Stereochemical Exploitation of the Chiral (+)-9-Phenyldeltacyclanyl Substituent in Diphosphanes and Their Ni, Pd and Pt Complexes

TLDR: In this paper, the reaction of (+)-9-phenyldeltacyclanyl moiety as a chiral phosphorus substituent contains eight configurationally fixed asymmetric carbon atoms.

Abstract: The (+)-9-phenyldeltacyclanyl moiety as a chiral phosphorus substituent contains eight configurationally fixed asymmetric carbon atoms. It is easily obtained from the reaction of norbornadiene and phenylacetylene via a Co-catalyzed enantioselective homo-Diels−Alder reaction, to give (+)-8-phenyldeltacyclene. In the reaction of (+)-8-phenyldeltacyclene with 1,2-(H2P)2C6H4 the trisubstitution product P,P,P′-tris[(+)9-phenyldeltacyclan-8-yl)-1,2-bis(phosphanyl)benzene, (+)δ-LH, is obtained, in which a single P−H bond at the stereogenic phosphorus atom is left. (+)δ-LH crystallizes as a pure diastereomer, which isomerizes in solution with respect to the secondary phosphorus atom at −20 °C resulting in a 64:36 diastereomer mixture. Substitution of the P−H hydrogen atom in (+)δ-LH by benzyl, 3-bromobenzyl, 6-bromo-n-hexyl and 3-(diphenylphosphanyl)phenyl gave the bis(tertiary) diphosphanes (+)δ-LR1−(+)δ-LR4. NiBr2, PdHal2 (Hal = Cl, Br, I) and PtHal2 (Hal = Cl, Br) complexes of (+)δ-LH and (+)δ-LR1−(+)δ-LR4have been synthesized. The complexes form two diastereomers differing in the configuration of the chiral P atom. X-ray structure analyses have been carried out with (+)δ-LH, [(+)δ-LR2]NiBr2, [(+)δ-LH]PdI2 and [(+)δ-LCl]PdI2. Interestingly, for [(+)δ-LH]PdI2 both diastereomers are found in the same crystal lattice in a 1:1 ratio. In [(+)δ-LH]PdI2 and [(+)δ-LCl]PdI2the configuration at the secondary phosphorus atom is stable in solution at room temperature, whereas in the free ligand (+)δ-LH it is configurationally labile. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)