Twelve chiral bis-3,4-diazaphospholane ligands and six alkene substrates (styrene, vinyl acetate, allyloxy-tert-butyldimethylsilane, (E)-1-phenyl-1,3-butadiene, 2,3-dihydrofuran, and 2,5-dihydrofuran) probe the influence of steric bulk on the activity and selectivity of asymmetric hydroformylation (AHF) catalysts. Reaction of an enantiopure bisdiazaphospholane tetraacyl fluoride with primary or secondary amines yields a small library of tetracarboxamides. For all six substrates, manipulation of reaction conditions and bisdiazaphospholane ligands enables state-of-the-art performance (90% or higher ee, good regioselectivity, and high turnover rates). For the nondihydrofuran substrates, the previously reported ligand, (S,S)-2, is generally most effective. However, optimal regio- and enantioselective hydroformylation of 2,3-dihydrofuran (up to 3.8:1 α-isomer/β-isomer ratio and 90% ee for the α-isomer) and 2,5-dihydrofuran (up to <1:30 α-isomer/β-isomer ratio and 95% ee for the β-isomer) arises from bisdiazaphospholanes containing tertiary carboxamides. Hydroformylation of either 2,3- or 2,5-dihydrofuran yields some of the β-formyl product. However, the absolute sense of stereochemistry is inverted. A stereoelectronic map rationalizes the opposing enantiopreferences.

We report the first case of a metal complex that degrades a neurotoxin mimic under extremely mild conditions (pH 6.8, room temperature). The metallocene bis(η5-cyclopentadienyl)molybdenum(IV) dichloride (Cp2MoCl2; Cp = η5-C5H5) efficiently hydrolyzes the compound O,S-diethyl phenylphosphonothioate (DEPP), whose core functional group mimics the neurotoxin VX. Moreover, this is one of the few examples where phosphonothioate degradation yields exclusively the desired P−S bond scission under mild aqueous conditions (pH 7.2, 30 °C). Activation parameters for DEPP hydrolysis by Cp2MoCl2 in aqueous THF/acetone indicate (E a = 86 kJ/mol, ΔH ⧧= 83 kJ/mol, and ΔS ⧧ = −10 J/(mol K)) an intramolecular hydrolytic process that goes through an ordered transition state. Alteration of the cyclopentadienyl ligand showed that ansa-Cp2MoCl2 with enhanced Mo(IV) electrophilicity significantly decreased DEPP hydrolysis, while (CpMe)2MoCl2 with increased Mo(IV) electron density had the opposite effect. These structure–activity relationships as well as the activation parameters indicate DEPP hydrolysis is achieved by nucleophilic attack of a Cp2Mo-bound hydroxide on the phosphonothioate.

Condensation reactions of enantiopure bis-3,4-diazaphospholanes (BDPs) that are functionalized with carboxylic acids enable covalent attachment to bead and silica supports. Exposure of tethered BDPs to the hydroformylation catalyst precursor, Rh(acac)(CO)2, yields catalysts for immobilized asymmetric hydroformylation (iAHF) of prochiral alkenes. Compared with homogeneous catalysts, catalysts immobilized on Tentagel resins exhibit similarly high regioselectivity and enantioselectivity. When corrected for apparent catalyst loading, the activity of the immobilized catalysts approaches that of the homogeneous analogues. Excellent recyclability with trace levels of rhodium leaching are observed in batch and flow reactor conditions. Silica-bound catalysts exhibit poorer enantioselectivities.

No abstract