Subject insertion reactions

The subjects of structure and bonding in metal isocyanide complexes have been discussed before 90, 156) and will not be treated extensively here. A brief discussion of this subject is presented in Section II of course, special emphasis is given to the more recent information which has appeared. Several areas of current study in the field of transition metal-isocyanide complexes have become particularly important and are discussed in this review in Section III. These include the additions of protonic compounds to coordinated isocyanides, probably the subject most actively being studied at this time insertion reactions into metal-carbon bonded species nucleophilic reactions with metal isocyanide complexes and the metal-catalyzed a-addition reactions. Concurrent with these new developments, there has been a general expansion of descriptive chemistry of isocyanide-metal complexes, and further study of the physical properties of selected species. These developments are summarized in Section IV. 

Vinylidenecarbene or allenylidene3 (R)2C=C=C has a lance-shaped, unsubstituted and sp-hybridized carbene center and, therefore, will not be easily subject to steric hindrance in its insertion reactions. On this assumption, (2-methyljpropenylidenecarbene or its carbenoid was chosen as a prototype of typical vinylidenecarbenes and its insertion reaction with several different types of alkoxides was investigated by employing two methods (A and B, Scheme 10) for carbene generation.20 The insertion products 20 were obtained almost exclusively except lithium allyloxide (Table 4, entry 10).21 By-products such as propargyl ether and allenyl ether were not formed at all. To be noted here, in... 

Successive multiple insertions of an aryl isocyanide (ArNC) into the S-S bond of a diaryl disulfide (ArS)2 occurs in the presence of Pd(PPh3)4 to produce the corresponding poly(imino)alkane endcapped with an arylthio group (Equation (65)).167 Products of higher molecular weights are formed when isolated poly(imino)alkanes are again subjected to the conditions of the insertion reaction (up to n — 9). 

Insertion reactions of C02 into the metal-hydride and metal-alkyl bonds are of considerable importance, since these reactions are involved not only in the catalytic cycle of the hydrogenation of C02 into formic acid but also in the catalytic cycle of co-polymerization of C02 and epoxide. In this regard, insertions of C02 into various metal-hydride, metal-alkyl, and similar bonds have been the subject of intense experimental investigation. For instance, C02 insertions into Cu(I)-CH3, Cu(I)-OR, Cu(I)-alkyl [26-28], Ru(II)-H [29], Cr(0)-H, Mo(0)-H, W(0)-H [30], Ni(II)-H and Ni(II)-CH3 bonds [31, 32] have been so far reported. 

Halpern et al. had already stressed the importance of radical mechanisms in the oxidative addition and insertion reactions of both [Rh(OEP)]2 and Rh(OEP) [338]. Thus, [Rh(OEP)]2 reacted with trimethylphosphite according to sequence (37), forming a rhodiophosphonate Rh(PO OMe 2) (OEP) and methyl radicals which were subject to further reactions [339]. In the presence of excess P(OMe)3, they were trapped by formation of MePO(OMe)2 in more than stoichiometric quantities, indicating a radical chain process. 

The oxime nitrogen lone pair of electrons must be properly oriented so as to interact with the rhodium carbenoid.84 Thus, subjection of the -oximino isomer 182 to a catalytic quantity of Rh2(OAc)4 in CH2C12 (40 °C) with a slight excess of DMAD afforded the bimolecular cycloadduct 184 in 93% yield. In sharp contrast, when the isomeric Z-oximino diazo derivative 183 was exposed to the same reaction conditions, only indanone-oxime 185 (80%) was obtained. The formation of this product is most likely the result of an intramolecular C-H insertion reaction. 

This is the second chapter of a two-part review concerned with insertion reactions of transition metal-carbon a-bonded compounds. The first chapter, which appeared in Volume 11 of this series (137), provided a broad introduction to the subject of insertion reactions in general and a detailed treatment of the carbon monoxide insertion and decarbonylation. Presented herein are the insertion and elimination reactions of sulfur dioxide and of a few other unsaturated molecules. The reactions of sulfur dioxide are accorded a complete literature coverage, whereas those of the other inserting species are treated selectively. Metal-carbon a-bonded compounds of the main group elements are discussed only in the context of comparisons with their transition metal analogs. 

