Thorsten Gust

Di(phosphavinyl) ethers (2,4-diphospha-3-oxapentadienes)

Hydrolytic cleavage of the P-chlorophosphaalkenes (RMe2Si)2C=PCl (R = Me: 1a; R = iPr: 1b) in the presence of triethylamine leads to di(phosphavinyl) ethers (2,4-diphospha-3-oxapentadienes) [(RMe2Si)2C=P]2O (2a, 2b) as main products, accompanied by alkylphosphinic acids (RMe2Si)2(H)CP(H)(O)OH (3a, 3b). The hydrolysis of (PhMe2Si)2C=PCl (1c) proceeds less selectively. Reactions with metal oxides under aprotic conditions provide 2a [impure, from 1a with (nBu3Sn)2O] and 2b [from iodophosphaalkene (iPrMe2Si)2C=PI with Ag2O] as oils. 1H, 13C, 29Si and 31P NMR spectra, however, allow unambiguous characterisation of 2a and 2b. Formation mechanisms, structure, and C=P-O π stabilisation of the oxabisphosphaalkene [(H3Si)2C=P]2O (2ʹ) were studied with DFT methods. The double [2+4] cycloaddition reaction of 2a with two equivalents of cyclopentadiene leads to the phosphinous anhydride 7 as a mixture of diastereomers whereas the addition of two equivalents of tetrachloro-o-benzoquinone proceeds in a diastereoselective fashion. An X-ray crystal structure determination of the resulting oxo-bridged bis(2-phospha-2,5-dioxa-3,4-benzophospholene) derivative 8 revealed the presence of a racemic mixture of (R,R)- and (S,S)-configurated molecules. The solid state structure of a by-product, bisylphosphonic tetrachlorocatechol monoester (Me3Si)2CH-P(=O)(OH)-o-OC6Cl4OH 9, was also determined crystallographically. Graphical Abstract Di(phosphavinyl) Ethers (2,4-Diphospha-3-oxapentadienes)

Diastereoselective Reactions of Sulfur- and Selenium-Bridged Bisphosphaalkenes with Tetrachloro-o-benzoquinone

2,4-Diphospha-3-thia- and 3-selenapentadienes [(Me 3 Si) 2 C = P] 2 E ( 1a : E = S; 1b : Se) react as bifunctional phosphaalkenes with two equivalents of cyclopentadiene and of tetrachloro-o-benzoquinone (TOB), furnishing 2a and 2b from double [2+4] cycloaddition reactions of the diene and 3a and 3b from the reactions of TOB with the P = C double bonds. The phosphanorbornane-related chalcogenophosphinous anhydrides 2a and 2b are obtained as pairs of isomers, whereas the reactions with TOB proceed diastereoselectively. X-ray crystallographic data confirm that bis-dioxaphospholene-related 3b consists of a mixture of (RR) and (SS) enantiomers. A third equivalent of TOB can be added oxidatively to one phosphorus atom of 3a and 3b , furnishing the spirocyclic compounds 6a and 6b with P(σ < eqid1 > λ < eqid2 > 5 < eqid3 > 5 ) connectivity. 3a and 6a are configurationally stable at room temperature, whereas the selenium derivatives 3b and 6b undergo slow isomerisation in solution.

Approaching P -Indoxyle, P -Indigo and P -Vinylchalcogenides

A great challenge in the chemistry of π -conjugated organophosphorus compounds and dyestuffs remains the preparation of phosphoindigo, in which the nitrogen atoms of indigo are replaced by phosphorus. Indolerelated benzophosphole (phosphindole) derivatives are well known, but only scattered information is available on their 3-oxo derivatives,1 which would be related to precursors of indigo or thioindigo. On the way to phosphoindigo, we studied a number of reactions to find suitable reagents and conditions for the oxidative coupling of known 1-ethoxy1-oxophosphindoline-3-one (1)1,2 or new phosphindoline-3-one (2) [ phosphoindoxyle] leading to the first 1,1′-diphosphaindigo derivatives.