Multiple bond linkages

The General Paucity of Rare Earth-Ligand Multiple Bond Linkages in an Organometalhc Context... 

Figure 5 Selected rare earth carbenes with formal metal-carbon multiple bond linkages...

One of the most important publications on this subject, considered frorn the chemical side, is that of Gertrude Woker. This investigator drew attention to the importance of multiple bonding. The double bond is often accompanied by a pleasant, but the triple or acetylenic linkage generally produces a disagreeable smell a multiplicity of double bond can produce an effect equivalent to a triple bond. 

In contrast to the other X-H additions surveyed in this chapter, there have been only a limited number of studies on the addition of P H linkages across C C (and C—O) multiple bonds. At the same time, there has been significant progress made in the development of catalytic systems for performing hydrophosphination and hydrophosphorylation compared to what was known pre-1982. 

Crystal structure analysis of [WCl(diphos)2(N2H2)]BPh4 368 clearly shows that the N2H2 ligand is indeed coordinated as a hydrazido(2-) group. The W—N—N linkage is linear with W—N and N—N distances of 1.73 and 1.37 A respectively. The short W—N distance clearly suggests a considerable multiple bond character to the W—N bond. 

Disilanes connected via both the Si-Si bond and an organic or an organo-metallic linkage are activated toward reaction with unsaturated substrates to form cyclic bis(silyl) products. Reactions of 3,4-benzo-l,l,2,2-tetraethyl-1,2-disilacyclobutene with diphenylacetylene or benzaldehyde catalyzed by Ni(PEt3)4 proceed with addition across the multiple bond to form the ring-expanded product.54 A second product is formed in a lesser amount in the case of diphenylacetylene, with insertion into the Si-C bond [Eq. (13)]. 

Ito and co-workers have also used the Pd(OAc)2/t-alkyl isocyanide catalyst to affect the double silylation of carbon-carbon multiple bonds in an intramolecular system to yield silacarbocycles.59 Alkenes or alkynes that are tethered to a disilanyl group through a carbon chain, an ether linkage, or an amine functionality undergo intramolecular addition of the disilane moiety to the multiple bond. Activation of the disilane by the presence of electron-withdrawing groups on silicon is not necessary for the reaction to... 

Although the term hydroboration is most commonly employed2-3 16 to denote the addition of a boron-hydrogen linkage to carbon-carbon multiple bonds, it has also been used for the two-step oxidative process to distinguish it from the process of reduction involving H-B addition and protonolysis. 18... 

The addition of aluminum hydride and alkyls to non-activated C-C multiple bonds (C=C or C=C) is referred to as hydroaluminaton and carboalumination, respectively. The reactions involve metathesis of each C-C multiple bond with Al-H or Al-C bonds, giving an Al-C =C-H (or Al-C-C-H) or A/-C=C-C (or A/-C-C-6) structure, respectively. These methods are of broad utility in the construction of Al-C linkages, including Al-alkenyl and Al-alkyl bonds, which can be further converted into C-C bonds (Equations (42)-(45)).192-196 Therefore, a great contribution has been made in synthetic applications, in addition to the mechanistic studies, of hydroalumination and carboalumina-tion since 1993.197-199... 

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