Metallacyclopropene structures identified by IRMPD spectroscopic investigation of the dehydrogenation reactions of Ta+ and TaO+ with ethene

Abstract

Species formed in the reactions of Ta + and TaO + with ethene are examined spectroscopically using infrared multiple photon dissociation (IRMPD) action spectroscopy. Ta + , TaC2H2 + , and TaO + are all observed to dehydrogenate ethene yielding [Ta,2C,2H] + , [Ta,4C,4H] + , and [Ta,O,2C,2H] + , respectively. For these species, IR action spectra are obtained in the 225 -3400 cm -1 range by monitoring fragmentation into the [Ta,2C] + , [Ta,4C,nH] + (n = 2, 3), and [Ta,O] + mass channels, respectively. The spectra are assigned to TaC2H2 + , Ta(C2H2)2 + , and OTaC2H2 + metallacyclopropene species on the basis of comparisons with scaled vibrational spectra from B3LYP/def2-TZVPPD geometry optimized structures. To further elucidate the chemistry observed, complete reaction coordinate pathways having quintet, triplet, and singlet spin for all three dehydrogenation reactions have also been examined.

Cyclotrimerization of Acetylene in Gas Phase V+(C2H2)n Complexes: Detection of Intermediates and Products with Infrared Spectroscopy

“…The most likely structure is therefore the 3/3 dimetallacycle (isomer 2c). This assignment is consistent with that reported by Armentrout and coworkers for the analogous Ta + (C 2 H 2 ) 2 complex, which has the same kind of dimetallacycle structure …”

“…This assignment is consistent with that reported by Armentrout and coworkers for the analogous Ta + (C 2 H 2 ) 2 complex, which has the same kind of dimetallacycle structure. 68 Isomer 2c, which appears to be present, is not the most stable structure predicted by theory. Initially, it is not clear whether DFT is misrepresenting the relative energies of these different structures or the experiment is kinetically trapping this metastable species.…”

“…In a closely related work, Armentrout and coworkers have recently reported the formation of Ta + (C 2 H 2 ) n metallacycles from metal−ethene dehydrogenation reactions. 68 In studies of multiligand complexes, our group found that the nickel cation formed a four-coordinate (4C) tetrahedral structure with acetylene. 63 In larger complexes, tentative evidence was obtained for a ligand-coupling reaction producing cyclobutadienyl adducts, 62 but no computational work was available at that time to confirm this proposal.…”

“…This work identified vanadium as an outlier, which formed an M + (C 2 H 2 ) metallacycle rather than a cation-π complex. In a closely related work, Armentrout and coworkers have recently reported the formation of Ta + (C 2 H 2 ) n metallacycles from metal–ethene dehydrogenation reactions . In studies of multiligand complexes, our group found that the nickel cation formed a four-coordinate (4C) tetrahedral structure with acetylene .…”

Pt+(C2H2)n Complexes Studied with Selected-Ion Infrared Spectroscopy

“…Metal ion–acetylene complexes have been investigated with mass spectrometry, computational chemistry, electronic spectroscopy, and IR spectroscopy. − IR photodissociation spectroscopy measurements compared to the predictions of theory have provided the most detailed information about structures and bonding. − Mono-acetylene complexes with a variety of metals form cation−π complexes, with metal ion binding in a symmetric position to the triple bond of acetylene. In these structures, the H–CC bond angle is changed, moving the hydrogen atoms away from the linear axis and away from the metal.…”