Metal carbonyl anions insertion reactions

We have recently observed that anionic alkyl and aryl derivatives of the group 6B metal carbonyls undergo insertion reactions with carbon dioxide to afford the corresponding carboxylates, e.g., as depicted in Eq. (25) (44, 72). An ORTEP representation of one such product of C02... 

Other alkenyl complexes have been formed by displacement of fluoride or chloride ion from fluoro-olefins by metal carbonyl anions, by reactions of the perfluoroalkenylsilver derivative with metal halide compounds, and by insertion of an alkyne into a metal-X bond, and parameters are given with structures [168] to [187]. (8, 86-91) As... 

Analogously, reaction of group 7 metal carbonyl anions M(CO)5 (M = Mn, Re) with MeC(CFFI), gave cyclopropylcarbinyl complexes. Flowever, whereas rhenium produces the normal (/-metal bonded cyclopropylcarbinyl complex, the manganese complex furnished (cyclopropylacetyl)Mn(CO)5, where carbonyl insertion into the manganese-alkyl bond occurred (equation 56)114. 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

Although a variety of new preparative routes has been developed in recent years (for reviews see refs 1 -10), the transformation of the metal-carbonyl carbon bond of a metal-carbonyl complex into a metal-carbene carbon bond is still the most useful and versatile method for preparing transition-metal carbene complexes. The addition of a carbanion to the carbon atom of a carbonyl ligand yields an anionic acyl complex that subsequently can be reacted with an electrophile to give a neutral carbene complex. Thus, the syntheses of anionic acyl and neutral carbene complexes are closely related, for almost all the carbene complexes considered in this section acyl complexes are precursors, although most have not been isolated and characterized. The syntheses of acyl complexes via CO insertion (for reviews see refs. 11, 12) or by reaction of metal carbonyl anions with acyl halides is outside the scope of this section. 

The carbonylation of a benzyl halide in the presence of iron pentacarbonyl to give a phenylacetic acid may serve to exemplify the interaction of a metal carbonyl, carbon monoxide, PT catalyst, aqueous sodium hydroxide, and the substrate [79]. Fe(CO)5 is attacked by QOH at the interphase, and the species formed is extracted into the depths of the oganic phase, where it reacts with CO and benzyl halide (Eqs. 13 and 14). This new anion 3 is the actual catalyst. It reacts with a second benzyl halide to give a non-ionic intermediate 4 (Eq. 15). By insertion of CO and attack of QOH, 4 is decomposed to the reaction product under regeneration of 3 (Eq. 16). Thus, the action of the PT catalyst is twofold. Firstly it transports the metal carbonyl anion. More important seems to be its involvement in the (rate-determining) decomposition step. A basically similar mechanism was proposed for cobalt carbonyl reactions [80], which have been modified somewhat quite recently (see below). 

In both this and the previous method of preparation, low yields are often found, due to competitive coupling reactions or to further reactions such as the decomposition of the M— R], products. Also tire metal anions are strong nucleophiles and they may cause the or mic halides to undergo elimination reactions. Metal-acyl complexes are often by-products of the reaction of organic halides with the metal carbonyl anions they are formed by insertion reactions (see p. 258). Indeed, acyl halides may be used to give metal-acyl complexes which are dien decarbonylated either thermally or by photochemi techniques [. Some metal-aryl complexes which are... 

Prior to our studies it was recognized that ion pairing with anionic metal carbonyls could promote CO insertion and related reactions (14-16). Both kinetic and non-kinetic evidence suggests the importance of ion pairs in these types of reactions (14,17). For example, a small cation was found to greatly accelerate the CO insertion reaction relative to the same reaction with a large cation, equation 6 (14). 

These complexes readily insert carbon monoxide between the alkyl and metal groups giving acylmetal complexes. As in the preceding examples, these complexes undergo alcoholysis readily to form esters and a hydride. The reaction is then made catalytic in the metal by adding a base to convert the hydride back into the carbonyl anion ... 

An intermediate In(Por)(Fe(CO)4)(CH3) species has been observed in the course of formation of the trinuclear complex (In(Por))2Fe(CO)4. In the first step, the reaction proceeds via a mechanism similar to that of an insertion reaction. Similar complexes with other metallate anions have been isolated following the same procedure As shown in Table 18, these complexes generally exhibit three bands in the carbonyl stretching region (2100-1850 cm ). The UV-visible spectra of the octaethylporphyrin derivatives belong to the hyper class. 

Much less is known about the abnormal insertion path bearing to the metallacarboxylic species (2) for which only a few claims exist. Nevertheless, the M-C(0)OH moiety can be stable and is easily formed upon reaction of a metal carbonyl species M(CO) with a hydroxo anion (OH ) (4.9) or by protonation of co-ordinated CO2 (4.10 and 4.11) or by insertion of CO2 in the M-H bond (Scheme 4.1). The formation of Ni-C(0)OH via proton attack at the oxygen of a coordinated q (C,0)-C02 has been reported for the reaction of Ni(PCy3)2(C02) with PhSH [24]. The resulting Ni-C02H moiety undergoes further protonation with... 

Alternatively, acyliron complexes can be obtained in a two-step sequence either from dicarbonyl(cyclopentadienyl)ferrates or from dicarbonyl(cyclopentadienyl)iron halides via alkyl-Fp complexes. The first method makes use of the nucleophilicity of [CpFe(CO)2] anions. Their reaction with alkyl halides provides alkyl-Fp complexes that, upon treatment with phosphanes or phosphites, undergo a migratory insertion of a carbonyl ligand into the metal-alkyl bond leading to an acyliron complex (Scheme 4-38). " ... 

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