Cubanes 1-functionalized

It is well-known, that in most carboxylic acid crystal structures, the conformation of the carboxyl group is synplanar and that the most frequent and dominant interlink is the syn-syn centrosymmetric dimer synthon, II. This synthon is found in nearly a third of all crystalline carboxylic acids, with or without any other functionality being present in the molecule, signifying robustness.1211 Against such a background, the crystal structures of 1,4-cubane-... 

Ferredoxins from thermoacidophilic archaea such as Thermoplasma acidophi-lum and Sulfolobus sp. contain, in addition to one 3Fe-4S (cluster I) and one 4Fe-4S (cluster II) cluster, one zinc centre tetrahedrally co-ordinated to three histidines in the N-terminal region and to one aspartate in the ferredoxin core domain. These Fds contain an unusually long N-terminal extension region of unknown function, which was not detected in other bacterial type Fds. Upon oxidative degradation of Fd from Sulfolobus sp. strain 7 (Fopt = 80 cluster II is selectively converted into a cubane 3Fe-4S,... 

Why did nature use an Fe-S cluster to catalyze this reaction, when an enzyme such as fumarase can catalyze the same type of chemistry in the absence of any metals or other cofactors One speculation would be that since aconitase must catalyze both hydrations and dehydrations, and bind substrate in two orientations, Fe in the comer of a cubane cluster may provide the proper coordination geometry and electronics to do all of these reactions. Another possibility is that the cluster interconversion is utilized in vivo to regulate enzyme activity, and thus, help control cellular levels of citrate. A third, but less likely, explanation is that during evolution an ancestral Fe-S protein, whose primary function was electron transfer, gained the ability to catalyze the aconitase reaction through random mutation. 

Eaton and co-workers also reported the synthesis of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane (39) ° The required tri- and tetra-substituted cubane precursors were initially prepared via stepwise substitution of the cubane core using amide functionality to permit ort/jo-lithiation of adjacent positions. The synthesis of precursors like cubane-1,3,5,7-tetracarboxylic acid was long and inefficient by this method and required the synthesis of toxic organomercury intermediates. Bashir-Hashemi reported an ingenious route to cubane-1,3,5,7-tetracarboxylic acid chloride (35) involving photochemical chlorocarbonylation of cubane carboxylic acid chloride (34) with a mercury lamp and excess oxalyl chloride. Under optimum conditions this reaction is reported to give a 70 8 22 isomeric mixture of 35 36 37... 

Efforts towards the synthesis of strained polycyclic hydrocarbons have been described. These compounds are of interest as fuels and fuel additives for advancedpropulsion. Chemistry has been devised for the attachment of azido functionality to the strained hydrocarbon nucleus. Highly unsaturated substituted cubanes have been synthesized. Ring-opening metathesis polymerization of basketene and 2,3-diazabicyclo[2.2.1]hept-2-ene has been studied. 

Adsorption of a condensed 1-hydroxy-adamantane layer at the Hg elec-trode/(Na2S04 or NaF) solution interface has been studied as a function of temperature by Stenina et al. [174]. Later, Stenina etal. [175] have determined adsorption parameters and their temperature dependence for a two-dimensional condensation of adamantanol-1 at a mercury electrode in Na2S04 solutions. They have also studied coadsorption of halide (F , Cl , Br ) anions and 1-adamantanol molecules on Hg electrode [176]. More recently, Stenina etal. [177] have described a new type of an adsorption layer comprising organic molecules of a cage structure condensed at the electrode/solution interface. This phenomenon was discovered for adsorption of cubane derivatives at mercury electrode. 

Ferredoxins with 4Fe4S clusters are small, low potential electron carriers that function in bacterial electron transfer. Like the binuclear clusters, each tetranu-clear cluster can reversibly accept a single electron. The tetranuclear prosthetic group is a cubane with iron and acid-labile inorganic sulfide groups at alternate vertices the four iron atoms and the four sulfides form interpenetrating tetrahedra of slightly different sizes. 

A number of nickel(II) alkoxyhalides of the types Ni(OMe)X, Ni3(OMe)5X, Ni3(OMe)4X2 (X = halides) and Ni(OMe)Cl MeOH were prepared by reacting either NaOMe or LiOMe with anhydrous nickel halides in methanol.1495 The structures of these complexes which exhibit ferromagnetic behaviour are thought to involve cubane-type clusters. Other complexes with miscellaneous ligands containing the OH function are collected in Table 76. 

Two homometallic octanuclear clusters, [FegS CNBu1) ] [37] and [Fe8S8 (PCy 3)61 [37,38], have been isolated (see earlier discussion), as has the related heterometallic cluster [Mo2Fe6S8(PEt3)6(tccat)2] [70], The latter cluster is the first example of an Fe—S edge-linked, reduced MoFe3S4 double-cubane with Mo atoms at the periphery of each cuboid subunit. The reduced double-cubane core is stabilized by triethylphosphane coordinated to the Fe atoms. The utility of such materials as precursors to potential cofactor models, both structural and functional, has yet to be explored. 

Non-activated methyl groups are never attacked in these reactions toluene can be functionalized but isolation of the resulting benzyl halides from these PTC mixtures is difficult. Most remarkable is that strained hydrocarbons such as cubane (5) or 2,4-didehydroadamantane (6) can also be halogenated with conservation of the cage [27], in marked contrast with the halogenation reactions of these substrates with halogen radicals [40]. Dihalogenations with either the same or a differ-... 

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