The four ttutin characteristic reactions of nitrenes are summarized in Scheme 2. All of these reactions have parallels in carbene chemistry for example, a full discussion of the C—insertion reaction of car-benes is given in Volume 3, Ch ter 4.2. The first reaction, the addition to an alkene to form an aziridine, is covered in detail in Volume 7, Chapter 3.S. The C—insertion reaction, the subject of this chapter, can, in principle, occur by severid mechanisms. However nx>st of the reactions are believed to involve... 

By the time the alkylation studies were started, the reactivity of the dicarbollide anions toward electrophilic agents had been studied mainly on insertion reactions of boron, or heteroatom, or transition metal into the place of the missing vertex of the icosahedron, restoring its structure. A broad area of metallocarboranes was developed as a result of these studies, which was the subject of many articles and reviews. 

Little is as yet understood concerning the transition states involved in the insertion process. In fact, there has been considerable recent controversy on this subject. For methylene insertion reactions the transition state was visualized earlier as a three-membered cyclic complex. 

Acetylene insertion reactions have been the subject of theoretical studies . 

The nature of these insertion reactions has been probed by subjecting the [P,C6,H6] adducts (formed by reacting P with benzene in a chemical ionization source) to CA . These experiments suggest that P inserts into the C—H bond to give 30 and also into the C—C bond to give 31. 

Assuming that olefin intermediates are produced on the surface of the Fischer-Tropsch catalyst, similar mechanisms for chain growth have been suggested. Alcoholic intermediates also have been proposed based on the isotope-labeling studies of Emmett et al. on iron surfaces. The understanding and control of the insertion reaction appears to be the key for controlling the product distribution. Clearly the mechanism of this reaction will be subjected to close scrutiny in the near future. 

The insertion reaction of a coordinated olefin into the Mt—C a-bond, where Mt is a group 4 metallocene, or a model of it, has been the subject of several theoretical studies se, 146-1 so,152,153,156,169-171,174,176,177,185-19o... 

Cyclopropenation. Cyclopropenes can be formed from alkynes by reaction with methyl diazoacetate using a rhodium(ll) carboxylate as catalyst. The reaction is not particularly subject to steric hindrance, but polar groups (CH2COOCH3) inhibit cyclopropenation markedly. Insertion reactions compete with cyclopropenation in the case of acetylenic alcohols. ... 

The formation of the next intermediate, 5, in a hydroxypalladation step has been the subject of controversy over many years. According to his kinetic investigations, Henry postulated a syn-attack (cis-ligand insertion reaction) of a complexed OH ion to the complexed olefin (Eq. (9.7)). 

It is clear that the construction of appropriately substituted monocyclic P-lactams has attracted great attention not only in the monobactam field, but also in the penem and carbapenem area of antibiotics. Since methods for the construction of the -lactam ring are now abundant, the main difficulties involved are primarily the stereocontrol and the instability of the final product. Although the carbene insertion reaction developed by the Merck group seems to be the most efficient route for the construction of the bicyclic ring system, the development of new procedures, specially for industrial applications, is desirable. It is beyond the scope of this article to provide a comprehensive account of all types of P-lactams appeared in the literature which, perhaps, in some cases could be used as carbapenem building blocks. On the other hand, it has been the purpose of this work to deal with those monocyclic P-lactams, which upon further elaboration, lead to PS-5 and PS-6 carbapenems and related compounds by established protocols. Less emphasis has been put on thienamycin because an excellent review on this subject has recently been published. I wish to apologise... 

Other electrophilic heterocumulenes (e.g., CS2, RNCO, RNCS, SO2) are also subject to insertion reactions. Accordingly, the insertion of CS2 into the M-N bond in metal dialkylamides produces dithiocarbamate derivatives and the reaction of SO2 with M-C bonds gives sulfinate complexes resulting from either 1,1-insertion [M-0S(0)R] or 1,2-insertion [M-S(R)02]. Rare examples of insertion of dioxygen into Pt-H bonds to generate remarkably stable hydroperoxide derivatives L Pt-OOH have also been reported. 

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