DFT calculation and AIM-analysis of the substituent influence on the structure of (1-azabuta-1,3-diene)tetracarbonyliron(0) complexes

1-Azabuta-1,3-dienes can coordinate to the tetracarbonyliron(0) moiety in four ways, to form (1-azabuta-1,3-diene)tetracarbonyliron(0) complexes with the ligand bonded in an η² fashion through the alkene, η² coordinated through its CN bond, σ-bonded to the lone pair of the nitrogen atom, or η³ coordinated through the CC-C moiety under concomitant coupling of the imine nitrogen with one of the carbonyl ligands to a carbamoyl species. In the experiment, the equilibrium between these species strongly depends on factors such as the nature of the substituents at the ligand, the solvent and the temperature. In this work, DFT calculations (B3LYP/LANL2DZ/6-31G* and 6-311++G**) and an AIM-analysis of the topology of the charge density were used to investigate the influence of the substituents at the 1-azabuta-1,3-diene ligand on the structural, electronic and energetic properties of these constitutional isomers. In most cases, the calculations correctly predict the observed structure, even in situations where the energy differences between related species are rather small. Substituents larger than CH₃ at N and H at C2 disfavour the structures with an η² coordination to the CN bond to such an extent that they cease to exist as minimum energy structures. Also the σ-N forms distort significantly with the introduction of substituents at N or C2 and become energetically less favourable. The geometries of the η²-alkene form do not change much upon substitution, whereas the η³ form tolerates steric strain best and becomes most favourable when the substituent at C2 is large. The activation barrier between the η²-alkene and the η³-allyl form is low (7.5-1.4 kcal/mol) and allows for an equilibration between these species. The conversion of the η²-alkene into the σ-N form requires almost complete dissociation of the ligand from the Fe(CO)₄ moiety. Accordingly, its activation barrier is higher (approx. 14 kcal/mol) and fairly independent of the nature of the substituents at the azabutadiene ligand.     

Cycloaddition reactions of 1,3-diazabuta-1,3-dienes with alkynyl ketenes

The cycloaddition reactions of ‘all-carbon’ 1,3-diazabuta-1,3-dienes with a few conjugated and unconjugated alkynyl ketenes are described. The reactions provide some interesting azetidinones and dihydropyrimidinones bearing an alkynyl moiety. The regiochemistry of cycloadduct is related with the degree of conjugation of the alkynyl ketene. Moreover, two alternative approaches to ‘all-carbon’ 1,3-diazabuta-1,3-dienes are reported.     

Cycloaddition reactions of 2,4-diphenyl-1,3-diazabuta-1,3-dienes with isocyanates and isothiocyanates

The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed.     

A facile method for the stereoselective preparation of (1E,3E)-4-substituted-1-amino-1,3-dienes via 1,4-elimination

The 1,4-elimination reaction of 1-amino-4-methoxy-(2Z)-alkenes is shown to proceed with high (1E,3E)-stereoselectivities to afford the corresponding 4-substituted-1-amino-1,3-dienes in good yield. The scope and stereochemical features of the synthetic method are described.     

Überraschende Reaktionen von 4,4-Bis(trifluormethyl)-1-oxa-3-azabuta-1,3-dienen: Tandem-Reaktion mit Acrylnitril

Summary 4,4-Bis(trifluoromethyl)-1-oxa-3-azabuta-1,3-dienes and acrylonitrile react in the presence of equimolar amounts of 4-dimethylaminopyridine (DMAP) to give 2:1-adducts. A sequential [4+2] cycloaddition is proposed.

Prof. Dr.Rolf Huisgen zum 75. Geburtstag gewidmet     

Synthesis of 2-amino-1,3-dienes by chromium-catalyzed addition of silylated propargyl bromides to imines

(Silyl)methylallenic amines were synthesized by the chromium-catalyzed addition of (4-bromobutynyl)trimethylsilane to tosyl imines. Regioisomeric mixtures of the desired allene and the corresponding alkyne were obtained. Allenic imines were then treated with TBAF to afford 2-aminomethyl-1,3-dienes in good yields (62-92%). In the presence of a Lewis acid, silylallenic imines were added to benzaldehyde dimethylacetal to give highly functionalized dienes with excellent yields and good to excellent diastereomeric ratios.     

