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The Schiff base 1‐benzyl‐N‐(3,5‐di‐tert‐butylsalicylidene)piperidin‐4‐amine (HL) and its acetatopalladium(II) complex having the formula [Pd(L)(OAc)] were synthesized. Both HL and [Pd(L)(OAc)] were characterized using elemental analysis and various spectroscopic (infrared, UV–visible, 1H NMR and 13C NMR) and mass spectrometric measurements. The molecular structure of the complex was determined using X‐ray crystallographic analysis. In the complex, the pincer‐like NNO‐donor L− and the monodenate OAc− provide a distorted square‐planar N2O2 coordination environment around the metal centre. The physicochemical properties and the spectroscopic features of [Pd(L)(OAc)] are consistent with its molecular structure. The complex was found to be an effective catalyst for the Suzuki–Miyaura cross‐coupling reactions of hydroxyaryl halides with arylboronic acids in predominantly aqueous media. The reactions afforded hydroxybiaryl products in good to excellent yields with a wide substrate scope.

Palladium catalyzed cross coupling reactions of (arylvinyl)tributyl stannanes with vinyl triflates resulted in the production of stereochemically pure trisubstituted E-and Z-olefins in very good yields. These olefins were transformed to the corresponding all-E-and 9Z-heteroaryl-retinoic acid analogs via Horner-Emmons reaction and subsequent basic hydrolysis in excellent yields.It is well known that all-E-retinoic acid and 9Z-retinoic acid (Scheme 1) are the ligand molecules for retinoic acid receptors (RARa, b, g) and retinoid X receptors (RXRa, b, g), respectively. 1 They are members of the nuclear receptor superfamily and exhibit significant biological functions which include cell differentiation, cell proliferation, embryonic development etc. through gene transcription. 2 In biological system, RXRs form functional heterodimers with other proteins of the nuclear receptors such as the RARs, the thyroid hormone receptor (TR), the vitamin D receptor (VDR) and the peroxisome proliferator-activated receptors (PPAR). These heterodimers bind to co-activator or co-repressor proteins with changing their conformation depending on the nature of the ligand molecule, and then activate or repress a wide variety of gene transcription. Currently great efforts have been found for the preparation of receptor-selective retinoids in order not only to define the functions of each receptor but also to develop the therapeutic agents. 3 In connection with our study on the stereoselective synthesis of retinoids, 4,5 we wish to report a convenient synthesis of all-E-and 9Z-heteroaryl-retinoic acid analogs 12 and 14 (Scheme 3), which replace the 2,6,6-trimethylcyclohexene ring of retinoic acid by the heterocyclic rings in order not only to decrease a hydrophobic character of analogs but also to investigate the interaction between the ligand and the receptor protein, by the application of a stereoselective, palladium catalyzed cross coupling reaction of (arylvinyl)-tributyl stannanes with E-and Z-vinyltriflates. 6,7 As the conversion of b-ionylideneacetaldehyde analog A to the corresponding retinoic acid has been already established using Horner-Emmons or Wittig reaction, 3,4 key step in our synthetic strategy is based on the coupling reaction of two segments B and C. Segment C was obtained from ethyl acetoacetate by the reported method 8 and the separation of two stereoisomers was easily performed by column chromatography (Scheme 1). Scheme 1Our synthetic approach toward heteroaryl-retinoic acids starts from the synthesis of (arylvinyl)tributyl stannanes 3 (Scheme 2). The arylaldehydes 1 were transformed to the acetylenes 2 by the standard procedure using carbon tetrabromide and triphenylphosphine and subsequent treatment with n-butyllithium. 9 Hydrostannylation 10 of 2 with n-Bu 3 SnH in the presence of a catalytic amount of AIBN at 50 °C for 12-16 hours afforded the corresponding (arylvinyl)tributyl stannanes 3 11 in moderate to good yields.Stille coupling reaction of 3a with (E)-vinyl triflate 5 8 in the presence of a catalytic amo...

