John C. Traeger

Electrospray Mass Spectrometry of Organometallic Compounds

Abstract The development of electrospray mass spectrometry (ESMS) for the characterization of organometallic compounds is discussed. The diverse range of both ionic and neutral species amenable to investigation, together with the ability to detect in situ reaction intermediates, is evidence that ESMS should be regarded as one of the major techniques available for organometallic solution studies.

The application of electrospray mass spectrometry to ionic inorganic and organometallic systems

Abstract Electrospray mass spectra have been observed for a number of ionic inorganic and organometallic compounds in dichloromethane/methanol (1:10) solutions. Intact principal ions were observed directly for [PPh 3 Bz] + , NBu 4 PF 6 (positive and negative), [Fe(C 5 H 5 )2] + and trans -[Cr(CO) 2 (dpe) 2 ] + (dpe=Ph 2 PCH 2 CH 2 PPh 2 ). The non-ionic compound Re(CO) 2 Br(η 1 -dpm)(η 2 -dpm)(dpm=Ph 2 PCH 2 PPh 2 ) was reacted with MeI to convert the pendant phosphorus to a phosphonium salt to give [Re(CO) 2 Br(η 1 -dpmMe)(η 2 -dpm)]I whose principal ion was observed. The heteropolymolybdate (NEt 4 ) 4 [S 2 Mo 18 O 62 ] in acetonitrile solution gave the intact [S 2 Mo 18 O 62 ] 4− ion. These systems show that electrospray mass spectrometry has great promise for investigating ionic compounds, particularly those that are not amenable to mass spectrometric studies via other ionization techniques.

A photoionization study of the energetics of the C7H7+ ion formed from C7H8 precursors☆

Abstract The photoionization efficiency curves for C 7 H 7 + , formed from several C 7 H 8 precursors, have been measured in the energy range 9–13 eV. By using extended signal-averaging techniques it has been possible to greatly increase the sensitivity of ion detection, hence minimizing the effect of kinetic shift for these fragmentation processes. As a result, cationic heats of formation have been obtained which are in good agreement with other thermochemical data.

A study of the allyl cation thermochemistry by photoionization mass spectrometry

Abstract The ionization energies and C3H5+ appearance energies for several C3H6 and C4H8 hydrocarbons have been measured by photoionization mass spectrometry. A 298 K heat of formation of 949.6±1.4 kJ mol−1, based on the stationary electron convention, is derived for the allyl cation in the gas phase; this results in a heat of formation for the allyl radical of 165.2±3.3 kJ mol−1. From corresponding measurements for the allyl halides, heats of formation at 298 K are obtained for 3-chloro-1-propene (−5.6 kJ mol−1), 3-bromo-1-propene (+47.7 kJ mo1−1) and 3-iodo-1-propene (+99.5 kJ mol−1), together with values for the contributions of C-(Cd)(H)2(X) groups to heats of formation.

Interactions of some crown ethers, cyclam and its tetrathia analogue with alkali, alkali earth and other metal ions: an electrospray mass spectrometric study

Abstract Electrospray mass spectrometry (ESMS) has been used to investigate the interactions in solution between three crown ethers (12-crown-4, 18-crown-6, dibenzyl-18-crown-6), 1,4,8,11-tetraazacyclotetradecane (cyclam) and its tetrathia analogue (S-crown) and a variety of metal ions. These include the alkali and alkali earth metal ions, various divalent transition metal ions and main group metal ions such as Cd2+ and Pb2+. The previously proposed relationships between the cation radius and the radius of the crown ether cavity which determine the stoichiometry of the complexes formed are dominant in solution. Although the cavity size of DB-18-C-6 is similar to that of 18-C-6, it behaves as though the cavity is effectively smaller as a result of its less flexible structure. Cyclam gave no complexes containing alkali and alkali earth cations, but ionic species were observed with the transition metal ions. S-crown did form ionic complexes with the alkali metal ions and transition metal ions, but not the alkali earth cations.

