Oxidation-Potential Tuning of Tungsten–Alkylidyne Complexes over a 2 V Range

Abstract

The electrochemistry and electronic structures of over 30 tungsten-alkylidyne compounds of the form W(CR)L(n)L'(4-n)X (R = H, Bu(t), Ph, p-C6H4CCH, p-C6H4CCSiPr(i)3; X = F, Cl, Br, I, OTf, Bu(n), CN, OSiMe3, OPh; L/L' = PMe3, 1/2 dmpe, 1/2 depe, 1/2 dppe, 1/2 tmeda, P(OMe)3, CO, CNBu(t), py), in which the alkylidyne R group and L and X ligands are systematically varied, have been investigated using cyclic voltammetry and density functional theory calculations in order to determine the extent to which the oxidation potential may be tuned and its dependence on the nature of the metal-ligand interactions. The first oxidation potentials are found to span a range of ∼2 V. Symmetry considerations and the electronic-structure calculations indicate that the highest occupied molecular orbital (and redox orbital) is of principal d(xy) orbital parentage for most of the compounds in this series. The dependence of the oxidation potential on ligand is a strong function of the symmetry relationship between the substituent and the d(xy) orbital, being much more sensitive to the nature of the equatorial L ligands (π symmetry, with respect to d(xy), ΔE1/2 ≅ 0.5 V/L) than to the axial CR and X ligands (nonbonding with respect to d(xy), ΔE(1/2) < 0.3 V/L). The oxidation potential is linearly correlated with the calculated d(xy) orbital energy (slope ≅ 1, R(2) = 0.97), which thus provides a convenient computational descriptor for the potential. The strength of the correlation and slope of unity are proposed to be manifestations of the small inner-sphere reorganization energy associated with one-electron oxidation.

Computational Redox Potential Predictions: Applications to Inorganic and Organic Aqueous Complexes, and Complexes Adsorbed to Mineral Surfaces

“…Interestingly, the orbital participates in the one electron oxidation process is the d xy (HOMO) orbital of W atom and the calculated HOMO orbital energies of these various complexes are linearly correlated with the experimental redox potentials. By altering the coordinating ligands, the electronic properties of the metal center can be fine-tuned and the expected redox properties can be obtained [134]. Similar to this study, the calculated redox potentials using the B3LYP method in water and DMSO solvents, produced excellent correlations with respect the HOMO and LUMO orbital energies for a number of Cu complexes [135].…”

“…The obtained slope values from these fitted lines showed a non-dependent behavior with respect to the metals, this confirms that the determined parameters are ligand specific [133]. Redox potentials for 30 octahedral tungsten-alkylidyne complexes with a variety of different coordinating ligands were calculated by employing the hybrid B3LYP DFT method [134]. Interestingly, the orbital participates in the one electron oxidation process is the d xy (HOMO) orbital of W atom and the calculated HOMO orbital energies of these various complexes are linearly correlated with the experimental redox potentials.…”

Structural and Electronic Variations of sp/sp2 Carbon-Based Bridges in Di- and Trinuclear Redox-Active Iron Complexes Bearing Fe(diphosphine)2X (X = I, NCS) Moieties

“…13−16 The covalently bonded and electronically delocalized bridging π ligand acts as a structurally well-defined rigid-rod intramolecular electron pathway, and by successively varying the metal center(s) 17 and the bridging 18 and nonbridging ligands, 19 it is possible to probe the relationship between molecular structure and spectroscopic and electrochemical properties. It was shown that the electronic delocalization extends over the length of the organometallic unit in most cases.…”

Photoinduced Charge Separation in Zinc–Porphyrin/Tungsten–Alkylidyne Dyads: Generation of Reactive Porphyrin and Metallo Radical States

“…These luminescent chromophores possess long-lived 3 A C H T U N G T R E N N U N G [(d xy ) 1 (p*-A C H T U N G T R E N N U N G (WCR)) 1 ] excited states (t em = 10 2 -10 3 ns), [8] are powerful photochemical reductants (E* / + < À2 V vs. FeCp 2 0/ + ) with small reorganization energies, [9] and their ground-state (d xy ) 2 /A C H T U N G T R E N N U N G (d xy ) 1 oxidation potentials are systematically tunable across a 2 V range through ligand variation. [10] As a result, these chromophores are well suited for photosensitizing a wide range of electroactive catalysts for difficult-to-reduce substrates, such as CO 2 . Further, unlike common transitionmetal chromophores, [W(CR)L 4 Excitation of the porphyrin-centered S 1 excited states of these dyads initiates intramolecular energy-transfer (ZnPor!1) and electron-transfer (1!…”

“…One class of compounds that possesses the properties to fulfill these requirements is that of (d xy ) 2 ‐configured tungsten–alkylidyne compounds of the type trans ‐[W(≡CR)L 4 X] (R=aryl, L=neutral ligand, X=anionic ligand). These luminescent chromophores possess long‐lived 3 [(d xy ) 1 (π*(WCR)) 1 ] excited states ( τ em =10 2 –10 3 ns),8 are powerful photochemical reductants ( E * /+ <−2 V vs. FeCp 2 0/+ ) with small reorganization energies,9 and their ground‐state (d xy ) 2 /(d xy ) 1 oxidation potentials are systematically tunable across a 2 V range through ligand variation 10. As a result, these chromophores are well suited for photosensitizing a wide range of electroactive catalysts for difficult‐to‐reduce substrates, such as CO 2 .…”