Three types of oxime species, i.e.,
4-morpholylcarbamidoxime
(hydroxyguanidine), phenylacetamidoxime and benzamidoxime
(amidoximes), and cyclohexanone oxime and benzophenone
oxime (ketoximes), react at room temperature with the 2-nitrilium closo-decaborate clusters, leading to 2-iminium closo-decaborates (14 examples; 57–94%). These species
were characterized by ICPMS-based boron elemental analysis, HRESI–-MS, molar conductivity, IR, 1H{11B}, and 11B{1H} NMR spectroscopies, and additionally
by single-crystal X-ray diffraction (for six compounds). On the basis
of kinetic data, ΔH
⧧, ΔS
⧧, and ΔG
⧧ of the additions were determined, showing a 4 order-of-magnitude
decrease in reactivity from the hydroxyguanidine to the aromatic
ketoxime as entering nucleophiles. The results of DFT calculations
indicate that the mechanism for these reactions is stepwise and is
realized through the formation of the orientation complex of the nitrone
form, R2R3CN+(H)O–, of oximes with [B10H9NCEt]−, giving further an acyclic intermediate (the rate-determining
step), followed by proton migration, leading to the addition product.
The calculated overall activation barrier for these transformations
is consistent with the experimental kinetic observations. This work
provides, for the first time, a broad nucleophilicity series of oximes,
which is useful to control various nucleophilic additions of oxime
species.
Synopsis Highlights Crystal structures of [Rh(R1COCHCOR2)(CO)2], where R1, R2 = CF3, C4H3S or Ph Metallophilic rhodium-rhodium interactions in the solid state Sigma-sigma interaction of dz2 molecular orbitals AIM bonding paths NBO LP(Rh dz2)-LP*(Rh pz) interaction
In the title compound, [Rh(C10H9O2)(CO)2], a distorted square-planar coordination geometry is observed around the RhI atom, formed by the O atoms of the bidentate ligand and two C atoms from the carbonyl ligands. The RhI atom is displaced from the plane through the surrounding atoms by 0.017 Å. In the crystal, C—H⋯O interaction is observed between a methyl group of the bidentate ligand and a carbonyl O atom. Metallophilic interactions [3.308 (3) and 3.461 (3) Å] between neighbouring RhI atoms are encountered in the crystal, resulting in the formation of a metal chain along the b-axis direction.
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