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.

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Nitrogen-bridged bidentate phosphaalkenes reveal several exceptional properties as a new class of P=C-unsaturated diphosphinoamine (PNP) ligands: N–Si bond cleavage of the first N-silylimino-bridged bis-phosphaalkene (R2C=P)2NSiMe3 (R = iPrMe2Si) with chlorides of AgI, AuI, and RhI leads to complexes of the 5c-6π-heteropentadienide imidobisphosphaalkene anion; double Cl– transfer from PtCl2 and PdCl2 to coordinated phosphaalkene phosphorus atoms of P-diphenylphosphanylamino phosphaalkenes R2C=PN(R')PPh2 (R' = Me3Si or iPrMe2Si; R = tBu, 1-Ada) furnishes unprecedented bis-chelate P-chloroylid complexes M[R2CP(Cl)N(R')PPh2]2 (M = Pd, Pt); CO- and RhI-induced coupling of two P-diphenylphosphanylamino phosphaalkenes under disilylketene elimination provides trigonal–bipyramidal RhIII complexes with novel tetradentate dianionic “PNP–C–PNP” ligands R2C[P(–)N(R')PPh2]2.

Review: 53 refs.