Gas Phase Study of the Kinetics of Formation and Dissociation of Fe(CO)₄L and Fe(CO)₃L₂ (L = C₂H₄ and C₂F₄)

Abstract

The bond dissociation energy for loss of C 2 H 4 from Fe(CO) 3 (C 2 H 4 ) 2 , produced by the reaction of C 2 H 4 + Fe(CO) 3 (C 2 H 4 ), has been determined as 21.3 ( 2.0 kcal/mol. An estimate is made for a lower limit for the bond dissociation energy of Fe(CO) 4 (C 2 H 4 ), which can be formed by reaction of CO + Fe(CO) 3 (C 2 H 4 ) or Fe (CO) 4 + C 2 H 4 with rate constants of (4.3 ( 0.8) × 10 -12 and (1.7 ( 0.2) × 10 -13 cm 3 /(molecule s) at 24 °C, respectively. The values for these bond dissociation energies are compared with those determined in prior studies of these systems. A new compound with infrared absorptions at 2147, 2091, and 2068 cm -1 is best assigned as Fe(CO) 3 (C 2 F 4 ) 2 . A rate constant of (5.4 ( 1.7) × 10 -12 cm 3 /(molecule s) at 24 °C is reported for the reaction of C 2 F 4 with Fe(CO) 3 (C 2 F 4 ) to form Fe(CO) 3 (C 2 F 4 ) 2 . Fe(CO) 4 (C 2 F 4 ) can be formed by reaction of C 2 F 4 and Fe(CO) 4 , with a rate constant of (1.8 ( 0.4) × 10 -14 cm 3 /(molecule s) at 24 °C. Infrared absorptions observed at 2135, 2074, and 2043 cm -1 are assigned to this species. The relative stabilities of the mono-and bisethylene and perfluoroethylene compounds of iron are compared. Where possible, they are also compared to the corresponding chromium compounds and are discussed in the context of current concepts regarding metal-olefin bonding.

Computational study of the energetics of3Fe(CO)4,1Fe(CO)4and1Fe(CO)4(L), L = Xe, CH4, H2and CO

“…[15][16][17][18] To provide support for the qualitative description of reactivity given above, it is important to be able to show that such NA-TST calculations can give near-quantitative agreement with experimental rate coefficients for spin-forbidden organometallic reactions. 19 Although relatively little experimental data of this type is available, one type of reaction, the gas phase addition of small molecules to triplet iron tetracarbonyl, has been studied extensively by Weitz et al [20][21][22][23][24][25][26][27][28] We have already shown 19 that NA-TST is able to predict the rate coefficient for addition of carbon monoxide to triplet Fe(CO) 4 to give singlet Fe(CO) 5 to within better than one order of magnitude, which is probably the best level of accuracy which can be expected using a statistical rate theory. This reaction 27,29 is roughly 500 times slower than the collisional rate, and we found that this is due partly to the fact that the MECP lies slightly (0.5 kcal mol À1 ) higher in energy than the reactants, and partly to the fairly low (5%) probability of surface hopping upon reaching the MECP.…”

Electric quadrupole and hexadecapole moments for X2CCX2, X = H, F, Cl, Br, and I*

“…Cheng et al 25 reported a photoionization study of the complexes (C 2 F 4 ) n ⋅O 2 , n =1,2, and the clusters (C 2 F 4 ) n , n =2,3. House and Weitz 26 studied the kinetics of formation and dissociation of Fe(CO) 4 (C 2 X 4 ) and Fe(CO) 3 (C 2 X 4 ) 2 , X = H, F, in the gas phase. A theoretical study of the bonding in iron tetracarbonyl complexes with C 2 X 4 , X = H, F, Cl, Br, I, CN, was reported by Cedeño et al 27.…”

A Gas-Phase Study of the Kinetics of Formation of Fe(CO)3DMB, Fe(CO)3(DMB)2, and Fe(CO)4DMB: The Bond Dissociation Enthalpy for Fe(CO)3(DMB)2 (DMB = 3,3-dimethyl-1-butene)

“…Such small values for the preexpo- nential factor and the activation energy for the reaction suggest that the decay of Fe(CO) 4 DMB involves a multiple step pathway and/or heterogeneous process taking place on the cell walls. 9 The latter possibility is bolstered by the fact that similar behavior observed for Fe(CO) 4 L (L ) C 2 H 4 , C 2 Cl 4 , and C 2 F 4 ) has been attributed to such processes. 9,28 Additionally, Fe(CO) 4 DMP is sufficiently stable at room temperature that an IR spectrum of the species has been obtained using standard techniques.…”

“…5,17 One factor that has been previously considered is the polarizability of the entering ligand. 17 Since a curve crossing must occur to produce stable products, a complex that has a longer lifetime on the triplet potential surface will, with all else Yes Fe(CO)3 + PD 29 (2.8 ( 0.3) × 10 -10 Yes Fe(CO)3 + propene 7 (2.6 ( 0.3) × 10 -10 Yes Fe(CO)3 + 1-pentene 8 (4 ( 1) × 10 -10 Yes Fe(CO)3(C2H4) + C2H4 15 (1.1( 0.3) × 10 -11 No Fe(CO)3(C2H4) + propene 7 (1.8( 0.3) × 10 -11 No Fe(CO)3(C2F4) + C2F4 9 (5. No Fe(CO)4 + 1,3-PD 29 (1.2( 0.1) × 10 -12 No Fe(CO)4 + 1,4-PD 29 (5.8( 0.3) × 10 -13 No Fe(CO)3(C2H4) + Fe(CO)5 9 (4( 2) × 10 -11 Fe(CO)3(C2Cl4) + Fe(CO)5 28 being equal, have a higher probability for curve crossing.…”