Synthesis and electron transfer studies of redox active trans-β-diketonate Ni(II) complexes

The synthesis of trans-[Ni(dbm)₂(RN=C(Me)NHR)₂] (dbm?=?1,3-diphenylpropanedionate; R?=?phenyl, p-tolyl, 3,5-dimethylphenyl, 3,5-dichlorophenyl) has been achieved by reaction of [Ni(dbm)₂(H₂O)₂] with two equivalents of the amidine ligands, RN=C(Me)NHR. X-ray crystallographic studies reveal that trans-[Ni(dbm)₂(RN=C(Me)NHR)₂] (R?=?3,5-dimethylphenyl) exhibits an intramolecular N?CH···O hydrogen bond, which along with the large steric bulk of the amidine ligands may enforce the trans geometry. Electrochemical studies show a strong dependence of the oxidation potential on the substituent groups despite their remote position. DFT calculations indicate that the HOMO consists of Ni-ligand ??* orbitals with a significant contribution from the amidine ligands.     

Synthesis of 1H‐quinazoline‐2,4‐diones from 2‐aminobenzonitriles by fixation of carbon dioxide with amidine moiety supported polymer at atmospheric pressure

1H‐Quinazoline‐2,4‐diones, which are key intermediates in the synthesis of medicines, were successfully synthesized from 2‐aminobenzonitriles by the fixation of CO₂ in the presence of a polystyrene derivative bearing amidine moiety [poly(amidine)]. A model reaction, that is, the reaction of 2‐aminobenzonitrile ( 1a ) with CO₂ in the presence of N‐methyltetrahydropyrimidine ( MTHP ) revealed that a catalytic amount of MTHP afforded 1H‐quinazoline‐2,4‐dione ( 2a ) quantitatively at atmospheric pressure. Several 1H‐quinazoline‐2,4‐diones ( 2a ‐ 2c ) were successfully synthesized from the corresponding 2‐aminobenzonitriles ( 1a ‐ 1c ) in the presence of poly(amidine). The poly(amidine) could easily be separated from the reaction mixture by filtration and reused in subsequent reactions owing to the heterogeneous system. These demonstrated that poly(amidine) is a useful heterogeneous polymer‐supported reagent for the synthesis of 1H‐quinazoline‐2,4‐diones from CO₂. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 653–657, 2009     

Solvent,ligand and temperature effects on the rates of reactions of cis-[PdCl2(CNR)(L)] with secondary amines

The kinetics of the reaction of cis-[PdCl₂(CN-p-C₆H₄Cl)(PPh₃)] with N-methylaniline yielding the carbene derivative cis-[PdCl₂ {C(NH-p-C₆H₄Cl)NMePh} (PPh₃)] have been studied in various solvents such as acetone, 1, 4-dioxane, 1,2-dichloroethane, and benzene. Overall rates for the stepwise process increase with decreasing ability of the solvent to form hydrogen bonds with the attacking amine. A kinetic study is also reported for the reactions of N-methylaniline with cis- [PdCl₂(CN-p-C₆H₄Me)(L)] in 1,2-dichloroethane (L = P(OMe)₃, P(OMe)₂Ph, PPh₃. PMePh₂, PMe₂Ph, PEt₃, PCy₃). The cis ligand L affects reaction rates through both steric and electronic factors. The nucleophilic attack of the amine on the CN carbon atom of coordinated isocyanide is favoured by low steric requirements and high π-acceptor ability of L. The activation parameters for the bimolecular nucleophilic attack when L = PPh₃ are △H^≠₂ = 9.8 ± 0.7 kcal/mol and △S^≠₂ = — 30 ± 2 e.u.     

