Organometallic complexes carbene

Organometallic complexes of copper, silver, and gold are ideal precursors for carbene complexes along with some C- and N-coordinated species. Their reactivity pattern, in particular in oxidative addition reactions, was the most comprehensively studied. 

Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing 0x0 or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the 0x0 and imido complexes is beyond the scope of the review and will not be covered here. 

Numerous studies aimed at the understanding of the mechanism of these processes rapidly appeared. In this context, Murai examined the behavior of acyclic linear dienyne systems in order to trap any carbenoid intermediate by a pendant olefin (Scheme 82).302 A remarkable tetracyclic assembly took place and gave the unprecedented tetracyclo[6.4.0.0]-undecane derivatives as single diastereomer, such as 321 in Scheme 82. This transformation proved to be relatively general as shown by the variation of the starting materials. The reaction can be catalyzed by different organometallic complexes of the group 8-10 elements (ruthenium, rhodium, iridium, and platinum). Formally, this reaction involves two cyclopropanations as if both carbon atoms of the alkyne moiety have acted as carbenes, which results in the formation of four carbon-carbon bonds. 

Alkoxy carbene complexes are useful starting compounds for other organometallic complexes,1 5 particularly methylidyne (carbyne) complexes.16 By modification of the coordinated (noncarbene) ligands or of the carbene ligand, other carbene complexes can be synthesized. The use of carbene complexes in organic syntheses has been reviewed recently.17 18... 

Table XIII contains data for organometallic complexes that do not fall into one of the preceding categories. The nonlinearities of the chloro complexes were used in conjunction with those of terminal acetylenes to demonstrate the importance of electronic communication between ligated metal and acetylide ligand in derivative metal acetylide complexes formed from combining these precursors.49133 134 Evaluation of vinylidene, as with sesqui-fulvalene and carbene, is only experimentally straightforward following metal complexation. The vinylidene cation [Ru(C=CHC6H4-4-N02)...

Also in many of the organometallic compounds various important organic ligands can function as CT acceptors (eg ethines, carbenes, arenes, or cyclohexadi-enyl or cycloheptatrienyl cations). Accordingly, organometallic complexes with such ligands are frequently characterized by the MLCT absorptions and their CT excitation can lead to emission or photo-oxidation [35,36]. 

Via Organometallic Intermediates. Metabolic reactions of xe-nobiotics such as halocarbons, hydrazines, or sydnones result in the formation of N-substituted porphyrins. An organometallic complex, in the form of an iron(II)-carbene (for the sydnones and halocarbons) or an iron(III)-<7-alkyl (c-aryl) (hydrazines), is an isolable intermediate in this process. The novelty of the biological organometallic chemistry has induced a flurry of research activity in this area. 

Aluminum Organometallic Chemistry Carbene Complexes Carbon-Carbon Carbon-Heteroatom Activation ... 

Metathesis, which is reversible and can be catalyzed by a variety of organometallic complexes, has been the subject of considerable investigation, and many reviews on this topic have been published.In 1970, Herisson and Chauvin proposed that these reactions are catalyzed by carbene (alkylidene) complexes that react with alkenes via the formation of metallacyclobutane intermediates, as shown in Figure 14-20. This mechanism, now known as the Chauvin mechanism, has received considerable support and is believed to be the pathway of the majority of transition metal-catalyzed olefin metathesis reactions. 

Keeping our target of homogeneous catalysis in mind, we adopted a broad definition of organometallic complexes and included compounds without metal-carbon bonds (e. g., metal-phosphine and metal-nitrosyl complexes) as far as they retain the structural and reactivity features of typical organometallic compounds. Recent developments, e. g., the substitution of phosphine by carbene ligands (cf Section 3.1.1.1), support the validity of this view. 

Reaction of a reduced Philipps catalyst with Fischer-type molybdenum or tungsten carbene or carbyne complexes led to very active bimetallic, heterogeneous olefin metathesis catalysts. Surface metal ions might be involved in bonding interactions with the organometallic complex, possibly leading to heterometallic species on inorganic oxides. ... 

A carbene is a molecule that contains a carbon atom with two bonds and two unpaired valence electrons. This leaves the carbon atom neutral in terms of formal charge (see Atoms and Molecules ), but still typically much more reactive than a typical carbon atom with four bonds. Carbenes are often found coordinated to metal centers in organometallic complexes. These carbene ligands are less reactive than a free carbene species, and actually you might be surprised to learn that organometallic carbene complexes aren t always prepared from the reactions of free carbenes with metal centers. As... 

Transfer of carbenes from stable, organometallic complexes has so far attracted relatively little attention, perhaps partly because of the complications often introduced by further reactions and side-reactions. Thus, the initial product of transfer of the ketenylidene carbene from complex (84) to cyclohexene loses carbon monoxide, the resulting norcaranylidene condensing with more cyclohexene to give (85), as outlined in an earlier Report. ... 

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