Other Unsaturated Molecules

This part of the review brings together insertion reactions of several diverse unsaturated molecules into transition metal-carbon a bonds. Most of the reactions presented here have appeared in the literature since about 1969-1970 they thus attest to a marked recent growth of interest in this field. 

Treatment of the subject in this section is not intended to be comprehensive. Instead, emphasis has been placed on the types of molecules reacting, the mode of the insertion (and/or elimination) and the structure of the product derived. The presentation is further restricted by excluding the insertion of the olefins, acetylenes, and other unsaturated hydrocarbons, as well as their fluorinated analogs. The above reactions 

Tetracyanoethylene inserts into the M—R bonds of CpFe(CO)2R (R = Me, Et, n-Pr, and CHaPh) 118,121a), CpCr(NO)aR (R = Me and CHaPh) 61, 118), and CpMo(CO)a(L)Me [L = PPhg and P(OPh)3] 118, 121a) to furnish metal keteniminato (XXI) and cyanoalkyl (XXII) complexes. For CpFe(CO)aR, the reactivity decreases in the approximate 

Metal-allyl complexes of formulas CpFe(CO)aCHaC(R) = CR R and CpMo(CO)3CHaC(R) = CR R , as well as analogous propargyl and cyclopropylmethyl complexes, react with (CN)aC=C(CN)a to give cycloaddition products 21a, 56, 120, 121) of the type discussed in Section V. 

The insertion reactions of alkyl and aryl isocyanides were recently reviewed 126, 142) and will not be treated exhaustively in the present article. 

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Osmate esters are important intermediates in the reactions of 0s04 in the stereospecific m-hydroxylation of alkenes and other unsaturated molecules [182],... 

Photoreduction occurs by hydrogen atom abstraction or by electron transfer. The first process is a common photochemical reaction of carbonyl derivatives and other unsaturated molecules in the presence of suitable hydrogen atom donors (which can be alcohols, paraffins, ethers, etc., that is, almost any molecule with a not-too-strong C—H bond). 

The mechanisms behind lipid oxidation of foods has been the subject of many research projects. One reaction in particular, autoxida-tion, is consistently believed to be the major source of lipid oxidation in foods (Fennema, 1993). Autoxidation involves self-catalytic reactions with molecular oxygen in which free radicals are formed from unsaturated fatty acids (initiation), followed by reaction with oxygen to form peroxy radicals (propagation), and terminated by reactions with other unsaturated molecules to form hydroperoxides (termination O Connor and O Brien, 1994). Additionally, enzymes inherent in the food system can contribute to lipid oxidization. 

Full papers have appeared on the formation and reactivity of the compounds ML(CNR)2 (M = Ni, Pd, Pt L = Oz, azobenzene, olefin, diazo-fluorene, acetylene) (231-237) (see also Sections IV,D,2 and V,D). Complexes of the type Ni(olefin)(CNBu )2 have been prepared for a large range of olefins (234, 237). The isocyanide stretching frequencies have been measured and related to the electron-withdrawing properties of the olefin. Other unsaturated molecules such as imines, diazenes, ketones, nitroso compounds, and acetylenes have been similarly studied. The effect of substituent change has been found to be cumulative and an empirical relationship has been developed to predict v(NC) (237). 

Addition to Other Unsaturated Molecules. When isocyanates are treated with alcohols, substituted methanes or carbamates are prepared (Reaction XIX). 

Having studied the reactions involving alkynes in some detail we turned our attention to other unsaturated molecules, and in particular simple hydrocarbons. Alkenes appear unreactive, though allenes, as shown in the following section, do yield novel products. 

The discussion of typical reactions of coordinated CO should be seen as an introduction to the reactivity of other unsaturated molecules bound to, and activated by, transition metals. 

As in the cases of other unsaturated molecules, such as ethylene (10) 1,1-difluoroethylene, and cyanogen, where ion-molecule dimerization seems to play a major role in determining the products of low temperature radiolysis, F—N=0 and Cl—N=0 also appear to undergo a dimerization and possibly a trimerization in addition to other kinds of reaction. 

I. Lanthanides and Actinides Insertion of Other Unsaturated Molecules A. Introduction and Scope. ... 

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. 

Cyclocotrimerizations of Alkynes with Other Unsaturated Molecules and Related Reactions... 

Three-Component Couplings of Alkynes, Alkenes, and Other Unsaturated Molecules... 

Since 1965, when the first dinitrogen complex with ruthenium(II) was discovered [3a] N2 complexes with several transition metal compounds have been prepared. As with other unsaturated molecules, in these complexes dinitrogen acts both as electron donor and electron acceptor, the latter properties being more pronounced. Different kinds of complex are obtained experimentally and considered theoretically (e.g. see review [3b]). 

They form addition compounds with olefines and other unsaturated molecules ... 

Alkenes, arenes and other unsaturated molecules attach to central atoms, using some or all of their multiply bonded atoms, to give organometallic complexes. While there are many similarities between the nomenclature of coordination and organometallic compounds, the latter differ from the former in clearly definable ways. Organometallic complexes are therefore treated separately in Chapter IR-10. 

Reactions of this type are postulated as equilibria in synthetically important insertion reactions of alkenes, alkynes and other unsaturated molecules into the Pd-C bonds of dimeric palladacycles.271,272 Further, this reaction can form the basis for... 

It should be pointed out before concluding this section, that although observed phosphorescence emission from native proteins is almost always characteristic of emission from the aromatic amino acids, a number of proteins have other unsaturated molecules incorporated into their native structure. Molecules such as heme, flavins and carotenoids when complexed with protein contribute to the near UV and visible absorption of the complex and may be involved in energy transfer with aromatic amino acids. Further, triplet probes can often be bound to specific sites in a protein [e.g. inhibitor molecules bound to the catalytic site of an enz5mie) to study such interesting problems as interactions of the probe with metal ions 18) (which may be present in the catalytic site) or with the aromatic amino acids i .20) Since such probes are not native to the protein they are not considered further in this report. 

The choice of maleic anhydride (MAH) as the functionalizing agent is suitable for several reasons. The most important one -- a fact which distinguishes MAH from other unsaturated molecules bearing functional groups - is that MAH, similarly as other 1,2-di-substituted olefins, does not homopolymerize easily. This makes the grafting product, EPM-g-SA, practically unmodified in its rubbery properties and miscible with the parent EPM. 

After these references of general applicability it will be convenient to discuss the large number of specific references to homogeneous hydrogenation of olefins and of other unsaturated molecules in order of the central metal atom in Periodic Table order. 

The migration (insertion) reaction may also occur in the case of many other unsaturated molecules such as SO2, CO2, N2, NO, nitriles, isonitriles, and ketones. The insertion of sulfur dioxide may proceed very rapidly. The NMR and IR measurements show that the reaction proceeds through O-sulfinates which subsequently undergo rearrangement to give stable S-sulfinates ... 

Insertion of other unsaturated molecules such as GO or isonitriles in this type of palladacycle affords new types of <7,77 -enylpalladium complexes where the size of the cycle is increased in one carbon atom (Scheme 79). Cyclopalladated complexes derived from ferrocene also undergo double insertion of alkynes to give Equation (56) shows an example. It has been found for these systems that asymmetrically substituted internal alkynes insert in a head-to-tail manner. ... 

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