Synthesis, stereochemical assignment, and enantioselective catalytic activity of late transition metal planar chiral complexes

Abstract

Planar chirality is an important form of molecular chirality that can be utilized to induce enantioselectivity when incorporated into transition metal catalysts. However, due to synthetic constraints, the use of late transition metal planar chiral complexes to conduct enantioselective transformations has been limited. Additionally, the published methods surrounding the stereochemical assignment of planar chiral compounds are sometimes conflicting, making proper assignment difficult. This review aims to provide clarity on the methods available to assign planar chirality and provide an overview on the synthesis and use of late transition metal planar chiral complexes as enantioselective catalysts.

Figure 1

Approaches to representing and viewing planar chiral molecules

Figure 2

Methods for assignment of planar chirality

Figure 3

Planar chiral ruthenium catalysts that have been used for enantioselective transformations.

Figure 4

Planar chiral iron catalysts that have been used for enantioselective transformations.

Figure 5

Planar chiral rhodium catalysts utilized in enantioselective transformations.

Figure 6

Planar chiral ruthenium cyclopentadienyl catalysts used in enantioselective allylic substitutions and polymerization reactions.

Figure 7

Ruthenium catalysts designed for stereoselective hydrogen transfer reactions.

Figure 8

Planar chiral iron catalysts used in asymmetric hydrogen transfer reactions.

Figure 9

The first planar chiral Rh indenyl catalyst used in asymmetric hydrogenation and two Jas Cp pre-catalysts used in a variety of transformations.

Figure 10

Rhodium catalysts developed by the Perekalin Group.

Figure 11

Rh indenyl catalyst from the Blakey group and two Rh Cp catalysts from the Wang Group

Figure 12

The only planar chiral Co catalysts used in asymmetric catalysis to date.

Figure 13

Co(III) intermediate of [2+2+2] cycloaddition

Scheme 1

Synthesis of tethered Cp ruthenium catalysts with alkyl phosphine linker.

Scheme 2

Faller and co-workers provided several tethered η ruthenium catalysts that originate from DavePhos.

Scheme 3

Shvo-type planar chiral Ru catalysts developed by Yamamoto, Wills, and Dou. *Complexes not shown.

Scheme 4

Perekalin and co-workers’ camphor-derived ligand for diastereoselective synthesis of (pR,pR)-19.

Scheme 5

Wang and co-workers’ paracyclophane-derived Ru-arene complex

Scheme 6

Wills and co-workers’ direct synthesis of Shvo-type planar chiral iron complexes from diyne precursors

Scheme 7

Examples of iron cyclopentadienone catalysts with fused alkyl backbones

Scheme 8

Synthesis of indenyl Rh catalysts from a neomenthyl-substituted indenyl lithiate.

Scheme 9

Waldmann’s modular approach to a family of planar chiral Rh Cp complexes. Planar chirality not designated as individual assignment varies according to the substitution pattern.

Scheme 10

A) Synthesis of Perekalin and coworkers Cp catalysts via [2+2+1]cyclization with chiral resolution. B) An (R)-myrtenal derived ligand for diastereoselective complexation. C) Perekalin’s planar chiral Rh(III) complex derived from on-metal cyclization of ^tBu acetylene.

Scheme 11

Synthesis of tetrafluorobenzobarrelene Rh catalyst by the Perekalin Group

Scheme 12

Synthesis of Blakey planar chiral rhodium indenyl catalyst relying on chiral HPLC for resolution.

Scheme 13

Wang and co-workers’ planar chiral Rh(III) Cp complex. Both nonchiral ligands and diastereomeric ligands were used to prepare the Cp complexes.

Scheme 14

Synthesis of planar chiral menthyl indenyl cobalt catalysts bearing cyclooctadiene or phosphite ligands.

Scheme 15

Asymmetric allylic amination and post-functionalization cyclization.

Scheme 16

Polymerization of monomers optimized for 1.3 to 1.8 weight distributions.

Scheme 17

Polymerization of diketones via allylic substitutions

Scheme 18

The use of spirocyclic C-riboside derived Shvo catalysts in asymmetric hydrogen transfer reactions.

Scheme 19

Asymmetric hydrogenation of acetophenone with camphor derived Ru catalyst.

Scheme 20

Rh-catalyzed hydrogenation of itaconic acid.

Scheme 21

Rh carbene insertion into B–H, Si–H, and N–H bonds.

Scheme 22

Co-catalyzed intermolecular [2+2+2] cycloaddition

Scheme 23

Co-catalyzed di-[2+2+2] cycloaddition to set two atropisomeric stereocenters