Catalytic asymmetric synthesis of polysubstituted cyclohexa-1,3-dienes from β-branched α,β-alkenals

3-Methyl- and 3-phenylbut-2-enal in the presence of (S)-prolinol (0.1 eq.) in benzene or THF react with the acidic monoesters of alkenylidene, and arylmethylidene-, and alkylidenemalonic acids at –10 to +22 °C to give optically active esters of 4,6-disubstituted cyclohexa-1,3-diene-l-carboxylic acids in moderate (10–43 %) yields. The enantiomeric purity of the products formed from the lint two types of acidic ylidenemalonates varies from 28 to 68 % and is higher than that observed in the case of related alkylidenemalonates. Under similar conditions cyclohexylideneacetaldehyde affords optically active derivatives of 1,5,6,7,8,8a-hexahydronaphthalene as mixtures ofcis andtrans isomers. The enantiomeric purity and absolute configuration of the cyclohexadienes thus obtained were determined using¹H NMR spectroscopy in combination with chiral solvating agents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 663–669, March, 1996.     

Construction of fused, bridged, and spiro bicyclic skeletons via nickel-catalyzed intramolecular cyclization of cyclic 1,3-dienes and a tethered aldehyde

Nickel-catalyzed intramolecular cyclization of cyclohexa-1,3-dienes and an aldehyde in a chain produced fused, bridged or spiro bicyclic skeletons depending on the length of the tether. This chemistry can be extended to cyclohepta-1,3-dienes and cyclohepta-1,3,5-trienes having an aldehyde moiety on the side chain.     

Highly electrochemiluminescent Ru(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one ligand

A series of new ruthenium(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one (DTDP) ligand, such as [Ru(DTDP)_n(L)_3−n]²⁺ (L = 2,2′-bipyridyl (bpy), 4,4′-dimethyl-2,2′-bipyridyl (dmbpy), o-phenanthroline (o-phen), 5-chloro-o-phenanthroline (o-phen-Cl), 2,2′-bipyridine-4,4′-dicarboxaldehyde (bpy-(CHO)₂), n = 1, 2, 3) were synthesized and examined as ECL materials. All the complexes were characterized in terms of electrochemical redox potential and relative ECL intensity, and were compared to the well-known tris(o-phenanthroline) ruthenium(II) complex. Most of the synthesized Ru(II) complexes containing the DTDP ligand exhibited more intense ECL emissions than [Ru(o-phen)₃]²⁺. In particular, the ECL intensities of [Ru(DTDP)(o-phen)₂]²⁺ and [Ru(DTDP)(bpy-(CHO)₂)₂]²⁺ were observed to be as high as 9-fold and 20-fold greater, respectively, than the ECL intensity of [Ru(o-phen)₃]²⁺.     

Synthesis of functionalized α-amino-phosphine oxides and -phosphonates by addition of amines and aminoesters to 4-phosphinyl- and 4-phosphonyl-1,2-diaza-1,3-butadienes

1,2-Diaza-1,3-butadienes derived from phosphine oxides and phosphonates and with optically active substituents on N-1 and C-3 are obtained by 1,4-elimination from chlorohydrazonoalkyl-phosphine oxides and -phosphonates in the presence of bases. Michael addition (1,4-addition) of ammonia, aliphatic and aromatic amines and aminoesters to these azo-alkenes gives functionalized α-amino-phosphine oxides and -phosphonates.     

Synthesis of substituted 2-amino-1,3-thiazine-6-thiones

The reaction of thiourea with l-acyl-2-bromoacetylenes in AcOH in the presence of BF₃·Et₂O affords 2-amino-4-phenyl(2-thienyl)-1,3-thiazine-6-thiones in high yields. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 11, pp. 1947–1949, November, 2000.     

Synthesis and characterization of some new mononuclear ruthenium complexes containing 4-(un)substituted dipyridylpyrazole ligands

A mononuclear ruthenium complex [Ru(bpy)₂(bpp)](PF₆) (1) and its halogenated and nitro derivatives [Ru(bpy)₂(Xbpp)](PF₆) (bpy = 2,2′-bipyridine; bpp = 3,5-bis(2-pyridyl)pyrazole; X = Cl, 2; X = Br, 3; X = I, 4; X = NO₂, 5) have been synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, elemental analysis. Complexes 2–5 have been further confirmed by X-ray diffraction. Their UV–Vis and emission spectroscopies, electrochemical measurements and acid–base properties are described. The results presented here reveal that the introduction of Cl, Br, I and NO₂ groups to the coordinated bpp⁻ ligand makes the absorption and emission maxima of the parent complex 1 blue-shifted, the oxidation potential of the Ru^II/Ru^III couple increased and the pK_a value decreased obviously. In addition, significant quenching of the emission by these groups is also observed.     

