Novel Organophosphorus Cage Compound Produced by an Unexpected Oxidative Coupling of 1 , 2 , 4-Triphosphole : Crystal and Molecular Structures of Two Isomers of Formula

Li(P3C2But2) reage com BrCH(SiMe3)2, via adicao oxidativa, formando um novo composto organofosforado de formula molecular P6C4But4 CHSiMe3 (1). O composto 1 foi caracterizado espectroscopicamente e sua estrutura molecular determinada atraves de difracao de raios X de monocristais. Juntamente com 1, foi caracterizado outro composto (2) com a mesma formula molecular, mas apresentando uma estrutura completamente saturada.


Introduction
The chemistry of organophosphorus compounds is in constant development, 1 and it was the synthesis of P≡CBu t in 1981, 2 the first stable phosphaalkyne at room temperature, that marked the beginning of this fascinating field of chemistry.This terbutylphosphaalkyne can undergo cyclo oligomerisation reactions to produce rings and cages.There are reports in the literature of compounds containing from 2 to 6 P≡CBu t units with structures similar to those of the hydrocarbon analogues. 3The anionic rings (P 3 C 2 Bu t 2 ) - ( 3) and (P 2 C 3 Bu t 3 ) -( 4) have also been used as starting materials for the syntheses of several cages compounds containing phosphorus, e.g.P 6 C 6 Bu t 6 , P 4 C 6 Bu t 6 H 2 , usually by oxidative coupling reactions using metal complexes 3 and protonating reagents. 4sing phosphaalkyne, P≡CBu t , and an iron complex, [Fe(η 6 -C 6 H 6 )(η 4 -C 10 H 10 )], Zenneck and co-workers 5   (6), whose structure is similar to that of compound 5 but with a GeI 2 fragment at the bridging position.

Results and Discussion
We report herein another oxidative coupling reaction involving the anionic ring 3 to give a new unsaturated structure of formula P 6 C 4 Bu t 4 CHSiMe 3 (1).This new cage compound has an open structure with two P=C double bonds and a CHSiMe 3 group bridging two phosphorus atoms.Another isomer of this species, compound 2, was isolated from the same reaction mixture.This compound has a completely saturated structure, similar to that observed for compounds 5 and 6, but with a CHSiMe 3 fragment at the bridging position, instead of CHBu t and GeI 2 , respectively.
Compounds 1 and 2 were synthesised from the reaction of equimolar amounts of 3 with a bulky group 7 BrCH(SiMe 3 ) 2 , in DME. 8 The mechanism of formation of both isomers is not clear, but one can speculate that it could take place via the well known 1,2,4-triphosphole (7) 9 which is also identified in the reaction mixture and probably dimerises to give 1 and 2 with loss of CH(SiMe 3 ) 3 , which was not isolated.Compound 2 was also prepared in low yield (6.4%) by Nixon and co-workers 10 using a cobalt complex to promote the coupling.
Compounds 1 and 2, both air and moisture stable, were characterised by mass spectrometry, 1 H, 13 C and 31 P NMR spectroscopy and had their structures determined by single crystal X-ray diffraction studies.
The mass spectrum of 1 exhibits a molecular ion peak at m/z 548, and the 31 P{ 1 H} NMR spectrum shows six resonances, two typical of sp 2 hybridised phosphorus with their chemical shifts in the high frequency region (δ 346.7 and 294.7) and only small couplings indicating that no direct P-P bonds are present. 11The remaining resonances are all typical of sp 3 phosphorus (δ 74.6, 45.6, 30.0 and -18.1).The resonance at δ 75.0 shows two large coupling constants ( 1 J P(1)P(2) 268.2 and 1 J P(1)P(5) 317. 5 Hz) giving evidence that this phosphorus atom is bonded to other two in a P-P-P network.

Supplementary Material
Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 173911 and 173912.Copies of the data can be obtained, free of charge, on apllication to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:+44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).