A reinvestigation of mono- and bis-ethynyl phosphonium salts: structural and computational studies and new reactivity

A series of mono- and bis-ethynyl phosphonium salts have been prepared via reaction of bromoacetylenes, Ph-C[equivalent to]C-Br or Br-C[equivalent to]C-[C.sup.6][H.sup.4]-C[equivalent to]C-Br, with various phosphines. Some of the derivatives reported are previously known, ([Ph-C[equivalent to]C-P[Ph.sub.3]]Br, [Ph-C[equivalent to]C-P[Me.sub.3]]Br, [Ph-C[equivalent to]C-P[Bu.sub.3]]Br, and [[Ph.sub.3]P-C[equivalent to]C-[C.sub.6][H.sub.4]-C[equivalent to]C-P[Ph.sub.3]][[Br.sub.2]]), however typically these are missing complete spectroscopic characterization and many have been prepared using much more complicated methods. The derivative [Ph-C[equivalent to]C-PP[Ph.sub.3]]Br is capable of inhibiting the growth of tumour cells and has been shown crystallographically to have a significant interaction with the heat shock proteins (HSP70 or DnaK). Thus, solid state structures for all seven phosphonium salts prepared have been reported as they may be of interest to others in this field. Sterically encumbered phosphines such as [Mes.sub.3]P did not react with Ph-C[equivalent to]C-Br; however, [(2,4,6-MeO-[C.sub.6][H.sub.2]).sub.3]P was found to slowly react at moderate temperature to give the expected alkynyl phosphonium salt. However, at higher temperatures, the alkynyl phosphonium undergoes an intramolecular cyclization to form a phosphonium analogue of a 1,4-oxazine. Finally, electronic structure calculations reveal the positive charge on the acetylenic [beta]-carbon, a result of a significant contribution of other canonical structures. The flexibility of the P-C[equivalent to]C bond has been investigated showing a low-energy barrier ( Key words: main group chemistry, phosphorus, phosphonium, X-ray crystallography. Nous avons prepare une serie de sels de mono-ethynylphosphonium et de bis-ethynylphosphonium en faisant reagir les bromoacetylenes Ph-C[equivalent to]C-Br ou Br-C[equivalent to]C-[C.sub.6][H.sub.4]-C[equivalent to]C-Br avec diverses phosphines. Certains des derives que nous presentons sont deja connus : ([Ph-C[equivalent to]C-P[Ph.sub.3]]Br, [Ph-C[equivalent to]C-P[Me.sub.3]]Br, [Ph-C[equivalent to]C-P[Bu.sub.3]]Br et [[Ph.sub.3]P-C[equivalent to]C-[C.sub.6][H.sub.4]-C[equivalent to]C-P[Ph.sub.3]][[Br.sub.2]]). Cependant, la plupart de ces derniers n'avaient pas fait l'objet d'une caracterisation spectroscopique complete et bon nombre d'entre eux avaient ete synthetises par des methodes beaucoup plus compliquees. Le derive [Ph-C[equivalent to]C-P[Ph.sub.3]]Br s'est revele capable d'inhiber la croissance des cellules tumorales et a montre par cristallographie une interaction importante avec les proteines de choc thermique (Hsp70 ou DnaK). Par consequent, nous avons publie les structures a l'etat solide des sept sels de phosphonium que nous avons prepares, car ces derniers pourraient presenter un interet pour d'autres chercheurs dans ce domaine. Les phosphines steriquement encombrees comme la [Mes.sub.3]P n'ont pas reagi avec le Ph-C[equivalent to]C-Br, quoique la [(2,4,6-MeO-[C.sub.6][H.sub.2]).sub.3]P a reagi lentement a ttemperaturemodereepourproduireseld'alcynylphosphoniumattendu.Cependant,:adestemperaturespluselevees,l'alcynylphos-phonium subit une cyclisation intramoleculaire pour former un analogue phosphonium de la 1,4-oxazine. Enfin, les calculs de structure electronique revelent que le carbone [beta] acetylenique est charge positivement; ce qui temoigne d'une contribution importante des autres structures canoniques. Nous avons etudie la flexibilite de la liaison P-C[equivalent to]C et nous avons observe que la barriere d'energie de flexion etait faible ( Mots-cles : chimie des elements du groupe principal, phosphore, phosphonium, radiocristallographie.
Introduction Since their initial discovery, (1) ethynylphosphonium salts continue to be popular and extremely valuable building blocks in organic synthesis. These compounds have classically been used as electrophiles, allowing for [...]