Molecular cumulene-type

High-molecular cumulene represents an insoluble dark-brown powder with the developed specific surface (200-300 m /g) and density 2.25 g/sm. At multihours heating at 1,000°C and the depressed pressure, polycumu-lene partially crystallizes. Two types of monocrystals have been found out in received after annealing a product by means of transmission electronic microscopy. Crystals corresponded to a- and p-modifications of carbyne. 

Here, we shall focus on ruthenium-catalyzed nucleophilic additions to alkynes. These additions have the potential to give a direct access to unsaturated functional molecules - the key intermediates for fine chemicals and also the monomers for polymer synthesis and molecular multifunctional materials. Ruthenium-catalyzed nucleophilic additions to alkynes are possible via three different basic activation pathways (Scheme 8.1). For some time, Lewis acid activation type (i), leading to Mar-kovnikov addition, was the main possible addition until the first anfi-Markovnikov catalytic addition was pointed out for the first time in 1986 [6, 7]. This regioselectiv-ity was then explained by the formation of a ruthenium vinylidene species with an electron-deficient Ru=C carbon site (ii). Although currently this methodology is the most often employed, nucleophilic additions involving ruthenium allenylidene species also take place (iii). These complexes allow multiple synthetic possibilities as their cumulenic backbone offers two electrophilic sites (hi). 

The molecular structure of linear carbon (carbine) is the chain with sp-hybridized atoms [1]. In order to explain a variety of carbine forms the structure of carbon chains with possible two types of bonds (Fig. 1) in the zigzag model was offered with polyine solid state [-(-C=C-)-]n and cumulene [=( C=)=]n fragments. For a polymeric c arbon c hain i n s olid s tate t he z igzag s tructure with c umulene t ype o f connection is most probable. It can be packing of zigzag carbon chains with linear sites of different length. 

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