Tuning the Electronic Communication in Heterobimetallic Mixed‐Valence Ions of (1‐Ferrocenyl)‐ and (2‐Ferrocenyl)indenyl Rhodium Isomers

Abstract

A series of heterobimetallic complexes of general structure [RhL(2){eta(5)-(2-ferrocenyl)indenyl}] (L(2)=cod, nbd, L=CO; cod=cyclooctadiene; nbd=norbornadiene) has been synthesised with the aim of tuning the metal-metal interaction in their mixed-valence ions generated both by chemical and electrochemical oxidation, and the results are compared with those obtained for [RhL(2){eta(5)-(1-ferrocenyl)indenyl}] isomers. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes evidencing a significant difference in the extent of planarity of the flexible bridging ligand between the 1- and 2-ferrocenyl isomers. Independent experimental probes, in particular the potential splitting in the cyclic voltammograms and the IT bands in the near-IR spectra, are rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods. These methods allow us to establish a trend based on the magnitude of iron-rhodium electronic coupling H(ab) ranging from valence trapped to almost delocalised ions. The quasi planar bridge and the olefin ancillary ligands make [Rh(nbd){eta(5)-(2-ferrocenyl)indenyl}](+) and [Rh(cod){eta(5)-(2-ferrocenyl)indenyl}](+) rare examples of heterobimetallic systems which can be classified as borderline Class II/Class III species.

Metal–Metal Electronic Coupling in syn and anti Stereoisomers of Mixed‐Valent (FeCp)2‐, (RhL2)2‐, and (FeCp)(RhL2)‐as‐Indacenediide Ions

“…Inspection of the pairs of MOs involved in the dominant monoelectronic transitions, that is, HOMOβ–LUMOβ and (HOMO−1)β–LUMOβ, reveals no appreciable MMCT character between the metal centres, as reported recently for other organometallic homobinuclear systems 3k. 19d, 30 These absorptions are better interpreted as allowed electronic transitions between filled and empty delocalised frontier levels (Figure 8 a).…”

“…The difference between the theoretical and the experimental energies is within the tolerance accepted for this kind of analysis on large open‐shell organometallic molecules 3l. 19d, 30, 41, 43…”

“…The choice of this functional was motivated by its successful performance reported in recent studies on electronic coupling in mixed‐valent organometallic complexes 3l. 19d, 30, 41 All‐electron 6‐31G(d,p) basis sets were used for C and H;42a,b Fe was described with Stuttgart relativistic small‐core ECP basis set 42c. This level of theory is abbreviated in the text as B3LYP/SDD,6‐31G(d,p).…”

(1,2,3,4,7-Pentamethylindenyl)rhodium complexes with arene ligands

“…The elongation value (0.044 Å ) is in the range for true g 5 -indenyl complexes Scheme In agreement with the redox behaviour of the related complex (g 5 -C 5 Ph 5 )Rh(1,5-C 8 H 12 ) [19], it undergoes two subsequent one-electron oxidations exhibiting features of chemical reversibility in the cyclic voltammetric time scale (or, the pertinent i pc /i pa ratios are constantly equal to 1 with the scan rates progressively increasing from 0.02 to 10.2 V s À1 ) [20], but in the longer times of macroelectrolysis only the monocation proved to be quite stable, as testified by cyclic voltammetry which afforded profiles quite complementary to the original ones. It is noted that the unsubstituted complex (g 5 -C 9 H 7 )Rh(1,5-C 8 H 12 ) only exhibits a partially chemically reversible one-electron oxidation [21]. Unfortunately, in contrast to the detailed investigations carried out on the reduction processes of (g 5 -C 5 Ph 5 )Rh-(1,5-C 8 H 12 ) and (g 5 -C 9 H 7 )Rh(1,5-C 8 H 12 ) [19,22], we could not study the cathodic activity of 1 because it was substantially masked by the solvent discharge.…”

Synthesis and structural characterization of ferrocenyl indenyl derivatives

“…Ferrocenyl indenyl derivatives have evoked increased interest, are more facilely prepared, and serve as a redox switch to modulate activities of other metallic centers. For instance, Santi has reported the synthesis and mixed valence properties in ferrocenyl-based bimetallic complexes [10][11][12][13]. Wang has reported the synthesis and crystal structure of ferrocene-bridged indenyl carbonyl complexes of iron, ruthenium and molybdenum [14].…”