Ethylenediamine (en) solutions of [eta(4)-P(7)M(CO)(3)](3-) ions [M = W (1a), Mo (1b)] react under one atmosphere of CO to form microcrystalline yellow powders of [eta(2)-P(7)M(CO)(4)](3-) complexes [M = W (4a), Mo (4b)]. Compounds 4 are unstable, losing CO to re-form 1, but are highly nucleophilic and basic. They are protonated with methanol in en solvent giving [eta(2)-HP(7)M(CO)(4)](2-) ions (5) and are alkylated with R(4)N(+) salts in en solutions to give [eta 2-RP(7)M(CO)(4)](2-) complexes (6) in good yields (R alkyl). Compounds 5 and 6 can also be prepared by carbonylations of the [eta(4)-HP(7)M(CO)(3)](2-) (3) and [eta(4)-RP(7)M(CO)(3)](2-) (2) precursors, respectively. The carbonylations of 1-3 to form 4-6 require a change from eta(4)- to eta(2)-coordination of the P-7 cages in order to maintain 18-electron configurations at the metal centers. Comparative protonation/deprotonation studies show 4 to be more basic than 1. The compounds were characterized by IR and H-1, C-13, and P-31 NMR spectroscopic studies and microanalysis where appropriate. The [K(2,2,2-crypt)](+) salts of 5 were characterized by single crystal X-ray diffraction. For 5, the M-P bonds are very long (2.71(1) Angstrom, average). The P-7(3-) cages of 5 are not displaced by dppe. The P-7 cages in 4-6 have nortricyclane-like structures in contrast to the norbornadiene-type geometries observed for 1-3. P-31 NMR spectroscopic studies for 5-6 show C-1 symmetry in solution (seven inequivalent phosphorus 1 nuclei), consistent with the structural studies for 5, and C-s symmetry for 4 (five phosphorus nuclei in a 2:2:1:1:1 ratio). Crystallographic data for [K(2,2,2-crypt)](2)[eta(2)-HP7W(CO)(4)]. en : monoclinic, space group C2/c, a = 23.067(20) Angstrom, b = 12.6931(13) Angstrom, c = 21.433(2) Angstrom, beta = 90.758(7)degrees, V = 6274.9(10) Angstrom(3), Z = 4, R(F) = 0.0573, R(w)(F-2) = 0.1409. For [K(2,2,2-crypt)](2)[eta(2)-HP7Mo(CO)(4)]. en : monoclinic, space group C2/c, a = 22.848(2) Angstrom, b = 12.528(2) Angstrom, c = 21.460(2) Angstrom, beta = 91.412(12)degrees, V = 6140.9(12) Angstrom(3), Z = 4, R(F) = 0.0681, R(w)(F-2) = 0.1399.