Protonation and hydrogen atom abstraction reactions in the synthesis of the [HP7M(CO)3]2- ions (M = Cr, W)

Ethylenediamine (en) solutions of [P7M(CO)(3)](3-) (M = Cr, W) react with weak acids to give [HP7M(CO)(3)](2-) ions where M = Cr (4a) and W (4b) in high yields. Competition studies with known acids revealed a pK(a) range for 4b in DMSO of 17.9 to 22.6. The [P7M(CO)(3)](3-) complexes also react with one-half equivalent of I-2 to give 4 through an oxidation/hydrogen atom abstraction process. Labeling studies show that the abstracted hydrogen originates from the [K(2,2,2-crypt)](+) ions or from the solvent (DMSO-d(6)) in the absence of [K(2,2,2-crypt)](+) or other good hydrogen atom donors. In the solid state, the ions have no crystallographic symmetry but in solution they show virtual C-s symmetry ((PNMR)-P-31 spectroscopy) due to an intramolecular wagging process. Crystallographic data far [K(2,2,2-crypt)](2)[HP7W(CO)(3)]: triclinic, P (1) over bar, a = 10.9709(8)Angstrom, b = 13.9116(10)Angstrom, c = 19.6400(14)Angstrom, alpha = 92.435(6)degrees, beta = 93.856(6)degrees, gamma = 108.413(6)degrees, V = 2831.2(4) Angstrom(3), Z = 2, R(F) = 7.65%, R(wF(2)) = 14.17% for all 7400 reflections. For [K(2,2,2-crypt)](2)[HP7Cr(CO)(3)]: triclinic, P (1) over bar, alpha = 12.000(3) Angstrom, b = 14.795(3) Angstrom, c = 17.421(4) Angstrom, alpha = 93.01(2)degrees, beta = 93.79(2)degrees, gamma = 110.72(2)degrees, V = 2877(2) Angstrom(3), Z = 2.