Interaction of Ferrocene Moieties Across a Square Pt4 Unit: Synthesis, Characterization, and Electrochemical Properties of Carboxylate-Bridged Bimetallic Pt4Fen (n = 2, 3, and 4) Complexes

Four types of square Pt4 complexes bearing two or more ferrocenecarboxylate ligands[Pt4(μ-OCOCH3)4(μ-OCOC5H4FeCp)4] (6); [Pt4(μ-OCOCH3)4(μ-OCOC5H4FeCp)3(μ-ArNCHNAr)], where ArNCHNAr = N,N′-diarylformamidinate) (7); trans-[Pt4(μ-OCOCH3)4(μ-OCOC5H4FeCp)2(μ-ArNCHNAr)2] (8); and cis-[Pt4(μ-OCOCH3)4(μ-OCOC5H4FeCp)2(κ4-N4-DArBp)2], where DArBp = 1,3-bis(benzamidinato)propane (9)were successfully prepared via reactions of [FeCp(η5-C5H4COOH)] (5) with the corresponding square Pt4 complexes, which have labile in-plane acetate ligands. The newly prepared Pt4 complexes (6–9) 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 6, some of the trans-Pt4Fe2 8, and the cis-Pt4Fe2 complexes 9. Weak interactions between two ferrocene moieties across the Pt4 core, providing ΔE1/2 values and Kc constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [nBu4N][BArF4] (where ArF = C6H3(CF3)2-3,5), which was a better supporting electrolyte for such an interaction than [nBu4N][PF6].