Cubanes review

These trinuclear complexes can act as metalloligands to afford a whole series of heterobimetallic M3M Q4 cubane-type complexes and several review articles on the topic have been published in the last decade [31, 32]. 

Only a trace of the corresponding cubane 167 is formed on irradiation of the tricy-clooctadiene 168 in pentane at ambient temperatures using a 125-watt mercury arc lamp. The principal product 169 is the result of rearrangement within a biradical intermediate79. A review of the synthetic approaches to cubane and to its reactions has been published77. The diene 170 photochemically converts on irradiation in pentane solution at 254 nm to yield a photostationary mixture of the cubane 171, the starting material 170 and the isomeric diene 17280. Other additions of this type have been used for synthesis of the propellaprismane 173, essentially a heavily substituted cubane, by the intramolecular (2 + 2)-photocycloaddition of the diene 17481. 

The latter are generally obtained as dimeric "double cubanes", which must be cleaved to produce the single cubane clusters. The preparation and properties of both linear (51,71,72) and cubane (51,71) Mo-Fe-S clusters have been reviewed in detail, and will not be discussed further here. 

Cyclopropanes are cleaved by a variety of transition metal derivatives. The first observation was that PtCl4 reacts to give a platinocyclobutane. Cyclobutanes appear to be less reactive, but cubane reacts with [Rh(CO)2Cl]2 leading to C—C bond cleavage. The subject of C—C bond cleavage has been reviewed. 

The most spectacular examples of the wide applicability of this method are the elegant syntheses of strained cubane- and homocubanecarboxylic acid derivatives,52 which have partially been reviewed (Houben-Weyl, Vol. 4/4, pp 94-119). 

Since the work of Dahl on synthesis and structural characterization of [Cp4Mo4S4] (89), many cubane-type complexes with Mo4S4 cores have been reported and reviewed (10,14,15). They have the general formula [Mo4S4L12] (Fig. 18), where L denotes ligating atoms with either neutral... 

Scheme 2.2, D) and tetrameric eight-membered (LiN)4 ring and cubane (Scheme 2.2, E and F) structures are also known. Comprehensive reviews of dimeric and other lithium amido stnictures were published in the 1990s. As a result only selected examples from the preceding literature are covered. ... 

This review surveys the structural aspect of cubane-type compounds with Mo404.nS (n = 0, 3, or 4) cores and incomplete cubane-type compounds with Mo304. S and W304. S (n = 0-4) cores (Fig. 1). Compounds with mixed-metal cubane-type cores M03MS4 (M = metals) are also included. Notes on synthetic procedures are given in Section... 

Cubane clusters in the specialized subset [S4Fe4(SR)4]z are 10s years old in Nature, as the mediators of biological electron transfer, but are only 13 years old (born 1972) in the laboratory. Comprehensive and detailed knowledge of all facets of the chemistry of these complexes is now available, mainly due to Holm and his collaborators. Complete expositions are contained in recent reviews.12-16... 

The recent upsurge of interest in iron-sulfur-nitrosyl complexes has been stimulated in part by the reported isolation of [Fe2(SMe)2(NO)4] from natural sources (12), by the obvious resemblances between these complexes and the naturally occurring [2Fe-2S] and [4Fe-4S] clusters of iron sulfur proteins (23, 14), and by the connections between tetrairon-sulfur-nitrosyls and cubane-type clusters (15). Most of the work in this area has been published in the past 5 years or so, and no review has previously been made. However, a number of excellent reviews of the wider aspects of metal-nitrosyl chemistry have appeared (16 19). 

The first such reaction published in 1908 by Ciamician and Silber was the light induced carvone —> carvonecamphor isomerization, corresponding to type b [1]. Between 1930 and 1960 some examples of photodimerizations (type c) of steroidal cyclohexenones and 3-alkylcyclohexenones were reported [2-5]. In 1964, Eaton and Cole accomplished the synthesis of cubane, wherein the key step is again a type b) photocycloisomerization [6]. The first examples of type a) reactions were the cyclopent-2-enone + cyclopentene photocycloaddition (Eaton, 1962) and then the photoaddition of cyclohex-2-enone to a variety of alkenes (Corey, 1964) [7,8]. Very soon thereafter the first reviews on photocycloaddition of a,(3-unsaturated ketones to alkenes appeared [9,10]. Finally, one early example of a type d) isomerization was communicated in 1981 [11]. This chapter will focus mainly on intermolecular enone + alkene cycloadditions, i.e., type a), reactions and also comprise some recent developments in the intramolecular, i.e., type b) cycloisomerizations. 

A variety of B N ring systems have been prepared that do not easily fall into the general classes described previously. Some of these rings include other heteroatoms, some include carbon, and they range in size from three-membered to eight-membered. Some examples of cubane cages are also known. Examples of these systems have appeared in previous reviews. Some representative new contributions in this area are summarized in this section. 

Thiolato and S-based ligands have often been also used to bridge two metals with the formation of heterobimetallic complexes. The synthesis and reactivity of cubane-type sulfido clusters containing titanium-late transition metals have been reviewed.1776,1777... 

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