Chiral bisphosphanes

[1,2-Bis(diisopropylphosphanyl)ethane-κ2P,P′](carbonato-κ2O,O′)nickel(II)

In the crystal of the title compound, [Ni(CO₃)(C₁₄H₃₂P₂)], the metal center in each of three independent mol­ecules shows slight tetra­hedral distortion from ideal square-planar coordination geometry, with angles between the normals to the planes defined by the cis-P—Ni—P and cis-O—Ni—O fragments of 3.92 (17), 0.70 (16) and 2.17 (14)° in the three mol­ecules. In the crystal, there are inter­molecular C—H⋯O hydrogen bonds that show a laminar growth in the ab plane.

[1,2-Bis-(diisopropyl-phosphan-yl)ethane-κP,P']dichloridonickel(II)

In the crystal structure of title compound, [NiCl₂(C₁₄H₃₂P₂)], the Ni^II atom lies on a twofold rotation axis and shows a slightly distorted square-planar coordination geometry, with a dihedral angle of 10.01 (8)° between the cis-Cl—Ni—Cl and cis-P—Ni—P planes. There is no significant inter­molecular inter­action except very weak C—H⋯Cl inter­actions. The crystal studied was a racemic twin.

[1,2-Bis-(diisopropyl-phosphan-yl)ethane-κP,P']dichloridonickel(II)-9H-carbazole (1/2)

In the title compound, [NiCl₂(C₁₄H₃₂P₂)]·2C₁₂H₉N, the neutral [Ni(dppe)Cl₂] complex [dppe is 1,2-bis­(diisopropyl­phosphan­yl)ethane] consists of a tetracoordinated Ni²⁺ cation and has a crystallographic twofold axis passing through the metal atom and the mid-point of the CH₂—CH₂ bond of the dppe ligand. The metal atom shows slight tetra­hedral distortion from an ideal square-planar coordination geometry, as reflected in the dihedral angle between NiCl₂ and NiP₂ planes of 15.32 (2)°. The 9H-carbazole ring system is essentially planar (r.m.s. deviation = 0.022 Å). In the crystal packing, there are two symmetry-related 9H-carbazole mol­ecules between two adjacent Ni^II complexes, with an angle between the carbazole mean planes of ca 77°.

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

A rotationally hindered and thus stereogenic biaryl axis is the structurally and stereochemically decisive element of a steadily growing number of natural products, chiral auxiliaries, and catalysts. Thus, it is not surprising that significant advances have been made in the asymmetric synthesis of axially chiral biaryl compounds over the past decade. In addition to the classic approach (direct stereoselective aryl-aryl coupling), innovative concepts have been developed in which the asymmetric information is introduced into a preformed, but achiral-that is, symmetric or configurationally labile-biaryl compound, or in which an aryl--C single bond is stereoselectively transformed into an axis. This Review classifies these strategies according to their underlying concepts and critically evaluates their scope and limitations with reference to selected model reactions and applications. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed.