Alkaline‐earth metal dimesitylphosphinites and their ether adducts – A structural study in solution and in the crystalline state

Abstract 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 [(L)MgR(μ‐OPMes 2 )] 2 (L/R=thf/Et ( 2‐Et ), Et 2 O/Br ( 2‐Br )), [(thf) 3 Ca(hmds)(OPMes 2 )] ( 3‐hmds ), [(thf) 3 Mg(OPMes 2 ) 2 ] ( 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 Schlenk‐type equilibria, interconverting these compounds into their homoleptic counterparts.imag

s‑Block Metal Base-Catalyzed Synthesis of Sterically Encumbered Derivatives of Ethane-1,2-diyl-bis(diphenylphosphane oxide) (dppeO₂)

The synthesis of ethane-1,2-diyl-bis(diarylphosphane oxides) and -phosphanes, containing bulky ortho-substituted P-bound aryl groups, poses severe challenges, such as drastic reaction conditions and low yields. A potassium base-mediated hydrophosphorylation of phenylacetylene with dimesitylphosphane oxide (Mes2P(O)H) yields an E/Z mixture of alkenyl-dimesitylphosphane oxide. The bulky mesityl group hampers the addition of a second diarylphosphane oxide. Contrary to this expected addition of a phosphane oxide across an alkyne yielding an alkenylphosphane oxide, the potassium base-mediated reaction of trimethylsilyl acetylene with Mes2P(O)H yields ethane-1,2-diyl-bis(dimesitylphosphane oxide) (2b); surprisingly, the TMS group is substituted by a hydrogen atom via a rather complex reaction mechanism. Excess TMS-CCH (5 equiv), ethereal solvents, soft alkali metal catalysts, and large catalyst loadings of 30 mol % are highly beneficial. Furthermore, at least one ortho-position must be alkylated, whereas very bulky aryl groups pose no obstacle. Di(n-alkyl)phosphane oxides and diphenylphosphane oxide do not show the described conversion but react completely different. Alternatively, ethane-1,2-diyl-bis(diarylphosphane oxides) are accessible via a metathetical approach of calcium acetylide CaC2 with diarylphosphane oxide in a superbasic solvent. Reduction of these phosphane oxides (2) to phosphanes (3) offers a library of bulky bidentate ligands for coordination chemistry at hard (e.g., Y3+) and soft metal ions (e.g., Pd2+)

s‑Block Metal Base-Catalyzed Synthesis of Sterically Encumbered Derivatives of Ethane-1,2-diyl-bis(diphenylphosphane oxide) (dppeO₂)

The synthesis of ethane-1,2-diyl-bis(diarylphosphane oxides) and -phosphanes, containing bulky ortho-substituted P-bound aryl groups, poses severe challenges, such as drastic reaction conditions and low yields. A potassium base-mediated hydrophosphorylation of phenylacetylene with dimesitylphosphane oxide (Mes2P(O)H) yields an E/Z mixture of alkenyl-dimesitylphosphane oxide. The bulky mesityl group hampers the addition of a second diarylphosphane oxide. Contrary to this expected addition of a phosphane oxide across an alkyne yielding an alkenylphosphane oxide, the potassium base-mediated reaction of trimethylsilyl acetylene with Mes2P(O)H yields ethane-1,2-diyl-bis(dimesitylphosphane oxide) (2b); surprisingly, the TMS group is substituted by a hydrogen atom via a rather complex reaction mechanism. Excess TMS-CCH (5 equiv), ethereal solvents, soft alkali metal catalysts, and large catalyst loadings of 30 mol % are highly beneficial. Furthermore, at least one ortho-position must be alkylated, whereas very bulky aryl groups pose no obstacle. Di(n-alkyl)phosphane oxides and diphenylphosphane oxide do not show the described conversion but react completely different. Alternatively, ethane-1,2-diyl-bis(diarylphosphane oxides) are accessible via a metathetical approach of calcium acetylide CaC2 with diarylphosphane oxide in a superbasic solvent. Reduction of these phosphane oxides (2) to phosphanes (3) offers a library of bulky bidentate ligands for coordination chemistry at hard (e.g., Y3+) and soft metal ions (e.g., Pd2+)

Potassium Dimesitylphosphinite Catalyzed Intermolecular Hydrophosphorylation of Alkynes

In this investigation we evaluated the scope of the intermolecular hydrophosphorylation (Pudovik reaction) of alkynes R¹–CC–R² (R¹ = H, alkyl, Ph; R² = alkyl, Ph, COOMe, SiMe₃, Si­(<i>i</i>Pr)₃) with bis­(2,4,6-trimethylphenyl)­phosphane oxide (dimesitylphosphane oxide, Mes₂P­(O)­H) in tetrahydrofuran at room temperature or 65 °C, catalyzed with 5 or 10 mol % of potassium dimesitylphosphinite (Mes₂P–O–K), yielding alkenyldimesitylphosphane oxides (Mes₂P­(O)–C­(R¹)C­(H)­R²). 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 <i>E</i>/<i>Z</i> isomer mixtures are obtained. <i>E</i>/<i>Z</i> isomerization occurs at elevated temperatures with an estimated energy barrier of 59 kJ mol^–1 (R¹ = Me; R² = Ph). Trimethylsilyl substituents at the alkyne functionality (R¹ = H, <i>n</i>Bu; R² = SiMe₃) destabilize the product, leading to degradation and formation of Mes₂P–O–SiMe₃ and R¹–CC–H