Divalent Platinum Complexes of the Carbanion 2-C6F4AsPh2: Monodentate or Bidentate Coordination?

The reaction of [PtI2(1,5-COD)] with 2-LiC6F4AsPh2 affords the planar platinum(II) fluoroaryl complex [PtI(kappa C-2-C6F4AsPh2)(1,5-COD)] (7), in which the arsenic atom is not coordinated to the metal atom. Attempts to prepare the bis(chelate) complex [Pt(kappa As-2,C-2-C6F4AsPh2)(2)] analogous to the known phosphorus compound failed. Removal of iodide ion from 7 with TlPF6 gave [Pt(kappa As-2,C-2-C6F4AsPh2)(1,5-COD)PF6 (8), in which 2-C6F4AsPh2 is now coordinated as a bidentate ligand, giving a four-membered chelate ring. Alternatively, protonolysis (with triflic acid) of the methyl complex [PtMe(kappa C-2-C6F4AsPh2)(1,5-COD)] (15), which is obtained from 7 and dimethylzinc, gives the triflate salt 16 of the same chelate cation. The chelate As,C ring in 8 is readily reopened when the complex is treated with pyridine or with halide ions, forming respectively [Pt(py)(kappa C-2-C6F4AsPh2)(1,5-COD)PF6 (9) and [PtX(kappa C-2-C6F4AsPh2](1,5-COD)] (X = Cl (10), Br (11), I (7)). The appearance of two pairs of olefinic COD resonances in the proton NMR spectra of 7, 10, 11, and 15 may indicate that there is restricted rotation about the Pt-kappa C-2-C6F4AsPh2 bond; the additional signals are not evident in the spectra of 8 or 16. Complexes 7 and 10 form the 1:1 adducts [PtX(mu-2-C6F4AsPh2)(1,5-COD)AuY].(X = CI, Y = I (12); X = Y = 1(13); X = Y = Cl (14)) by attachment of gold(I) halides to their dangling arsenic atoms. In 12 the halides are scrambled between platinum and gold. The X-ray structures of 7, 8, 9, 12, 15, and 16 are reported, and possible reasons for the poorer chelating ability of 2-C6F4AsPh2 in comparison with that of 2-C6H4PPh2 are discussed.