Bidentate 1,2‐Ferrocenyl Diphosphine Ligands

Abstract

IntroductionFerrocene as a (at the time rather exotic) backbone for chiral ligands was introduced by Kumada and Hayashi [1], based on Ugis pioneering work related to the synthesis of enantiopure ferrocenes (see Figure 4.1). PPFA as well as BPPFA and BPPFOH were not only the first ferrocene-based ligands but also the first ligands to exhibit both central and planar chirality and they proved to be very effective ligands for a variety of asymmetric transformations. From this starting point, several ligand families with a range of structural variations and types of chiral element have been developed in the last few years, very often starting from Ugi amine. In this chapter we will focus on the application of diphosphines developed over time where the two diphosphine moieties are attached to only one of the cyclopentadienyl (Cp) rings in a 1,2-arrangement. As a consequence these ligands can have a mix of chiral elements: planar chirality due to the ferrocene moiety, central chirality due to stereogenic carbon and/or phosphorus centers and, in one case, even axial chirality. Several recent reviews covering various aspects of ferrocene-based chiral ligands can serve to put the present account into a broader perspective [2]. Furthermore, we have recently summarized the synthetic procedures for most of the ligands described here [3].This chapter is organized according to the five types of arrangement of the two diphosphine moieties at the Cp ring (see Figure 4.2).Type A: Both PR 2 groups are directly attached to the Cp ring.Type B: One PR 2 group is directly attached to the Cp ring, the second PR 2 group is attached to the a position of a side chain.Type C: One PR 2 group is directly attached to the Cp ring, the second PR 2 group is attached to the b position of a side chain.

Indirect Nonbonded Nuclear Spin–Spin Coupling: A Guide for the Recognition and Understanding of “Through-Space” NMR J Constants in Small Organic, Organometallic, and Coordination Compounds

“…1,2-Substituted ferrocenyl diphosphines of the type 20a are compounds which present large 31 P– 31 P nonbonded SSCCs (Scheme ). Significant interest in these species is related to their usefulness in transition metal coordination and catalysis. , For instance, in 2010 a survey of the relevant solid-state structures reported yielded more than 15 structures in which large TS J PP couplings are clearly observed between homoannular phosphorus separated by four nonconjugated covalent bonds or more. The term homoannular stands for atoms attached to the same cyclopentadienyl ring …”

Diastereoselective Pd-Catalyzed C–H Arylation of Ferrocenylmethanamines with Arylboronic Acids or Pinacol Esters

“…Many chiral ferrocene ligands, including those employed in industry, such as Josiphos, Xyliphos, Walphos, or Taniaphos, possess a combination of planar and central chirality . For this reason, we decided to study the chiral-ligand-enhanced diastereoselective Pd-catalyzed C–H arylation of chiral ferrocenyl amines.…”

Walphos versus Biferrocene-Based Walphos Analogues in the Asymmetric Hydrogenation of Alkenes and Ketones

“…Originally, these derivatives were developed and used as ligands for hydrogenation catalysts, but a variety of additional applications have subsequently been reported. 2 …”

“…All of these ligands are based on a phenylferrocenylethyl backbone, and they vary only in the substituents on their phosphino units (R 1 and R 2 ; Chart ). Originally, these derivatives were developed and used as ligands for hydrogenation catalysts, but a variety of additional applications have subsequently been reported …”