Taming a Functional Group: Creating Air‐Stable, Chiral Primary Phosphanes

Abstract

No rings of fire! Enantiopure primary phosphanes have been developed which are remarkably stable to air oxidation in both solid and solution states (see example). This new class of stable ligand synthon appears to owe its stability to conjugation in their aryl backbones with the extended π ring system. Even one extra ring is good enough.

Synthesis and structure of ferrocenylmethylphosphines, their borane adducts, and some related derivatives

“…The anomalous air-stability of the primary and secondary phosphines 2 and 3 remains unexplained, especially in comparison to tertiary phosphine 4, which is moderately air-sensitive in solution [22]. Although an earlier study reported that 4 did not react with some early transition metal complexes [4d], and octahedral complexes have not yet been obtained, it readily formed square planar Pt(P(CH 2 Fc) 3 ) 2 Cl 2 (14) as a mixture of cis and trans isomers.…”

“…Calc. for C 22 22.4 (d,J = 30,CH 2 ). IR: 2384IR: (broad), 2355IR: (shoulder), 1122IR: , 1081IR: , 1045IR: , 1020.…”

λ5‐Phospha[7]helicenes: Synthesis, Properties, and Columnar Aggregation with One‐Way Chirality

“…The palladium-catalyzed cross-coupling of rac-6 with ethyl phenylphosphinate gave a 46 % yield of the monophosphrous compound rac-7 as a mixture of diastereomers (axial chirality and P-centered chirality). [13] l 3 -Phospha[7]helicene rac-9, which has a phosphole moiety, was obtained by the reduction of rac-7 with LiAlH 4 [13c, 14] and a subsequent palladium-catalyzed intramolecular P-arylation. As the phosphorus center of rac-9 is susceptible to oxidation under ambient conditions, rac-9 was directly oxidized without purification to give racemic l 5 -phospha[7]helicene rac-1, which has a phosphole oxide moiety, in a 34 % overall yield from rac-7.…”

P‐Phenyl‐2,2,6,6‐tetramethylphosphorinan‐4‐ol: An Air‐Stable P,O‐Type Ligand for Palladium‐Mediated Cross‐Coupling Reactions

“…It is not clear, using the Barder–Buchwald model12a why oxidation of 2a cannot readily proceed from the axial lone pair on phosphorus in 2a , we note only that both types of ligand consist of a conformationally restricted sterically hindered phosphane. A marked dichotomy in primary phosphane stability was also recently described by Gilheany and co‐workers 12b. A unifying concept that explains the unusual stability of certain phosphanes is elusive although clearly the introduction of one aryl group (contrasting 2b to 2a ) contributes significantly to the stability of ligand 2a .…”