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Synthesis, Structure, and Reactivities of [η2-P7M(CO)4]3-, [η2-HP7M(CO)4]2-, and [η2-RP7M(CO)4]2- Zintl Ion Complexes Where M = Mo, W

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posted on 13.03.1996, 00:00 by Scott Charles, James C. Fettinger, Bryan W. Eichhorn
Ethylenediamine (en) solutions of [η4-P7M(CO)3]3- ions [M = W (1a), Mo (1b)] react under one atmosphere of CO to form microcrystalline yellow powders of [η2-P7M(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 [η2-HP7M(CO)4]2- ions (5) and are alkylated with R4N+ salts in en solutions to give [η2-RP7M(CO)4]2- complexes (6) in good yields (R = alkyl). Compounds 5 and 6 can also be prepared by carbonylations of the [η4-HP7M(CO)3]2- (3) and [η4-RP7M(CO)3]2- (2) precursors, respectively. The carbonylations of 13 to form 46 require a change from η4- to η2-coordination of the P7 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 1H, 13C, and 31P 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) Å, average). The P73- cages of 5 are not displaced by dppe. The P7 cages in 4−6 have nortricyclane-like structures in contrast to the norbornadiene-type geometries observed for 13. 31P NMR spectroscopic studies for 5−6 show C1 symmetry in solution (seven inequivalent phosphorus nuclei), consistent with the structural studies for 5, and Cs symmetry for 4 (five phosphorus nuclei in a 2:2:1:1:1 ratio). Crystallographic data for [K(2,2,2-crypt)]22-HP7W(CO)4]·en:  monoclinic, space group C2/c, a = 23.067(20) Å, b = 12.6931(13) Å, c = 21.433(2) Å, β = 90.758(7)°, V = 6274.9(10) Å3, Z = 4, R(F) = 0.0573, Rw(F2) = 0.1409. For [K(2,2,2-crypt)]22-HP7Mo(CO)4]·en:  monoclinic, space group C2/c, a = 22.848(2) Å, b = 12.528(2) Å, c = 21.460(2) Å, β = 91.412(12)°, V = 6140.9(12) Å3, Z = 4, R(F) = 0.0681, Rw(F2) = 0.1399.