Rhodium(I) carbonyl complexes of quinoline carboxaldehyde ligands and their catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO)₂Cl]₂ reacts with quinoline (a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde (b), quinoline-3-carboxaldehyde (c), and quinoline-4-carboxaldehyde (d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)₂Cl(L)] (1a-1d), where L = a-d. The complexes 1a-1d have been characterised by elemental analyses, mass spectrometry, IR and NMR (¹H, ¹³C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh?Rh = 3.573 Å). 1a-1d undergo oxidative addition (OA) with different electrophiles such as CH₃I, C₂H₅I and I₂ to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = -CH₃ (2a-2d), R = -C₂H₅ (3a-3d)} and [Rh(CO)Cl(L)I₂] (4a-4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a-1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551-1735 h⁻¹] compared to that of the well known Monsanto’s species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a-1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity.     

Electrophilic aromatic addition reaction (AdEAr) to anthracene

After finding in a previous study that naphthalene and quinoline can react via electrophilic aromatic addition reaction (Ad_EAr), we applied this to anthracene. When anthracene was reacted with bromine in methanol in the presence of NaHCO₃ and pyridine, 9,10-dihydro-9,10-dimethoxyanthracene (2) was obtained in 82% yield in the absence of substitution products or oxidative demethylation products like anthraquinone. The same reaction in ethanol produced 9,10-diethoxy-9,10-dihydroanthracene (9) in much lower yield (45%). In addition, we investigated the reactivity of addition product 2. Treatment of 2 with DDQ in benzene at 65 °C for 12 h produced 9,10-dimethoxyanthracene (3) in 62% yield, and 2 was rapidly transformed to 9-methoxyanthracene (4) in methanolic NaOH in 10 min. Moreover, the acid-catalyzed aromatization of 2 in 1-propanol at 75 °C for 10 min gave 9-n-propoxyanthracene (8) in 65% yield.     

Silicon-carbon unsaturated compounds. 77. Thermal behavior of cis- and trans-1-silacyclobut-3-ene formed from pivaloyl[tert-butylbis(trimethylsilyl)]silane and tert-butylacetylene

The reaction of tert-butylbis(trimethylsilyl)silyl potassium with pivaloyl chloride gave pivaloyl[tert-butylbis(trimethylsilyl)]silane (1) in 89% yield. The cothermolysis of 1 with tert-butylacetylene at 140 °C for 24 h produced the mixture consisting of cis- and trans-1,2,3-tri(tert-butyl)-2-(trimethylsiloxy)-1-(trimethylsilyl)-1-silacyclobut-3-ene (cis-2 and trans-2) in a ratio of 0.7: 1, in 88% combined yield. The thermolysis of the mixture, cis-2 and trans-2, at 250 °C for 24 h proceeded to give trans-1,2,4-tri(tert-butyl)-1-(trimethylsiloxy)-2-(trimethylsilyl)-1-silacyclobut-3-ene (4) as a single product in 96% yield. Similar treatment of cis- and trans-2 at 190 °C for 15 h afforded silylcyclopropene 3 quantitatively, which underwent further isomerization at 250 °C to give trans-1-silacyclobut-3-ene 4 in quantitative yield.     

Molecular design, synthesis and electro-optic properties of novel Y-type polyurethanes with high thermal stability of second harmonic generation

2,4-Di-2^′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3^′-dimethoxy-4,4^′-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 2,4-dioxybenzylidenemalononitrile group as a nonlinear optical (NLO) chromophore, which constitutes a part of the polymer backbone. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 260 °C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) giving T_g values around 143-156 °C. The approximate lengths of aligned NLO-chromophores estimated from AFM images of poled polymer films were about 10 nm. The SHG coefficients (d₃₃) of poled polymer films were around 7.4 × 10⁻⁹ esu. These Poled polymers exhibited a greater thermal stability of dipole alignment even at 10 °C higher than T_g, and no SHG decay was observed below 155 °C due to the partial main chain character of the polymer structure and extensive hydrogen bonds between urethane linkage, which is acceptable for NLO device applications.     

