Derivatives of the Transition Metals

Trifluoromethyl Derivatives of the Transition Metal Flements 1984 Synthesis and Properties of Aryl... 

TTifluoromethyl Derivatives of the Transition Metal Elements John A. Morrison... 

CycIobutadienyl derivatives of the transition metals are prepared by dehalogena-tion of 3,4-dihalocyclobutene with a zero-valent metal carbonyl. The zero-valent metal can act as a halogen acceptor and a mole of metal halide is obtained along with the cyclobutadienylcarbonyl-metal complex ... 

Carbon monoxide is an organic molecule that deserves special mention in any discussion of organotransition metal chemistry, because many organic derivatives of the transition metals are derived from metal carbonyls... 

Allyl derivatives of the transition metals can be classified as (7-allyl or TT-allyl. In the former, the allyl ligand contributes one electron n = 1) to the allyl-metal bond, while in the latter the allyl ligand may be regarded as contributing three electrons n = 3) to the allyl-metal bond. Probably the first transition metal complex containing a 7r-allyl ligand was described by Pritchard (198) in 1952, although the composition and structure of the product were not known precisely. The substance was reformulated as... 

Early attempts to prepare stable, isolable, cr-bonded organic derivatives of the transition metals were almost uniformly unsuccessful, except for certain organometallic derivatives of platinum and gold. It has already been mentioned that the V-bonded organochromium compounds of Hein and co-workers were in fact 7r-bonded arene-chromium derivatives. A detailed and critical account of these earlier studies was written in 1955 by Cotton (53). 

Another possible explanation for enhanced stabilities of perfluoro-alkyltransition metal compounds concerns possible multiple bonding between the metal and the fluorocarbon group 230). Whatever the reason, a large number of fluorocarbon derivatives of the transition metals have now been described, and a study of their synthesis, properties, and reactions constitutes an important new branch of organotransition metal chemistry. Fluoroalkyltransition metal compounds were first described in 1959 J 8), while perfluoroary 1-transition metal derivatives were discovered in 1963 201, 234). Some typical syntheses of fluorocarbon-transition, metal compounds are shown below ... 

One of the first reactions which occurs is exchange of groups between the two metal centers, resulting in the formation of alkyl or aryl derivatives of the transition metal. These compounds are unstable and ultimately decompose, liberating a hydrocarbon fragment with simultaneous reduction of the transition metal The mechanism of these reduction reactions may proceed by way of free radicals in some cases and by concerted paths in other cases. Discussions of this process (6) have been... 

That such bonding is operative in many carbon-metal bonds is indicated by the superior stability of phenyl and acetylenic derivatives of the transition metals (Section II. E) and the reduced reactivity of vinylboranes (92, 98). Trivinylborane, for example, has a reduced acceptor tendency towards ammonia and does not react with oxygen. Investigations have aimed at looking for similar effects with vinylstannanes (112) and vinylgermanes (108). Yet in alkynylgermanes and alkynylstannanes it appears that the adjacent triple bond labilizes the carbon-metal bond. Both types undergo... 

Section 3.2.B.iv discussed the oxidation of alcohols using derivatives of the transition metal Cr(VI), many of which required acidic conditions. Many alcohols, especially those bearing sensitive functional groups, require neutral oxidizing conditions. The development of PDC and related reagents helped to solve... 

Low-valent organometallic complexes and several organic-modified derivatives of the transition metals decompose to give short-lived nucleation particles of zerov-alent metals in solution, which may be stabilized by colloidal protecting agents. This decomposition is typically initiated by an external force, such as sonication or thermolysis, " or by introduction of a chemical agent such as Hj or CO. PVP stabilized, 45 nm Co nanoparticles can be prepared by decomposition of Co2(CO)g at 130-170°C in decaline or ethylene glycol solvents, as shown in Equation 6.3. ... 

In addition to derivatives involving direct Rf—metal bonds, this chapter includes compounds in which a fluoroaliphatic moiety Rf is attached to a transition metal via another atom e.g. P, As, or S). In general, chelate complexes of fluorinated jS-diketones are not considered, since these have been dealt with in Chapter 3 (see p. 173). Per- and poly-fluorinated aromatic derivatives of the transition metals are discussed in Chapter 6 (p. 420). 

Research on alkyl and aryl derivatives of the transition metals has flourished in recent years. The last fully comprehensive review of this area was prepared by Coates (1) in 1960, although excellent reviews of individual areas have appeared recently. For example, King (2) discussed metathetical syntheses of alkyl complexes, Heck (J) has described alkyl and acyl cobalt compounds, and Cross (4) has summarized the chemistry of platinum derivatives. Tabulations of individual organometallic compounds have been assembled by Dub (5) and Kritskaya (6). 

In addition to brief discussions of physical techniques as applied to organic derivatives of the transition metals, we include a short section on stability of these compounds. 

Dipole moments are often recorded for organic derivatives of the transition metals. Although this property is characteristic of the molecule as a... 

Other alkylcobalt and alkyltitanium compounds, especially those with branched alkyl substituents, also decompose by olefin elimination. The isobutyl complex, [(CH3)2CHCH2Co(CN)s] , slowly loses isobutene at room temperature (115). The unique stability of methyl derivatives of the transition metals relative to other alkyl derivatives is partly due to the absence of a j8-hydrogen atom which can be transferred to the metal. The... 

Homolytic cleavage of the C—M bond is the most common process for thermal or photolytic decomposition of alkyl and aryl derivatives of the transition metals. In terms of a molecular orbital scheme, the process involves transfer of an electron from a bonding orbital to a C—M antibonding orbital. Electronic factors which broaden the energy gap between these orbitals should stabilize the compound toward homolytic decomposition. 

Alkyl derivatives of the transition metals are key intermediates in many catalytic reactions of olefins. These intermediates are well characterized in... 

Metal carbonyls have been known for over 70 years. Within the last 35 years derivatives of the anions of the metal carbonyls have been synthesized. Within the last 10 years various derivatives of the metal carbonyl anions have acquired significance as intermediates in the preparation of interesting organometallic derivatives of the transition metals. In this chapter applications of anions derived from the metal carbonyls and the substituted metal carbonyls in syntheses of unusual organometallic derivatives of transition metals and the chemistry of the organometallic derivatives thus synthesized will be discussed. 

---