Strong Π-acceptor Properties Research Articles

Synthesis, Characterization of N-Pyrrolylphosphanes Based on Heterocyclic Amine Backbones and Their Application in Hydroformylation of 1-Octene

A new class of N-pyrrolylphosphanes based on new heterocyclic amines have been synthesized, characterized and applied in homogeneous rhodium-catalyzed hydroformylation of 1-octene. These ligands possessing strong π-acceptor properties effectively facilitate the olefin isomerization. The steric effect of ligands has also been examined. Large steric tetraphosphane ligand afforded better regioselectivity, and the L/B ratio of about 6.4 was obtained at low synthesis gas pressure (5 bar). New heterocyclic amines have been developed, and two type pyrrole-based ligands possessing strong π-acceptor and weak o-donor properties have been prepared. High regioselectivity has been achieved in the rhodium-catalyzed hydroformylation of terminal olefin.

Coordination Properties of Bridging Diazene Ligands in Unusual Diiron Complexes

Saouma, Muller, and Peters recently (J. Am. Chem. Soc., 2009) reported the synthesis of several diiron complexes with two types of bridging diazene HN═NH ligands, designated μ-η1:η1 (bridging end-on) and μ-η2:η2 (bridging side-on), with tridentate phosphine {XBPR3} ligands ({XBPR3} = XB(CH2PR2)3−; X = Ph; R = Ph, CH2Cy). In the present study the energies, optimized geometries, and vibrational frequencies of these complexes with X = H and R = H, CH3, CF3 were obtained theoretically, and the electronic structures were analyzed in terms of iron−diazene donor−acceptor interactions. Natural bond orbital analysis indicates that both bridging end-on and side-on diazenes possess strong π-acceptor properties, which cause significant occupation of their antibonding π*(N−N) LUMOs and weakening of the N−N bonds as the result of coordination. The most pronounced weakening was obtained in complexes with bridging side-on diazene, where interaction of iron d-AOs with π*(N−N) orbitals of the diazene ligands results in the...

Synthesis and characterization of ruthenium(II) azoimine-diphosphine mixed-ligand complexes

A novel family of the general type cis-[Ru II(dppe)LCl 2] {L = C 6H 5N NC(COCH 3) NAr, Ar = 2,4,6-trimethylphenyl (L 1), 2,5-dimethylphenyl (L 2), 4-tolyl (L 3), phenyl (L 4), 4-methoxyphenyl (L 5), 4-chlorophenyl (L 6), 4-nitrophenyl (L 7), 2,5-dichlorophenyl (L 8); dppe = Ph 2P(CH 2) 2PPh 2} has been synthesized. These complexes have been characterized through analytical, spectroscopic (IR, UV–Vis, and NMR) and electrochemical (cyclic voltammetry) techniques. In addition, complex 4 (where L = L 4) has been further characterized by X-ray diffraction analysis. Crystallographic, electrochemical and electronic spectral data are all consistent with the azomethine ligands possessing strong π-acceptor properties. These π-acceptor properties can be “tuned” by a judicious choice of substituent on the azomethine ligand.

Syntheses, crystallography and spectroelectrochemical studies of ruthenium azomethine complexes

Three novel families of azomethine ligands L of the type C 6H 5N NC(COCH 3) N(4-YC 6H 4) ( 6), C 6H 5N NC(CO 2CH 3) N(4-YC 6H 4) ( 7) and 4-ClC 6H 4N NC(CO 2CH 3) N(4-YC 6H 4) ( 8), [Y = H ( a), CH 3 ( b), Cl ( c), Br ( d), C 10H 7 ( e), OCH 3 ( f), NO 2 ( g)] have been synthesized and reacted consecutively with RuCl 3, 2,2′-bipyridine (bpy) and lithium chloride in ethanol under refluxing conditions to produce three novel families of trans-[Ru II(bpy)LCl 2] complexes. These complexes were characterized by elemental analysis, IR, 1H NMR, UV–Vis spectroscopy and cyclic voltammetry. Crystallographic studies of two ruthenium(II) azomethine complexes ( 13 and 18) show that the Ru(II) ion occupies a distorted octahedral coordination sphere in which the chloride ligands are trans to each other and the azomethine and bipyridine nitrogen donor atoms are equatorially coordinated. Crystallographic, electrochemical, electronic spectral data and time-dependent DFT calculations are all consistent with azomethine ligands possessing strong π-acceptor properties. These π-acceptor properties can be “tuned” by a judicious choice of substituents on the azomethine ligand.

New Carbon-Phosphorus Macrocycles

The synthesis of several phosphole and phosphinine-based macrocycles is described. The first ones are flexible as a result of the low inversion barrier of phosphorus. The mixture of isomers can be directly used in coordination chemistry. The second ones are not plagued by conformational problems and display strong π-acceptor properties.

New Carbon-Phosphorus Macrocycles

The synthesis of several phosphole and phosphinine-based macrocycles is described. The first ones are flexible as a result of the low inversion barrier of phosphorus. The mixture of isomers can be directly used in coordination chemistry. The second ones are not plagued by conformational problems and display strong π-acceptor properties.

Selective Isomerization of 1,5-Cyclooctadiene to 1,4-Cyclooctadiene Catalyzed by Bis(acetylacetonato)nickel–Triethyldialuminum Trichloride–Phosphorus Ligand

Abstract The isomerization of 1,5-cyclooctadiene (1,5-COD) with Ni(acac)2–Et3Al2Cl3–phosphorus ligand (Ni : Al2 : P=1 : 10 : 3) was first examined with varying P ligands in toluene in order to find suitable conditions for the formation of 1,4-COD. The product distribution depended largely on the P ligands. For several phosphites possessing very strong π-acceptor properties, the main product was 1,4-COD. In particular, the less-bulky bicyclic phosphite, 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (L-3) was very effective and gave 1,4-COD in a high selectivity of 93% at 66% conversion (1,5-COD/ Ni=500, molar ratio) by employing a low temperature of −30°C. However, the reaction stopped before reaching completion because the catalyst was deactivated by the accumulation of 1,4-COD product. The conversion, depending on the 1,5-COD/toluene ratio (volume) rather than the 1,5-COD/Ni ratio, increased with a decrease in the 1,5-COD/ toluene ratio and was 66–69% at a ratio of 0.19. On the other hand, the catalyst (P: L-3) was much less active for 1,4-COD than for 1,5-COD and was deactivated quickly under the same reaction conditions. This appeared to result in a high selectivity of 1,4-COD in the isomerization of 1,5-COD. The mechanistic implications of the experimental results are discussed.