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Carbene radicals, in which the carbene is bonded to an open-shell metal with the carbene carbon possessing a radical character. Carbene radicals have features of both Fischer and Schrock carbenes, but are typically long-lived reaction intermediates. The "second generation" of the Grubbs catalysts for alkene metathesis features an NHC ligand.
Carbyne molecules are generally found to be in electronic doublet states: the non-bonding electrons on carbon are arranged as one radical (unpaired electron) and one electron pair, leaving a vacant atomic orbital, rather than being a triradical (the quartet state).
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Bonding scheme of carbene radical complexes as compared to Schrock and Fischer-type carbene complexes. Carbene radicals are a special class of organometallic carbenes.The carbene radical can be formed by one-electron reduction of Fischer-type carbenes using an external reducing agent, or directly upon carbene formation at an open-shell transition metal complex (in particular low-spin cobalt(II ...
Carbene complexes have been synthesized from most transition metals and f-block metals, [2] using many different synthetic routes such as nucleophilic addition and alpha-hydrogen abstraction. [1] The term carbene ligand is a formalism since many are not directly derived from carbenes and most are much less reactive than lone carbenes. [2]
Bonding between carbene and the metal centre involves a strong σ donation from sp 2 orbital to an empty d orbital on metal centre and a weak π back donation from the metal centre to the empty p z orbital. Because the π donation is weak, the carbene carbon is electrophilic in nature. [1] Because of this bonding property, Fischer carbenes ...
The net reaction gives a transition metal carbene complex: L n M≡CR + HX → L n (X)M=CHR. These complexes can also undergo photochemical reactions. In some carbyne complexes, coupling of the carbyne ligand to a carbonyl is observed. Protonation of the carbyne carbon and conversion of the carbyne ligand into a π-allyl. [13]
Methylene (IUPAC name: Methylidene, also called carbene or methene) is an organic compound with the chemical formula CH 2 (also written [CH 2] and not to be confused with compressed hydrogen, which is also denoted CH 2). It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct.