Journal of the Chemical Society, Dalton Transactions p. 3491 - 3502 (1996)
Update date:2022-08-03
Topics:
Atkinson, Francis L.
Blackwell, Helen E.
Brown, Nathan C.
Connelly, Neil G.
Crossley, John G.
Orpen, A. Guy
Rieger, Anne L.
Rieger, Philip H.
The complex [FeL2(NO)2] (L = PEt3 1a, L = PPh3 1b or L2 = dppe 1c) prepared from [{Fe(μ-I)(NO)2}2] and PPh3 or Ph2PCH2CH2PPh2 (dppe) {in the presence and absence of [Co(cp)2] (cp = η5-C5H5) respectively} undergo one-electron oxidation at a platinum electrode in CH2Cl2. The complex [{Fe(μ-dppm)(NO)2}2] 2, prepared from [{Fe(μ-I)(NO)2}2] and Ph2PCH2PPh2 (dppm) in the presence of [Co(cp)2], undergoes two sequential one-electron oxidations. Complex 1b with [Fe(cp)2]+ gave 1b+, X-ray studies of which show a distorted tetrahedral geometry with near C2v symmetry. Oxidation of 1b leads to substantial lengthening of the Fe-P bonds and changes in the P-Fe-P and N-Fe-N angles. These changes are consistent with significant Fe-P π-bonding character in the singly occupied molecular orbital of 1b+. Cation 1b+ reacts with halide ions, giving [FeX(PPh3)(NO)2] (X = Cl or I) and then [FeX2(NO)2]-; and with OPPh3 to give [Fe(OPPh3)(PPh3)(NO)2]+ 3+. X-Ray studies on the last, as its [PF6]- salt, show a distorted tetrahedral geometry; the co-ordination angles at iron approach trigonal bipyramidal with the PPh3 ligand in one apical site and the other apical site vacant. The complex [Fe(OPPh3)2(NO)2]+ 4+ resulted from the reaction between [{Fe(μ-I)(NO)2}2] and OPPh3 in the presence of TlPF6. An analysis of the ESR spectra of the paramagnetic cations 1b+, 3+ and 4+, together with extended-Hueckel MO calculations on models of 1b+ and 3+, suggest that the complex catalysts formed from [{Fe(μ-Cl)(NO)2}2] and Ag+ or Tl+ are also four-co-ordinate 17-electron radicals. A crystallographic database study of four-co-ordinate dinitrosyl complexes of iron and other metals confirms that the N-Fe-N and O ... Fe ... O angles are linearly related. Consideration of these geometric effects, and those resulting from oxidation of 1b, in the light of a model proposed by Summerville and Hoffmann provides insight into the bonding in these and related species.
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