Steric Effect Of Methyl Group Research Articles

Electrocatalytic Water Oxidation by Mononuclear Cu(II) Aliphatic Tetraamine Complexes

AbstractWe report here electrocatalytic water oxidation by a series of mononuclear Cu(II) aliphatic tetraamine complexes at various pH. In phosphate buffer solution of pH 12, the Cu(II)‐Tren (Tren is tris‐(2‐aminoethyl)amine) complex is decomposed to generate a Cu oxide/hydroxide film with phosphate incorporated on the electrode surface which can catalyze water oxidation with a small onset overpotential of 420 mV and a low Tafel slope of 48 mV dec−1. By contrast, the other two Cu(II) complexes, Cu(II)‐Me3(Tren) (Me3(Tren) is (tris‐(2‐(methylamino)ethyl)amine)) and Cu(II)‐Me6(Tren) (Me6(Tren) is tris‐(3‐methyl‐3‐azabuty)amine), having the ligands that sharing the same molecular skeleton of Tren but with methyl group substituents, are noneffective to form the surface‐bound active species. The experimental results indicate that the Cu(II)‐Tren complex decomposes by intra‐complex proton‐coupled electron transfer (PCET) from the amine ligand to the higher‐oxidation‐state Cu with significant pH/buffer base effects. At pH 9, water oxidation with Cu(II)‐Tren transforms from heterogeneous to homogeneous featuring a single‐site catalysis mechanism. Moreover, the comparison of the three Cu(II) complexes at this pH also suggests a steric effect of methyl groups on the catalysis performance. As pH decreases further to 7, Tren, with pKb ∼5.9, becomes less coordinating and precipitation of a Cu3(PO4)2 film during electrolysis leads to electrode passivation, which inhibits the homogeneous water oxidation at this pH.

Sintesis Senyawa Turunan 2-Metoksi-3H-Azepina Melalui Reaksi Termal antara Alkylnitrobenzena dan Tributilphosphina

Although photolysis of phenyazide has been widely reported to give 3 H -azepine, the thermal deoxygenation reaction of alkylnitrobenzene derived similar products hitherto unexplored. Novel synthesis of 2-methoxy-3 H -azepine derivatives was carried out using alkylnitrobenzene with tributylphosphine (Bu 3 P) reacted at 150°C for 24 hours in the presence of methanol. Reaction of m -nitrobenzene with the above methods gave two isomers of 3 H -azepine, namely, 2-methoxy-6-methyl-3 H -azepine and 2-methoxy-4-methyl-3 H -azepine in 61%. Reaction of 2,3-dimethylnitrobenzene with Bu 3 P afforded the three isomers, that is, 2-methoxy-6,7-dimethyl-3 H -azepine; 2-methoxy-3,4-dimethyl-3 H -azepine and 7-methoxy-5,6-dimethyl-4 H -azepine. Reaction of 3,5-dimethylnitrobenzene gave the sole product of 2-methoxy-4,6-dimethyl-3 H -azepine in 42%. In contrast, reaction of 2,6-dimethylnitrobenzene didn’t give any product because the steric effect of methyl groups attached on C2 and C6. Structure elucidation of all novel products have confirmed by HETCOR.

Assembly of 1D, 2D and 3D silver(I) coordination polymers with nitrilotriacetate and 2-aminopyrimidyl mixed ligands

Three mixed ligands coordination polymers (CPs) [Ag1.5(apym)(nta)0.5]n (1), [(NH4)Ag2(mapym)(nta)·(H2O)3]n (2), [Ag2(dmapym)3(Hnta)]n (3) (apym=2-aminopyrimidine, mapym=4-methyl-2-aminopyrimidine, dmapym=4, 6-dimethyl-2-aminopyrimidine, H3nta=nitrilotriacetate) were synthesized and characterized. For 1–3, as the substituents change from H to one methyl and two methyl groups, the dimensionalities of 1–3 decrease from three-dimension (3D) to one-dimension (1D) due to the steric effect of methyl groups. For 1, the μ2-apym ligands link the Ag(I) ions to form a 1D double-chain incorporating ligand unsupported Ag···Ag interaction. The nta3− ligands extend the 1D double-chain into a 3D framework. In 2, one heptadentate nta3− ligand binds four Ag(I) ions and incorporates μ2-mapym ligand to link metal centers to form a 2D sheet which can be simplified to be a 103 net. Complex 3 features a 1D chain structure incorporating Hnta2− and monodentate dmapym ligands. The substituents on the pyrimidyl ring intensively influence the coordination environments of metal ion and the coordination modes of the carboxyl group, and thus determine the structures of the CPs. The photoluminescent properties of 1–3 were also investigated.

