Carbenes, and

Comments We have to explore new chemistry here and the main problem does seem to be getting fire right combination of diene and carbene reagent. Perhaps not such a good route. 

CO is a representative species for Q, -insertion its insertion into C—Pd bonds affords acylpalladium complexes such as 15. Mechanistically, the CO insertion is 1.2-alkyl migration to coordinated CO. This is an important step in carbonyiation. SO , isonitriies, and carbenes are other species which undergo a.a-insertion. 

Organometallic Compounds. The predominant oxidation states of indium in organometalUcs are +1 and +3. Iridium forms mononuclear and polynuclear carbonyl complexes including [IrCl(P(C3H3)3)2(CO)2] [14871-41-1], [Ir2014(00)2] [12703-90-1], [Ir4(CO)22] [18827-81 -1], and the conducting, polymeric [IrCl(CO)3] [32594-40-4]. Isonitnle and carbene complexes are also known. 

Photolysis of dlazirines to nitrogen and carbenes is a general reaction and plays a greater role in carbene chemistry than photolysis of linear diazo compounds. Whereas the latter are often obtained only under the conditions of their thermal decomposition from suitable precursors, diazirines are obtainable in a pure state in most cases. Photolysis has the further advantage to permit nitrogen extrusion at atmospheric pressure, even with low-boiling materials. 

Vinyl Triflalc Chemistry Unsaturated Cations and Carbenes... 

Dimethylbenzimidazolium iodide serves as a starting material for free carbenes (99CEJ1931, 99JA10626, 00AGE541) and carbene complexes (99JOM(585)241). Thus, with palladium(II) acetate it gives [L Pdl ] where L is... 

The Group VI organometallic chemistry is mainly characterized by the occurrence of N- and C-coordination and carbene complex-formation, as well as by some unique cases of Se- (Te-) coordination, ring opening and deselenation. The Group VII organometallic chemistry is known for the carbene and chelate structures of the derivatized thiazoles. 

Organoiron chemistry offers the C-coordination mode, carbene series, ring opening and detelluration. Organoruthenium and especially organoosmium species are sometimes peculiar along with the classical cases of N-coordination and carbene formation, C,N- and S,N-cases can be traced. 

In 1999, Bob Atkinson wrote [1] that aziridination reactions were epoxida-tion s poor relation , and this was undoubtedly true at that time the scope of the synthetic methods available for preparation of aziridines was rather narrow when compared to the diversity of the procedures used for the preparation of the analogous oxygenated heterocycles. The preparation of aziridines has formed the basis of several reviews [2] and the reader is directed towards those works for a comprehensive analysis of the area this chapter presents a concise overview of classical methods and focuses on modern advances in the area of aziridine synthesis, with particular attention to stereoselective reactions between nitrenes and al-kenes on the one hand, and carbenes and imines on the other. 

The facile thermal decomposition of the dimethyl and diethyl derivatives of (II) to nitrogen and carbene intermediates is emphasized by the readily discernible correlations between the reactant and product orbitals. On the other hand, the greater delocalization of the molecular orbitals of (I) may be a factor in its preference to rearrange, without decomposition, to methyl acetylene and allene. 

Cocyclizations of internal alkynes and carbene complexes 57 with larger substituents R1 (e.g., R z Pr) not only lead to formation of an increased proportion of the regioisomers 60b, but also to that of the isomeric cyclopentadi-enes 61, which would result from 60a by 1,2-migration of the dimethylamino... 

The insertion of a carbene into a Z-H bond, where Z=C, Si, is generally referred to as an insertion reaction, whereas those occurring from Z=0,N are based on ylide chemistry [75]. These processes are unique to carbene chemistry and are facilitated by dirhodium(II) catalysts in preference to all others [1, 3,4]. The mechanism of this reaction involves simultaneous Z-H bond breaking, Z-car-bene C and carbene C-H bond formation, and the dissociation of the rhodium catalyst from the original carbene center [1]. 

The intermediate in the second mechanism is identical with that postulated by Skell and Starer (1959) in the formation of carbonium ions from alkoxide and carbenes. 

There are four types of organic species in which a carbon atom has a valence of only 2 or 3/ They are usually very short lived, and most exist only as intermediates that are quickly converted to more stable molecules. However, some are more stable than others and fairly stable examples have been prepared of three of the four types. The four types of species are carhocations (A), free radicals (B), carbanions (C), and carbenes (D). Of the four, only carbanions have a complete octet around the carbon. There are many other organic ions and radicals with charges and unpaired electrons on atoms other than carbon, but we will discuss only nitrenes (E), the nitrogen analogs of carbenes. 

The SET mechanism is chiefly found where X = I or NO2 (see 10-104). A closely related mechanism, the SrnE takes place with aromatic substrates (Chapter 13). In that mechanism the initial attack is by an electron donor, rather than a nucleophile. The Srn 1 mechanism has also been invoked for reactions of enolate anions with 2-iodobicyclo[4.1.0]heptane. An example is the reaction of l-iodobicyclo[2.2.1]-heptane (15) with NaSnMe3 or LiPPh2, and some other nucleophiles, to give the substitution product. Another is the reaction of bromo 4-bromoacetophenone (16) with Bu4NBr in cumene. " The two mechanisms, Sn2 versus SET have been compared and contrasted. There are also reactions where it is reported that radical, carbanion, and carbene pathways occur simultaneously. ... 

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