Phosphorus-carbon cage compounds

Phosphaalkynes - Starting Point for the Synthesis of Phosphorus-Carbon Cage Compounds ... 

The common link between the two areas of research mentioned above (carbon cages and polycyclic phosphanes) is provided by the phosphorus-carbon cage compounds — the topic of the present chapter. In accord with the philosophy of this book, we will concentrate mainly on the results from our own laboratories and outline their position in the wider perspectives... 

Phosphaalkynes also play a prominent role as dienophiles in Diels-Alder reactions hence the X -phosphinines 13 [23] are formed from cyclic 1,3-dienes such as a-pyrone or cyclopen-tadienones by way of extrusion of CO2 or CO, respectively reactions with anthracene provide an access to the phosphabarrelene series [24]. This type of reaction is also of significance for the construction of phosphorus-carbon cage compounds. The same is true for homo-Diels-Alder reactions which, with 2-phosphabicyclo[2.2.2]octa-2,5-diene as reaction partner, lead to the diphosphatetracyclodecenes 14 [25]. Last but not least, ene reactions with phosphaalkynes as enophiles [25] are also valuable for the construction of polycyclic phosphorus-carbon compounds. The reactions of 9 with 2,3-dimethyl-2-butene (- 15) [26, 27] emphasize this behavior. 

Figure 6-1 History selection of the first phosphorus-carbon cage compounds.

Inter- and intramolecular cycloaddition sequences, in some cases in combination with ene reactions, play a signiHcant part in the construction of phosphorus-carbon cage compounds. Phosphaalkynes are transformed sequentially into phosphaalkenes and Anally to cages made up of phosphonis/carbon single bonds in these processes. 

Scheme 6-9 IVopone as reaction partner for phosphaalkynes in the construction of phosphorus-carbon cage compounds 43 and 45.

The chemistry of the diphosphirenes is an almost completely unexplored field to date only one stable member of this compound class is known [46]. However, tungsten pentacarbonyl complexes of the type 47 at least show a tendency for ring opening (Scheme 6-10). The phosphinidine or carbene intermediates thus formed serve as starting materials for the construction of further novel phosphorus-carbon cage compounds. 

In addition to the above-mentioned Cp2Zr-phosphaalkyne dimer complexes 59, aluminum compounds of the type 71 are also of major significance for the construction of phosphorus-carbon cage compounds, since the metal unit can be removed easily. 

Highly interesting isomerization reactions occur within the phosphaalkyne cyclotetramer system 75/76/54a and 77 (Scheme 6-18), the likes of which have not been previously seen in the chemistry of phosphorus-carbon cage compounds. It is worthy of note that the tetraphos-phacubanes 53 do not take part in such processes. 

Regitz M, Hoffman A et al (1995) Phosphaalkynes—starting point for the synthesis of phosphorus-carbon cage compounds. In Stang PJ, Diederich F (eds) Modem acetylene chemistry, 1st edn. VCH, Weinheim... 

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