Ruthenium piano-stool complexes containing mono- or bidentate pyrrolidinylalkylphosphines and their reactions with small molecules

Ruthenium piano-stool complexes incorporating the new bidentate aminoalkylphosphine ligand 1,2-bis(dipyrrolidin-1-ylphosphino)ethane (dpyrpe, I) or its monodentate counterpart bis(pyrrolidin-1-yl)methylphosphine (pyr₂PMe, II) have been prepared, [(C₅R₅)RuCl(PP)] (R = Me and PP = dpyrpe, 1; R = Me and PP = (pyr₂PMe)₂, 2; R = H and PP = dpyrpe, 3). Complexes 2 and 3 have been characterized by X-ray crystallography. Complexes 1 and 2 react with NaBAr₄^f in the presence of ligand L to yield [Cp^∗Ru(L)(dpyrpe-κ²P)][BAr^f₄] (L = MeCN, 4a; CO, 4b; N₂, 4c) and [Cp^∗Ru(L)(pyr₂PMe)₂][BAr₄^f] (L = MeCN, 5a; CO, 5b; N₂, 5c). Complex 4a was crystallographically characterized. The CO complexes 4b and 5b were examined using IR spectroscopy in an attempt to establish the electron-donating capabilities of I and II. Complex 1 oxidatively adds H₂ in the presence of NaBAr₄^f to yield the Ru(IV) dihydride [Cp^∗RuH₂(dpyrpe-κ²P)][BAr₄^f], 7.     

Columnar catenar bisoxazoles and bisthiazoles

Three new series of catenar liquid crystals 1a–c derived from heterocyclic bisoxazoles and bisthiazoles exhibiting columnar phases were reported. All compounds 1a–c exhibited hexagonal columnar phases, which were confirmed by powder XRD diffractometer. Compounds 1a have a slightly wider temperature range of columnar phases than that of compounds 1b, which might be attributed to higher dipole polarized in 1a. A N_cell and R_ar value equal to 2.54–2.76 and 19.99–20.45 Å² within a slice of 9.0 Å thick were obtained for three derivatives 1a–c (all ns=12), indicating that a single molecule was packed within columns in Col_h phases. All derivatives showed good stabilities at temperature below T=408 °C on TGA. The PL spectra of all compounds 1a–c showed one intense peak at λ_max=505–510 nm, and these photoluminescent emissions originated from quinoxaline moiety.     

Preparation,characterization and thermal degradation study of poly(amide imide)s based on tri-component mixture of PMDA/BTDA,diamines and acid chloride

A series of poly(amide imide)s (PAIs) having alternate (amide–amide) and (imide–imide) units (polymers 1–14 and 22–35), and random distribution of amide-imide linkages (polymers 15–21 and 36–42) were prepared by low temperature solution polymerization of benzene-1,2,4,5-tetracarboxylic dianhydride (PMDA)/benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA), diamines (cyclic and aromatic) and acid chloride in dimethylforamide. All the polymers were readily soluble in polar aprotic solvents with inherent viscosities in the range of 0.134–0.878. The process of cycloimidization of poly(amide amic acid)s (PAAs) to PAIs was investigated by TGA and FT-IR techniques at four different temperatures i.e., 175, 200, 225, and 260 °C. The rate of cycloimidization was calculated by taking into account the theoretical weight loss (W_T), obtained from [n × M_w (H₂O)/M_w (R_U)] W, where M_w (H₂O) molecular weight of water, W weight of PAA taken for TGA, M_w (R_U) the molecular weight of repeat unit of PAA, n number of water molecules eliminated per repeat unit of PAA upon cycloimidization. For a particular diamine, the extent of percentage cycloimidization at the end of the isothermal heating was higher for PAAs containing trimellitic anhydride chloride (TMAc) unit, irrespective of the nature of the dianhydride and diamine. Thermal and thermooxidative degradation of PAIs was investigated by TGA in nitrogen and oxygen atmosphere. The initial decomposition temperatures (IDT) of polymers are above 260 °C, and vary widely (from 260 to 501 °C) depending upon the structure of the polymer backbone. PAIs containing TMAc exhibited higher thermal stability as compared to those polymers having diacid chloride units, in both N₂/O₂ atmospheres.     

