Template synthesis of 1,4,7-triphosphacyclononanes

Iron(II) templates based on a [(eta(5)-Cp-R)Fe](+) core have been employed forthe successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP(3)R'(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(9aneP(3)R'(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 = H-5 < (Me3Si)H-4 < 1,3-(Me3Si)(2)H-3 approximate to Me-5. 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, 71, 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)(2)C5H3)Fe(9-aneP(3)H(2)C(2)H(3))]PF6, 4c, and [(eta(5)-Me3SiC5H4)Fe(9-aneP(3)Et(3))]BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br-2/H2O to give the trioxide 9-aneP(3)(O)(3)Et-3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful.