Stereochemistry of Metallocenes

(+)-trans-Chlorido-{2-[(Rp)-2-(methyl-sulfan-yl)ferro-cen-yl]-2,5,6,7-tetra-hydro-pyrrolo-[1,2-c]imidazol-3-yl-idene}bis(tri-phenyl-phosphane-κP)palladium(II) hexa-fluorido-phosphate di-chloro-form disolvate

The title solvated complex, [FePd(C5H5)(C12H13N2S)Cl(C18H15P)2]PF6·2CHCl3, bearing a chiral ferrocenyl pyrrolo-imidazolyl-idene N-heterocyclic carbene (NHC) ligand, was synthesized by oxidative addition of a chloro-imidazolium salt to Pd(PPh3)4. The PdII ion is coordinated in a slightly distorted square-planar coordination geometry, with the Cl atom trans to the coordinating C atom of the pyrrolo-imidazolyl-idene ligand. The complex features a pendant thio-ether group that is not involved in coordination to Pd. In the crystal, weak C-H⋯F and C-H⋯π inter-actions connect the components of the structure, forming chains propagating along [1-10]. The fused pyrrolidine ring is in an envelope conformation, and the flap atom was refined as disordered over two sets of sites, with occupancies of 0.77 (4) and 0.23 (4).

Crystal structure of (μ-N,N'-di-benzyl-dithio-oxamidato-κN,S:N',S')bis-[(η(3)-crotyl)palladium(II)]

In the centrosymmetric dinuclear title compound, [Pd2(C4H7)2(C16H14N2S2)], the metal atom is η(3)-coordinated by three C atoms of a crotyl ligand [Pd-C = 2.147 (4), 2.079 (5) and 2.098 (5) Å], the longest distance influenced by the steric inter-action with the benzyl substituents of the di-benzyl-dithio-oximidate (DTO) ligand. The Pd-N and Pd-S bonds to this ligand are 2.080 (3) and 2.3148 (9) Å, respectively, completing a square-planar coordination environment for Pd(II). The benzyl groups are oriented so as to maximize the inter-action between a benzylic H atom and an S atom, resulting in a dihedral angle of 77.1 (2)° between the benzene rings and the metal complex plane. In the crystal, no inter-complex hydrogen-bonding inter-actions are present.

Catalyzed Asymmetric Arylation Reactions

Addition and substitution reactions with carbon nucleophiles are fundamental processes in organic synthesis, and the development of general catalytic asymmetric variants thereof is still a major challenge today. In contrast to enantioselective alkyl transfer reactions, the corresponding arylations have not yet reached a high level of maturity. The existing protocols are either of no general applicability or are limited in terms of selectivity. This article summarizes established routes for catalytic asymmetric aryl transfer together with the latest developments in this area. The scope and limitations of this reaction are discussed.