New Bimetallic Reactivity in Pt₂^II,II/Pt₂^IV,IV Transformation Mediated by a Benzene Ring

Abstract

A new Pt 2 II,II complex with the formula Pt 2 (TPAB)Me 4 ( 1 ), where TPAB = 1,2,4,5-tetrakis(5-( p -C 7 H 15 Ph)-7-azaindol-1-yl)benzene, has been synthesized. This molecule has excellent solubility in common solvents, which enabled our investigation of its reactions with a variety of oxidants to form Pt 2 IV,IV species and the reverse reactions of the Pt 2 IV,IV species back to 1 via reduction. Despite the lack of direct Pt···Pt interactions, the two Pt centers in 1 display distinct bimetallic cooperativity mediated by the central phenyl ring of the TPAB ligand. The most unusual finding is that the reactivity of 1 with MeOTf is highly dependent on the amount of molecular oxygen present in the reaction medium. In the absence of O 2, the reaction of 1 with MeOTf produced [Pt 2 IV,IV (TPAB)Me 6 ][OTf] 2 ( 6 ), while in the presence of O 2, complex 7, Pt 2 IV,IV (TPAB)Me 4 (OTf) 2, was obtained. Compound 1 was found to react readily with O 2 at one atmosphere and ambient temperature to produce an insoluble and not yet fully characterized solid that further reacts with MeOTf to produce 7 quantitatively. NMR and single-crystal X-ray diffraction analyses established that the two Pt IV centers in 6 are five-coordinate with a square-pyramidal geometry, while in 7 the two Pt IV centers are six-coordinate with an octahedral geometry. Most significantly, the central phenyl ring of the TPAB ligand was transformed to a cyclohexyldienyl in 7, while it remains unchanged in 6 . Complex 1 also reacts readily with other oxidants such as CHCl 3, PhICl 2, Br 2 (CBr 4 ), I 2, and H 2 O 2 to produce Pt 2 IV,IV (TPAB)Me 4 X 2 (X = Cl, 2; Br, 3; I, 4; OH, 5 ). The structures of 2 − 5 are similar to that of 7, showing the generality of the central phenyl ring mediated oxidation of the Pt 2 II,II system. Complexes 2 and 7 can be reduced and converted back to complex 1 via reactions with BH 4 −, as established by NMR experiments.