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1 2008

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Związki i kompleksy poliynowe : strategia syntezy i zastosowania

Osowska K., Szafert S.

Wiadomości Chemiczne

2008

[Z] 62, 5-6

479-511

The previous two decades have witnessed a series of major breakthroughs in carbon allotrope chemistry [1, 2]. This field has attracted scientists from all disciplines and plays a leading role in the nanotechnology boom. A lot of discussion is devoted to the new polymeric sp carbon allotrope termed "carbyne", which until now remains an unsettled topic. In order to model and understand its potential properties research on known - natural and synthetic - polyynes or polyynediyl systems has been undertaken. The review gives a brief summary on the results of this research. It describes isolation and properties of many natural polyynes. This includes diynes [13-21], triynes [22-26], and tetraynes [27, 28], which were derived from many natural sources [6-10]. Most of these compounds possess very interesting biological activities that range from antibacterial properties through antifunginal, antiseptic, anti-cancer and anti-HIV activity [11-12]. Next some of the synthetic organic and organometallic examples are presented. The former includes compounds with more than 20 carbon atoms in the chain that are often terminated with extremely bulky (even dendrimeric) [29-38] or heteroatom containing endgroups [39-45]. Such compounds constitute an ideal base for many theoretic calculations. The classification of alkynyl complexes is given as well as few examples of crystallographically characterized long carbon chain organometallic compounds [55-56]. The review differentiates the complexes of main group and transition metals. The former are less represented but are often crucial in the synthesis of transition metal alkynyl complexes [57-60]. Next we summarized the most practical approaches to the synthesis of polyynes. The common pathway includes four steps: (1) synthesis of terminal group precursor, (2) introduction of acetylene fragment, (3) chain elongation, and (4) termination of the carbon chain including dimerization. Methods for C?C introduction to organic compounds are represented by numerous homo and heterocoupling protocols. The most frequently used are Sonogashira [64-66] and Stille [67, 68] couplings although in some cases other methods (Negishi, Kumada-Tamao-Corriu or Suzuki coupling) are more effective. Instead, conventional synthesis of alkynyl complexes includes reaction of metal halides with common alkynylating agents as alkynyl compounds of group 1 metals [71-73] although more sophisticated methods are also known [74-82]. Chain elongation is the most important part of the polyyne synthesis. The major protocol for this step is Cadiot-Chodkiewicz coupling first introduced in 1957 [83]. Lately, many modifications of this method were developed although the main idea remained unchanged [84-87]. With time some other protocols were applied for this step from which the most interesting are Fritsch-Buttenberg-Wiechell [89-91] and elimination reaction [92-93]. Finally, organic and organometallic polyynes application potential is discussed. Apart from their use in synthetic organic chemistry [99-113] they are being utilized for the production of polymeric materials via topochemical crystal-to-crystal polymerization [118-120]. They also reveal some medical applicability [114-115].