Recent developments in the chemistry of bicyclic 6-6 systems: Chemistry of pyrido[1,2-c]pyrimidines

The present review provides a study on the structural features, reactions, and synthetic methodologies of pyrido[1,2-c]pyrimidines. The maximum deviation from the mean plane of the pyridopyrimidine skeleton of 4-(pyridin-2-yl)-1H-pyrido[1,2-c]pyrimidine-1,3(2H)-dione indicated a reasonably planar system. The aim of this review is to give an overview of the diverse methodologies that have been reported on the chemistry of pyrido[1,2-c]pyrimidines. The different synthetic routes have been grouped according to the way the pyrido[1,2-c]pyrimidine moiety has been created. Thus, pyrido[1,2-c]pyrimidine compounds were obtained by the formation of one bond α to the bridgehead nitrogen atom [6+0(β)] and formation of two bonds from ([3+3], [4+2], and [5+1]) atom fragments. The mechanistic pathways of the reactions are discussed.     

二(三苯基膦)乙基黄原酸金属配合物的晶体结构和谱学表征

0IntroductionTheincreasingcommercialvalueoftransitionmetalcomplexesofxanthateshasarousedconsiderableinterestingintheirchemistry.Whiletheiranalyticalapplicationsarewellknown犤1犦,theyarenowfindingextensiveuseinvulcanizationofrubber,frothfloatationprocessforconcentrationofsulphideores,asantioxi-dants,lubricants犤2,3犦,andhavebeenfoundtopossessfungicidalandinsecticidalactivity犤4犦.Inrecentyears,therehasbeengrowinginterestinthestudyofd10metalcomplexes,whichexhibitrichphotophysicalandpho-tochemica…     

Unprecedented Oxycyanation of Methylenecyclopropanes for the Facile Synthesis of Benzoxazine Compounds Containing a Cyano Group

A novel intramolecular oxycyanation of methylenecyclopropanes is reported that proceeds through oxidative cleavage of the N?CN bond and subsequent palladium transfer from N to O of the amide group. A range of substituted benzo[d][1,3]oxazines with a cyano group are readily furnished by this newly developed oxycyanation reaction. Tris(4‐trifluoromethylphenyl)phosphine as a ligand has been found to be crucial to effectively promote the transformation with high chemo‐ and regioselectivity. Moreover, the reaction outcome can be significantly affected by the electronic effect of the acyl group attached to the nitrogen atom of methylenecyclopropanes. When R³ is a chloromethyl group, the pyrrolo[2,3‐b]quinoline derivative is obtained by thermal‐induced [3+2] cycloaddition of methylenecyclopropane to the methanediimine intermediate.     

A new phosphorothioic triamide structure: P(S)[NHCH2C6H5]3

The structure of N,N′,N′′‐tribenzylphosphorothioic triamide, C₂₁H₂₄N₃PS, (I), and analysis of the bond‐angle sums at the N atoms for this compound, and for 74 structures with a P(S)[N]₃ skeleton and the N atom in a three‐coordinate geometry found in the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53 , 662–671], are reported. For (I), the bond‐angle sum at one of the N atoms [359 (1)°] shows a nearly planar configuration, while the other two show a nonplanar geometry with bond‐angle sums of 342 (1) and 347 (1)°. The location of the atoms attached to the nonplanar N atoms suggests an anti orientation of the corresponding lone electron pairs (LEPs) on these N atoms with respect to the P=S group. For 74 structures with a P(S)[N]₃ skeleton and with the N atom in a three‐coordinate geometry, the bond‐angle sums at the N atoms were found to be in the range 293–360°. Among 307 such three‐coordinate N atoms, 39% (120 N atoms) have bond‐angle sums in the range 359–360°, in accordance with sp² hybridization, and 45% (138 N atoms) have bond‐angle sums in the range 352–359°, with hybridization close to sp². For the orientation of the LEP with respect to the P=S group, the anti orientation was found to be a general rule for N atoms, with the corresponding bond‐angle sums deviating by more than 8° from the planar value of 360°. In the title structure, the S atom takes part in intermolecular (N—H...)(N—H...)S hydrogen bonds, connecting the molecules into extended chains parallel to the b axis. The co‐operation of one N atom in an N—H...S hydrogen bond as an H‐atom donor, and in an N—H...N hydrogen bond as an acceptor, is a novel feature of the crystal structure.     

