Interaction of ferrocene moieties across a square Pt4 unit: synthesis, characterization, and electrochemical properties of carboxylate-bridged bimetallic Pt4Fe(n) (n = 2, 3, and 4) complexes

Four types of square Pt(4) complexes bearing two or more ferrocenecarboxylate ligands--[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(4)] (6); [Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(3)(μ-ArNCHNAr)], where ArNCHNAr = N,N'-diarylformamidinate) (7); trans-[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(2)(μ-ArNCHNAr)(2)] (8); and cis-[Pt(4)(μ-OCOCH(3))(4)(μ-OCOC(5)H(4)FeCp)(2)(κ(4)-N(4)-DArBp)(2)], where DArBp = 1,3-bis(benzamidinato)propane (9)--were successfully prepared via reactions of [FeCp(η(5)-C(5)H(4)COOH)] (5) with the corresponding square Pt(4) complexes, which have labile in-plane acetate ligands. The newly prepared Pt(4) 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-Pt(4)Fe(2)8, and the cis-Pt(4)Fe(2) complexes 9. Weak interactions between two ferrocene moieties across the Pt(4) core, providing ΔE(1/2) values and K(c) constants, were revealed electrochemically, using cyclic and differential-pulse voltammetry in dichloromethane containing [(n)Bu(4)N][BAr(F)(4)] (where Ar(F) = C(6)H(3)(CF(3))(2)-3,5), which was a better supporting electrolyte for such an interaction than [(n)Bu(4)N][PF(6)].