Date of Award
Department or Program
David S. Glueck
Chapter 1: Synthesis, Structure, Dynamics, and Enantioface-Selective η3-Benzyl Coordination in the Chiral Rhodium Complexes Rh(diphos*)(η3-CH2Ph) Abstract: The rhodium benzyl complexes Rh(diphos*)(η3-CH2Ph) (1-14, diphos* = chiral bis(phosphine)) were prepared either by treatment of Rh(COD)(η3-CH2Ph) (15, COD = 1,5-cyclooctadiene) with diphos*, or from the reaction of [Rh(diphos*)(Cl)]2 (16- 20) with PhCH2MgCl. For C2-symmetric diphos*, observation of one set of NMR signals for complexes 1-12 suggested that the two diastereomers in which different 3-benzyl enantiofaces were coordinated to rhodium interconverted rapidly on the NMR time scale via suprafacial shifts; observation of five inequivalent aryl 1H NMR signals showed that antarafacial shifts were slow on the NMR time scale. With C1-symmetric ligands, complexes 13-14 gave rise to two sets of NMR signals, consistent with fast suprafacial shifts but slow antarafacial shifts on the NMR time scale.
Chapter 2: Rhodium-Catalyzed Asymmetric Dehydrocoupling: Enantioselective Synthesis of a P-Stereogenic Diphospholane with Mistake-Correcting Diastereoselectivity Abstract: Catalytic asymmetric dehydrocoupling of secondary phosphines is a potentially valuable route to enantiomerically enriched P-stereogenic diphosphines for use as ligands or building blocks for chiral bis(phosphines). Rh(diphos*) catalyst precursors converted a rac/meso mixture of PhHP(CH2)3PHPh (1) to the C2-symmetric P-stereogenic anti-diphospholane PhP(CH2)3PPh (2) in up to a 58:42 enantiomeric ratio (er) with complete diastereoselectivity via catalyst-mediated isomerization of the intermediate syndiphospholane 3 to 2 (mistake correction by conversion of the diastereomer meso-3 to chiral C2-2). NMR studies of catalytic reactions identified the resting state Rh((R,R)-i-Pr- DuPhos)(PhHP(CH2)3PPh) (4) and suggested a proposed mechanism for stereocontrolled P-P bond formation via oxidative addition and reductive elimination steps.
Chapter 3: Rhodium-Catalyzed Asymmetric Dehydrocoupling-Cyclophosphination of Supermesitylphosphines Abstract: Catalytic asymmetric dehydrocoupling-cyclophosphination is a potentially valuable route to bulky enantiomerically enriched P-stereogenic phospholanes. Rh(diphos*) and Co(diphos*) catalyst precursors converted PH2Mes* (1, Mes* = 2,4,6- (t-Bu)3C6H2) and PHPh(Mes*) to the secondary and tertiary phosphines PR(2- CH2CMe2C6H3-4,6-(t-Bu)2) (R = H (3) or Ph (Ph-3)). The resting states Rh((R,R)-i-Pr- DuPhos)(PR(2-CH2CMe2C6H3-4,6-(t-Bu)2)(H) (R = H (3) or Ph (Ph-3)) were formed diastereoselectively (dr = 2:1 and 11:1). The catalytic reaction was proposed to occur via iv C-H activation in Rh(diphos*)(PRMes*), followed by P-C reductive elimination, ligand substitution, P-H oxidative addition, and reductive elimination of H2.
Chachula, Sarah T., "Rhodium-Catalyzed Asymmetric Synthesis of P-P and P-C Bonds" (2023). Dartmouth College Ph.D Dissertations. 170.