Kelley R. Lane

A tandem flowing afterglow-triple quadrupole instrument

Abstract A new hybrid mass spectrometer is described for the characterization of structures of products generated in a flowing afterglow apparatus by triple quadrupole tandem mass spectrometry. Examples are given of isomeric ion differentiation using daughter spectra generated by collision-induced dissociation of mass selected ions. Parent spectra allow systematic characterization of the complex mixture of product ions produced by electron impact ionization and subsequent ion/molecule condensation reactions of Fe(CO)5. Cluster ions, including trimers consisting of three amines solvating a proton, can be generated and their unimolecular kinetics provides information about gas phase basicities. Small differences in dimer and trimer fragmentation behavior are interpreted in terms of steric effects operating in the trimer.

Hydride transfer to transition-metal carbonyls in the gas phase. Formation and relative stabilities of anionic formyl complexes

Abstract The hydride binding energies of Fe(CO) 5 , Cr(CO) 6 , Mo(CO) 6 and W(CO) 6 ( HA (M(CO) n ) = D[(CO) n − MCOH − ]) have been estimated from bimolecular hydride transfer reactions in the gas phase. Hydride transfer to the metal carbonyls yields the corresponding anionic formyl complexes and the hydride affinity bracketing experiments establish HA (Fe(CO) 5 ) = 56±4 kcal mol −1 and HA (Cr(CO) 6 ) = HA (Mo(CO) 6 ) = HA (W(CO) 6 ) = 44±4 kcal mol −1 . Gas-phase heats of formation and metal-carbon bond strengths for the metal formyl anions are derived from the hydride binding energies. The hydride affinity ordering for the metal carbonyls parallels their relative reactivities towards nucleophilic addition in solution and correlates with the relative magnitudes of their CO-stretching force constants ( k co ). The new metal formyl data are combined with known or estimated heats of formation for metal hydrides to show that CO-insertion into the metal-hydrogen bond is thermodynamically unfavourable for these systems.

Nucleophilic Addition Reactions of Negative Ions with Organometallic Complexes in the Gas Phase

Nucleophilic addition and substitution reactions involving metal compounds are among the most widely applied and extensively documented reactions in organometallic chemistry. From the familiar and time-honored Grignard syntheses(1) to the most recent methods for preparing organolanthanides(2) and organoactinides,(3) nucleophilic reactions are found in innumerable synthetic procedures for forming carbon-metal bonds.(4) Nucleophilic addition continues to be the method of choice for preparing anionic transition metal acyls, formyls, hydrides, η3-allyls, η5-cyclohexadienyl complexes, and other lowoxidation-state intermediates for both stoichiometric and catalytic metal-mediated organic synthesis.(5,6) Current efforts to activate CO, CO2, and other small molecules using catalytic cycles in homogeneous solution frequently employ nucleophilic addition strategies in conjunction with transition metal complexes as catalysts.(7,8) For example, the industrially important water-gas shift reaction has been shown to exhibit catalysis in aqueous alkaline solutions containing a wide variety of mono-and polynuclear metal carbonyls.(9–11) Furthermore, the Reppe reaction, the Wacker oxidation, and most homogeneous models for the Fischer-Tropsch process all involve nucleophilic attack on a metal-coordinated ligand during one or more of the key steps in the proposed mechanisms.(5,12–14)