Kinetic Resolution of Planar-Chiral (η⁵-Bromocyclopentadienyl)manganese(I) Complexes by Molybdenum-Catalyzed Asymmetric Ring-Closing Metathesis

Abstract

Kinetic resolution of racemic planar-chiral (η5-1-alkenyl-2-bromocyclopentadienyl)­manganese­(I) complexes 1 was realized by the molybdenum-catalyzed asymmetric ring-closing metathesis. While vinyl-Cp derivative 1a was resolved in excellent enantioselectivity with the k rel values of up to 127, the selectivity in the ARCM reaction of allyl-Cp derivative 1b was modest (k rel = 3.0). ARCM product 2a, which was obtained in an enantiomerically pure form by the two successive ARCM reactions or recrystallization of the enantiomerically enriched products, was found to be a versatile synthetic precursor to various planar-chiral cymantrene derivatives.

Application of Polysaccharide-Based Chiral HPLC Columns for Separation of Nonenantiomeric Isomeric Mixtures of Organometallic Compounds

“…In 2017, we reported the synthesis of planar-chiral bridged (η 5 -formylcyclopentadienyl)manganese(I) dicarbonyl complex (R)-1a by the reaction shown in Scheme 1. 8 The bromo-substituent in (R)-4 was lithiated by the lithium−bromine exchange reaction using t BuLi, and a following reaction with DMF provided (R)-1a in variable yield ranging 32−80%. The variable yield in this reaction could be partly ascribed to the formation of undesirable double-bond regioisomer (R)-1b.…”

“…Tetrahydrofuran was distilled from benzophenone-ketyl under nitrogen prior to use. ( R )- or ( S )-[(η 5 -1-Bromo-2-(3-diphenylphosphino-2-methylpropenyl)-cyclopentadienyl- P )]­manganese­(I) dicarbonyl (( R )- or ( S )- 4 ), 1,1′-dibromoferrocene, and 4-bromo-2-methylbutene were prepared according to the reported methods. All the other chemicals were obtained from commercial sources and used as received unless otherwise noted.…”

Enantioselective Preparation of Planar‐Chiral Transition Metal Complexes by Asymmetric Olefin‐Metathesis Reactions in Metal Coordination Spheres

“…The ARCM kinetic resolution of racemic planar‐chiral manganese complexes rac ‐ 19 proceeds in the presence of ( S )‐ Mo5 (Scheme 15). [31] The enantioselectivity in the kinetic resolution of rac ‐ 19 was sensitive to the lengths of the ω‐alkenyl substituents in the η 5 ‐cyclopentadienides. The kinetic resolution of rac ‐ 19 a , which was with a vinylcyclopentadienide, was highly enantioselective with k rel =127, and unreacted ( R )‐ 19 a was recovered in 98 % ee together with cyclized product ( S )‐ 20 a in 93 % ee.…”

Molybdenum-Catalyzed Enantioselective Synthesis of Planar-Chiral (η5-Phosphacyclopentadienyl)manganese(I) Complexes and Application in Asymmetric Catalysis

“…In the last few decades, we have been interested in modulating transition-metal complexes by the ring-closing metathesis (RCM) reaction. − The RCM strategies have been successfully extended to the enantioselective counterparts by using the Schrock–Hoveyda chiral molybdenum alkylidene catalysts, and various planar-chiral transition-metal complexes have been prepared in excellent enantioselectivity either by the kinetic resolution of the racemic substrates or by the desymmetrization of the C s -symmetric precursors (Scheme ). These are examples of the catalytic asymmetric synthesis of planar-chiral transition-metal complexes, which is a research area that is now rapidly developing. , The asymmetric ring-closing metathesis (ARCM) protocol was applicable to the desymmetrization of prochiral phosphaferrocenes, and the corresponding planar-chiral species were obtained in up to 99% ee (Scheme b)…”