Successful application of a “forgotten” phosphine in asymmetric catalysis: A 9-phosphabicyclo[3.3.1]non-9-yl ferrocene derivative as chiral ligand

Hendrikus C.L. Abbenhuis, Urs Burckhardt, Volker Gramlich, Christoph Köllner, Paul S. Pregosin, Renzo Salzmann, Antonio Togni

    Research output: Contribution to journalArticleAcademicpeer-review

    74 Citations (Scopus)

    Abstract

    The technical mixture phobane”, containing the two isomers 9-phospha-9H-bicyclo[3.3.1]-nonane (3a) and 9-phospha-9H-bicyclo[4.2.1]nonane (3b) in a ~2:1 ratio was reacted with N,N-dimethyl-(S)-l-[(R)-2-(diphenylphosphino)ferrocenyl]ethylamine (4) in acetic acid. The clean amine substitution product is the new chiral biphosphine 5. When only 2 equiv of 3 were reacted with 4, a 4:1 mixture of the two isomeric products 5a and 5b were obtained. However, the use of a 10-fold excess of 3 afforded the pure [3.3.1]-isomer 5a, 9-phospha-9-[(S)-l-{(R)-2-(diphenylphosphino)ferrocenyl}ethyl][3.3.1]bicyclononane, in 68% isolated yield. (S)-(R)-5a crystallizes in the orthorhombic space group P212121, Z = 4, α = 7.393(3) Å, b = 19.261(5) Å, and c = 19.546(8) Å. 5a was used in the asymmetric Pd-catalyzed alkylation of l,3-diphenyl-3-acetoxypropene with dimethyl malonate. Enantioselectivities up to 85% ee were obtained. The cationic Pd—allyl complexes [Pd(η3-C3H5)(5a)]O3SCF3(6) and [Pd(η3-PhCHCHCHPh)(5a)]O3SCF3 (7) were prepared and characterized by X-ray diffraction. Complex 6 crystallizes in the monoclinic space group P21, Z = 2, α = 9.162(4) Å, b = 16.069-(5) Å, c = 11.816(5) Å, and β = 96.86(3)°. Crystalline 7 was obtained as a CH2Cl2 monosolvate and belongs to the triclinic system: space group P1, Z = 1, a = 11.07(2) Å, b = 11.216(14) Å, c = 11.888(16) Å, a = 62.37(9)°, β = 65.96(11)°, and γ = 70.29(11)°. The ligand assumes very different conformations in its complexes, as compared to the free state. Multidimensional 31P, 13C, and 1H NMR studies reveal that 7 exists in solution as a mixture of four isomers. Aspects of the selective equilibria were elucidated using 31P- and 1H-exchange spectroscopy.

    Original languageEnglish
    Pages (from-to)759-766
    Number of pages8
    JournalOrganometallics
    Volume14
    Issue number2
    DOIs
    Publication statusPublished - 1 Jan 1995

    Fingerprint Dive into the research topics of 'Successful application of a “forgotten” phosphine in asymmetric catalysis: A 9-phosphabicyclo[3.3.1]non-9-yl ferrocene derivative as chiral ligand'. Together they form a unique fingerprint.

    Cite this