G. Innorta

Use of the mass spectrometer in the elucidation of organometallic complex structures: study of two new carbonyl clusters of cobalt, SCo4(CO)9[P(CH3)2]2 and S2Co3(CO)7P(CH3)2

Abstract The formation of two new cobalt carbonyl cluster compounds, SCo 4 (CO) 9 [P(CH 3 ) 2 ] 2 (I) and S 2 Co 3 (CO) 7 P(CH 3 ) 2 (II) in the reaction of Co 2 (CO) 8 with (CH 3 ) 2 P(S)P(S)(CH 3 ) 2 is described. Their compositions have been elucidated from their mass spectra, emphasis being laid on the 13 C and 34 S satellites of the principal peaks. This procedure is discussed in detail, and is recommended for more general use in organometallic chemistry.

A reinvestigation of the mass spectra of substituted ferrocenes: accurate fragmentation pathways and ionic structures by analysis of metastable ion spectra

Abstract The mass spectra of substituted ferrocenes have been reinvestigated making intensive use of the metastable ions. The observed primary fragmentation of the molecular ions are different in some respects from those previously postulated. The study of the metastable ions characteristics of the ions at m/z 186 and m/z 121 indicates that their structures are independent of their precursor ions.

Kinetic studies in various media on some hydrogenation reactions catalyzed by polymer-anchored RhCl(PPh3)3

Abstract A study has been made of the hydrogenation of cyclohexene, 1-hexene and styrene at atmospheric pressure catalysed by RhCl (PPh 3 ) 3 supported on styrene-divinylbenzene copolymers with 1%, 2% and 4% cross linking. The dependence of the hydrogenation rate on the concentration of the olefin, the amount of catalyst, and the nature of the solvent was investigated. The hydrogenation rate is lower than for homogeneous catalysis but the dependence of the rate on the examined parameters is similar. The ratio between the rates for 1-hexene and cyclohexene is higher than that in the homogeneous phase. This increase in selectivity may due to steric hindrance around the active sites of the resin. The solvent effects revealed that the hydrogenation rate also depends on the degree of swelling of the resin.

Mass spectrometric evidence for Pπdπ bonding between sulfur and the group IVB elements

Comparison of the ionization energies of C6H5SX(CH3)3 (X = C, Si, Ge, Sn and Pb) with those of X(CH3)4 compounds, shows that the absolute values are lower and in a narrower range in the former series; in addition, the carbon derivative does not follow the trend observed for the other compounds. pπdπ bonding between S and X (X = Si, Ge, Sn and Pb) is invoked to explain the results. This proposal is also in agreement with the SX bond energies in these compounds, with the ionization energies in the series S[X(CH3)3]2 (X = C, Si, Ge and Sn), and with the ionization and bond dissociation energies of the compounds C6H5SSi(CH3)3, C6H5SSi(CH3)2Cl and C6H5SSiCl3.

Interpretation of the mass spectra of substituted chromium and tungsten carbonyls by means of appearance potential measurements

Abstract The 50 eV mass spectra of M(CO) 5 PR 3 complexes (M = Cr and W; R = OCH 3 , OC 2 H 5 , n-C 4 H 9 and C 6 H 5 have been determined. The chromium derivatives and the P(OCH 3 ) 3 , P(OC 2 H 5 ) 3 and P(C 6 H 5 ) 3 tungsten derivatives show ions predominantly formed by CO elimination. This behaviour is related to the higher activation energy for the rupture of P—R compared with that of MCO bonds. The spectra of the P(n-C 4 H 9 ) 3 and P(O-n-C 4 H 9 ) 3 tungsten derivatives, on the other hand, are dominated by ions obtained by partial fragmentation of the heteroligands. The heptacoordination capability of tungsten, the length of the R chain, and energetic factors are responsible for the appearance of these new fragmentation pathways.

Entropy effects in gas phase ion-molecule association reactions

Abstract The kinetics of gas phase reactions of the ions C 5 H 5 M + (M=V, Co, Ni and Ru) with oxygen (Me 2 CO, Me 2 O, MeOH, Me 2 CHOH, H 2 O) and nitrogen (NH 3 , NH 2 Me, NHMe 2 , NMe 3 ) donor ligands have been studied by Ion Trap Mass Spectrometry. The kinetic data confirm the previously found dependence of the log of the rate constants upon the ligand ionization energy. To get some insight on the origin of the existing barrier to the reaction some experiments were performed at various temperatures; it was found that the kinetic constants increased when the temperature decreased. The results are compatible with an entropy effect on the free energy of activation as also shown by some calculations performed for the reaction of the C 5 H 5 Fe + ion with water.

Kinetic features of olefin hydrogenations catalyzed by polymer-anchored palladium acetate

Abstract Palladium acetate anchored to polystyrylbipyridine has been used to catalyze the hydrogenations of monoalkenes at atmospheric pressure. Its kinetic behaviour and catalytic activity are independent of the metal oxidation state. The catalyst displays selectivity with respect to steric hindrance at the double bond, the hydrogenation rate decreasing on going from 1-hexene and 1-octene to cyclohexene and cyclooctene. The conversion of terminal double bonds into internal double bonds during the hydrogenations is unappreciable. Different properties and kinetic behaviour are observed after treatment of the catalyst with LiAlH 4 ; in particular, the treated catalyst induces fast isomerization reactions.

Gas phase reactions of the ion C5H5Fe+: A kinetic study

The kinetics of gas phase reactions of the ion C5H5Fe+ with oxygen (Me2CO, Me2O, MeOH, iso-propanol, H2O) and nitrogen (NH3, NH2Me, NHMe2, NMe3) donor ligands have been studied by ion trap mass spectrometry. While in the literature reactions of the ion Fe+, with the same ligands, the principal reaction path involves fragmentation in almost all the reactions of the ion C5H5Fe+, formation of adduct ions is the major reaction path. The reactivity of these two ions is briefly compared in the ion trap conditions. Kinetic data for the ion C5H5Fe+ indicate that the reactions show a large range of efficiency and a linear correlation is found between the log of the reaction rate constants and the ionization energy of ligands with the same donor atom.

Kinetics and mechanism of ligand substitution reactions of RuCl3NOL2 complexes

Abstract A kinetic and mechanistic study on the ligand substitution reactions of RuCl3NOL2 (L = AsPh3 or SbPh3) complexes is reported. These reactions proceed via a dissociative step. The competition of different ligands for the intermediate RuCl3NOL has been investigated; steric effects seem to influence the ability of the ligands to attack this pentacoordinated intermediate.

Mass spectrometric study of η-C5H5Fe(CO)2 EMe3 complexes (E = Si, Ge, Sn and Pb)

Abstract The complexes η-C5H5Fe(CO)2EMe3 (E = Si, Ge, Sn and Pb)and η-C5H5Fe(CO)2X (X = Cl, CH3, I, SnCl3) have been studied by mass spectrometry. Ionization energy data show an easier ionization going down along the IV group, except for the carbon derivative whose I.P. is lower than that of the silicon derivative. Values of D(FeE) increase from Si to Sn and decrease from Sn and Pb. The results do not permit to establish the role of the possible π back bonding between Fe and E. The 50 eV mass spectra are briefly discussed in terms of competitive fragmentations of the molecular ions.