Juanita M. Cassidy

Structure and Mössbauer effect study of [Et4N]2[Fe2(CO)8]

Abstract The reduction of [Et4N]2[Pb{Fe(CO)4}3] leads to the well known [Et4N]2[Fe2(CO)8] as determined by single crystal X- bis[tetracarbonylferrate(1 −)], C24H40Fe2N2O8, FW = 596.28 g/mol, monoclinic, P21/n (#14), a = 9.492(3), b (2)°, V = 1432.5(8) A3, Dx = 1.38 g/cm3, Z = 2, μ = 10.56 cm−1, λ(Mo-Kα) = 0.71069 A, F(000) = 62 for 1869 unique reflections with I > 3σ(I). As in other salts, the anion of [Et4N]2[Fe2(CO)8] consists of two iron atoms situ each of which is coordinated to four carbonyls in a trigonal bipyramidal fashion with the FeFe bond in an axial site. Unexpectedly, the Fe longer than reported for the [PPN]+·2CH3CN, [PPh4]+·2CH3CN and [Fe(pyridine)6]2+ salts. The Mossbauer effect spectra have been measured at 78 and 296 K, are presented and discussed. bl]

Crystal structures of phenyl-substituted cyclopropanes. IV. the crystal structure (at 21‡C and −100‡C) and the phenyl ring conformation in 4-cyclopropylacetanilide

The crystal structure of 4-cyclopropylacetanilide was investigated at room temperature (21‡C) and at −100‡C in order to determine the orientation of the phenyl ring with respect to the cyclopropane moiety and the effect of this substituent on the stereochemistry of the three-membered ring. The compound was chosen because it is one of the few species containing a simple phenyl ring as the sole cyclopropane ring substituent and whose crystals are suitable for X-ray diffraction at room temperature. The substance crystallizes in space groupP2l/c at either temperature (no phase transitions) with cell constants: (at 21‡C)a=9.725(2),b=10.934(3), andc=9.636(2) å,Β=106.13(1)‡;V=984.21 å3 andd(calc;z=4)=1.182 g cm−3. The relevant parameters for the −100‡C structure area=9.557(4),b=10.980(2), andc=9.641(2) å,Β=106.34(3)‡;V=970.76 å3 and d(calc;z=4)=1.199 g cm−3. Final values wereR(F)=0.042, Rw=0.035, using unit weights, and its nonhydrogen atoms were used to phase the low-temperature data, whose final discrepancy indices wereR(F)=0.051,Rw=0.061. The phenyl substituent is almost exactly in the bisecting conformation with respect to the C-C-C angle at the point of attachment to cyclopropane and conjugative effects are clearly evident in the lengths of the cyclopropane ring [1.494(3), 1.498(3), and 1.474(4) å, the later being the distal bond]. If one omits the terminal methylene fragments at C10 and C11, the atoms comprising the acetanilide fragment and the substituted carbon of the cyclopropane ring lie in a nearly perfect plane. Molecular mechanics as well as semiempirical (AM1) calculations were carried out in order to determine the structure of the energy-minimized configurations in the two computational environments. The molecular conformations thus obtained are close to that experimentally observed from the X-ray diffraction experiment. In both theoretical models, the lowest energy conformation is that in which the plane of the phenyl ring bisects the cyclopropane C-C-C angle as was experimentally observed. Finally, the shape of the conformational barrier as a function of the orientation of the plane of the phenyl ring was computed, giving a maximum barrier to rotation of 2.2 kcal/mol. Similar calculations were carried out for two other aryl cyclopropanes, whose rings (naphthalene and anthracene) cannot adopt the bisecting position. Comparisons of experimental geometrical parameters as well as of the barriers to rotation are presented.

Solution dynamics of tin and lead iron carbonyl compounds and the solid state structure of [Et4N]2[Sn{Fe2(CO)8}{Fe(CO)4}2]

Abstract The dynamic rearrangement processes of CO ligands on the Main Group-iron carbonyl compounds, E[Fe2(CO)8]2 (Ia, E  Pb), [Et4N]2[E{Fe2(CO)8}{Fe(CO)4}2]([Et4N]2[IIa], E  Pb; [Et4N]2[IIb], E  Sn) and [Et4N]2[Pb{Fe(CO)4}3] ([Et4N]2[IIIa], E  Pb; [Et4N]2[IIIb], E  Sn) were investigated by variable temperature 13C NMR spectroscopy. In Ia, all of the carbonyl ligands exhibit fast exchange over the entire temperature range studied. Limiting spectra were obtained for [Et4N]2[II] while the fluxional processes for [Et4 N]2[IIIa] were slowed but not completely resolved. Variable temperature spectra for [Et4N]2[II] provide evidence for the occurrence of two simultaneous independent carbonyl rearrangement processes, one centered on the Fe(CO)4 groups and one on the Fe2(μ-CO)2(CO)4 moiety. The dynamics of [Et4N]2[IIIa] suggest that the trigonal planar geometery is preserved in solution. Calculated activation energies for CO scrambling in [Et4N]2[II] and [Et4N]2[IIIa] range from 5.8 to 9.2 kcal/mol. The single crystal structure of [Et4N]2[IIb] was determined: monoclinic space group, Cc (No. 9) with a = 11.572(6) A, b = 22.46(1) A, c = 17.049(4) A, β = 103.00(3)°, V = 4318(3) A3 and Z = 4. The structure was refined to R = 4.8% and Rw = 5.5% for 2665 observed reflections. The anion exhibits a distorted tetrahedral configuration around Sn, with the Main Group element coordinated to two Fe (CO)4 groups and one Fe2(CO)8 unit.