Alkyl complexes chemistry

Alkyl halides are encountered less frequently than their oxygen-containing relatives alcohols and ethers, but some of the kinds of reactions they undergo—nucleophilic substitutions and eliminations—are encountered frequently. Thus, alkyl halide chemistry acts as a relatively simple model for many mechanistically similar but structurally more complex reactions found in biornolecules. We ll begin in this chapter with a look at how to name and prepare alkyl halides, and we ll see several of their reactions. Then in the following chapter, we ll make a detailed study of the substitution and elimination reactions of alkyl halides—two of the most important and well-studied reaction types in organic chemistry. 

Silylene complexes are not only stable with donor substituents but also with simple alkyl residues at silicon. These alkyl complexes still have a sufficient thermodynamic stability, but otherwise are reactive enough to allow a rich and diverse chemistry. Particularly the chlorocompounds 7 and 11 are valuable starting materials for further functionalization reactions the details of these reactions will be discussed in the forthcoming sections. The data for the known compounds are summarized in Table 1. 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

Synthesis and Chemistry of Mixed Imido-Alkyl Complexes. . . 181... 

Synthetic organic chemistry applications employing alkane C-H functionalizations are now well established. For example, alkanes can be oxidized to alkyl halides and alcohols by the Shilov system employing electrophilic platinum salts. Much of the Pt(ll)/Pt(rv) alkane activation chemistry discussed earlier has been based on Shilov chemistry. The mechanism has been investigated and is thought to involve the formation of a platinum(ll) alkyl complex, possibly via a (T-complex. The Pt(ll) complex is oxidized to Pt(iv) by electron transfer, and nucleophilic attack on the Pt(iv) intermediate yields the alkyl chloride or alcohol as well as regenerates the Pt(n) catalyst. This process is catalytic in Pt(ll), although a stoichiometric Pt(rv) oxidant is often required (Scheme 6).27,27l 2711... 

Grigg, R. Sridharan, V. Transition Metal Alkyl Complexes Multiple Insertion Cascades. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 299-321. 

Casey has suggested that the hydrogenation of alkenes by Shvo s catalyst may proceed by a mechanism involving loss of CO from the Ru-hydride complex, and coordination of the alkene. Insertion of the alkene into the Ru-H bond would give a ruthenium alkyl complex that can be cleaved by H2 to produce the alkane [75], If this is correct, it adds further to the remarkable chemistry of this series of Shvo complexes, if the same complex hydrogenates ketones by an ionic mechanism but hydrogenates alkenes by a conventional insertion pathway. 

The extension to other cases is straightforward but tedious, and the principal results for low-spin octahedral species are summarised in Table 2, which shows some interesting features. At this level of discussion, R loss is never assisted. The question of demotion only arises where the t2g subshell is less than full. Two-electron demotion is is only possible for R loss from cf , cf, and systems, and in all of these it is actually term-term assisted. R" loss is assisted by the demotion of one electron fotd, d, or d curves, but among these it is only term-term assisted for d. R loss is clearly assisted by the demotion of a single electron for all d" (n < 6), but is only term-term assisted for n = 1 and n = 2. (These predictions are quite different from those of Ref. which refers exclusively to second order terms in R loss). The only configurations with n < 6 for which no process shows first order term-term assistance are d and d. This is a gratifying result and tends to promote confidence in the usefulness of the theory. The relative ease of preparation of Cr(III) alkyl complexes has often been noted and t/ is exemplified by the Co(IV) alkyls now known to be accessible by electrochemical oxidation of Co(III) Presumably a parallel chemistry of Fe(III) awaits discovery. 

In transition metal chemistry, ligand variation has proven to be the key to obtaining highly active polymerization catalysts. In particular, sterically hindered monocationic alkyl complexes with an empty site seem to be well suited for polymerization. The steric bulk prevents (associative) -hydrogen transfer, while the positive charge destabilizes the free hydride and thus opposes (dissociative) /(-elimination. 

In contrast to the extensive coordination chemistry of Ni—C (alkyl) complexes, examples of nickel complexes containing Ni—N (dialkylamide) a bonds are lacking.1123... 

The nickel(II) macrocycles catalyze the decomposition of alkyl halides (187, 188) and the chemistry, which involves nickel-alkyl complexes, has been investigated recently (189) in some detail. 

Organolanthanide compounds display a remarkable chemistry with the simplest carbonyl derivative, namely carbon monoxide [280-287]. Organolanthanide activation of carbon monoxide was first observed by employing the monomeric alkyl complex Cp2 Lu(f Bu)(TH F) (Scheme 37) [281a]. Reaction of one equivalent CO yielded single insertion of CO into the Ln-fBu bond to form a r 2-acyl complex. However, excess CO yielded a multiple insertion and coupling of four molecules of CO led to an enedione diolate moiety which bridges two lutetium atoms (Table 18). 

There will undoubtedly be many new catalysts described in the near future. In particular, we anticipate that later transition-metal complexes will play a much larger role in this type of chemistry. Although bis-Cp complexes of Groups 3 and 4, the lanthanides, and the actinides have shown exceptional activity and thus far have dominated reported investigations on catalytic homodehydrocoupling, it is most unlikely that they are unique in this property. It is to be expected that other classes of complexes, such as mono-Cp and -rj -alkyl complexes of these elements, will also be active. Other directions for future evolution are the development of catalysts that are air stable, that are tolerant of more functionalities on substrates, and that are more easily manipulated. 

Another class of heteroleptic alkyl complexes contains 7t-donating ancillary ligands such as RU[N(Si(CH3)3)2]3 (R = CH3, H, BH ). The hydride species can be converted into the methyl species via reaction with BuLi and CH3Br. The methyl compound has exhibited insertion chemistry with small molecules including aldehydes, ketones, nitriles, and isocyanides (206). Stable metallacyde compounds are also known, ie,... 

Two reports included multidentate ligands as supports for amination chemistry. First, 4,4 -Di-tert-butyl-2,2 -bipyridyl ( Bu2bpy) stabilizes the thermally sensitive [LuR 3] unit, giving the [(tBu2bpy)Lu(R )3]- This tris(alkyl) complex readily reacts with Ph3COH, 2,6- Pr2C6H3NH2, 2,4,6-tBu3C6H2NH2, and N,N -dicyclohexylcarbodiimide to afford a variety of Lu(III) tris(alkoxide),... 

The latter is outside the scope of organometallic chemistry, but within the first two topics the work involved three main themes olefin and acetylene complexes, alkyl and aryl complexes, and hydride complexes. As continuous subsidiary themes throughout ran the complex chemistry of tertiary phosphines and such ligands, the nature of the trans effect, and the nature of the coordinate bond. All the work from 1947 to 1969 was carried out in the Butterwick Research Laboratories, later renamed Akers Research Laboratories, of Imperial Chemical Industries Ltd., and I am indebted to that Company and particularly to Mr. R. M. Winter, the Company s Controller of Research, and Sir Wallace Akers, its Director of Research, who in 1947, made available to me the opportunity to develop my research in my own way, in those laboratories. 

A review of the literature reveals that cyclopentadienyl or substituted cyclopentadienyl ligands play an important role in stabilizing alkyl complexes of the actinides, and there is a great deal of organometaUic chemistry associated with these complexes. 

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