The condensation of a six membered cyclic phosphonyl-phosphanyl anion with an~ 8unsaturated aldehyde leads to the direct generation of a 1,3-butadienyl phosphane according to a Wittig-Horner type elimination.
The 1,3-butadienyl phosphanes Z2P(CH=CH)2R (Z=R,RO,NR2) are compounds of particular interest in the field of coordination chemistry Decause they [epresent the fusion between two very popular ligands: a tricoordinated phosphorus and a conjugated diene I. However the potential they afford for building complexes has been largely unexplored due to the difficulties to prepare such unsaturated phosphorus structures 2. As far as we know the first synthetic approach reported in 19803 consists in the reduction/complexation of a parent phosphine sulfide and is a five-step process. More recently it has been proposed a different strategy which is a transfer reaction from zirconium dienyls to phosphorus 4 but though the process is shorter (two-step) it requires a quite sophisticated starting material (enyne). In this comunication, we present a new and more facile access to the title compounds which is based on a Wittig-Horner 6ype reaction. We previously described a performing one-pot preparation of e, 8 -unsaturated tetracoordinated phosphorus species Z2P(O)CH=CHR where the direct generation of a methylene diphosphonic anion was involved 5. Analogously it was attractive to generate unsymmetrical methylene anions i.e. bearing two phosphorus atoms in different coordination number (pIII/pIV)(~ Scheme I) andreact themwith ~ ,8-unsaturated aldehydes in order to built butadienyl phosphanes systems. Unfortunately though the phosphonyl-phosphanyl entity ~ is easily obtained by condensation of diethyl methylphosphonate ! on a chlorophosphane 2 in presence of 2 eq. of LDA, the further addition of a carbonyl reagent RCH=CHCHO doesn't induce the Wittig-Hornet elimination. The reaction stopped at the formation of the aldol adduct 4 which exhibits a great resistance to decomposition into conjugated olefin (after 3h at + 60Β°3 4 is recovered unchanged). 3 and 4 have been characterized in situ by 31p NMR [6 (CDCI3) fpm :-