4,5‐Di­hydro‐3‐methyl‐5‐(4‐methyl­phenyl)‐1H‐pyrazole‐1‐carboxamidinium acetate acetone hemisolvate

The X‐ray structure analysis of the unexpected product of the reaction between 4‐(4‐methyl­phenyl)­but‐3‐en‐2‐one and amino­guanidine revealed the title compound, C₁₂H₁₇N₄⁺·C₂H₃O₂^?·0.5C₃H₆O, consisting of a protonated amidine moiety joined to a substituted pyrazoline ring at the N1 atom. The amidine group is protonated and the positive charge is delocalized over the three C—N bonds in a similar manner to that found in guanidinium salts. The amidinium moiety of the cation is linked to the acetate anions through four N—H?O hydrogen bonds, with N?O distances of 2.749 (4), 2.848 (4), 2.904 (4) and 2.911 (4) Å. The pyrazoline ring adopts a flattened envelope conformation and the substituted phenyl ring is oriented perpendicular to the attached heterocycle. The acetone solvate molecule lies across a twofold rotation axis.     

The balance of steric and conjugative effects in the opening of arylsubstituted oxiranes. Stereochemistry of the ring opening of 1-(1′-naphthyl)-1,2-epoxycyclohexane

The steric course of the ring opening of 1-(1′-naphthyl)-1,2-epoxycyclohexane (3) has been investigated and compared with that of the similar reactions of 1-phenyl-1,2-epoxycyclohexane. Reaction of 3 with KOH in DMSO-H₂O gives small yield of trans diol 4. Reaction of 3 with CCl₃COOH and HCl in low polarity aprotic solvents takes place with complete retention of configuration. However reaction with H₂SO₄ in H₂O is not completely stereospecific and shows a greater tendency than the phenyl substituted epoxide towards cis opening. Explanations of the observed stereochemical results, particularly with respect to the ability of the 1-naphthyl group to stabilize the intermediate carbocation, are discussed.     

Hydroformylation of vinylsilanes with Rh(acac)(CO)2/tris(N-pyrrolyl)phosphine catalytic system

Rh(acac)(CO)₂ as catalyst precursor with a small excess of free N-pyrrolylphosphine ([P(NC₄H₄)₃]:[Rh] = 3–10) was found to be very active in hydroformylation of vinyltrisubstituted silanes at 80 °C and 10 atm CO/H₂ = 1. After 2 h the yields of aldehydes were 80 % (n/iso = 8) for vinyltrimethylsilane, 100 % (only n-isomer) for vinyldimethylphenylsilane and 95 % (n/iso = 5.5) for vinyltrimethoxysilane. The rate of hydroformylation of vinyltrimethylsilane is ca. three times higher than that of other vinylsilanes. 3,3-Dimethyl-1-butene undergoes hydroformylation much slower than vinyltrimethylsilane probably because of its high steric hindrance and the reaction produces 4,4-dimethylpentanal as the only product.     

Cyclic acyl amidines as unexpected C4-donors for fully substituted pyridine ring formation in the base mediated reaction with malononitrile

A new one-step, pseudo four-component approach for the synthesis of fully substituted pyridines via ring-opening of the cyclic acyl amidine of 3-amino-1H-isoindol-1-one and its aza-analogues during the reaction with malononitrile in the presence of sodium methoxide, followed by pyridine ring closure is reported. This method allows the one-step preparation of previously unknown 2-(pyridin-4-yl)(hetero)aryl carboxamides in good yields under mild reaction conditions.     

Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2,6‐diisopropylphenyl)pivalamidine