7‐Fluorotubercidin: a halogenated derivative of a naturally occurring nucleoside antimetabolite

The title compound [systematic name: 4‐amino‐5‐fluoro‐7‐(β‐d ‐ribofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine], C₁₁H₁₃FN₄O₄, exhibits an anti glycosylic bond conformation, with a χ torsion angle of −124.7 (3)°. The furanose moiety shows a twisted C2′‐endo sugar pucker (S‐type), with P = 169.8 (3)° and τ_m = 38.7 (2)°. The orientation of the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a γ torsion angle of 59.3 (3)°. The nucleobases are stacked head‐to‐head. The extended crystal structure is a three‐dimensional hydrogen‐bond network involving O—H...O, O—H...N and N—H...O hydrogen bonds. The crystal structure of the title nucleoside demonstrates that the C—C bonds nearest the F atom of the pyrrole system are significantly shortened by the electronegative halogen atom.     

Doppelkomplexsalze von Co(II), Ni(II) und Cu(II) mit Thioharnstoffliganden im Kationkomplex und Thiocyanatliganden im anionkomplex

Three new double complex compounds of the following type were obtained: [CoThio ₄][Co(SCN)₄], [NiThio ₄][Ni(SCN)₄] and (CuThio ₄) (CuCo(SCN)₄). The melting points of the compounds were determined, and the molecular weight of the first. The IR-spectra were studied and the metal-ligand bond interpreted. It was shown that the metal-thiourea bond in all compounds is formed via the sulphur atom. In the complex anion of the first and second compounds Co(II) and Ni(II) are coordinated with SCN^– through the nitrogen atom. In the third, more complicated compound, Cu(II) is coordinated to SCN^– through the sulphur atom, and Co(II) through the nitrogen atom, a bridging bond being formed.     

C[triple‐bond]C—H systems as hydrogen‐bond donors and acceptors: trans‐1,2‐diethynylcyclo­hexane‐1,2‐diol and trans‐1,4‐diprop‐2‐ynylcyclo­hexane‐1,4‐diol monohydrate

The title 1,2‐diol derivative, C₁₀H₁₂O₂, crystallizes with two independent but closely similar mol­ecules in the asymmetric unit. Only two of the four OH groups are involved in classical hydrogen bonding; the mol­ecules thereby associate to form chains parallel to the short c axis. The other two OH groups are involved in O—H⋯(C[triple‐bond]C) systems. Additionally, three of the four C[triple‐bond]C—H groups act as donors in C—H⋯O inter­actions. The 1,4‐diol derivative crystallizes with two independent half‐mol­ecules of the diol (each associated with an inversion centre) and one water mol­ecule in the asymmetric unit, C₁₂H₁₆O₂·H₂O. Both OH groups and one water H atom act as classical hydrogen‐bond donors, leading to layers parallel to the ac plane. The second water H atom is involved in a three‐centre contact to two C[triple‐bond]C bonds. One acetyl­enic H atom makes a very short `weak' hydrogen bond to a hydr­oxy O atom, and the other is part of a three‐centre system in which the acceptors are a hydroxy O atom and a C[triple‐bond]C bond.     

(Nitro‐κN)[2‐(phenyldiazenyl‐κN2)pyridine‐κN](2,2′:6′,2′′‐terpyridine‐κ3N)ruthenium(II) tetrafluoroborate

The Ru—N bond distances in the title complex, [Ru(NO₂)(C₁₁H₉N₃)(C₁₅H₁₁N₃)]BF₄ or [Ru(NO₂)(tpy)(azpy)]BF₄, [tpy is 2,2′:6′,2′′‐ter­pyridine and azpy is 2‐(phenyl­azo)­pyridine], are Ru—N_py 2.063 (4), Ru—N_azo 2.036 (4), Ru—N_nitro 2.066 (3) Å, and Ru—N_tpy 2.082 (4), 1.982 (3) and 2.074 (4) Å. The azo N atom is trans to the nitro group. The azo N=N bond length is 1.265 (5) Å, which is the shortest found in such complexes to date. This indicates a multiple bond between Ru and the N atom of the nitro group, and π‐­backbonding [dπ(Ru) π*(azo)] is decreased.     

