Photooxidation of Metal Carbynes

Abstract

Radical cations formed upon photooxidation of the metal carbyne complexes (n 5 -C 5 H 5 )L 1 L 2 M≡CR (M is Mo or W; L 1 and L 2 are CO or P(OMe) 3 ; and R is alkyl or aryl) were found to be extremely reactive. Depending on the reaction conditions, either the radical cations exhibited the ligand-exchange and atom--abstraction processes that are typical of metal radicals, or the carbyne ligands underwent a series of highly unusual rearrangements to yield organic products. When organic products were generated, they were formed with good stereochemical and regiochemical control.REACTIVE ORGANIC FRAGMENTS CAN BE STABILIZED with transi tion metals so that they can be used for synthesis under ordinary reaction conditions. One example is the extensive utilization of metal carbenes in organic synthesis (2). It is thus somewhat surprising that there are so few reported cases of generation of organic products from the closely related metal carbynes. Although the chemistry of metal carbynes has been explored (2), most of the reported reactions involve conversion into other carbyne complexes by exchange of ancillary ligands; interconversion of car byne, carbene, and vinylidene complexes; or [2 + 2] cycloaddition with alkenes and alkynes followed by metathesis or polymerization. With the exception of polymers and metathesis products, organic species derived from the carbyne ligand are almost never generated.One method for inducing new modes of reactivity in metal complexes is one-electron (l-e~) oxidation. The differences in reaction rates between 18-e~ complexes and their 17-e~ counterparts can be quite dramatic (3-5). Reaction manifolds that are not available to an 18-e~ complex can thus become accessible to its corresponding 17-e~ radical cation. This chapter

Photophysics of Tungsten and Molybdenum Arylcarbyne Complexes. Observation of the Lowest Excited State by Laser Flash Photolysis

“…In previous work, a photooxidation reaction involving irreversible electron transfer from a series of tungsten and molybdenum aryl- and alkylcarbynes to halogenated solvents was observed . Following generation of the carbyne radical cation, both metal-centered reactions typical of metal radicals and unusual ligand-centered processes ensue …”

Enhanced Dual Visible Light Fluorescence from the 2,2‘-Dipyridyl Tungsten Alkylidyne Complex [W(⋮CC6H4NMe2-4)(O2CCF3)(CO)2{κ2-2,2‘-(NC5H4)2}]: An Organometallic Twisted Intramolecular Charge Transfer State

“…The emission of visible light from polypyridyl tungsten(0) d 6 complexes is well established, while the photophysics of group 6 metal Fischer alkylidyne complexes, though somewhat less studied, is nevertheless of topical relevance to the quest for the development of light-emitting metal complexes for applications in molecular electronic control, communication, and sensing . Photoluminescence from low-valent organometallic species is unusual, given the propensity for such complexes to undergo ligand dissociation as the primary photoprocess, or in the case of Fischer alkylidynes, to be activated to further reactivity resulting in ligand-based transformations or metal-centered radical reactions. 3e,, Photoluminescence from metal alkylidyne complexes has been specifically reviewed by Hopkins . Low quantum yield emission of red light (λ em ≈ 750 nm, Φ em ≤ 6.9 × 10 -4 ) has been observed with the complexes [M(⋮CAr)(CO){P(OMe) 3 }(η 5 -C 5 H 5 )] ( 1 , M = W, Mo; Ar = Ph, C 6 H 4 Me-2, C 10 H 7 -2) and attributed to a 3 d M −π* M ⋮ CAr triplet state .…”