N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C(tBu)‐N(H)‐C₂H₄‐Py) ( 1 ), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}] ( 6 ), [Mg{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}₂] ( 3 ), and heteroleptic [{(Me₃Si)₂N}Ae{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}], with Ae being Ca ( 2 a ) and Sr ( 2 b ). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β‐metalation and an immediate deamidation reaction yielding [(thf)₂Na{Dipp‐N=C(tBu)‐N(H)}] ( 4 a ) or [(thf)₂K{Dipp‐N=C(tBu)‐N(H)}] ( 4 b ), respectively, as well as 2‐vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI₂ in tetrahydrofuran yields N‐(2,6‐diisopropylphenyl)pivalamidine (Dipp‐N=C(tBu)‐NH₂) ( 5 ), or [(thf)₄Ca{Dipp‐N=C(tBu)‐N(H)}₂] ( 7 ), respectively. The reaction of AN(SiMe₃)₂ (A=Na, K) with less bulky formamidine Dipp‐N=C(H)‐N(H)‐C₂H₄‐Py ( 8 ) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 a ) or [(thf)K{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 b ), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β‐metalation/deamidation of N‐(2‐pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single‐crystal X‐ray structure analysis and are maintained in solution.     

Bis(alkyl) yttrium complex containing a new tridentate amidinate ligand: synthesis and structure

New potentially tridentate amidine containing the quinoline fragment in the lateral chain, viz., NC₉H₆-8-NHC(Bu^t)N-2,6-Prⁱ ₂-C₆H₃ (1), was synthesized by the reaction of chloroimine 2,6-Prⁱ ₂-C₆H₃-N=C(Bu^t)Cl and lithium derivative of 8-aminoquinoline NC₉H₆-8-NHLi. The elimination of alkane under the action of amidine 1 on Y(CH₂SiMe₃)₂(THF)₂ in THF affords bis(alkyl) yttrium complex [NC₉H₆-8-NC(Bu^t)N-2,6-Prⁱ ₂-C₆H₃]Y(CH₂SiMe₃)₂(THF) (2), monomeric in the crystalline state.     

Unexpected regiochemistry in the reaction of benzotriazole with KBH4: synthesis of a new class of poly(azolyl)borate ligands

The reaction of KBH₄ with molten benzotriazole leads to the formation of a series of poly(benzotriazoly)borate anions [H_nB(C₆H₄N₃)_4−n]⁻ where n = 2, 1 and 0 depending on the temperature. The regiospecificity of the process differs from that of pyrazole/BH₄⁻ reactions in the BN bond-formation takes place in a manner that maximises steric crowding at boron (i.e. at the triazole N(1) atoms). The complex-forming abilities of the new ligands have been investigated, and show some interesting differences from those of the poly(1-pyrazolyl)borate analogues.     

A Regioselective Biginelli‐like Reaction Controlled by the Size of Alicyclic Mono‐ketones

A regioselective Biginelli‐like reaction of alicyclic mono‐ketones, aromatic aldehydes, and urea in ionic liquid [BPY]BF₄ has been investigated. The process is controlled by the size of alicyclic mono‐ketones and the steric hindrance of aromatic aldehydes. The reaction of cyclopentanone with urea and aromatic aldehydes afforded 7‐arylidene‐3,4,6,7‐tetrahydro‐4‐aryl‐1H‐cyclopenta[d]pyrimidin‐2(5H)‐ones ( 4 ). When cyclohexanone was used as the source of active methylene to react with urea and aldehydes with slight steric hindrance groups under the same condition, 8‐arylidene‐3,4,5,6,7, 8‐hexahydro‐4‐arylquinazolin‐2(1H)‐ones ( 6 ), a homologue of 4 , were yielded, whereas 4,8‐bisaryloc‐tahydro‐1H‐pyrimido[5,4‐i]‐quinazoline‐2,10(3H,11H)‐diones ( 7 ) were obtained via the simple one‐pot reaction of cyclohexanone, urea, and aromatic aldehydes with high steric hindrance groups. The possible transitional states and mechanism of the regioselective process were discussed.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

Preparation of N,N,N′-tris(trimethylsilyl)amidines; a convenient route to unsubstituted amidines

