Iron carbonyl Subject

Several trinuclear iron carbonyl clusters have been subjected to a Fenske-Hall MO treatment by Buhl and co-workers. Hall has released details of the methodology for calculating potential energy surfaces for carbonyls, phosphines etc. using a variety of electron correlation techniques. 

Before considering the subject systematically, a few illustrative examples are given. Iron carbonyl complexes of monoolefins of the type I have considerable potential in organic synthesis (Section III,A,1). 

The iron-alkyne interaction is important because there are practical applications in organic synthesis, such as the iron carbonyl-mediated coupling of alkynes and CO. As a result, the reactions of alkynes with iron carbonyls have thus been the subject of many studies since the first report in 1953. Surprisingly, up until 1997, however, there was only one well-documented example of an Fe(CO)4(r7 -alkyne) species 3 (see Scheme 7). This is in part because complexes of this type are highly sensitive to the preparative conditions. Takats and co-workers have prepared a series of complexes of this type 3a-3e from Fe(CO)s (see Scheme 7) under carefully controlled photolysis conditions. The complexes Fe(CO)4(77 -alkyne) are shown to react with an excess of alkyne and CO, thus confirming early proposals that they are key intermediates in the coupling of alkynes with CO. ... 

Iron pentacarbonyl is approximately one-third as potent as nickel carbonyl when inhaled by rats for 30 minutes. Effects from inhalation of high concentrations of the chemical are expected to be similar to those of nickel carbonyl, which include frontal headache, vertigo, nausea, vomiting, and sometimes substernal and epigastric pain. Generally these early effects disappear when the subject is removed to fresh air. 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

Further restrictions to the scope of the present article concern certain molecules which can in one or more of their canonical forms be represented as carbenes, e.g. carbon monoxide such stable molecules, which do not normally show carbenoid reactivity, will not be considered. Nor will there be any discussion of so-called transition metal-carbene complexes (see, for example, Fischer and Maasbol, 1964 Mills and Redhouse, 1968 Fischer and Riedel, 1968). Carbenes in these complexes appear to be analogous to carbon monoxide in transition-metal carbonyls. Carbenoid reactivity has been observed only in the case of certain iridium (Mango and Dvoretzky, 1966) and iron complexes (Jolly and Pettit, 1966), but detailed examination of the nature of the actual reactive intermediate, that is to say, whether the complexes react as such or first decompose to give free carbenes, has not yet been reported. A chromium-carbene complex has been suggested as a transient intermediate in the reduction of gfem-dihalides by chromium(II) sulphate because of structural effects on the reaction rate and because of the structure of the reaction products, particularly in the presence of unsaturated compounds (Castro and Kray, 1966). The subject of carbene-metal complexes reappears in Section IIIB. 

Ruthenium Dicarbonyl, Ru(CO)a.—Ruthenium, like iron, yields a carbonyl derivative. It is obtained as an orange-yellow deposit upon subjecting ruthenium black to the action of carbon monoxide at 300° C. under a pressure of 400 atmospheres. The product is extracted from the residue by solution in alcohol. It is insoluble in benzene and in hydrochloric acid, but soluble in nitric acid and in bromine, gas being evolved. When heated, a mirror of metallic ruthenium is produced.5 In contradistinction to the other carbonyls of this group of metals ruthenium dicarbonyl is not volatile. 

The area of alkyne cluster chemistry has been the subject of two previous review articles. The first is concerned largely with alkyne-cobalt chemistry (16), while the second provides a comprehensive, systematic review of alkyne-substituted homo- and heterome-tallic carbonyl clusters of the iron, cobalt, and nickel triads (17). This latter review covers the literature up to the end of 1981. The present work does not set out to be fully comprehensive, but rather reflects the authors own interests in the subject. A number of key examples are... 

All ligands receive a separate subject entry, e.g., 2,4-Pentanedione, iron complex. The headings Ammines, Carbonyl Complexes, Hydride complexes, and Nitrosyl complexes are used for the NH, CO, H, and NO ligands. 

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