Substituent effects of fused Hammick silylenes via density functional theory survey

A combination of gas-phase ion trap mass spectrometry experiments and density functional theory (DFT) calculations have been used to examine the role of substituents on the decarboxylation of 25 different coordinated aromatic carboxylates in binuclear complexes, [(napy)Cu2(O2CC6H4X)]+, where napy is the ligand 1,8-naphthyridine (molecular formula, C8H6N2) and X = H and the ortho ( o), meta ( m) and para ( p) isomers of F, Br, CN, NO2, CF3, OAc, Me and MeO. Two competing unimolecular reaction pathways were found: decarboxylation to give the organometallic cation [(napy)Cu2(C6H4X)]+ or loss of the neutral copper benzoate to yield [(napy)Cu]+. The substituents on the aryl group influence the branching ratios of these product channels, but decarboxylation is always the dominant pathway. Density functional theory calculations reveal that decarboxylation proceeds via two transition states. The first enables a change in the coordination mode of the coordinated benzoate in [(napy)Cu2(O2CC6H4X)]+ from the thermodynamically favoured O, O-bridged form to the O-bound form, which is the reactive conformation for the second transition state which involves extrusion of CO2 with concomitant formation of the CO2 coordinated organometallic cation, [(napy)Cu2(C6H4X)(CO2)]+, which then loses CO2 in the final step to yield [(napy)Cu2(C6H4X)]+. In all cases the barrier is highest for the second transition state. The o-substituted benzoates show a lower activation energy than the m-substituted ones, while the p-substituted ones have the highest energy, which is consistent with the experimentally determined normalised collision energy required to induce fragmentation of [(napy)Cu2(O2CC6H4X)]+.

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Substituent Effects in 3,3’ Bipyrazole Derivatives. X-ray Crystal Structures, Molecular Properties and DFT Analysis

Acta Chimica Slovenica ◽

10.17344/acsi.2021.6756 ◽

2021 ◽

Vol 68 (3) ◽

pp. 718-727

Author(s):

Ibrahim Bouabdallah ◽

Tarik Harit ◽

Mahmoud Rahal ◽

Fouad Malek ◽

Monique Tillard ◽

...

Keyword(s):

Crystal Structure ◽

Density Functional Theory ◽

Solid State ◽

Dft Calculations ◽

Single Crystal ◽

Crystal Structures ◽

Density Functional ◽

Substituent Effects ◽

Functional Theory ◽

X Ray

The single crystal X-ray structure of new 1,1’-bis(2-nitrophenyl)-5,5’-diisopropyl-3,3’-bipyrazole, 1, is triclinic P I–, a = 7.7113(8), b = 12.3926(14), c = 12.9886(12) Å, α = 92.008(8), β = 102.251(8), γ = 99.655(9)°. The structural arrangement is compared to that of 5,5’-diisopropyl-3,3’-bipyrazole, 5, whose single crystal structure is found tetragonal I41/a, a = b = 11.684(1), c = 19.158(1) Å. The comparison is also extended to the structures previously determined for 1,1’-bis(2-nitrophenyl)-5,5’-propyl-3,3’-bipyrazole, 2, 1,1’-bis(4-nitrophenyl)-5,5’-diisopropyl-3,3’-bipyrazole, 3, and 1,1’-bis(benzyl)-5,5’-diisopropyl-3,3’-bipyrazole, 4. Density Functional Theory (DFT) calculations are used to investigate the molecular geometries and to determine the global reactivity parameters. The geometry of isolated molecules and the molecular arrangements in the solid state are analyzed according to the nature of the groups connected to the bipyrazole core.

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