The Schiff bases N-(acyl)-N-(ferrocenylidene)hydrazines (HFcah (1) and HFcbh (2), where acyl = acetyl in 1 and benzoyl in 2 and H represents the dissociable amide proton) were synthesized in high yields (74 and 81%) by condensation reactions of equimolar amounts of ferrocene-carboxaldehyde and the corresponding acylhydrazines in presence of acetic acid in refluxing methanol. Reactions of Ni(OAc) 2 •4H 2 O, the Schiff bases (1 and 2) and NaOAc • 3H 2 O in 1:2:4 mole ratio in refluxing methanol afforded the diamagnetic iron(II)-nickel(II)iron(II) species [Ni(Fcah) 2 ] (3) and [Ni(Fcbh) 2 ] (4) in 60 and 68% yields, respectively. Both Schiff bases and the two trinuclear complexes were characterized by elemental (CHN) analysis, mass spectrometric, various spectroscopic (IR, UV-Vis and 1 H NMR) and cyclic voltammetric measurements. Molecular structures of 2, 3 and 4 were determined by single crystal X-ray diffraction studies. The cyclopentadienide rings in the ferrocene moieties are essentially in eclipsed conformation in all three structures. Deprotonated Schiff base ligands in each complex (Fcah − in 3 and Fcbh − in 4) act as five-membered chelate ring forming azomethine-N and amidate-O donors and assemble a square-planar trans-N 2 O 2 coordination environment around the nickel centre. The redox active 1-4 exhibit an iron centred redox couple in the potential range 0.23-0.50 V (vs. Ag/AgCl).

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Reaction of [RhCp*Cl 2 ] 2 (Cp* = pentamethylcyclopentadienyl anion), 4-bromo-N-(1-pyrenylidene)aniline (Hpyan, H represents a proton of the 1-pyrenyl ring) and CH 3 CO 2 Na in 1:2:6 mole ratio in dichloromethane provides the half-sandwich, cyclometallated rhodium(III) complex [RhCp*(pyan)Cl]. X-ray crystallographic study confirms the bidentate 1-pyrenyl ortho-C and azomethine-N coordination mode of (pyan)and the half-sandwich 'piano-stool' structure of [RhCp*(pyan)Cl]. In dichloromethane, the diamagnetic, redox active complex displays a metal-centred oxidation at E 1/2 = 1.14 V (versus Ag/AgCl).

Synthesis, characterization, and physical properties of benzyl‐N′‐(4‐R‐benzoyl)‐N‐(2,6‐diisopropylphenyl)carbamimidothioates, HL1 (R = H) and HL2 (R = Cl), and their nickel(II) complexes having the general molecular formula [Ni(L1/2)2] (1 and 2) have been reported. Elemental analysis, magnetic susceptibility, solution electrical conductivity, and various spectroscopic (IR, UV–Vis, and 1H NMR) measurements were used to characterize HL1, HL2, and the two complexes (1 and 2). The molecular structures of all four compounds were determined by single‐crystal X‐ray crystallographic studies. The structures of HL1 and HL2 showed the imino‐ketone form of both compounds. In each of 1 and 2, the six‐membered chelate ring forming iminolate‐O and azomethine‐N donor two (L1/2)− ligands form a square‐planar trans‐N2O2 coordination environment around the metal center. The spectroscopic characteristics of HL1, HL2, 1, and 2 are consistent with their molecular structures. Both complexes were successfully employed as efficient catalysts in Kumada–Corriu CC cross‐coupling reactions of aryl bromides with phenylmagnesium bromide. The reactions provided biaryl products in good to excellent yields with a good substrate scope.

Reactions of 1-((2-hydroxy-5-R-phenylimino)methyl)naphthalen-2-ols (H 2 L n , n = 1-3 for R = H, Me, Cl, respectively) with [Pd(PPh 3 ) 2 Cl 2 ] and Et 3 N in toluene under reflux produced three new mononuclear square-planar palladium(II) complexes with the general formula [Pd(L n )(PPh 3 )] (1, R = H; 2, R = Me; 3, R = Cl). All the complexes were characterized using elemental analysis, solution conductivity and various spectroscopic (infrared, UV-visible and NMR) measurements. Molecular structures of 1-3 were confirmed using single-crystal X-ray diffraction analysis. In each complex, the fused 5,6-membered chelate rings forming phenolate-O, azomethine-N and naphtholate-O donor (L n ) 2À and the PPh 3 form a square-planar ONOP coordination environment around the metal centre. Infrared and NMR spectroscopic features of 1-3 are consistent with their molecular structures. Electronic spectra of the three complexes display several strong primarily ligand-centred absorption bands in the range 322-476 nm. All the complexes were found to be effective catalysts for carbon-carbon cross-coupling reactions of arylboronic acids with aromatic and heteroaromatic aldehydes to form the corresponding diaryl ketones.