Ruthenium Catalyzed Reactions of Aldehydes: Molecular Structures of Ruthenium Complexes with Aldehyde Ligands

Abstract

RuCl(H)(CO)(PPh 3 ) 3 ](2) was found to catalyze, in the presence of H 2 C=CHSiMe 3 (3), the trimerisation of aldehydes RCHO [R=Et (4a), i-Bu (4b)] yielding 1,3,5-trioxanes (5) and the aldol condensation yielding a,b-unsaturated aldehydes (6). When (4a) was used as a reactant, from these reaction mixtures, the ruthenium complex [RuCl 2 (CO)(PPh 3 ) 2 (EtCH@CMeACHO-jO)] (7) having the aldol condensation product as the ligand crystallized. In the analogous reaction with (4b), the complex [RuCl 2 (CO)(PPh 3 ) 2 (i-BuCHO-jO)] (8) with the aldehyde as ligand was obtained. The constitution of these complexes was established by single-crystal X-ray diffraction measurements. The ruthenium centers are octahedrally coordinated having the aldehyde and the carbonyl ligand in mutually trans positions (coordination index: OC-6-12). The aldehydes are monodentately coordinated via the carbonyl oxygen atom (jO). The coordination induced elongations of the C@O double bonds [1.242(4) Å (7), 1.234(4) Å (8)] indicate an activation of the aldehydes. Furthermore, the RuACO bond lengths [1.842(4) Å (7), 1.823(4) Å (8)] exhibit a relatively low trans influence of the aldehyde ligands. The formation of the complexes (7) and (8) give an indication that the Lewis acidity of the ruthenium center is of importance for aldehyde activation in the catalytic process.

Unexpected Role of Anionic Ligands in the Ruthenium‐Catalyzed Base‐Free Selective Hydrogenation of Aldehydes

“…Such a reaction could be highly favored by steric congestion caused by bulky carboxylate ligands. After aldehyde coordination to give Int3 (step b) and insertion into the RuH bond to give Int4 (step c),21 coordinated H 2 in Int5 (formed in step d) may be deprotonated by RCO 2 − 22 to afford neutral Int6 along with the corresponding carboxylic acid (step e). The protonation of Int6 would finally regenerate Int1 and provide the desired primary alcohol.…”

Mixed ligand cobalt and palladium complexes containing triphenylphosphine and a hydrazone: Synthesis and application in non-linear optics

“…A sharp peak at around 8.5 ppm in the complex has been assigned to azomethine proton of the hydrazone where the nitrogen of −C=N− is participating in complex formation. [21][22][23][24][25][26] The 1 H NMR spectra of the complexes are provided in the Supporting Information. In the 13 C NMR spectra of the complexes (Supplemental Figures S3 and S6), resonances were observed in the 151-to 155ppm series was due to the azomethine carbon.…”

Synthesis, characterization of N,N′-bis(2-hydroxynaphthalidene)phenylene-1,2-diamine with M(II)(M=Ni, Zn and Fe) Schiff-base complexes and their non-linear optical studies by z-scan technique

“…1 H NMR spectral data of the complexes nickel(II) and zinc(II) complex exhibits a multiplet around 6.9-7.9 ppm which has been assigned to the protons of phenyl groups present in Schiff base ligand. A peak observed at 8.5 ppm in the complex has been assigned to azomethine proton (-C@N-) [33][34][35]. The absence of a resonance due to phenolic hydrogen indicates the deprotonation of the Schiff base.…”