Syntheses, structures and luminescent properties of silver(I) coordination polymers based on aminopyrimidyl derivatives and 1,2,3,4-butanetetracarboxylic acid

Two mixed-ligand silver(I) coordination polymers (CPs) of the formula {[Ag 4(mapym) 2(butca)(H 2O) 4]·2H 2O} n ( 1) and [Ag 4(dmapym) 6(butca)·2H 2O] n ( 2) (mapym = 2-amino-4-methylpyrimidine, dmapym = 2-amino-4,6-dimethylpyrimidine, H 4butca = 1,2,3,4-butanetetracarboxylic acid) were prepared by reactions of Ag 2O and 2-aminopyrimidyl ligands with H 4butca under the ammoniacal condition. Both complexes were characterized by element analysis, IR and X-ray single-crystal diffraction. In 1, a pair of μ 2-mapym ligands bind four Ag(I) ions to form [Ag 4(mapym) 2] subunits which stack into one-dimensional (1D) chains via inter-subunit π⋯π interaction. The μ 6-κ 1:κ 2:κ 1:κ 2-butca ligands extend the 1D chains into a two-dimensional (2D) sheet which can be simplified into a 4 4- sql net. When mapym was replaced by dmapym, we obtained 2 as a 1D chain incorporating μ 6-κ 1:κ 2:κ 1:κ 2-butca and μ 1-dmapym ligands. The dimensions of 1– 2 decrease from 2D to 1D mainly due to the steric effect of methyl groups. Additionally, the hydrogen-bonding, π⋯π and C–H⋯π interactions also direct the self-assembly of supramolecular architectures. The photoluminescence properties of the 1 and 2 were investigated in the solid state at room temperature.

Assembly of silver(I) coordination polymers incorporating pyromellitic acid and N-heterocyclic ligands

Five mixed ligands coordination polymers [Ag 4(apym) 2(pma)·(H 2O) 2] n ( 1), {[Ag 4(dmapym) 4(pma)·(H 2O) 2]·(H 2O) 6} n ( 2), [Ag 2(apyz) 2(H 2pma)·(H 2O) 4] n ( 3), {[Ag 4(apyz) 2(pma)·(H 2O) 2]·(H 2O) 2} n ( 4) and [Ag 4(NH 3) 8(pma)·(H 2O) 6] n ( 5) (apym = 2-aminopyrimidine, dmapym = 4, 6-dimethyl-2-aminopyrimidine, apyz = 2-aminopyrazine, H 4pma = pyromellitic acid) were synthesized and characterized. For 1 and 2, as the substituents change from H to methyl, the dimensions of 1– 2 decrease from three-dimension (3D) to one-dimension (1D) due to the steric effect of methyl groups. For 3 and 4, as the ratios of Ag 2O/apyz/pma vary from 1:1:1 to 2:1:1, the structure of 3 is a 1D ladder structure built from Ag-apyz double chains and pma anions, while the structure of 4 is a two-dimension (2D) grid. As excess ammonia is added to above four reaction systems, the structure of 5 contains unprecedented {[Ag(NH 3) 2] +} n chains and pma anions. The substituent on the pyrimidyl ring, ratios of reactants, solvent systems and ligand isomers intensively influence the coordination environments of metal ion and the coordination modes of the carboxyl group, and thus determine the structures of the coordination polymers. The photoluminescent properties of 1– 5 were also investigated.

Steric Effect of Methyl Group in Regioselective Tritiation of Toluamides.

Tritiation by the hydrogen isotope exchange in toluamides with HTO was studied in the presence of RhCl3⋅3H2O as a catalyst. It was established by chemical degradation that the exchange reaction occurred with virtually 100% regioselectivity at the o-position (s) (C2 and C6 positions) of all the toluamides. The methyl group was not tritiated. The exchange in m-toluamide was very strongly hindered at the C2 position between the methyl and the amido group. The exchange at the C6 position was more strongly prevented in o-toluamide than in m-toluamide. These findings are explained on the basis of the steric effect of the methyl group in agreement with the previously suggested mechanism that the exchange proceeds via initial coordination of the substrate compound to rhodium (III) chloride trihydrate.