A short-cut from 1-acetyl adamantane to 2-(1-adamantyl)pyrroles

The oxime of 1-acetyl adamantane 2 is added to acetylene (KOH/DMSO, 70 °C, initial acetylene pressure 13 atm, 30 min) to afford the corresponding O-vinyl oxime 5 in 80% yield. The latter upon heating (DMSO, 120 °C, 1 h) gives 2-(1-adamantyl)pyrrole 3, 1-acetyl adamantane 1, and adamantane (6:3:1 mass ratio), the yield of the pyrrole 3 being 83% (based on 1-acetyl adamantane 1 consumed). Under harsher conditions (NaOH/DMSO, 130 °C, atmospheric pressure of acetylene, 4 h) oxime 2 reacts with acetylene to furnish pyrrole 3, 1-acetyl adamantane 1, 1-vinyl adamantane 9, and adamantane (6:7:3:1 mass ratio), with the isolated yield of pyrrole 3 reaching 34%. Under pressure (NaOH/DMSO, 120 °C, initial acetylene pressure 14 atm, 1 h) the same reaction leads to 2-(1-adamantyl)-1-vinylpyrrole 4 and ketone 1 in 48% (based on consumed ketone 1) and 24% yields, respectively. The pyrrole 4 is easily deprotected to the corresponding 1H-pyrrole 3 in 77% yield by treatment (aqueous MeCN) with Hg(OAc)₂ and NaBH₄.     

Microwave synthesis of bis(tetrazolato)-Pd complexes with PPh3 and water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). The first example of C-CN bond cleavage of propionitrile by a Pd Centre

[2 + 3] Cycloaddition reactions of the di(azido)-Pd^II complex trans-[Pd(N₃)₂(PPh₃)₂] (1) with an organonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PPh₃)₂] (3) [R = Me (3a), Ph (3b), 4-ClC₆H₄ (3c), 4-FC₆H₄ (3d), 2-NC₅H₄ (3e), 3-NC₅H₄ (3f), 4-NC₅H₄ (3g)]. The reaction of trans-[Pd(N₃)₂(PPh₃)₂] (1) with propionitrile (2h) also affords, apart from trans-[Pd(N₄CEt)₂(PPh₃)₂] (3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N₄CEt)(PPh₃)₂] (3h′) which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pd^II. The [2 + 3] cycloadditions of [Pd(N₃)₂(PTA)₂] (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PTA)₂] (5) [R = Ph (5a), 2-NC₅H₄ (5b), 3-NC₅H₄ (5c), 4-NC₅H₄ (5d)]. All these reactions are greatly accelerated by microwave irradiation (1 h, 125 °C, 300 W). Taking advantage of the hydro-solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-[Pd(N₄CPh)₂(PTA)₂] (5a) was achieved. The complexes were characterized by IR, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopies, ESI⁺-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre were found.     

Si-C coupling reaction of polychloromethanes with HSiCl3 in the presence of Bu4PCl: Convenient synthetic method for bis(chlorosilyl)methanes

