Rh{(η4-cod) or (PPh3)2}-Schiff base complexes with a Z′ = 2 structure: Syntheses, spectroscopy, thermalanalyses and DFT/TDDFT

• Rh{(η4-cod) or (PPh3)2}-Schiff base complexes.
• Two symmetry-independent molecules in the asymmetric unit to give a Z′ = 2 structure.
• 31P NMR show two doublets due to two asymmetric P-atoms bound to the Rh(I) trans to N and O atoms, respectively.
• DFT/TDDFT calculations correspond well to the experimental results.

Reaction of Schiff bases with [Rh(η4-cod)(acetate)]2 (cod = 1,5-cyclooctadiene) provides [Rh(η4-cod){N(C6H5)2-oxo-1-naphthaldiminato-κ2N,O}] (1) and [Rh(η4-cod){(R)-N-(p-BrC6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O}] (2), respectively. Compound 2 reacts with triphenylphosphine (PPh3) to give [Rh(PPh3)2{(R)-N-(p-BrC6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O}] (3). Molecular structure determination for 1 reveals that the 2-oxo-1-naphthaldiminate ligand is coordinated to the Rh(η4-cod)-fragment with six-membered N,O-chelation in distorted square planar geometry. The structure shows two symmetry-independent molecules in the asymmetric unit to give a Z′ = 2 structure. Optimized structures correspond well to the experimental results. Electronic spectra by TDDFT show combined metal-metal and metal-ligand transition bands at 411 (1) or 402 (2) nm with the highest MO contributions of ca. 81% for HOMO-1 to LUMO, comparable to the experimental bands. Electronic spectra in different solvents show a negative solvatochromic trend with increasing dielectric constants and acceptor number of solvents, respectively. 1H NMR spectra show two multiplets for exo- and endo-methylene protons, and two doublets for olefinic protons of cod-ligand, respectively. 31P NMR spectra show two sets of doublets at δ 38.59 and 39.55 ppm due to two asymmetric P-atoms coordinated to the rhodium trans to N and O atoms, respectively in 3. DSC analyses demonstrate an irreversible phase transformation from crystalline to isotropic liquid phase.

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