeric mixture. The dichloro derivative
undergoes metathesis reactions with silver or sodium salts, yielding the corresponding cyano, thiocyanato, cyanato,
and fluoro species. The structures of all complexes have been determined by single-crystal X-ray analysis. The
oxidative addition products have Pt−Pt distances in the range 2.65−2.79 Å (cf. 2.89 Å in the lantern diplatinum(II)
structure), consistent with the presence of a Pt−Pt bond. Electrochemical data lead to the conclusion that an initial
rapid one-electron process and subsequent chemical reactions produce the dihalodiplatinum(III) lantern structure
when mixtures of the lantern and half-lantern complexes are oxidized by halogens. The electrochemical data also
explain why chemical reduction of the dihalodiplatinum(III) complex produces only the lantern diplatinum(II) complex.