High-Resolution Electron Spectroscopy and Rotational Conformers of Group 6 Metal (Cr, Mo, and W) Bis(mesitylene) Sandwich Complexes

Abstract

Group 6 metal-bis(mesitylene) sandwich complexes are produced by interactions between the laser-vaporized metal atoms and mesitylene vapor in a pulsed molecular beam source, identified by photoionization time-of-flight mass spectrometry, and studied by pulsed-field ionization zero-electron kinetic energy spectroscopy and density functional theory calculations. Although transition metal-bis(arene) sandwich complexes may adopt eclipsed and staggered conformations, the group 6 metal-bis(mesitylene) complexes are determined to be in the eclipsed form. In this form, rotational conformers with methyl group dihedral angles of 0 and 60° are identified for the Cr complex, whereas the 0° rotamer is observed for the Mo and W species. The 0° rotamer is in a C(2v) symmetry with the neutral ground state of (1)A1 and the singly positive charged ion state of (2)A1. The 60° rotamer is in a C(i) symmetry with the neutral ground state of (1)A(g) and the ion state of (2)A(g). Partial conversion of the 60 to 0° rotamer is observed from He to He/Ar supersonic expansion for Cr-bis(mesitylene). The unsuccessful observation of the 60° rotamer for the Mo and W complexes is the result of its complete conversion to the 0° rotamer in both He and He/Ar expansions. The adiabatic ionization energies of the 0° rotamers of the three complexes are in the order of Cr-bis(mesitylene) < W-bis(mesitylene) < Mo-bis(mesitylene), which is different from that of the metal atoms. These metal-bis(mesitylene) complexes have lower ionization energies than the corresponding metal-bis(benzene) and -bis(toluene) species.

Spectroscopic Characterization of Nonconcerted [4 + 2] Cycloaddition of 1,3-Butadiene with Lanthanacyclopropene To Form Lanthanum–Benzene in the Gas Phase

“…In these calculations, we used the Becke’s three-parameter hybrid functional with the correlation functional of Lee, Yang, and Parr (B3LYP) and the 6-311+G­(d,p) basis set for C and H and the effective-core-potential SDD basis set for La. We have extensively used the DFT method and found it generally produced adequate results for the spectral and structural assignments of organometallic complexes. − ,− No symmetry restrictions were imposed in the initial geometry optimizations, but appropriate point groups were used in the subsequent optimizations to help identify electronic symmetries. For each optimized stationary point, a vibrational analysis was performed to identify the nature of the stationary point (minimum or saddle point).…”

Effect of a single methyl substituent on the electronic structure of cobaltocene studied by computationally assisted MATI spectroscopy

“…The molecular structures of the neutral (doublet) and cationic (singlet) methylcobaltocene were optimized at the BPW91/ TZVP, B3PW91/6-311+G(d,p), B3PW91/6-311++G(d,p), B3LYP/ 6-311++G(d,p) and TPSSh/6-311+G(d,p) levels of DFT. These combinations of the GGA (BPW91) or hybrid (B3PW91) functionals and triple-z split valence basis sets have demonstrated earlier good performance when modelling the MATI spectra of bisarene complexes, [46][47][48][49][50][51][52][53][54][55][56][57][58] mixed sandwiches 59 and decamethylmanganocene. 45 The 10% exact exchange TPSSh meta-type functional 69 produced high-quality results for transition-metal systems.…”

“…DFT-supported MATI spectroscopy appeared to represent a powerful instrument for studying not only accurate ionization and vibrational energies of metallocenes, 28,45 bisarene complexes [46][47][48][49][50][51][52][53][54][55][56][57][58] or mixed sandwich systems 59 but also structural behaviors of these organometallics on ionization. 28,45,59 This opens new opportunities for investigations of substituent effects in sandwich compounds.…”

Ionization of Decamethylmanganocene: Insights from the DFT-Assisted Laser Spectroscopy

“…Among metallocenes, the MATI spectrum has so far been recorded only for Cp 2 Co [ 52 ]. The MATI/ZEKE data have been obtained also for some bisarene complexes [ 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ] and few mixed sandwiches [ 66 ]. These studies demonstrated new possibilities provided by the MATI and ZEKE techniques for detecting substituent effects and structural changes of sandwich molecules upon ionization [ 67 ].…”