Photochemical metathesis of a tungsten-carbene complex

A comparative study on aldol‐type condensation reactions of cyclic, acyclic and substituted cyclic ketones by the W(CO)6/CCl4/UV system

“…32 Oxygen abstraction from a ketone by 4 should initially include the coordination of a second ketone, whereas a similar mechanism has been proposed for the metathesis reactions of olefins by a tungsten-carbene complex. 33 Following the coordination of the second ketone, subsequent formation of a metallo-oxo-cyclobutane, 5, takes place. Oxygen containing metallacycles has been well documented.…”

Photoinduced Reactions of Metal Carbenes in Organic Synthesis

“…The process was highly regioselective, undergoing acylation exclusively para to the activating group. Ketenes react with tertiary allylic amines in the presence of Lewis acids to give zwitterionic intermediates which undergo [3,3]-sigmatropic rearrangement [119]. Photolysis of chromium carbene complexes in the presence of tertiary amines results in similar chemistry [120].…”

“…The visible spectra of Fischer carbene complexes consist of a very weak band above 500 nm, assigned to a spin-forbidden metal-to-ligand charge transfer band (MLCT), a moderately intense band between 350 and 450 nm assigned as a spinallowed MLCT, and a weaker band at 300-350 nm assigned as a ligand field (LF) transition [2]. A lower energy LF band is usually masked by the more intense MLCT, although it has been observed in some nonheteroatom-stabilized carbene complexes [3]. The HOMO is metal dp-pp centered while the LUMO is carbenecarbon pp centered [4].…”

“…Tungsten alkoxycarbene complexes underwent similar anti-syn rearrangements but were much less prone to undergo CO loss [5][6][7][8][9][10]. 3. No CO-insertion products (metal-ketene complexes) were observed, even when specifically sought [9,10].…”

Hexacarbonyls and Carbonyl Complexes of Carbon σ-Bonded Ligands of Chromium, Molybdenum and Tungsten

“…This photochemical process is suppressed by 1 atm o f CO and it appears that photochemical excitation proceeds by loss o f a cis -carbonyl ligand to form a [W(CO) 4 (=CPh 2 )] fragment, which binds the alkene before undergoing metallacyclobutane formation and metathetical exchange. 362 Cyclopropylidene complexes (M = Cr, Mo or W) (Equation (23)) are formed in high yield through the use of LiC=COEt as the organolithium source in a standard Fischer carbene type synthesis, which differs in that the expected product [Cr(CO) 5 Bridging alkylidenes have been reviewed. 344 There are relatively f e w examples of simple bridged M-M complexes for group 6 metals.…”