First Resolution of a Free Secondary Phosphine Chiral at Phosphorus and Stereospecific Formation and Structural Characterization of a Homochiral Secondary Phosphine−Borane Complex

Abstract

The R(P) diastereomer of (-)-menthylmesitylphosphine, (R(P))-1, has been isolated with high configurational purity at phosphorus by fractional crystallization of an (R(P))-1/(S(P))-1 = 43/57 mixture from acetonitrile containing a trace of sodium acetylacetonate as a proton scavenger or by deboranation of the corresponding borane complex (S(P))-2 with diethylamine, thereby effecting the first resolution of a secondary phosphine chiral at phosphorus. The crystal and molecular structure of (S(P))-2 has been determined. The ready isolation of (S(P))-2 of 97% diastereomeric purity in 66% yield from an equilibrium (R(P))-2/(S(P))-2 = 28/72 mixture in n-hexane by second-order asymmetric transformation and its quantitative and stereospecific conversion under mild conditions into (R(P))-1 of similar purity augurs well for the future of the resolved secondary phosphines in stereoselective syntheses.

Configurationally homogeneous diastereomers of a linear hexa(tertiary phosphine): Enantioselective self-assembly of a double-stranded parallel helicate of the type (P)-[Cu3(hexaphos)2](PF6)3

“…At the end of each reaction, the morpholine was removed by distillation under reduced pressure, and the residue was stirred in aqueous methanol to extract the morpholine-borane adduct; the free phosphine was filtered off, dried in vacuo, and recrystallized from dichloromethane-methanol. The enantiomerically pure hexa(tertiary phos- ¶ Secondary phosphines, chiral at phosphorus, can be resolved under strictly acid-free conditions (21). The structure of the cation is that of a parallel double helix with each strand of the hexa(tertiary phosphine) completing Ϸ2.5 turns of a P helix around three tetrahedral copper ions of P configuration (Fig.…”

Nucleophilic addition and substitution at coordinatively saturated boron by facile 1,2-hydrogen shuttling onto a carbene donor

“…1A). 1,2 Similarly, the adduct formation of hydroboranes with amines yields amine–boranes (Fig. 1B), a well-known family of potential hydrogen storage materials.…”

Monoterpenoids

“…372 The diastereoisomerically pure chiral phosphine-borane complex 190 has been obtained via fractional crystallisation of a P-(R,S) mixture, and treatment of 190 with Et 2 NH afforded 191, the first secondary phosphine that is homochiral at phosphorus to be successfully isolated. 373 The diastereoisomeric telluronium ylides 192 have been synthesised as a mixture and, in an attempt to separate them, five-fold recrystallisation led to a product of constant [ ] D . However, the optical purity was low when judged by 1 H NMR.…”