ChemInform Abstract: THE MOLECULAR COMPLEXES. XI. THE COMPLEXES OF TOLUIDINES AND N‐METHYLTOLUIDINES WITH IODINE IN CARBON TETRACHLORIDE

The interactions of iodine with toluidines (o-, m-, and p-) and N-methyltoluidines (o-, m-, and p-) in solution have been investigated through spectrophotometric measurements. The results indicate that toluidines and N-methyltoluidines form the one-to-one charge-transfer complexes with in solution. By comparing the values of the formation constants of the complexes, it is concluded that the relative stabilities of the -amine complexes decrease in the following orders: p-toluidine >m-toluidine >aniline >o-toluidine, N-methyl-p-toluidine >N-methyl-m-toluidine >N-methylaniline >N-methyl-o-toluidine, N-methyltoluidines >toluidines. These results can be explained by the electron-releasing character and the steric effect of methyl group in the amine molecules.

Cationic polymerization of dimethyl‐1,3‐butadienes

AbstractThe cationic polymerizations of dimethyl‐1,3‐butadienes with various catalysts in methylene chloride and toluene have been investigated. The activity of catalysts decreased in the order WCl6 > AcClO4 > SnCl4·TCA > BF3OEt2. The homopolymerization rate of dimethyl‐1,3‐butadienes with WCl6, AcClO4, and SnCl4·TCA decreased in the order 1,3‐dimethyl‐1,3‐butadiene > 2,3‐dimethyl‐1,3‐butadiene > 1,2‐dimethyl‐1,3‐butadiene > 2,4‐hexadiene. The polymers prepared with WCl6, SnCl4.TCA, and BF3OEt2 were rubberlike polymers or white powders, whereas those prepared with AcClO4 were oily oligomers. The 1,4‐propagation increased in the order 1,2‐dimethyl‐1,3‐butadiene < 1,3‐dimethyl‐1,3‐butadiene < 2,3‐dimethyl‐1,3‐butadiene < 2,4‐hexadiene. This order may indicate that the steric effect of methyl group determine primarily the microstructure of the polymer. The relative reactivity of dimethyl‐1,3‐butadienes toward a styryl cation decreased in the order 1,3‐dimethyl‐1,3‐butadiene > 1,2‐dimethyl‐1,3‐butadiene > 2,3‐dimethyl‐1,3‐butadiene > 2,4‐hexadiene. This order may be explained in terms of the stability of the resulting allylic cation.

Synergistic extraction of zinc(II) in the presence of cadmium(II) with TTA and a pyridine base

The extraction procedure for the separation of zinc (II) from cadmium(II) is as follows: Twenty ml of the aqueous solution (pH=5.7) is equilibrated with the equal volume of 5×10-3M 2-thenoyltrifluoroacetone (TTA=Htta) and 5×10-2M 2, 6-lutidine in carbon tetrachloride by shaking the mixture for 5 min. Only zinc is selectively extracted into the organic phase.The synergistic effect caused by pyridine (py) could be explained through the formation of an adduct, Zn(tta)2(py)2 or Cd(tta)2(py)2. On the other hand, the main synergistic adduct formed by using 2, 6-lutidine was found to be Zn(tta)2(2, 6-lut.). The difference in the composition of adducts in the above cases is attributable to the steric effect of methyl groups in 2, 6-lutidine. The steric effects by the presence of other ortho-substituents of pyridine were also studied.

The influence of the nitro-group upon side-chain reactivity. Part IV. The inhibition of α-proton extraction from 4-nitrobenzyl chloride by the steric effect of methyl groups in the 3- and 5-positions

The fast α-proton extraction from 4-nitrobenzyl chloride by alkali in dioxan, leading to the formation of 4,4′-dinitrostilbene by the α-E1cB mechanism (the rate-determining step is formation of a carbene intermediate), is greatly retarded by one methyl group in the 3-position and completely inhibited by two methyl groups in the 3- and 5-positions; instead, alcohols and ethers are formed by the SN2 displacement of the halogen by the alkali and by the formed alkoxides. Kinetic investigations, and evaluation of the Arrhenius parameters, on the chlorides with the alkali in dioxan, alone or in presence of added alkoxides, demonstrate clearly the steric effect of the methyl groups. Infrared and ultraviolet spectra of the chlorides and related structures throw much light on the results.