High-Nuclearity Pt-Tl-Fe Complexes: Structural, Electrochemistry, and Spectroelectrochemistry Studies

Resumen

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C6F5)2(C≡CFc) 2]2- and [Pt(bzq)(C≡CFc)2]- (Fc = ferrocenyl) complexes react with Tl+ to form discrete octanuclear (PPh3Me)2[{trans,cis,cis-PtTl(C 6F5)2(C≡CFc)2}2] (1), [PtTl(bzq)(C≡CFc)2]2 (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl2(C6F 5)2(C≡CFc)2]2 (3) derivatives, stabilized by both PtII•••TlI and Tl I•••η2(alkynyl) bonds. By contrast, Q2[trans-Pt(C6F5)2(C≡CFc) 2] (Q = NBu4) reacts with Tl+ to give the one-dimensional (1-D) anionic [(NBu4){trans,trans,trans-PtTl(C 6F5)2(C≡CFc)2}]n (2) and neutral [trans,trans,trans-PtTl2(C6F 5)2(C≡CFc)2]n (4) polymeric chains based on [PtFc2]2- platinate fragments and Tl + (2) or [Tl•••Tl]2+ (4) units, respectively, connected by PtII•••TlI and secondary weak κ-η1 (2) or η2 (4) alkynyl•••TlI bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh3MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2′ (Q = PPh3Me). Two slightly different pseudopolymorphs were found for 2′, depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)4]2- with 2 equiv of Tl+ affords the tetradecanuclear sandwich type complex [Pt2Tl4(C≡CFc)8] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl+ with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E1/2 (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl+ coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C 6F5)2(C≡CFc)2]2- and complex 3. © 2010 American Chemical Society.