Cage system

Phosphorus forms a number of cage-like molecules based on arrangements (6.928) which have (ideally at least) C3v symmetry and threefold symmetry axes. The first of these (6.928a) and its sulphide, is made according to scheme (6.929). 

New polycyclic polyphosphorus hydrocarbon cage compounds are continually being reported. Phosphaalkenes and phosphaalkynes are used in these syntheses (6.570-6.572) [101-106]. Various isomers have already been characterised as, for example, those of (PC Bu)n (6.933). One form of (PC Bu)6 is isostructural with Ci2H,2 and a possible P,2 form of elemental phosphorus (4.29). 

Triphosphinines (6.933) have attracted special interest because of the reactions in which they can participate. Isomeric forms are shown in (6.933) (on top row). They appear to be mostly yellow oils or solids which have to be stored in the dark under inert gases. Related to these are other interesting compounds [107,108]. 

Some quite complex cage-like structures have been synthesized, for example. 

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CO)3-9-7 -Cp-2,8-Me2-l,4,9-Fe2CoC2B4H4, a nine-vertex polyhedral cage system . ... 

Scheme 4.31. Synthesis of carbo- and hetero-cage systems.

Dicyanopyridazine 4-145 has been used for the synthesis of carbo- and het-ero-cage systems employing nonconjugated dienes such as cyclooctadiene 4-146, or 4-148 or 4-150 to give 4-147, 4-149 and 4-151, respectively (Scheme 4.31) [50]. In a similar way, dihydrofurans, dihydropyrans, pyrrolines, and enol ethers have also been used [51],... 

In this section, the synthesis and some chemistry of cage systems involving negatively charged boron atoms carrying, three phosphine groups coordinated to Co, Fe, Sn, Tl, Ru, Ir in different valence states are considered. 

The breeding material available is genetically adapted to cage systems. 

Fig. 16 (a) R (D + RX) and P (D,+ + R + X ) zero-order potential energy surfaces. Rc and Pc are the caged systems, (b) Projection of the steepest descent paths on the X-Y plane J, transition state of the photoinduced reaction j, transition state of the ground state reaction W, point where the photoinduced reaction path crosses the intersection between the R and P zero-order surfaces R ., caged reactant system, (c) Oscillatory descent from W to J on the upper first-order potential energy surface obtained from the R and P zero-order surfaces. 

There are a few communications concerning cycloadditions of nitrile oxides to unsaturated oxa and aza cage systems. Benzo- and mesitonitrile oxides RCNO give, with five substituted 7-oxanorbomenes 106, mixtures of the corresponding exo-adducts 107 and 108 in nearly quantitative yields. No traces of compounds resulting from the endo-face attack was detected (274). Substituents at positions 5 and 6 of 106 render the process highly regioselective. 

Several books and general reviews are already available on phosphorus ring and cage systems (16). This one will focus more specifically on the coordination chemistry of molecular tetraphos-phorus-based doso-compounds, including itself and closely related analogs, and will also include structural data on both free and coordinated species. The questions of the transmission of electronic and structural effects through the molecular frame, and of the extent oftt-bonding, will be critically considered. 

Polynitro derivatives of pentacyclo[5.4.0.0 .0 °.0 ]undecane have attracted interest as potential high-energy explosives. Molecular strain in this caged system could arise from both the constrained norbomyl moiety and the cyclobutane ring. Additional strain would be expected from nonbonding interactions if the S-endo and 1 l-endo positions were substituted with gm-dinitro groups. 

Chemical structures of several chelators. Ferroxamine (ferrioxamine) without the chelated iron is deferoxamine. It is represented here to show the functional groups the iron is actually held in a caged system. The structures of the in vivo metal-chelator complexes for dimercaprol, succimer, penicillamine, and unithiol (see text) are not known and may involve the formation of mixed disulfides with amino acids. 

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