The hydrophosphorylation of phenylacetylene with di(aryl)phosphane oxides Ar2P(O)H (Pudovik reaction) yields E/Z‐isomer mixtures of phenylethenyl‐di(aryl)phosphane oxides (1). Alkali and alkaline‐earth metal di(aryl)phosphinites have been studied as catalysts for this reaction with increasing activity for the heavier s‐block metals. The Pudovik reaction can only be mediated for di(aryl)phosphane oxides whereas P‐bound alkyl and alcoholate substituents impede the P−H addition across alkynes. The demanding mesityl group favors the single‐hydrophosphorylated products 1‐Ar whereas smaller aryl substituents lead to the double‐hydrophosphorylated products 2‐Ar. Polar solvents are beneficial for an effective addition. Increasing concentration of the reactants and the catalyst accelerates the Pudovik reaction. Whereas Mes2P(O)H does not form the bis‐phosphorylated product 2‐Mes, activation of an ortho‐methyl group and cyclization occurs yielding 2‐benzyl‐1‐mesityl‐5,7‐dimethyl‐2,3‐dihydrophosphindole 1‐oxide (3).

In this investigation we evaluated the scope of the intermolecular hydrophosphorylation (Pudovik reaction) of alkynes R 1 −CC−R 2 (R 1 = H, alkyl, Ph; R 2 = alkyl, Ph, COOMe, SiMe 3 , Si(iPr) 3 ) with bis(2,4,6-trimethylphenyl)phosphane oxide (dimesitylphosphane oxide, Mes 2 P(O)H) in tetrahydrofuran at room temperature or 65 °C, catalyzed with 5 or 10 mol % of potassium dimesitylphosphinite (Mes 2 P−O−K), yielding alkenyldimesitylphosphane oxides (Mes 2 P(O)−C(R 1 ) C(H)R 2 ). This procedure requires substituents with a −I effect at the CC triple bond, whereas alkyl-substituted alkynes are inactive under these reaction conditions. The hydrophosphorylation proceeds regioselectively, but E/Z isomer mixtures are obtained. E/Z isomerization occurs at elevated temperatures with an estimated energy barrier of 59 kJ mol −1 (R 1 = Me; R 2 = Ph). Trimethylsilyl substituents at the alkyne functionality (R 1 = H, nBu; R 2 = SiMe 3 ) destabilize the product, leading to degradation and formation of Mes 2 P−O−SiMe 3 and R 1 −CC−H.Article pubs.acs.org/Organometallics

Dedicated to Prof. Sjoerd Harder on the occasion of his 60 th birthday.Alkaline-earth metalation of dimesitylphosphane oxide Mes 2 P-(O)H (1) in ethereal solvents with dialkylmagnesium and alkylmagnesium bromide as well as the homoleptic bis(trimethylsilyl)amides of calcium, strontium, and barium yields(2-thf) and [(thf) 4 Ae(OPMes 2 ) 2 ] (Ae = Ca (3-thf), Sr (4-thf), and Ba (5-thf)), depending on the applied stoichiometry. Exchange of thf ligands in 3-thf by oligodentate ethers allows isolation of [(thf) 2 (dme)Ca(OPMes 2 ) 2 ] (3-dme), [(thf) 2 (diglyme)Ca(OPMes 2 ) 2 ] (3-diglyme) and [(thf)(triglyme)Ca(OPMes 2 ) 2 ] (3-triglyme). Contrary to this finding, oligodentate amines are unable to substitute ligated thf ligands in 3-thf. In ethereal solutions, the heteroleptic complexes 2-Et, 2-Br and 3-hmds show Schlenktype equilibria, interconverting these compounds into their homoleptic counterparts.

Reduction of 2‐benzyl‐1‐mesityl‐5,7‐dimethyl‐2,3‐dihydrophosphindole 1‐oxide (2‐O), which was prepared by catalytic addition of dimesitylphosphane oxide across phenylacetylene via dimesityl‐phenylethenylphosphane oxide (1), with excess of trichlorosilane in toluene yielded 2‐benzyl‐1‐mesityl‐5,7‐dimethyl‐2,3‐dihydrophosphindole (2). Straightforward oxidation of 2 with sulfur and selenium in toluene at 110 °C allowed the isolation of crystalline colorless 2‐benzyl‐1‐mesityl‐5,7‐dimethyl‐2,3‐dihydrophosphindole 1‐sulfide (2‐S) and 1‐selenide (2‐Se). The hindered rotation of the P‐bound mesityl group around the P–C bond is indicative of significant intramolecular steric strain. Despite this strain, the P–E bond lengths (E = S, Se) lie in expected ranges.