Coupling reaction of polychloromethanes CH_4−nCl_n (n = 2-4) with HSiCl₃ in the presence of tetrabutylphosphonium chloride (Bu₄PCl) as a catalyst occurred at temperatures ranging from 30 °C to 150 °C. The reactivity of polychloromethanes increases as the number of chlorine-substituents on the carbon increases. In the reactions of CCl₄ with HSiCl₃, a variety of coupling products such as bis(chlorosilyl)methanes CH₂(SiCl₃)(SiXCl₂) [X = Cl (1a), H (1b)], (chlorosilyl)trichloromthanes Cl₃CSiXCl₂ [X = Cl (2a), H (2b)], and (chlorosilyl)dichloromthanes Cl₂HCSiXCl₂ [X = Cl (3a), H (3b)] were obtained along with reductive dechlorination products such as CHCl₃ and CH₂Cl₂ depending on the reaction temperature. In the reaction of CCl₄, 2a is formed at the initial stage of the coupling reaction and converted to give CHCl₃ at low temperature of 30 °C, to give 1a, 3a, and CHCl₃ at 60 °C, and to afford 1a as major product and CH₂Cl₂ in competition above 100 °C. Si-H bond containing silylmethanes can be formed by the H-Cl exchange reaction with HSiCl₃. Reaction of CHCl₃ with HSiCl₃ took placed at 80 °C to give three compounds 1a, 3a, and CH₂Cl₂, and finally 3a was converted to give 1a and CH₂Cl₂ at longer reaction time. While the condition for the reaction of CH₂Cl₂ with HSiCl₃ required a much higher temperature of 150 °C. Under the optimized conditions for synthesizing bis(chlorosilyl)methanes 1a,b, a mixture of 1a and 1b were obtained as major products in 65% (1a:1b = 64:1) and 47% (42:5) yields from the reaction of CCl₄ and CHCl₃ at 100 °C for 8 h, respectively, and in 41% (34:7) yield from that of CH₂Cl₂ at 170 °C for 12 h. In the Si-C coupling reaction of polychloromethanes with HSiCl₃, it seems likely that a trichlorosilyl anion generated from the reaction of HSiCl₃ with Bu₄PCl is an important key intermediate.     

Preparation and nonlinear optical properties of novel Y-type polyesters with highly enhanced thermal stability of second harmonic generation

3,4-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride and adipoyl chloride to yield novel Y-type polyesters (4-5) containing 3,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constituted parts of the polymer main-chains. The resulting polymers 4-5 are soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis with glass-transition temperatures obtained from differential scanning calorimetry in the range 89-91 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength were around 2.47 pm/V. The dipole alignment exhibited high thermal stability even at 10 °C higher than T_g, and there is no SHG decay below 100 °C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Synthesis and properties of soluble and light-colored poly(amide-imide-imide)s based on tetraimide-dicarboxylic acid (TIDA) and various aromatic diamines: TIDA from 4,4′-oxydiphthalic anhydride, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, and 3-aminobenzoic acid

A new tetraimide-dicarboxylic acid (TIDA) I was synthesized starting from 3-aminobenzoic acid (m-ABA), 4,4′-oxydiphthalic anhydride (ODPA), and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (BAFPB) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP). A series of organosoluble, light-colored poly(amide-imide-imide)s (PAII, III_a-j) was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines (II_a-j). All the polymers were readily soluble in a variety of organic solvents such as NMP, N,N-dimethyl acetamide (DMAc), dimethyl sulfoxide, and even in less polar m-cresol and pyridine. Polymer films cast from DMAc had the cutoff wavelengths between 374 and 384 nm and had the b^∗ values in the range of 14.8-30.2. Polymers III_a-j afforded tough, transparent, and flexible films, which had tensile strengths ranging from 87 to 103 MPa, elongations at break from 11% to 37%, and initial moduli from 1.9 to 2.3 GPa. The glass transition temperatures of these polymers were in the range of 242-274 °C. They had 10% weight loss temperature above 526 °C and showed the char yield more than 55% residue at 800 °C in nitrogen.     

Reactivity of cyclopalladated compounds derived from biphenyl-2-ylamine towards carbon monoxide, butyl isocyanide and alkynes

