A Detailed Kinetico-Mechanistic Investigation on the Palladium C-H Bond Activation in Azobenzenes and Their Monopalladated Derivatives.

Palladium C-H bond activation in azobenzenes with R and R at positions of the phenyl rings (R = NMe, R = H (); R = NMe, R = Cl (); R = NMe, R = I (); R = NMe, R = NO (); R = H, R = H ()) and their monopalladated derivatives, using -[PdCl(DMF)], has been studied in detail by H NMR spectroscopy in -dimethylformamide- (DMF-) at room temperature; the same processes have been monitored in parallel via time-resolved UV-vis spectroscopy in DMF at different temperatures and pressures. The final goal was to achieve, from a kinetico-mechanistic perspective, a complete insight into previously reported reactivity results. The results suggest the operation of an electrophilic concerted metalation-deprotonation mechanism for both the mono- and dipalladation reactions, occurring from the coordination compound and the monopalladated intermediates, respectively.

Mechanism of Mechanochemical C-H Bond Activation in an Azobenzene Substrate by Pd Catalysts.

Mechanism of C-H bond activation by various Pd catalysts under milling conditions has been studied by in situ Raman spectroscopy. Common Pd precursors, that is PdCl , [Pd(OAc) ] , PdCl (MeCN) and [Pd(MeCN) ][BF ] , have been employed for the activation of one or two C-H bonds in an unsymmetrical azobenzene substrate. The C-H activation was achieved by all used Pd precursors and their reactivity increases in the order [Pd(OAc) ] View Article and Find Full Text PDF

Reversible Gas-Solid Ammonia N-H Bond Activation Mediated by an Organopalladium Complex.

N-H bond activation of gaseous ammonia is achieved at room temperature in a reversible solvent-free reaction using a solid dicyclopalladated azobenzene complex. Monitoring of the gas-solid reaction in real-time by in situ solid-state Raman spectroscopy enabled a detailed insight into the stepwise activation pathway proceeding to the final amido complex via a stable diammine intermediate. Gas-solid synthesis allowed for isolation and subsequent structural characterization of the intermediate and the final amido product, which presents the first dipalladated complex with the Pd-(μ-NH)-Pd bridge.

Vapour-induced solid-state C-H bond activation for the clean synthesis of an organopalladium biothiol sensor.

Room-temperature accelerated aging in the solid state has been applied for atom- and energy-efficient activation of either one or two C-H bonds of azobenzene and methyl orange by palladium(ii) acetate. Organopalladium complexes are prepared in quantitative reactions without potentially harmful side products. Dicyclopalladated methyl orange is water-soluble and is a selective chromogenic biothiol sensor at physiologically-relevant micromolar concentrations in buffered aqueous media.

Mechanochemical reactions studied by in situ Raman spectroscopy: base catalysis in liquid-assisted grinding.

In situ Raman spectroscopy was employed to study the course of a mechanochemical nucleophilic substitution on a carbonyl group. We describe evidence of base catalysis, akin to catalysis in solution, achieved by liquid-assisted grinding.

Mechanochemical C-H bond activation: rapid and regioselective double cyclopalladation monitored by in situ Raman spectroscopy.

The first direct mechanochemical transition-metal-mediated activation of strong phenyl C-H bonds is reported. The mechanochemical procedure, resulting in cyclopalladated complexes, is quantitative and significantly faster than solution synthesis and allows highly regioselective activation of two C-H bonds by palladium(II) acetate in asymmetrically substituted azobenzene. Milling is monitored by in situ solid-state Raman spectroscopy which in combination with quantum-chemical calculations enabled characterization of involved reaction species, direct insight into the dynamics and reaction pathways, as well as the optimization of a milling process.

Dicyclopalladated complexes of asymmetrically substituted azobenzenes: synthesis, kinetics and mechanisms.

Two series of new dicyclopalladated complexes {(DMF)PdCl(μ-R(1)C6H3N═NC6H3R(2))PdCl(DMF)} of 4,4'-functionalized azobenzenes with substituents of varying electron-donating or electron-withdrawing strength (R(1) = H, NMe2; R(2) = H, Cl, Br, I, OMe, PhNH, CO2H, SO3Na, or NO2) have been synthesized and fully characterized. (1)H NMR spectroscopy along with the ESI mass spectrometry unambiguously identified the new complexes in the solution, and their solid-state structures were determined by X-ray crystallography. The presence of easily exchangeable solvent ligands was confirmed by (1)H NMR spectroscopy, X-ray experiments, and ESI mass spectrometry.

New insight into solid-state molecular dynamics: mechanochemical synthesis of azobenzene/triphenylphosphine palladacycles.

Solid-state reactions of dicyclopalladated azobenzenes and triphenylphosphine lead to the thermodynamically favorable bridged complexes. It was demonstrated for the first time that very complex molecular dynamics involving a series of structural transformations is also feasible in the solid state.

Unusual azobenzene/bipyridine palladacycles: structural, dynamical, photophysical and theoretical studies.

Two types of Pd(ii) azobenzene/bipyridine complexes with unusual coordination mode of azobenzenes, PdCl{(mu-Cl)(mu-R(1)C(6)H(3)N=NC(6)H(3)R(2))}Pd(bpy) 1a-4a and [(bpy)PdCl(mu-NH(2)C(6)H(3)N=NC(6)H(4))Pd(bpy)]Cl 3b were formed by the reaction of dicyclopalladated azobenzenes (DMF)PdCl(mu-R(1)C(6)H(3)N=NC(6)H(3)R(2))PdCl(DMF) with excess of bpy, where bpy=2,2'-bipyridine; R(2)=H and R(1)=H (1), CH(3) (2), NH(2) (3) or R(1)=N(CH(3))(2) and R(2)=NO(2) (4). Neutral species 1a-4a were obtained in acetone, while in DMSO or MeOH the ionic complex 3b was produced. When dissolved, 3b decomposes to 3a and free bpy; however in DMSO upon addition of bpy 3b crystallizes again.

Synthesis and characterization of dicyclopalladated complexes of azobenzene derivatives by experimental and computational methods.

A series of doubly cyclopalladated complexes of azobenzene and its unsymmetrical substituted derivatives, namely, {LPdCl(mu-AZB)LPdCl}, where AZB is azobenzene, 4-methylazobenzene, 4-aminoazobenzene, or 4-(dimethylamino)-4'-nitroazobenzene, while L is N,N-dimethylformamide, dimethylsulfoxide, or pyridine, have been prepared. Their structural and spectroscopic properties were determined by X-ray diffraction analysis as well as by (1)H NMR, IR, UV-vis, and fluorimetric studies. Experimental results were rationalized by quantum chemical calculations.

Simple route to the doubly ortho-palladated azobenzenes: building blocks for organometallic polymers and metallomesogens.

A new class of doubly cyclopalladated complexes, {PdCl(dmf)}2(mu-azb) (1) and {PdCl(dmf)}2(mu-aazb) (2), has been prepared in dimethylformamide (dmf) by reaction of azobenzene (azb) and 4-aminoazobenzene (aazb), respectively, with an excess of PdCl2(CH3CN)2 complex. Recrystallization of 1 and 2 in dimethyl sulfoxide (dmso) yields complexes {PdCl(dmso)}2(mu-azb) (3) and {PdCl(dmso)}2(mu-aazb) (4), respectively. The crystal structures of 1 and 4 have been determined by X-ray diffraction.