Complex carbine

A recent study of proton transfer from rhenium Fisher-type carbine complexes (13) shows that the reactions lead to the formation of an aromatic product (14), following the same rules as reactions that lead to the formation of products stabilized by simple resonance. The conjugate bases of these carbine complexes represent aromatic heterocycles, i.e., substituted furan, selenophene, and thiophene derivatives, respectively. The aromatic stabilization of these heterocycles is known to follow the order furan < selenophene < thiophene (Scheme 1) [43],... 

Scheme 1 Proton transfer from carbine complex 13 to give aromatic product 14...

The rhodium A-heterocyclic carbine complex [Rh(IMes)(COD)] [IMes = A,A -bis(2,4,6-trimethylphenyl)imidazol-2-ylidine COD = cycloocta-1,5-diene] catalyses the 4 + 2 + 2-carbocyclization of 1,6-enynes (191) to carbocycles [(192) and (193)] (Scheme 54).226 Computational and experimental evidence of a new reaction pathway for the diastereospecific intermolecular rhodium-catalysed 4 + 2 + 2-carbocyclization (g) reactions of 1,6-enynes with r-components has been reported.227... 

This exchange reaction is clean and only occurs at a significant rate in aqueous solutions. Although the mechanism was not well established, the solvolysis of one of the halides followed by deprotonation to form the corresponding carbine complex is most consistent with the results. This mechanism may provide an insight into the mechanisms of decomposition that are facilitated by high dielectric solvents [52]. 

TOWARDS THE SYNTHESIS OF CARBINE COMPLEXES OF GOLD AND COPPER CARBENE COMPLEXES... 

Carbine complexes of gold and copper are unknown. As a preliminary to the synthesis of such compounds, we studied the affinity of the metals... 

The control of stereochemistry with chromium carbine complexes has been reviewed. The DBR can create a new stereocenter in three ways. First, the arene tricarbonyl chromium complex contains a plane of chriality, thus the complexes 35 and ent-35 are enantiomers when RL Ri and RS R2. Second, when phenyl substituents are included in the reactants the resulting biaryls can posess axial chirality if there is hindered rotation about the new aryl-aryl bond as in 36. Finally, all DBRs with differentially p-disubstitued alkenes give rise to cyclohexadienones 37 with a new stereocenter adjacent to the carbonyl. When Ri and R2 are not hydrogen, tautomerization cannot occur and the final product possesses a chiral center. 

Fig. 1 Structure of hydrid scorpionate complex 6 and N-heterocyclic carbine complex 7.

The catalytic decomposition of alkyldiazoacetates comprises the formation of the intermediate complex of alkyldiazoacetate and the catalyst [55, 56]. The generated alcoxicarbonylcarbene at further nitrogen splitting [57] is stabilized by the catalyst with the carbine complex formation, in-... 

The output of the cyclopropanation products is determined by the reactivity of the >C=C< double bond in the alkene as well as the stability and reactivity of the carbine complex L M=CH(0)R which fully depend on the catalyst used [55, 56],... 

In 2003, Guillemin had reported the design and synthesis of recyclable IL-supported ruthenium carbine complex... 

It was reported [53] that the LP influences the molecular and electronic distortions observed in [Cr(C6H6)(CO)3] and related carbine and carbene complexes. The mutual orientation of the first-neighboring CO groups in these species reflects more the balance between the molecular shape and the tendency of the molecules to lie as close as possible (close-packing principle), rather than an electronic requirement of the CO-CO intermolecular interactions. 

Oxidation of pentacarbonyl[amino(arylthioalkyl)carbine]chromium(0) complexes 131 with A -sulfonyloxaziridine 132 afforded the corresponding sulfoxides 133 in good to excellent yields <1995SL666>. The oxidation is chemoselective, affording only sulfoxide products whereas the use of dimethyloxirane resulted in overoxidation to sulfones. 

Methylation of rjAldehyde complexes forms Fischer carbines 1997JA12772... 

Kijima, M. Sakai, Y. Shirakawa, H. Electrochemical synthesis of carbine catalyzed by nickel complex. Synth. Metals 1995, 71, 1837. 

Several reports exist on the use of ionic Uquids as solvent for ligand-free Heck reactions. Zhang found that 2-n-butyl-l,l,3,3-tetramethyIguanidinium acetate was an exceUent solvent for a Ugand-free Heck reaction with 0.16mol% of PdCl2. Remarkably, this reaction needs no extra base, presumably since the solvent can act as a base [73]. EarUer studies found slower reactions using imidazolium type ionic Uquids as solvent when compared to conventional media [33, 74]. Presumably, this is due to formation of palladium carbine-type complexes [75]. 

Polymer-supported carbine-palladium complexes were used for the Mizoroki-Heck reaction in water [152]. The product could be separated by extraction with diethyl ether. However, the catalytic activity decreased after reuse of the catalyst. The authors claim that... 

Two potential isomers of carbine-olefin complexes that precede [2-I-2] processes. 

The Dotz benzannulation reaction (DBR) is the reaction of an a,P unsaturated Fischer carbene with an alkyne to produce a highly substituted phenol. Alternatively, the DBR can be considered a metal templated 3 + 1 + 2 cycloaddition of an allylic carbine (3 carbon unit), carbon monoxide (1 carbon unit), and an alkyne (2 carbon unit). The initial product of the reaction is the arene chromium tricarbonyl complex of the phenol as in 4. These complexes are typically unstable in air such that workup and purification of the product lead to the complete loss of the metal. Chromium is the most often used metal for the benzannulation. Molybdinum, tungsten, and manganese have been used but usually give mixtures of products and require harsh reaction conditions. 

T -Complexes contain a metal-carbon single bond (Figure 1.1). The organic group may be alkyl, vinyl, alkynyl, aryl or acyl. With the exception of the acyl complexes, there are analogous compounds of more familiar metals, such as magnesium and zinc. It is also possible to have complexes with metal-carbon double and triple bonds these are known as carbenes and carbines. Cumulenes are also known, such as in vinylidene complexes. 

In recent years, catalytic applications of half-sandwich metal complexes have been extensively developed. A series of (p-cymene)Ru(II) complexes containing pyrazole-based iV-heterocyclic carbine (pyrazoUn-3-ylidene) ligands (Fig. 21.13a and b) showed excellent catalytic y3-alkylation of secondary alcohols with primary alcohols and the dimerization of phenylacetylene [30]. 

They differ, both in the imidazoline or imidazolidine-derived Ai-heterocyclic carbine and in the substituents R on the N-atoms, as well as in the alkylidene fragment. Most importantly, the activity of the catalysts 27-29 is significantly higher than that of the parent Grubbs carbene 19 and comes close to that of Schrock s Mo alkylidene complex 18. In combination with exceptional thermal stability and resistance towards oxygen and moisture, together with compatibility with many... 

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