The tris(trimethylsilyl)amidines RC(NSiMe₃)N(SiMe₃)₂ (R  C₆H₅, p-CH₃C₆-H₄, p-ClC₆H₄, p-MeOC₆H₄, p-Me₂NC₆H₄, p-CF₃C₆H₄, p-C₆H₅C₆H₄ and CF₃) are prepared by the reaction of the respective nitriles with (Me₃Si)₂NLi·OEt₂ in ether to give intermediates RC(NLi)N(SiMe₃)₂. Heating these intermediates with ClSiMe₃ in toluene affords the products, which are isolated by vacuum distillation, in high yield. With 1,4-dicyanobenzene, two equivalents of reagents affords the per(trimethylsilyl)-1,4-diamidine. Hydrolysis of the intermediates with 6N ethanolic HCl affords the unsubstituted amidine hydrochlorides RC(NH)NH₂·HCl (R  C₆-H₅, p-MeOCh₆H₄, p-ClC₆H₄, p-O₂NC₆H₄) in high yield.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Hydrosilylation of ketones catalyzed by tricarbonyl(naphthalene)manganese cation

The naphthalene manganese complex [(η⁶-C₁₀H₈)Mn(CO)₃]BF₄ (1) has been used as an effective catalyst for the hydrosilylation of ketones to give the corresponding sec-alcohols in high yields after hydrolysis. The yields for aryl ketones are dependent on the reaction medium with the highest in CH₂Cl₂ and the steric bulkiness and electronic properties of substituents. As the steric bulkiness increases, the yield decreases and as the electron-donating ability of the substituent on the substrate increases, the yield increases. Catalytic activity of 1 is explained by the ring slippage η⁶→η⁴.     

Synthesis of a new class of bisheterocycles via the Heck reaction of eudesmane type methylene lactones with 8-bromoxanthines

The eudesmane-type methylene lactones (isoalantolactone, alantolactone, 4,15-epoxyisoalantolactone, 2′,2′-dichloro-4H-spiro[cyclopropane-1′,4-eudesma-11(13)-en-8β,12-olide], and alantolactone) react with 8-bromoxanthines (8-bromocaffeine, 8-bromotheobromine, 8-bromo-3-butyltheobromine, 8-bromotheophylline, 8-bromo-9-butyltheophylline) under Heck reaction conditions to produce the target (E)-13-(2,6-dioxo-2,3-dihydro-1H-purin-8-yl)eudesma-4(15),11(13)-dien-8β,12-olides and the subsequent endocyclic isomers - 11-(2,6-dioxo-2,3-dihydro-1H-purin-8-yl)-13-normethyleudecma-4(15)-7(11)-dien-8α,12-olides. It was revealed that the yield and product ratio depends on the reaction conditions and the structure of methylene lactone. The effectiveness of Pd(OAc)₂–caffeine catalytic system has been demonstrated in this reaction. The electric eel acetylcholinesterase inhibitory activity of the eudecmanolide-xanthine hybrids was evaluated. Among the new type bisheterocycles compound 27 with butyl and 2-oxodecahydronaphtho[2,3-b]furan-3(2H)-ylidene)methyl substituents at C-7 and C-8 of the xanthine core showed moderate activity with IC₅₀ value of 40 μM.     

Hydrothermal synthesis and characterization of a new layered gallophosphate JGP-L1 with a Ga/P ratio of non-unity

A new compound, Ga₆(OH)₄(HPO₄)₂(PO₄)₅·C₈H₂₈N₅·3H₂O (denoted JGP-L1), with a gallophosphate layer and a Ga/P ratio of 6/7 has been synthesized hydrothermally by using tetraethylenepentamine as template. It is characterized by powder X-ray diffraction (XRD), elemental analysis, inductively coupled plasma, and TGA analysis and structurally determined by single-crystal XRD analysis. JGP-L1 crystallizes in the orthorhombic, space group Pna2₁ (no. 33), with a=16.422(3), b=11.898(2), c=18.730(4) Å, V=3659.6(13) Å³ and Z=4. The structure of JGP-L1 is built up by alternating of Ga(OH)₂O₄ octahedra, Ga(OH)O₄ trigonal bipyramids and PO₄ (or HPO₄) tetrahedra to form inorganic sheets. It is noteworthy that JGP-L1 was synthesized with extremely low reactant concentration, where the reaction mixture exhibits a H₂O:Ga₂O₃ molar ratio of 2220:1.     

