Complexes tetracarbonyl

Transition metals readily form complexes, such as [Fe(CN)6], the ferrocyanide ion, Ni(CO)4, nickel tetracarbonyl, and [CuC ], the copper tetrachloride ion. MO theory applied to such species has tended to be developed independently. It is for this reason that the terms crystal field theory and ligand field theory have arisen which tend to disguise the fact that they are both aspects of MO theory. 

For tetranuclear cluster complexes, three stmcture types are observed tetrahedral open tetrahedral (butterfly) or square planar, for typical total valence electron counts of 60, 62, and 64, respectively. The earliest tetracarbonyl cluster complexes known were Co4(CO)22, and the rhodium and iridium analogues. The... 

Nitrondte anions react with (7t- illyl CQbait complexes prepared from acyladonof 1,3-thenes by acetylcobait tetracarbonyl to produce nitro enones fEq. 5.50. ... 

The first and rate-determining step involves carbon monoxide dissociation from the initial pentacarbonyl carbene complex A to yield the coordinatively unsaturated tetracarbonyl carbene complex B (Scheme 3). The decarbonyla-tion and consequently the benzannulation reaction may be induced thermally, photochemically [2], sonochemically [3], or even under microwave-assisted conditions [4]. A detailed kinetic study by Dotz et al. proved that the initial reaction step proceeds via a reversible dissociative mechanism [5]. More recently, density functional studies on the preactivation scenario by Sola et al. tried to propose alkyne addition as the first step [6],but it was shown that this... 

Both MeMn(CO)5 and PhMn(CO)5 react with acetylenes to yield vinyl ketone tetracarbonyl complexes, most likely via a pathway involving CO insertion [Eq. (18)] 14, 36). Reactions of these same alkyls with 1,3-dienes may proceed similarly 16, 95, 96). The chelating ligand o-styryldiphenyl-phosphine (L—L) converts MeMn(CO)j into two products 25) whose structures (XXII and XXIII) were elucidated by X-ray crystallography 24). An unusual migration of COMe onto L—L occurs subsequently to the initial insertion step. 

Alkali Metal Derivatives of Metal Carbonyls, 2, 1S7 Alkyl and Aryl Derivatives of Transition Metals, 7, 1S7 Alkyl cobalt and Acylcobalt Tetracarbonyls, 4, 243 Allyl Metal Complexes, 2, 32S... 

In the case of the hexacarbonyls, the rate-expression contains not only the same type of first-order term but in addition one second-order overall. For good entering groups (but not CO, for example) the rate expression contains a term strictly first-order in both the complex and the entering nucleophile. The first-order rates of CO exchange are practically identical with the rates of substitution in hydrocarbon solvents, but there is nevertheless some acceleration in ether (THF, dioxan) solutions. This solvent-dependence is not so well-marked ° as in the case of nickel tetracarbonyl. The second-order rate of substitution very strongly depends upon the basicity of the entering nucleophile... 

Nitronate anions react with (jl-allyl)cobalt complexes prepared from acylation of 1,3-dienes by acetylcobalt tetracarbonyl to produce nitro enones (Eq. 5.50).74... 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

Recent mechanistic studies were conducted by Ragaini et al. using tetracarbonyl rhodate complexes. Several potential intermediates such as (152) have been isolated.584 585 The catalytic system has been optimized and the influence of solvent was examined.586 2-Hydroxypyridine has a large activating effect on the [PPN][Rh(CO)4]-based catalytic system for the reductive carbonylation of nitrobenzene to Me phenylcarbamate 587... 

Diaryl thioketones are converted by diiron enneacarbonyl into products of orthometallation.141 Oxidative or photochemically induced deligation of these complexes provides an unusual and valuable synthetic entry into compounds in the uncommon isobenzothiophene category142,151 (Scheme 84). Moreover, the photochemical procedure provides the novel complex, (tetracyanoethylene)tetracarbonyl iron. The orthometallated complexes (68) can also be used to prepare isobenzofurans (see Section IV,B,5). 

A variety of experimental methods has been used to study the thermal chemistry of the unsaturated iron fragments produced by photolysis. For example, regeneration of 1Fe(CO)s was observed upon heating low-temperature matrices in which Fe(CO)5 had been photolyzed (35). These condensed-phase reactions are rather complex, as in some cases, components of the inert matrix may form adducts Fe(C0)4L or Fe(CO)sL (L = N2, Xe, CH4), so that the reaction observed is not simply CO addition to an unsaturated iron tetracarbonyl fragment. The same reactions were studied in the gas phase, using flash... 

Iron tetracarbonyl and various related unsaturated iron complexes show a remarkably rich diversity of spin-forbidden chemistry. Various reactions of these species have been the object of a large number of experimental studies, including many careful studies of reaction kinetics. These experiments provide an excellent set of data with which to evaluate the power of computation to rationalize observations in a qualitative way, as well as to account in a more quantitative way for experimental observations. The computational work described above is largely drawn from our own published work (23-27), including some unpublished data for some of the reactions (85,87). Nevertheless, many other groups have carried out insightful ab initio and DFT studies of many of the species and processes described. 

Some 7r-allylmanganese(I) tetracarbonyl complexes, partly substituted by phosphites or phosphines, are apparently active for olefin hydrogenation (534). 

These studies were extended to hydrosilation of cyclopentadiene with trichlorosilane (52). This is most difficult with platinum catalysts. Palladium complexes favored production of 1 1 adducts as a mixture of 3- and 4-trichlorosilylcyclopentene. Nickel complexes produced substantial amounts of 1 2 adducts as trichlorosilyl-substituted 4,7-methylene-4,7,-8,9-tetrahydroindanes, with the exception of nickel tetracarbonyl, which was very active and selectively formed almost exclusively 3-trichlorosi-lylcyclopentene with no 1 2 adduct. 

Preparation of Tungsten Tetracarbonyl Complexes with Bidentate P.O-Bound... 

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