Carbon Bond Insertion

In the gas phase, Fe+, Co, and NF metal ions react with isobutane with facile C-C bond cleavage. In fact, in the case of the Co+ ion, C-C bond cleavage appears to be preferred over C-H bond scission.The Co ion reacts with ( L, to Ce cycloalkanes exclusively by C-C bond insertion to provide metallacycles, which themselves decompose largely by C-C bond cleavage pathways. All these reactions must proceed through the intermediacy of hypercarbon-containing species. The reaction pathway for cyclopentane is shown in Equation (6.103)  

In the case of linear alkanes such as n-hexane, the he ion inserts into the central C-C bond followed by P-methyl transfer [Eq. (6.104)]. Again, these reactions presumably involve hypercarbon intermediates. 

The naked metal ion insertion reaction seems to indicate that high M-C bond strengths allow easy C-C bond cleavage for the bare ions. Apparently this is not the case for coordinated metals. Although C-C bond breaking appears to be kinetically facile as the initial step for the unhindered metal complexes, in the case of usual metal complexes, steric congestion at the metal center seems to retard such a process. C-H activation is generally both thermodynamically and kinetically favored over C-C activation nevertheless, appropriate selection of reaction conditions and catalyst systems may allow C-C activations.  

The lack of alkane C-C activation also arises from the fact that two relatively weak M-C bonds are formed in the process [Eq. (6.105)]. However, in strained molecules such as small-ring cycloalkanes (cyclopropanes, cyclobutanes), relief of strain is an additional favorable factor. Furthermore, C-C activation can be rendered thermodynamically more favorable when an extra driving force is available, such as formation of an aromatic structure or by utilizing an activating functionality. 

The first example of a reaction with a strained C-C bond in a metal complex was studied in 1955 by Tipper. PtCb reacted with cyclopropane to give an adduct that was formulated as [PtCl2(C3H6)]2. The correct platinacyclobutane structure was later elucidated by Chatt and coworkers - by isolating it as a bis(pyridine) adduct [Eq, (6.106)]  

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The process is photoreversible, reverting to starting materials upon photolysis at 420 nm Higher alkanes yield products resulting from C—H activation only, whereas cyclopropane reacts by attack at the carbon-carbon bond. Insertion adducts of Cu, Ag and Au are susceptible to secondary photolysis, yielding R -i- MH and RM -t- H. 

When allene derivatives are treated with aryl halides in the presence of Pd(0), the aryl group is introduced to the central carbon by insertion of one of the allenic bonds to form the 7r-allylpalladium intermediate 271, which is attacked further by amine to give the allylic amine 272. A good ligand for the reaction is dppe[182]. Intramolecular reaction of the 7-aminoallene 273 affords the pyrrolidine derivative 274[183]. 

The monometallic mechanism is illustrated in Fig. 7.13a. It involves the monomer coordinating with an alkylated titanium atom. The insertion of the monomer into the titanium-carbon bond propagates the chain. As shown in... 

Trifluorovinyltm derivatives have been reacted with SO2, however, only low yields of insertion into the tin-carbon bond of the Irifluorovinyl group were detected [20],... 

Strategy Here, in effect, you reverse the steps required in Example 22.2, this time converting a name to a structure. Start with a five-carbon skeleton, insert a double bond at the 2-position, and, finally, put an ethyl group at the 3-position. 

Table IV presents the results of the determination of polyethylene radioactivity after the decomposition of the active bonds in one-component catalysts by methanol, labeled in different positions. In the case of TiCU (169) and the catalyst Cr -CjHsU/SiCU (8, 140) in the initial state the insertion of tritium of the alcohol hydroxyl group into the polymer corresponds to the expected polarization of the metal-carbon bond determined by the difference in electronegativity of these elements. The decomposition of active bonds in this case seems to follow the scheme (25) (see Section V). But in the case of the chromium oxide catalyst and the catalyst obtained by hydrogen reduction of the supported chromium ir-allyl complexes (ir-allyl ligands being removed from the active center) (140) C14 of the...

Alkynylcarbene complexes react with strained and hindered olefins yielding products that incorporate up to four different components by the formation of five new carbon-carbon bonds [15b]. This remarkable transformation is explained by an initial [2+2] cycloaddition followed by CO insertion. The resulting intermediate suffers a well precedented [1,3]-migration of the metal fragment to generate a non-heteroatom-stabilised carbene complex intermediate which reacts with a new molecule of the olefin through a cyclopropana-tion reaction (Scheme 85). 

The search for the racemic form of 15, prepared by allylic cyclopropanation of farnesyl diazoacetate 14, prompted the use of Rh2(OAc)4 for this process. But, instead of 15, addition occurred to the terminal double bond exclusively and in high yield (Eq. 6) [65]. This example initiated studies that have demonstrated the generality of the process [66-68] and its suitability for asymmetric cyclopropanation [69]. Since carbon-hydrogen insertion is in competition with addition, only the most reactive carboxamidate-ligated catalysts effect macrocyclic cyclopropanation [70] (Eq. 7), and CuPF6/bis-oxazoline 28 generally produces the highest level of enantiocontrol. 

A. Insertion Reactions into Metal-Carbon Bonds... 

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. 

In the reaction of Ni(CNBu )4 and methyl iodide oligomerization of the isocyanide was observed the only isolable nickel complex was (I), shown below. This product is believed to arise through sequential insertions of three isocyanides into a nickel-carbon bond. Upon further treatment with additional isocyanide at a temperature greater than 60° C one obtains a polymer (RNC) presumably through multiple isocyanide insertion reactions. The addition of benzoyl chloride to Ni(CNBu )4 gave two isolable compounds Ni(CNBu )3(COPh)Cl (74%) and (II) (8.2%). This latter reaction, and the isolation of (II) in particular, suggests that the proposed mechanism for polymerization of isocyanides is reasonable. 

Insertion Reactions of Transition Metal-Carbon -Bonded Compounds I Carbon Monoxide Insertion... 

Carbon monoxide insertion is not restricted to transition metal-carbon bonds, although M—C is by far the most common substrate involved. Reactions have also been reported which lead to insertion of CO into M—O (114) and M—N (199) bonds. 1,1-Additions of M—H (27, 114) and M—M (104) linkages to CO have been postulated, too. However, direct replacement of CO, without rupture of the W—H bond, is indicated for the reaction between CpW(CO)3H (or -D) and PPhj (5) ... 

Carbon monoxide insertion into Ni—C bonds has been postulated in carbonylation reactions involving (7r-C3H5NiX)2 (X = C1, Br, or I) (112, 123a). 

Carbon monoxide insertion reactions into Cu—C, Ag—C, or Au—C bonds are not known. 

Infrared Intensities of Metal Carbonyl Stretching Vibrations, 10, 199 Infrared and Raman Studies of w-Complexes, 1, 239 Insertion Reactions of Compounds of Metals and Metalloids, 5, 225 Insertion Reactions of Transition Metal-Carbon o-Bonded Compounds I Carbon Monoxide Insertion, 11, 88... 

The Baeyer-Villiger oxidation reaction was discovered more than 100 years ago by Adolf von Baeyer and Victor Villiger. By this reaction, ketones are converted into the corresponding esters. In organic chemistry, peracids are commonly used as catalyst to perform this atypical oxidation reaction that results in oxygen insertion into a carbon—carbon bond (Fig. 1). 

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