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The homonuclear heavy Group 14 double bonded systems, that is the heavier analogue of alkenes (R2E=ER2, E = Si, Ge, Sn, Pb) feature conformational flexibility around their double bonds and absorb in the visible region, representing the relatively narrow HOMO-LUMO gap.
The unsymmetrically substituted disilene, that has remained synthetically challenging for long until 20071, exhibits unusual reactivity patterns.2 Model compounds with Walsh-Ĉ conjugative interactions have been synthesized by the insertion of isocyanide into unsymmetrically substituted Si=Si double bond, that reveals significant potential in polymer chemistry.3 An atom-economic, catalyst- and by-product free protocol for the synthesis of ċ-Ĉ conjugated organosilicon hybrid polymers by utilizing regiospecific cycloaddition reactions of terminal alkynes to unsymmetrically substituted Si=Si bonds (disilene) at room temperature has been established. Potentially modular approach to this polymerization methodology will be discussed. Silicon cluster with dismutational aromaticity has been synthesized from the disila analogue of vinyl lithium (lithium disilenide)4 in conjunction with cationic silicon species.5 Recently NHC-stabilized silagermenylidene, the heavier analogue of vinylidene has been isolated. The rearrangement products and their ligating potential in transition metal chemistry will be discussed.6 Another very recent breakthrough achievement that will be discussed, is the reductive coupling of carbon monoxide by low-valent silicon compounds which is otherwise predominantly restricted to highly reducing transition metals.
The chemistry of homonuclear metal-metal multiple bonds of the d-block transition metals kick started with the recognition of multiple bond in [Re2Cl8]2- and have grown exuberantly since then. The first catalytic applications of the homonuclear quadruply bonded Group 6 metal clusters (M = Cr, Mo, W) for radical addition and polymerization reactions via single electron transfer process has been studied.7 The higher catalytic activity and the involved reaction mechanism of the mono-carboxylato substituted Mo2 complexes will be discussed. Water-Gas Shift reaction8 and C-H bond activations9 on dimetal platform will also be discussed.
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