Oxidant-Induced Hydride Abstraction from [Pt(μ-PBut2)(H)(PBut2H)]2Yielding [Pt2(μ-PBut2)2(H)(PBut2H)2]C3(CN)5. Spectroscopic, Crystallographic, and Theoretical Comparison of the Structures of Two “Tautomers”

The platinum(II) phosphido-bridged dihydride [Pt(μ-PBu t 2 )(H)(PBu t 2 H)] 2, 1, reacts with tetracyanoethylene (TCNE) in toluene to give the charge-transfer complex 1 ·TCNE, which is stable only in the solid state. By dissolving 1 ·TCNE in polar solvents, electron transfer occurs rapidly, followed by loss of one of the hydrido ligands and formation of the unsaturated Pt(II)Pt(II) derivative [Pt 2 (μ-PBu t 2 ) 2 (H)(PBu t 2 H) 2 ] + TCNE -, 2a . Recrystallization of 2a in the air gives crystals of [Pt 2 (μ-PBu t 2 ) 2 (H)(PBu t 2 H) 2 ] + [C 3 (CN) 5 ] -, 2b, whose structure was solved by X-ray diffraction. The same type of reaction was observed when 1 was reacted with tetracyanoquinodimethane (TCNQ), forming the analogous, structurally characterized, TCNQ - salt of cation 2 + . What happened to the hydrido ligand displaced from 1 was better seen when 1 was reacted with an equimolar amount of [Cp 2 Fe]PF 6 as the oxidant (Cp = cyclopentadienyl). In this case we isolated a 1:1 mixture of ( 2 )PF 6, 2d, and [Pt 2 (μ-PBu t 2 )(μ-H)(PBu t 2 H) 3 (H)]PF 6, 3d, the latter also known to form by the reaction of complex 1 with strong acids. According to this observation, the reaction of 1 with two equivalents of [Cp 2 Fe]PF 6 and one of triethylamine (NEt 3 ) gives quantitatively [NEt 3 H]PF 6 and 2d . The electronic structure of cation 2 + was also investigated by means of ab initio and density functional calculations. Ignoring the different metals, cation 2 + can be considered a “tautomer” of the known phosphine-bridged dipalladium cation [Pd 2 (μ-PBu t 2 )(μ-PBu t 2 H)(PBu t 2 H) 2 ] +, 4 + . Differences and analogies between the structures of the two cations were investigated by means of spectroscopic, crystallographic, and theoretical (ab initio and density functional) analyses.