Ruthenium-catalyzed addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols

Monomeric ruthenium(0) complexes containing redox-coupled dienone ligands were found to catalyze the regio-selective addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols.     

Novel photoinitiated cationic copolymerizations of 4-methylene-2-phenyl-1,3-dioxolane

Photoinitiated polymerization of 4-methylene-2-phenyl-1,3-dioxolane ( 1 ) was carried out using either tris (4-methylphenyl) sulfonium hexafluoroantimonate or 4-decyloxyphenyl phenyliodonium hexafluoroantimonate as initiators. ¹H-NMR analyses confirmed exclusive ring-opening while DSC and SEC were used to determine the glass transition temperatures (T_gs) and molecular weights, respectively. Photoinitiated cationic copolymerizations of 1 were investigated with several acyclic and cyclic monomers. Copolymerization of 1 with vinyl ethers and a spiroorthoester resulted in copolymers whose thermal properties were dependent on comonomer ratios. Copolymers of 1 and dihydrofuran or dihydropyran afforded soluble polymers with T_gs significantly higher than the homopolymer of 1 . © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2207–2219, 1997     

A novel route to poly(α-hydroxyacrylic acid) derivatives by the hydrolysis of polymers containing 1,3-dioxolan-4-one moiety

The alkali hydrolysis of poly(2,2-dimethyl-5-methylene-1,3-dioxolan-4-one) and poly(2,2-dimethyl-5-methylene-1,3-dioxolan-4-one-co-styrene) was carried out with a sodium hydroxide solution (40%) in tetrahydrofuran at room temperature to obtain poly(α-hydroxyacrylic acid) or poly(α-hydroxyacrylic acid-co-styrene) with number-average molecular weights of 39,000–73,000 in 41–86% yields. The styrene unit in the hydrolyzed copolymer hindered the formation of a lactone ring. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1629–1633, 2001     

Supramolecular structures of Mn2+, Co2+ and Zn2+ complexes containing 1,3-bis(4-pyridyl)propane and aminosalicylate anion

In this study, the synthesis, spectroscopic properties and crystal structures of three new supramolecular compounds named [Mn₂(bpp)₄(H₂O)₄](AS)₄·H₂O (1), [Co₂(bpp)₄(H₂O)₄](AS)₄·H₂O (2) and [Zn(bpp)(AS)₂] (3), have been described, where bpp is 1,3-bis(4-pyridil)propane and AS^?  is aminosalicylate anion. By analysing the similarities between the X-ray powder diffraction results, it has been observed that compounds 1 and 2 are isomorphous, exhibiting an orthorhombic system with space group Pccn; for compound 3, another orthorhombic system was observed, with space group Aba2, which displays coordination between the Zn²⁺ metal ion and the aminosalicylate anion; this can be considered the first case in the literature involving the direct coordination to the metal ion. The vibrational spectra of compounds 1 and 2 are very similar. In the Raman spectra, the main bands are observed at ca. 1625 and 1020 cm^? 1, referring to the ^? O–C = O and CC/CN stretching modes of AS^?  and bpp ligands, respectively.     

Synthesis of electron-poor 4-halo-2-azabuta-1,3-dienes by Rh(II)-catalyzed diazo ester-azirine coupling. 2-Azabuta-1,3-diene-2,3-dihydroazete valence isomerism

The Rh₂(OAc)₄-catalyzed reaction of alkyl 2-acyl-2-diazoacetates and dimethyl diazomalonate with methyl 2-bromo- and 2-chloro-3-phenyl-2H-azirine-2-carboxylates gives rise to electron-poor 4-halo-substituted (3E)-2-azabuta-1,3-dienes. Their formation proceeds with complete stereoselectivity via ring-opening of the intermediate azirinium ylide. 2-Azabuta-1,3-dienes with electron-withdrawing substituents at the 1,1,4-positions are stable compounds at room temperature, but are in equilibrium with cyclic valence isomers, 2,3-dihydroazetes, at elevated temperatures.     

1,3-Dipolar addition of nitrones to symmetrically substituted allenes: for the determination of absolute configuration of chiral allenes by NMR spectroscopy

5-Methyl-5-phenylpyrroline N-oxide was proved to be a useful 1,3-dipole for determining the absolute configuration of chiral allenes by means of NMR spectroscopy.