The reactivity of the dimeric cyclopalladated compounds derived from biphenyl-2-ylamine (μ-X)₂[κ²-N2′,C1-1-Pd-2-{(2′-NH₂C₆H₄)C₆H₄}]₂ [X = OAc (1), X = Cl (2)] towards unsaturated organic molecules is reported. Compound 1 reacted with carbon monoxide and ^tbutyl isocyanide producing phenanthridin-6(5H)-one and N-tert-butylphenanthridin-6-amine in 63% and 88% yield, respectively. Compound 2 reacted separately with diphenylacetylene and 3-hexyne, affording the mononuclear organopalladium compounds [κ²-N2″,C1-η²-C2,C3- 1-Pd{(R-CC-R)₂-2′-(2″-NH₂C₆H₄)C₆H₄}Cl] [R = Ph (5), R = Et (6)] in 50-60% yield, which derived from the insertion of two alkyne molecules into the C-Pd σ bonds of 2. The crystal structure of compounds 5 and 6 has been determined. Compound 5 crystallized in the monoclinic space group P2₁/n with a = 13.3290(10) Å, b = 10.6610(10) Å and c = 22.3930(10) Å and β = 100.2690(10)°. Compound 6 crystallized in the triclinic space group with a = 7.271(7) Å, b = 10.038(3) Å and c = 16.012(5) Å, and α = 106.79(3)°, β = 96.25(4)° and γ = 99.62(4)°. The crystal structures of 5 and 6 have short intermolecular Pd-Cl?H-N-Pd non-conventional hydrogen bonds, which associated the molecules in chains in the first case and in dimers in the second.     

Cationoid rearrangements in reactions of perfluoro-1-arylbenzocyclobutenes with antimony pentafluoride

In the presence of antimony pentafluoride at 130 °C, the four-membered ring of perfluoro-1-(2-ethylphenyl)benzocyclobutene (2) undergoes cleavage, forming perfluoro-2-ethyl-2′-methyldiphenylmethane (5). Compound 5 is converted, under the action of SbF₅ at 170 °C, to perfluoro-8,9-dimethyl-1,2,3,4-tetrahydrofluorene (8). Perfluoro-1-(4-ethylphenyl)benzocyclobutene (3) remains unchanged at 130 °C, whereas at 170 °C it gives a mixture of perfluorinated 4′-ethyl-2-methyldiphenylmethane (9), 6-ethyl-1,2,3,4-tetrahydroanthracene (11) and 2-ethyl-9,10-dihydroanthracene (12). When heated with SbF₅ at 170 °C, perfluoro-1-phenylbenzocyclobutene (1) remains unchanged. Solution of compounds 2, 3, 5 and 9 in SbF₅-SO₂ClF generated the perfluorinated 1-(2-ethylphenyl)-1-benzocyclobutenyl (29), 1-(4-ethylphenyl)-1-benzocyclobutenyl (30), 2-ethyl-2′-methyldiphenylmethyl (31) and 4′-ethyl-2-methyldiphenylmethyl (32) cations, respectively.     

Recoverable cationic Pd-catalyzed Heck reaction under thermomorphic mode

The reaction of allylpalladium chloride dimer and 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy, 1a-c, in the presence of AgOT_f resulted in the synthesis of cationic complex, [Pd(η³-allyl)(4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy)](OT_f), 2a-c where R_f = C₉F₁₉ (a), C₁₀F₂₁ (b), C₁₁F₂₃ (c), respectively. The solubility curves of 2a-c which began from virtually zero below −40 °C and increased dramatically at slightly higher temperature were quantitatively measured. Upon changing from −40-90 °C there was several orders of magnitude increase of solubility for 2a-c. The cationic Pd-catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling usage with 2b,c as the catalyst using DMF as the solvent at 140 °C for 3 h in each run. At the end of each cycle, the product mixtures were cooled to −30 °C, and then catalysts were recovered by decantation. The products were quantified by GC analysis or by the isolated yield. The Heck reaction of C₆H₅I with methyl acrylate could be catalyzed by 2b with good recycling results for a total of 15 times and also with a 100% selectivity favoring the trans product. To our knowledge, this is the first example of cationic Pd-catalyzed Heck reaction under the thermomorphic mode.     