CATIONIC PHOSPHINE COMPLEXES OF GOLD(I) : AN ELECTROSPRAY MASS SPECTROMETRIC STUDY

Abstract Electrospray (ES) mass spectra have been observed for a number of cationic gold(I) phosphine derivatives in dichloromethane/methanol solution. For complexes of the types [Au(PR3)2]+ and [Au(PR3)3]+ the intact ions were observedbut ions of the type [Au(PR3)4]+ were not detected in the gas phase. The tris(ligand) complexes [Au(PR3)3]+ are relatively unstable in the gas phase and the product ions [Au(PR3)2]+ are readily produced by collisional activation, either in the electrospray ion source or by using tandem mass spectrometry. In solution, mixed ligand gold(I) complexes are known to exchange rapidly on the NMR timescale at room temperature, but ESMS techniques can identify the individual components of such mixtures. Reactions in solution between ClAu(PPh3) and a number of potentially bidentate diphosphine and related ligands have been monitored by ESMS. The ES technique provides a unique insight into the changing equilibria which occur in solution as the relative proportions of the constitutents change.

Heat of formation for the formyl cation by photoionization mass spectrometry

Abstract The ionization energies and HCO + appearance energies for a series of organic compounds have been measured by dissociative photoionization mass spectrometry. A 298 K heat of formation of 825.6±2.7 kJ mol −1 , based on the stationary electron convention, is derived for the formyl cation in the gas phase which results in an absolute proton affinity for CO of 594±3 kJ mol −1 . From a discussion of the heat of formation for the formyl radical, the adiabatic ionization energy for HCO is estimated to be 8.10±0.05 eV.

Ionization and dissociation by electron impact III. CH4 and SiH4

Abstract The electron impact induced ionization and dissociation of CH4 and SiH4 have been studied using a quadrupole mass spectrometer. Deconvoluted first differential ionization efficiency curves are presented and structural features of the parent and fragment ion curves discussed in terms of their contribution to the total differential ionization cross section. A comparison is made with the corresponding photoionization and photoelectron spectra.

The electrospray mass spectra of phosphoric acid, methylphosphonic acid and its alkyl esters, and their complexes with alkali and alkali earth metal ions

Positive and negative ion electrospray mass spectra were obtained directly from water/alcohol solutions for phosphoric acid, methylphosphonic acid and its mono(1,2,2-trimethylpropyl) ester and bis(1-methylethyl) ester. Collisional activation and tandem mass spectrometry (MS/MS) of both the cations and anions of the phosphonates resulted in hydrogen rearrangement with loss of neutral alkenes to give the respective methylphosphonic acid anion (m/z 95) and methylphosphonic acid cation (m/z 97). Solutions of this series of compounds, which comprise a neutral, mono-basic, di-basic and tri-basic ligand, were complexed with alkali and alkali earth metal ions. The peaks observed in the positive ion electrospray mass spectra, and their propensity for fragmentation under collisional activation, were found to be consistent with the predicted stabilities of the complexes.

Electrospray mass spectrometric studies of some cationic and anionic Group 6 and Group 7 metal carbonyl complexes

Abstract Electrospray mass spectra derived from dichloromethane or dichloromethane/methanol solutions of cationic and anionic metal carbonyl compounds are reported for the first time. The cations investigated are the seven coordinate species [M(CO)2(PP)2 X]+ (M  Mo, W; PP  diphosphine or similar ligand; X  F, Cl, Br, I) and carbonyl phosphonium or arsonium cations of the types [M(CO)3(η-PPMe)(η2-PP)], (M  Cr, Mo, W), [M′(CO)2(η2-PPMe)(η2PP)X]+ (M′ Mn, Re). These cations were prepared by the action of Mel on M(CO)3(η1PP)(η2-PP) and [M′(CO)2(η1PP)(η2PP)X, respectively, each of which contains a pendant Group 15 atom. The anionic species investigated are [M(CO)5X]− and [M′(CO)4X2]−. In all cases the dominant peak in the mass spectrum corresponds to the principal ion known to be present in solution.