Redox-Active Complexes Containing Group 8 Metal Centers Linked by C₂Bridges

Abstract

A series of complexes containing dicarbon ligands bridging redox-active group 8 metal−ligand fragments M(dppe)Cp‘ (M = Fe, Ru, Os; Cp‘ = Cp, Cp*) have been prepared. These complexes give up to four one-electron anodic processes at a platinum electrode, with separations of successive oxidation potentials of ca. 850 mV, giving rise to large comproportionation constants, K C (ca. 1012). Examples of the 36-electron neutral, 35-electron monocationic, and 34-electron dicationic species, together with some related monoprotonated complexes, have been isolated. Structural studies of the 36-, 35-, and 34-electron species derived from the dicarbon complex featuring two Ru(dppe)Cp end-caps (7) show that shortening of the M−C and lengthening of the C−C bonds occur upon oxidation. A complementary spectroelectrochemical investigation has revealed an intense band near 14 300 cm-1 associated with [7]PF6, which is tentatively attributed to a Ru(d)−[Ru(d)/C2(π)]* transition, rather than a genuine IVCT band. These observations have been rationalized using DFT calculations and collectively indicate that the frontier orbitals are delocalized over both group 8 metal centers and the carbon chain.

Long-distance electronic interaction in a molecular wire consisting of a ferrocenyl–ethynyl unit bridging two [(η5-C5H5)(dppe)M] metal centers

“…3, the redox behavior in 1 and 2 is dominated by the two reversible Ru 2+ / Ru 3+ redox couples (E 1/2 at 0.05 and 0.57 V in 1; 0.10 and 0.27 V in 2) and reversible ferrocene-based Fe 2+ /Fe 3+ redox couples (E 1/2 at 0.86 V in 1; 0.73 and 0.87 V in 2) vs. Ag/AgCl. For complex 3, one reversible Ru 2+ /Ru 3+ redox couple (E 1/2 at 0.14 V) and three (7); Fe1-C2, 2.026(7); Fe1-C3, 2.027(6); Fe1-C4, 2.048(7); Fe1-C5, 2.037(7); Fe1-C6, 2.072(7); Fe1-C7, 2.035(6); Fe1-C8, 2.033(6); Fe1-C9, 2.026(7); Fe1-C10, 2.041(7); Fe2-C11, 2.093(7); Fe2-C12, 2.085(7); Fe2-C13, 2.075(7); Fe2-C14, 2.077(7); Fe2-C15, 2.087(7); Fe2-C17, 1.883 (9) Quasi-reversible and irreversible waves were observed in the CV measurements of complexes 1 [20], [(g 5 -C 5 H 5 )(PPh 3 ) 2 Ru-C"C-Ph] [35], [(g 5 -C 5 H 5 )(PPh 3 ) 2 Ru-C"C-fc] (fc = ferrocenyl) [30], and [(g 5 -C 5 H 5 )(dppe)Ru-C"C-fc]. Therefore, differential pulse voltammetry was employed to obtain better-resolved potential information in our study, because the Fe 2+ /Fe 3+ redox process for 2 and 3 was quasi-reversible in the CV experiment.…”

“…Recently, the study of homo-and hetero-metallic binuclear transition metal complexes in which the end-capped metal centers are connected by p-conjugated organic linear spacers has been an intriguing area of research, since such system may provide the possibility to study the electronic coupling between the redox-active end-capped metal centers, or propose as models for molecular wires. In this context, end-capping of unsaturated organic spacers with various redox-active groups, such as ferrocene, ruthenium(II) polypyridine [4][5][6][7][8][9], [RuL 2 Cl] (L 2 = 2PPh 3 , Ph 2 PCH 2 CH 2 PPh 2 (dppe)) [10,11], and [M(g 5 -C 5 H 5 )L 2 ] (M = Fe(II), Ru(II), and Os(II)) metal centers [12][13][14][15][16][17][18][19][20][21], have been most studied where they are intended to promote the long-range electronic coupling. The nature of the end-capped metal center and p-conjugated organic spacer plays significantly important role in determining the magnitude of electronic coupling.…”

Refining the Interpretation of Near‐Infrared Band Shapes in a Polyynediyl Molecular Wire

“…[22] The higher-energy shoulder in [1] + is therefore assigned to an MLCT transition that gains intensity in rotameric forms with approximately orthogonal disposition of the Cp rings around the RuC 4 Ru axis.…”

Syntheses, structural characterisation and electronic structures of some simple acyclic amino carbene complexes

“…19,21 For example, in the case of half-sandwich complexes MCl(L 2 )Cp′ (L = phosphine or L 2 = chelating bis( phosphine), Cp′ = Cp, Cp* etc. 24 In the case of the formation of terminal vinylidene complexes [M(vCvCH 2 )-(L 2 )Cp*] + from MCl(L 2 )Cp*, HCuCSiMe 3 and NH 4 PF 6 , methanol remains a suitable solvent; 25 however, the less sterically restricted Cp derivatives require the use of either a bulkier alkyl alcohol (such as t BuOH) 26 or prolonged reaction time in a non-nucleophilic solvent, such as CH 2 Cl 2 . 19,22,23 Whilst the ancillary ligands and the R group provide a degree of steric protection for the electrophilic α-carbon, prolonged reaction leads to the conversion of the vinylidene to the corresponding methoxy carbene [M{vC(OMe)CH 2 R}(L 2 )Cp′] + .…”

“…The compounds [Fe(vCvCH 2 )(dppe))Cp]PF 6 ([1a]PF 6 ), 26 [Ru(vCvCH 2 )(dppe)-Cp]PF 6 ([1b]PF 6 ), 26 The compound [Fe(vCvCH 2 )(dppe)Cp]PF 6 (0.10 g, 0.14 mmol) was added to dry degassed CH 2 Cl 2 (15 ml) in a dry, degassed Schlenk flask connected to a gas bubbler. Dichloromethane was dried over CaH 2 , all other solvents were standard reagent grade and used as received.…”