Cobalt(III)-Peroxo Complexes Containing 1,2-Bis(dimethylphosphino)ethane (dmpe) or 1,3-Bis(dimethylphosphino)propane (dmpp). Molecular Structures of [Co(O2)(dmpe)2]B(C6H5)4 and [Co(O2)(dmpp)2]BF4·H2O

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Abstract
Monomeric (yellow) and dimeric (red) cobalt(III)–dioxygen complexes containing 1,2-bis(dimethylphosphino)ethane (dmpe) have been prepared from [Co(dmpe)2]+ and [Co(dmpe)2]2+, respectively, by air oxidation. The 1,3-bis(dimethylphosphino)propane (dmpp) complex afforded only the monomeric dioxygen complex by either preparative method. The crystal structures of [Co(O2)(dmpe)2]B(C6H5)4 (1) and [Co(O2)(dmpp)2]BF4·H2O (2) have been determined by X-ray analysis. Crystal data for 1; monoclinic, P21⁄a, a=18.011(12), b=18.761(10), c=11.455(6) Å, β=107.78(4)°, V=3686(4) Å3, Z=4, and R=0.064. Crystal data for 2; orthorhombic, Pbcn, a=14.540(5), b=13.123(4), c=13.138(2) Å, V=2507(1) Å3, Z=4, and R=0.076. The complex ions in both 1 and 2 have a trigonal-bipyramidal coordination geometry when the O2 group bonded to the Co atom in the side-on form at a coordination site of the trigonal plane is assumed to be a unidentate ligand. Bond lengths. Co–O (1.858(7)–1.881(4) Å) and O–O (1.414(12) and 1.425(6) Å), and O–O stretching frequencies (877 and 862 cm−1) indicate that both 1 and 2 are the peroxo complexes. The monomeric dioxygen complexes react immediately with SO2 and with concd HCl to afford [Co(SO4)(dmpe or dmpp)2]+ and cis-[CoCl2(dmpe or dmpp)2]+, respectively. The red dimeric trans-[(dmso)(dmpe)2Co(μ-O2)Co(dmpe)2(dmso)](BF4)4 (dmso=dimethyl sulfoxide) complex was isolated and characterized.

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