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Edwards PG, Haigh R, Li D, Newman PD: Template synthesis of 1,4,7-triphosphacyclononanes. J Am Chem Soc. 2006 Mar 22;128(11):3818-30.
Iron (II) templates based on a [(eta (5)-Cp (R)) Fe]+ core have been employed for the successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP3R'3) from a range of appropriately functionalized coordinated diphosphines and monophosphines. 1,2-Diphosphinoethane (1,2-dpe) or (2-phosphinoethyl) phenylphosphine (Phdpe) undergo a base-catalyzed Michael-type addition to trivinylphosphine, divinyl (benzyl) phosphine, or divinyl (phenyl) phosphine in [(eta (5)-Cp (R)) Fe (diphosphine)(monophosphine)]+ complexes (2a-j) to give [(eta (5)-Cp (R)) Fe (9aneP3R'3)]+ derivatives (4a-j) containing coordinated triphosphacyclononanes bearing one (with Phdpe) or two (with 1,2-dpe) secondary phosphine donors. The rates of macrocyclization show a dependence on the nature of the substituent (s) R on the cyclopentadienyl ligand with increased rates being observed along the series R = H5 < (Me3Si) H4 < 1,3-(Me3Si) 2H3 approximately = Me5. For coupling reactions with trivinylphosphine, a pendant vinyl function remains in the macrocyclic product (4a-g) which is readily hydrogenated to the corresponding ethyl derivatives (5a-g). Further functionalization of coordinated secondary phosphines in the initially formed macrocycles (5a-g) is achieved by proton abstraction followed by addition of the appropriate alkyl halide electrophile and gives rise to tritertiary-triphospha-cyclononanes (7a-g, 7l, 7m). All new complexes have been fully characterized by spectroscopic and analytical methods in addition to the structural determination by single-crystal X-ray techniques of [{eta (5)-(Me3Si) 2C5H3) Fe (9-aneP3H2C2H3)] PF6, 4c, and [(eta (5)-Me3SiC5H4) Fe (9-aneP3Et3)] BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br2/H2O to give the trioxide 9-aneP3 (O) 3Et3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful. |
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