Homoleptic,sigma-Bonded Octahedral [M(CO)_6]_2 Cations of Iron(ll),Ruthenium(ll),and Osmium(ll):Parti:Syntheses,Thermochemical and Vibrational Characterizations,and Molecular Structures as [Sb_2F_(11)]~-and [SbF_6]~-Salts.A Comprehensive,Comparative

摘要

Homoleptic octahedral,superelectrophilic sigma-bonded metal carbonyl cations of the type [M(CO)_6]~(2+)(M=Ru,Os)are generated in the Bronsted-Lewis conjugate superacid HF/SbF_5 by reductive carbonylation of M(SO_3F)_3(M=Ru,Os)or OsF_6.Thermally stable salts form with either [Sb_2F_(11)]~-or [SbF_6]~-as anion,just as for the previously reported [Fe(CO)_6]~(2+)cation.The latter salts are generated by oxidative(XeF_2)carbonylation of Fe(CO)_6 in HF/ SbF_5.A rationale for the two diverging synthetic approaches is provided.The thermal stabilities of [M(CO)_6][SbF_6]_2 salts,studied by DSC,range from ~(18)O deg C for M=Fe to 350 deg C for M=Os before decarbonylation occurs.The two triads [M(CO)_6][SbF_6]_2 and [M(CO)_6][Sb_2F_(11)]_2(M=Fe,Ru,Os)are extensively characterized by single-crystal X-ray diffraction and vibrational and ~(13)C NMR spectroscopy,aided by computational studies of the cations.The three [M(CO)_6][SbF_6]_2 salts(M=Fe,Ru,Os)crystallize in the tetragonal space group P4/mnc(No.128),whereas the corresponding [Sb_2F_(11)]~-salts are monoclinic,crystallizing in space group P2_1ln(No.14).In both triads,the unit cell parameters are nearly invariant of the metal.Bond parameters for the anions [SbF_6]~ and [Sb_2F_(11)]~-and their vibrational properties in the two triads are completely identical.In all six salts,the structural and vibrational properties of the [M(CO)_6]~(2+)cations(M=Fe,Ru,Os)are independent of the counteranion and for the most part independent of M and nearly identical.Interionic C...F contacts are similarly weak in all six salts.Metal dependency is noted only in the ~(13)C NMR spectra,in the skeletal M-C vibrations,and to a much smaller extent in some of the C-0 stretching fundamentals(A_(1g)and T_(1u)).The findings reported here are unprecedented among metal carbonyl cations and their salts.