Oxidation Chemistry of Metal-Bonded C₄Chains:  A Combined Chemical, Spectroelectrochemical, and Computational Study

Abstract

The known complex {Cp(PPh3)2Ru}2(μ-C⋮CC⋮C) (3-Ph) and its PMe3-substitution product {Cp(PPh3)(PMe3)Ru}2(μ-C⋮CC⋮C) (3-Me) have been shown by cyclic voltammetry to undergo a series of four stepwise one-electron oxidation processes. Successive oxidation potentials (V) for the first three reversible processes of 3-Ph (3-Me) are −0.23 (−0.26), +0.41 (+0.33), and +1.03 (+0.97); the fourth, irreversible oxidation at +1.68 (+1.46) V is accompanied by chemical transformation followed by further oxidation. Chemical oxidation of 3-Ph with 1 or 2.5 equiv of AgPF6 in CH2Cl2/1,2-dimethoxyethane gave the one- and two-electron oxidized species [3-Ph][PF6] and [3-Ph][PF6]2, respectively. The chemical and electrochemical studies have been complemented by a series of detailed spectroelectrochemical experiments to obtain spectral data associated with the 3 n + (n = 0−4) species from 1500 to 40 000 cm-1, without necessitating the isolation of each individual species. Theoretical techniques have been employed in order to probe the structure of the conjugated all-carbon ligand at each stage of oxidation. Both the metal centers and the carbon atoms of the C4 bridge are affected, with removal of electrons housed in MOs delocalized over all atoms of the Ru−C4−Ru chain. Comparison of models with different ligand surroundings suggests that molecules containing strong electron-donating ligands should be more easily oxidized.

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

“…[4b, 6,7] Charge delocalisation along the six-atom MC 4 M chain is increased in complexes of the heavier metals, e.g., {ML n } = [RuA C H T U N G T R E N N U N G (PPh 3 ) 2 Cp] (1), [8] [RuA C H T U N G T R E N N U N G (dppe)Cp*], [9] [OsA C H T U N G T R E N N U N G (dppe)Cp*], [10] and [Re(NO)A C H T U N G T R E N N U N G (PPh 3 )Cp*].…”

“…[8] However, reinvestigation of the NIR spectrum of [1] + revealed a high energy shoulder that was not included in the original analysis ( Figure 1). [8] The NIR band envelope in [1] + is not solvatochromic ( Figure S12 in the Supporting Information), consistent with a highly delocalised (or strongly coupled) system.…”

“…[8] However, reinvestigation of the NIR spectrum of [1] + revealed a high energy shoulder that was not included in the original analysis ( Figure 1). [8] The NIR band envelope in [1] + is not solvatochromic ( Figure S12 in the Supporting Information), consistent with a highly delocalised (or strongly coupled) system. However, the two-state Hush treatment of such strongly coupled systems predicts only a single asymmetric band, [17][18][19] no obvious vibrational progression fits the approximately 3000 cm À1 separation of the principal band and the shoulder, and spin-orbit splitting in Ru complexes is also too small (typically around 1000 cm À1 ) [19] to account for the observed separation of the component bands.…”

“…The calculated spin density in the resulting fully optimised trans- [1'] + structure is evenly distributed over the RuC 4 Ru chain (see the Supporting Information), whereas Mulliken population analysis of the a-SOMO, the a-HOMO and the b-HOMO show appreciable diynediyl bridge (45, 57 and 57 %, respectively) and metal character (34, 37 and 37 %) in line with earlier analyses. [8] Time-dependent DFT (TDDFT) calculations (BLYP35/ DCM) revealed a single intense (m trans = 9.5 D) transition at 11 702 cm À1 arising from the excitation from the b-HOMOÀ1 to the b-SOMO. Given the distribution and nodal properties of these orbitals, this excitation is best described as a p-p* transition ( Figure 2).…”

Syntheses and Structures of Buta-1,3-Diynyl Complexes from “on Complex” Cross-Coupling Reactions

“…These four processes correspond well to the four oxidation processes described for the analogous buta-1,3-diyndiyl (-C≡CC≡C-) complex {Ru(PPh 3 ) 2 Cp} 2 (µ-C≡CC≡C). 86,87 In + is sufficiently kinetically and thermodynamically stable to be isolated, and has been explored in a number of contexts. 86,87 The closely related hexa-1,3,5-triyn-1,6-diyl complex {Ru(dppe) 2 Cp} 2 (µ-C≡CC≡CC≡C) exhibits three redox processes in the potential window explored, the first two of which were reversible, the third being only partially chemically reversible.…”