Although discrete nano-sized compounds consisting of a monolayer sheet of multiple atoms have attracted much attention, monolayer transition metal nanosheets are difficult to access. Here we report a template synthesis of the folding metal nanosheet (2) consisting of 11 palladium atoms by treatment of a ladder polysilane, decaisopropylbicyclo[2.2.0]hexasilane (1), with Pd(CN t Bu) 2 . Crystallographic analysis reveals that the compound is composed of two monolayer Pd 7 sheets sharing three palladium atoms at the junction. Each Pd atom is stabilized by Pd-Si s-bonds, Pd-Pd bonds and coordination of isocyanides. Ligand exchange of 2 from CN t Bu to CN(2,4,6-Me 3 -C 6 H 2 ) is accompanied by structural rearrangement, leading to the formation of another folding Pd 11 nanosheet (3) consisting of two edge-sharing Pd 7 sheets. The shapes of the Pd 7 sheets as well as the dihedral angle between the two Pd 7 sheets are dependent on the substituent of the isocyanide ligand.

Palladium-catalyzed reactions of dodecamethylcyclohexasilane [(SiMe2)6] (1) with alkynes led to efficient preparation of 1,1,4,4-tetramethyl-1,4-disilacyclohexadienes (3). The reactions were best catalyzed by Pd(0) species generated from Pd2(dba)3·CHCl3 and 1-isocyanoadamantane (AdNC). Terminal and internal alkynes bearing aryl and alkyl substituents could be used as substrates, and the reaction allowed gram-scale preparation of 3. A dimethylsilylene (Me2Si:) species, generated by activation of Si–Si bonds in 1 by Pd(0) species, was involved in the reaction mechanism. The DFT calculations suggest that oxidative addition of Si–Si bonds in 1 to Pd­(CNAd)2 species is followed by extrusion of a Me2SiPd­(CNAd) intermediate. Reaction of the resulting palladium-coordinated silylene with an alkyne forms a silacyclopropene, which dimerizes to give 3. The extrusion is accompanied by ring contraction of 1 to generate (SiMe2)5, which also contributes to formation of 3 and (SiMe2)4 by the Pd(0)-catalyzed reaction with an alkyne. Extrusion of Me2SiPd­(CNAd) and ring contraction generated more than five Me2Si: species from (SiMe2)6 (1).

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