Reactions of group 13 metal trialkyls with oxamides

Alkyl aluminum-, gallium-, and indium oxamidates Me₄Al₂(dpoa) (1), Me₄Al₂(dboa) (2), Me₄Ga₂(dpoa) (3), Me₄Ga₂(dboa) (4), ^tBu₄Ga₂(dpoa) (5) and Me₄In₂(dboa) (6) (dpoa-H₂ = N,N′-diphenyloxamide, dboa-H₂ = N,N′-di-tert-butyloxamide) have been prepared and characterized. Compounds 1-3, 5 and 6 exist in the form of isomers a only, with a skeleton framework of the molecules consisting of two almost flat, coplanar and fused MNOC₂ (M = Al, Ga, In) heterocyclic rings. Depending on the reaction conditions, the compound 4 was obtained as the isomer 4a or as the mixture of two isomers 4a and 4b. Molecular structures of the compounds 1a-6a have been determined by X-ray crystallography. A structure of the isomer 4b was proposed on the basis of NMR spectroscopy. A skeleton framework of the 4b molecule consists of two fused different cycles, GaO₂C₂ and GaN₂C₂.     

Synthesis, characterization and Schlenk equilibrium studies of methylmagnesium compounds with O- and N-donor ligands - the unexpected behavior of [MgMeBr(pmdta)] (pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine)

MgMe₂ (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe₂(thf)}₂(μ-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt₃, and tmeda (N,N,N′,N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt₃ (6); tmeda (7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8) were obtained. Reactions of MgMeBr with pmdta (N,N,N′,N″,N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) · MgBr₂(pmdta) (10) and [{MgMe₂(pmdta)}₇{MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe₂(pmdta)] (12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and ¹H and ¹³C NMR spectroscopy. The coordination-induced shifts of the ¹H and ¹³C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent ¹H NMR spectroscopic measurements (from 27 to −80 °C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); diglyme (5); NEt₃ (6); tmeda (7)) in thf-d₈ solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at −80 °C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4-6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d₈ revealed no dismutation into [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) even up to −100 °C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] (9c), [MgMe₂(pmdta)] (12c), and [MgBr₂(pmdta)] (13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ? 12c + 13c) was calculated to be K_gas = 2.0 × 10⁻³ (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be K_thf = 1.2 × 10⁻³ and K_ether = 3.2 × 10⁻³ (298 K), respectively.     

Synthesis of 2,3-disubstituted benzofurans and indoles by π-Lewis acidic transition metal-catalyzed cyclization of ortho-alkynylphenyl O,O- and N,O-acetals

The PtCl₂-catalyzed cyclization reaction of ortho-alkynylphenyl acetals 1 in the presence of COD (1,5-cyclooctadiene) produces 3-(α-alkoxyalkyl)benzofurans 2 in good to high yields. For example, the reaction of acetaldehyde ethyl 2-(1-octynyl)phenyl acetal (1a), acetaldehyde ethyl 2-(cyclohexylethynyl)phenyl acetal (1c), and acetaldehyde ethyl 2-(phenylethynyl)phenyl acetal (1f) in the presence of 2 mol % of platinum(II) chloride and 8 mol % of 1,5-cycloocatadiene in toluene at 30 °C gave the corresponding 2,3-disubstituted benzofurans 2a, 2c, and 2f in 91, 94, and 88% yields, respectively. Moreover, the reaction of N-methoxymethyl-2-alkynylanilines 3 was catalyzed by PdBr₂, affording the corresponding 2,3-disubstituted indoles 4 in moderate yields. For example, the reaction of N-methoxymethyl-2-(1-pentynyl)-N-tosylaniline (3a) and N-methoxymethyl-2-(phenylethynyl)-N-tosylaniline (3b) in the presence of 10 mol % of PdBr₂ in toluene at 80 °C gave 3-methoxymethyl-2-propyl-1-tosylindole (4a) and 3-methoxymethyl-2-phenyl-1-tosylindole (4b) in 33 and 33% yields, respectively.     

Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h′]diquinolines with palladium and platinum

Benzo[1,2-h: 5,4-h′]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand (1a) and its derivatives (1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by ¹H and ¹³C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl₄, Pd(OAc)₂, and K₂PtCl₄ to form the cyclometalated Pd(NCN)Cl (2a-c, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.