The chemistry of octamethyl-1,2-disilacyclobutane. Some SiSi cleavage and insertion reactions

Catalytic bismetallative multicomponent coupling reactions: scope, applications, and mechanisms

Catalytic reactions have played an indispensable role in organic chemistry for the last several decades. In particular, catalytic multicomponent reactions have attracted significant attention due to their efficiency and expediency towards complex molecule synthesis. The presence of bismetallic reagents (e.g. B-B, Si-Si, B-Si, Si-Sn, etc.) in this process renders the products enriched with various functional groups and multiple stereocenters. For this reason, catalytic bismetallative coupling is considered an effective method to generate the functional and stereochemical complexity of simple hydrocarbon substrates. This review highlights key developments of transition-metal catalyzed bismetallative reactions involving multiple π components. Specifically, it will highlight the scope, synthetic applications, and proposed mechanistic pathways of this process.

The first stable mononuclear silyl palladium hydrides

The reaction of tertiary silanes with the low valent palladium complex [(mu-dcpe)Pd]2 affords equilibrium mixtures with mononuclear silyl palladium hydrides. These complexes have been characterized by NMR spectroscopy and, in one case, by X-ray crystallography. The silyl palladium hydride complexes rapidly interchange silicon and hydride coordination environments in solution which give rise to extraordinary temperature-dependent kinetic isotope effects for the fluxional process. An intermediate 2eta-Si-H complex is proposed for the interchange.

Palladium/Me(3)SiOTf-catalyzed bis-silylation of alpha,beta-unsaturated carbonyl compounds without involving oxidative addition of disilane

In the presence of a catalytic amount of Me(3)SiOTf and palladium(0), the addition of disilane to alpha,beta-unsaturated carbonyl compounds proceeds under very mild conditions via eta(3)-siloxyallylpalladium generated by the reaction of enone, enal, or aromatic aldehyde with palladium and Me(3)SiOTf.

A DFT computational study of the bis-silylation reaction of acetylene catalyzed by palladium complexes

In this paper we have investigated at the DFT(B3LYP) level the catalytic cycle for the bis-silylation reaction of alkynes promoted by palladium complexes. A model-system formed by an acetylene molecule, a disilane molecule, and the Pd(PH(3))(2) complex has been used. The most relevant features of this catalytic cycle can be summarized as follows: (i) The first step of the cycle is an oxidative addition involving H(3)Si-SiH(3) and Pd(PH(3))(2). It occurs easily and leads to the cis (SiH(3))(2)Pd(PH(3))(2) complex that is 5.39 kcal mol(-1) lower in energy than reactants. (ii) The transfer of the two silyl groups to the C-C triple bond does not occur in a concerted way, but involves many steps. (iii) The cis (SiH(3))(2)Pd(PH(3))(2) complex, obtained from the oxidative addition, is involved in the formation of the first C-Si bond (activation barrier of 18.34 kcal mol(-1)). The two intermediates that form in this step cannot lead directly to the formation of the final bis(silyl)ethene product. However, they can isomerize rather easily (the two possible isomerizations have a barrier of 16.79 and 7.17 kcal mol(-1)) to new more stable species. In both these new intermediates the second silyl group is adjacent to the acetylene moiety and the formation of the second C-Si bond can occur rapidly leading to the (Z)-bis(silyl)ethene, as experimentally observed. (iv) The whole catalytic process is exothermic by 41.54 kcal mol(-1), in quite good agreement with the experimental estimate of this quantity (about 40 kcal mol(-1)).

Synthesis, Structure, and Reactivity of 1,2-(1',1',2',2'-Tetramethyldisilane-1',2')carborane

The novel strained compound 1,2-(1',1',2',2'-tetramethyldisilane-1',2')carborane (1) was synthesized by the reaction of 1,2-dilithiocarborane and dichlorotetramethyldisilane. Compound 1 was characterized by solution methods and its structure determined by single-crystal X-ray diffraction. In contrast to its organic analogue o-(disilanyl)phenylene, the reaction of 1 with ethanol leads to cleavage of a Si-C bond rather than a Si-Si bond. Similarly to other cyclic disilanes, exposure of a solution of 1 to oxygen leads to the insertion of an oxygen atom into the Si-Si bond. The structure of the oxygen inserted product was also determined by X-ray crystallography. The general chemistry and attempts at polymerizing 1 are briefly discussed.