Interaction of Ferrocene Moieties Across a Square Pt₄ Unit: Synthesis, Characterization, and Electrochemical Properties of Carboxylate-Bridged Bimetallic Pt₄Fe_<i>n</i> (<i>n</i> = 2, 3, and 4) Complexes

Abstract

Four types of square Pt₄ complexes bearing two or more ferrocenecarboxylate ligands[Pt₄(μ-OCOCH₃)₄(μ-OCOC₅H₄FeCp)₄] (<b>6</b>); [Pt₄(μ-OCOCH₃)₄(μ-OCOC₅H₄FeCp)₃(μ-ArNCHNAr)], where ArNCHNAr = <i>N</i>,<i>N′</i>-diarylformamidinate) (<b>7</b>); <i>trans</i>-[Pt₄(μ-OCOCH₃)₄(μ-OCOC₅H₄FeCp)₂(μ-ArNCHNAr)₂] (<b>8</b>); and <i>cis</i>-[Pt₄(μ-OCOCH₃)₄(μ-OCOC₅H₄FeCp)₂(κ⁴-<i>N</i>₄-DArBp)₂], where DArBp = 1,3-bis(benzamidinato)propane (<b>9</b>)were successfully prepared via reactions of [FeCp(η⁵-C₅H₄COOH)] (<b>5</b>) with the corresponding square Pt₄ complexes, which have labile <i>in-plane</i> acetate ligands. The newly prepared Pt₄ complexes (<b>6</b>–<b>9</b>) with ferrocene moieties as pendants were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS), combustion analyses, and single-crystal X-ray analysis for <b>6</b>, some of the <i>trans</i>-Pt₄Fe₂ <b>8</b>, and the <i>cis</i>-Pt₄Fe₂ complexes <b>9</b>. Weak interactions between two ferrocene moieties across the Pt₄ core, providing Δ<i>E</i>_1/2 values and <i>K</i>_c constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [^<i>n</i>Bu₄N][BAr^F₄] (where Ar^F = C₆H₃(CF₃)₂-3,5), which was a better supporting electrolyte for such an interaction than [^<i>n</i>Bu₄N][PF₆]