Reaction of ninhydrin with enamino amides of the 3,3-dimethyl-1,2,3,4-tetrahydroisoquinoline series and drotaverine

“Push–pull” enamines of the 1,2,3,4-tetrahydroisoquinoline series, 2-(3,3-dimethyl-1,2,3,4-tetrahydroisoquinolin- 1-ylidene)acetamides, reacted as 1,3-binucleophiles with ninhydrin to form tricyclic tetrahydroindeno[1,2-b]pyrrole system. The nucleophilic centers in the enamines were the amide NH₂ group and ß-carbon atom of the enamine fragment. The reaction of ninhydrin with 2-[2,2-dimethyl-2,3-dihydrobenzo[f]-isoquinolin-1(4H)-ylidene]-1-(pyrrolidin-1-yl)ethanone involved only addition to the ß-carbon atom of the enamine fragment. The different reaction directions were rationalized by steric effect of two methyl groups in position 3 of the isoquinoline ring. The Knoevenagel condensation product was obtained by the reaction of ninhydrin with drotaverine (base). The structure of the 1,3-addition product, (3aS,8bS,Z)-{2,2-dimethyl-2,3- dihydrobenzo[f]isoquinolin-4(1H)-ylidene}-3a,8b-dihydroxy-1,3,3a,8b-tetrahydroindeno[1,2-b]pyrrole-2,4-dione, was confirmed by X-ray analysis.     

Remarkably strong polarization of amidine fragment in the crystals of 1-imino-1H-isoindol-3-amine

Results of the X-ray diffraction studies of 1-imino-1H-isoindol-3-amine and its derivatives reveal unusual distribution of bond lengths within the NH₂–C=N amidine fragment in the considered crystals. In the crystal phase, single C–N bond is shorter or at most has the same length as double C=N bond, while in isolated molecules both these bonds have expected lengths, according to the calculations by MP2/6-311G(d,p) and MP2/cc-pvtz methods. It is demonstrated that so unusually strong polarization of the amidine fragment is induced by polar environment in solid state. This effect stabilizes the amino-imino tautomer of 1-imino-1H-isoindol-3-amine, which becomes more stable than the diimino tautomer possessing the lowest energy in the gas phase.     

Mono- and bi-iron chalcogenocarboxylate complexes

A series of thiocarboxylato and selenocarboxylato monomeric CpFe(CO)₂ECORCOCl and dimeric [CpFe(CO)₂ECO]₂R iron complexes have been synthesized and characterized. The interaction of (μ-E_x)[CpFe(CO)₂]₂ (E = S; x = 2–4. E = Se; x = 1) with di-acid chlorides (ClCORCOCl) in a 1:1 molar ratio gave the monomeric complexes CpFe(CO)₂ECORCOCl for R = 1,3-C₆H₄, 2,6-C₅H₃N, 1,2-C₆H₄. However, the dimeric complexes [CpFe(CO)₂ECO]₂R were obtained from the same reactants in a 2:1 metal-to-ligand molar ratio in which R is 1,3-C₆H₄, 2,6-C₅H₃N or C₂H₄. The monomer versus dimer production mainly depends on the electronic and steric factors of the R-moiety. The new monomeric and dimeric thio- and selenocarboxylato iron complexes have been characterized by spectroscopic techniques (¹H- and ¹³C-NMR, IR) and by elemental analysis. The structures of [CpFe(CO)₂SCO]₂(1,3-C₆H₄) and its seleno analogue [CpFe(CO)₂SeCO]₂(1,3-C₆H₄) were determined by X-ray structure determination.