Metal Carbonyls and Some Derivatives

Checked by William L. Jolly, Gordon Austin, William Covby,S 

Cyclopentadienyl carbonyls of several transition metals have been reported during the last decade, and these compounds have been shown to undergo a variety of interesting reactions. Two general methods have been used to prepare these materials treatment of metal carbonyls with cyclopentadiene or cyclopentadienylsodium, and the reac- 

The only known syntheses of cyclopentadienylvanadium tetracarbonyl, C6H6V(CO)4, are based on the reaction of bis(cyclopentadienyl)vanadium with carbon monoxide under pressure. The procedure given below is based on this reaction but avoids isolation of pyrophoric bis-(cyclopentadienyl)vanadium by direct carbonylation of the solution obtained from vanadium(III) chloride and cyclopentadienylsodium. 

For this synthesis anhydrous vanadium (III) chloride is required. This may be purchased, or prepared either from vanadium(V) oxide via vanadium(IV) chloride or by refluxing vanadium(V) oxide with excess hexachloropropene for several days and filtering the purple solid produced. 

three-necked flask is fitted with a nitrogen inlet, reflux condenser, and stirrer. After flushing the apparatus Anderson Chemical Co., Weston, Mich. 

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Cyclopentadienyl metal carbonyls and some derivatives, synthesis 31... 

New chemistry of metal carbonyls and their derivatives is summarized below. However, as in previous Reports many carbonylmetal complexes are reviewed in other chapters. Herein we highlight significant results of general interest. A Bibliography at the end of the chapter lists papers which were noted during our survey of the literature. In this introductory section the reader s attention is drawn to some novel discoveries related to new carbonylmetal chemistry. 

Single-crystal X-ray and neutron diffraction studies on metal carbonyls and their derivatives are summarized in the last chapter of this Report. Here we mention some results of special interest. 

The chemistry of the thiazoles does, of course, bear some similarity to that of the oxazoles. Metallated thiazoles and thiazole derivatives have found use, for example, both as carbonyl equivalents and masked acetaldehyde enolates. Additionally, as will be exemplified below, thiazole derivatives have served as catalysts for benzoin-type condensations, and they have provided access to a unique class of activated acid derivatives. 

Tellurophene and its derivatives give molecular complexes of a different kind with a variety of substances such as mercuric chloride, picric acid, 2,4,7-trinitrofluorenone, 1,3,5-trinitrobenzene, transition metal carbonyls and chlorides, and tetracyanoethylene. Some of these complexes have been used in the characterization of tellurophene derivatives and will be referred to in the Appendix. 

About thirty-five reactions which involve homogeneous catalysis by the metal carbonyls or their derivatives are known. This paper will attempt to shed light on the mechanisms of these reactions and will point out some implications in regard to heterogeneous catalysis. 

Most of the reactions of PH3 with the carbonyls of the transition metals and with a variety of carbonyl derivatives can essentially be classified according to three main types of reactions (i) substitution of CO ligands, of other neutral Ti-acceptor ligands like, e.g. PR3, weak 0-, S-, N-donor ligands, and alkenes, or of anionic ligands, (ii) cleavage of metal-metal bonds, and (iii) oxidative addition. Only in a few cases combinations of two or three of these reaction types or completely different reactions are observed. Most reviews dealing with the chemistry of phosphanes, with complexes of transition metals, or with transition metal carbonyls and derivatives cover only some aspects of the coordination chemistry of PH3 see e.g. [1,4, 14, 16, 22, 24, 27 to 29]. 

Table III contains results from metal carbonyl complexes, some efficient examples being depicted in Fig. 5. In many cases, the most important contribution to the nonlinearity derives from other ligands (N-donor ligands, carbocycles, and car-benes). Many pyridine and arene complexes have EFISH-derived negative p values, consistent with these complexes undergoing a decrease in dipole moment or change in direction of dipole moment between the ground and excited states.

Carbon monoxide [630-08-0] (qv), CO, the most important 7T-acceptor ligand, forms a host of neutral, anionic, and cationic transition-metal complexes. There is at least one known type of carbonyl derivative for every transition metal, as well as evidence supporting the existence of the carbonyls of some lanthanides (qv) and actinides (1) (see AcTINIDES AND THANSACTINIDES COORDINATION COMPOUNDS). 

For the activation of a substrate such as 19a via coordination of the two carbonyl oxygen atoms to the metal, one should expect that a hard Lewis acid would be more suitable, since the carbonyl oxygens are hard Lewis bases. Nevertheless, Fu-rukawa et al. succeeded in applying the relative soft metal palladium as catalyst for the 1,3-dipolar cycloaddition reaction between 1 and 19a (Scheme 6.36) [79, 80]. They applied the dicationic Pd-BINAP 54 as the catalyst, and whereas this type of catalytic reactions is often carried out at rt or at 0°C, the reactions catalyzed by 54 required heating at 40 °C in order to proceed. In most cases mixtures of endo-21 and exo-21 were obtained, however, high enantioselectivity of up to 93% were obtained for reactions of some derivatives of 1. 

Generally, in the nucleophilic addition to carbonyl groups, either magnesium compounds or alkali metal compounds (such as the Li, Na and K derivatives) are used. In some cases even potassium carbonate or piperidine were used as the base for condensation with sulfones. Good results were obtained when concentrated aqueous NaOH was used under phase-transfer conditions288,297,333. 

Depolarization data on trimethylphosphine oxide are now available and the relationship between the symmetric and asymmetric POP vibrations has been equated for diphosphates, and some halogen and metal salt derivatives. The polarization of a carbonyl group produced by its conjugation with an ylide causes a large decrease in vco- This shift to lower frequency is increased further when a double bond is interposed, thus increasing the extent of conjugation. -... 

It is only since the early 1980s that significant progress has been made with aldol reactions. This chapter introduces some of the most important developments on the addition of metallic enolates and the more important of the related allylic metal derivatives to carbonyl compounds. These processes are depicted as paths A and B in Scheme 3-1. 

In the reaction of group 13 element halides with metal carbonyl dianions, the analysis is more complex than observed for the reactions with metal monoanions. Upon addition of metal dianions to EX3 or REX3, either one or two halide ions may be eliminated. When only one halide ion is eliminated per added metal dianion, the complexes may still be viewed as E3+ derivatives (Equations (33)-(36)).19 This may be controlled to some extent by the stoichiometry of the reaction. Comparison of Equations (33)19 and (34)19 shows that the electron demand at the main group element can be satisfied by coordination either to an electron-rich metal center 26 or formation of a halide bridge 27. Ligand-stabilized forms may also be prepared in this fashion (Equation (36)).19... 

Whereas a large number of metal-sulfur clusters are present in nature, carbonyl clusters are exclusively products of chemical synthesis. They have been widely used in industrial catalytic processes17 and some of these processes are triggered by the redox aptitude of these species.lc g As for the metal-sulfur clusters, we will briefly discuss their structures and their propensity to donate/accept electrons in order of increasing nuclearity. We will consider only homonuclear and homoleptic metal-carbonyl derivatives. However, it is noted that heteronuclear derivatives are gaining considerable interest due to the synergistic effect of metal-metal bonds possessing a polar character.lc,ld... 

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