Alkyl and Related Complexes

Stable transition-metal alkyls were initially synthesized in the first decade of the twentieth century many such complexes are now known. The metal-ligand bonding in these complexes may be viewed as primarily involving covalent sharing of electrons between the metal and the carbon in a sigma fashion  

In terms of electron counting, the alkyl ligand may be considered a 2-electron donor CR3 (method A) or a 1-electron donor CR3 (method B). Significant ionic contribution to the bonding may occur in complexes of highly electropositive elements, such as the alkali metals and alkaline earths. 

Many synthetic routes to transition-metal alkyl complexes have been developed. Two of the most important of these methods are  

Reaction of a transition-metal halide with organolithium, organomagnesium, or organoaluminum reagent 

Reaction of a metal carbonyl anion with an alkyl halide 

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Reactions of carbon subsulphide and of elementary phosphorus, sulphur and selenium with complexes of the platinum metals Sulphur dioxide insertion reactions of transition metal alkyls and related complexes... 

For a monograph, see Roberts, R.M. Khalaf, A.A. Friedel-Crafts Alkylation Chemistry Marcel Dekker NY, 1984. For a treatise on Friedel-Crafts reactions in general, see Olah, G.A. Friedel-Crafts and Related Reactions Wiley NY, 1963-1965. Volume 1 covers general aspects, such as catalyst activity, intermediate complexes, and so on. Volume 2 covers alkylation and related reactions. In this volume the various reagents are treated by the indicated authors as follows alkenes and alkanes, Patinkin, S.H. Friedman, B.S. p. 1 ... 

Insertion reactions of platinum(II) alkyl and aryl complexes (144, 153, 171), nucleophilic displacement of isocyanide from [Pt(PRj)2(CNCH3)2] (147) and additions of alcohols and related substances to isocyanides bonded to platinum (8, 9, 25, 33, 34, 100, 117) were discussed earlier. 

Six methods have been used for the synthesis of Me3SiCH2M and related complexes (see Table VII). These all have counterparts in Me—M and related chemistry (73). The most widely applicable [e.g., Eq. (125)] is based on a Hal/R exchange using a metal alkyl, e.g., Me3SiCHjLi,... 

Synthesis and Properties of Alkyl, Alkenyl, Aryl, and Related Complexes of Silver 197... 

Nickel-cyclam and related complexes can also be used though previous reports indicated that the turnover of Ni/(tet a) in acetonitrile is low [85]. The process has now been reinvestigated to show that Ni/(tet a) can been used in catalytic conditions (2%) in DMF containing NH4CIO4 as proton source to perform the alkylation of unsaturated esters, ketones, or nitriles (Table 9) [86]. Yields are good if the terminal carbon of the double bond is not substituted (Ri = H). 

Since their early studies Eley et al. (1959) (see Eley, 1967) have largely confined their attentions to the study of the electronic and structural properties of bipyridinium2+ (TCNQ)2" and related complexes (Ashwell et al., 1975a, b, c Ashwell et al., 1977a, b, c Eley et al., 1977). Most complexes, such as 4,4-bipyridyl (TCNQ)2, five (N,N-dialkyl-4,4 -bipyridylium)2+ (TCNQ)J+ salts (alkyl = methyl, ethyl, propyl, isopropyl and benzyl ), and l,2-di(N-ethyl-4-pyridinium) ethylene2+ (TCNQ), are low gap semiconductors except one form of the last compound which exhibited metallic behaviour. The asterisked complexes comprise planar sheets of TCNQ molecules grouped in tetrads. 

Other methods for obtaining complexes of ethylene and other alkenes include ligand substitution reactions, reduction of a higher valent metal in the presence of an alkene, and synthesis from alkyl and related species [reductive elimination, of an allyl or hydride, for example hydride abstraction from alkyls protonation of sigma-allyls from epoxides (indirectly)] [74a],... 

A versatile route to RS-substituted dithiolenes entails S-alkylation of the trithiocarbonate dmit2 (see Section II.C.l), which provides an efficient means to introduction of diverse functionality to the dithiolene backbone. Subsequent to S-alkylation, the resulting S=CS2C2(SR)2 is converted to the dithiocarbonate 0=CS2C2(SR)2 with Hg(OAc)2 in acetic acid (63, 83, 84). Such dithiocarbo-nates are more easily hydrolyzed than the trithiocarbonates (72, 85). This approach has been used for the synthesis of Ni[S2C2(S(CH2) Me)2]2 (n = 2-11) (86) and related complexes with pendant alkene substituents (Eq. 8) (87). 

This indicates that the stannylene ligand is strongly held. Additionally, attempts at coordinating other bases to the vacant orbital of the stannylene failed with this and related complexes of Sn[CH(SiMe3)2 (78). That is noteworthy, since analogous dialkylstannylene-chromiumpenta-carbonyl complexes with smaller alkyl groups attached to the tin are unstable in the absence of coordinated base (101). 

The -acyls, ) -iminoacryls and related complexes originate from the migratory insertion (see Migratory Insertion) of C=0 or isocyanides C=NR into a metal-alkyl bond. These complexes are of interest mainly because of their relevance to catalytic CO reduction and the C-C bond formation in Fischer-Tropsch (see Fischer- Tropsch Process) reactions. 

Re Carbonyl Alkyls, Aryls, Acyls, and Related Complexes... 

The Homoleptic Alkyl and Aryl Complexes and the Related Compounds... 

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