Carbene- and carbyne-like behavior of the Mo-P multiple bond in a dimolybdenum complex inducing trigonal-pyramidal coordination of a phosphinidene ligand

The phosphinidene complex [Mo2Cp(micro-kappa1:kappa1,eta5-PC5H4)(CO)2(eta6-R*H)] (2; Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) has substantially different Mo-P bonds and displays a high reactivity located at the short Mo-P bond. Sideways cycloaddition or addition processes are observed toward RCCR, HCl, and [Fe2(CO)9], to give respectively metallacyclobutene and arylphosphide-bridged and heterometallic phosphinidene-bridged derivatives, a behavior reminiscent of the nucleophilic mononuclear phosphinidene complexes (carbene-like behavior), which is in good agreement with the ground-state electronic structure of 2 derived from density functional theory calculations. However, the reaction of 2 with [Co2(CO)8] implies the addition of two cobalt fragments to its short Mo-P bond and thus reveals a carbyne-like behavior of compound 2. In most of the new products, the P atom displays an unprecedented trigonal-pyramidal-like environment, instead of the expected tetrahedral distribution of bonds.     

CH3--MoF], [CH2=MoHF], and [CH[triple bond]MoH2F] formed by reaction of laser-ablated molybdenum atoms with methyl fluoride: persistent photoreversible interconversion through alpha-hydrogen migration and agostic interaction

Simple molybdenum methyl, carbene, and carbyne complexes, [CH3--MoF], [CH2=MoHF], and [CH[triple chemical bond]MoH(2)F], were formed by the reaction of laser-ablated molybdenum atoms with methyl fluoride and isolated in an argon matrix. These molecules provide a persistent photoreversible system through alpha-hydrogen migration between the carbon and metal atoms: The methyl and carbene complexes are produced by applying UV irradiation (240-380 nm) while the carbyne complex is depleted, and the process reverses on irradiation with visible light (lambda>420 nm). An absorption at 589.3 cm(-1) is attributed to the Mo--F stretching mode of [CH3--MoF], which is in fact the most stable of the plausible products. Density functional theory calculations show that one of the alpha-hydrogen atoms of the carbene complex is considerably bent toward the metal atom (angle-spherical HCMo=84.5 degrees ), which provides evidence of a strong agostic interaction in the triplet ground state. The calculated C[triple chemical bond]Mo bond length in the carbyne is in the range of triple-bond values in methylidyne complexes.     

On the Nature of the Positronic Bond

Recently it has been proposed that the positron, the anti-particle analog of the electron, is capable of forming an anti-matter bond in a composite system consists of two hydride anions and a positron [Angew. Chem. Int. Ed. 57 , 8859–8864 (2018)]. In order to dig into the nature of this novel bond the newly developed multi-component quantum theory of atoms in molecules (MC-QTAIM) is applied to this positronic system. The topological analysis reveals that this species is composed of two atoms in molecules, each containing a proton and half of the electronic and the positronic populations. Further analysis elucidates that the electron exchange phenomenon is virtually non-existent between the two atoms and no electronic covalent bond is conceivable in between. On the other hand, it is demonstrated that the positron density enclosed in each atom is capable of stabilizing interactions with the electron density of the neighboring atom. This electrostatic interaction suffices to make the whole system bonded against all dissociation channels. Thus, the positron indeed acts like an anti-matter glue between the two atoms.     

X-ray study of the third polymorphic structure of μ-oxo-bis[(octaethylporphinato)iron(III)]: [(OEPFe)2O)]

Exposure of a dichloromethane solution of [OEPFe^IIICl], where OEP is the dianion of octaethylporphyrin, to dioxygen results in its transformation into the μ-oxo bridged compound [(OEPFe)₂O)]. The structure of [(OEPFe)₂O)] is determined by X-ray diffraction analysis. It contains binuclear centrosymmetric [(OEPFe)₂O]. The Fe atom is five-coordinated to four N atoms of the porphyrin ring and to one bridging O atom. The compound is characterized by an average Fe-N bond length of 2.096 ?. The Fe-O bond distance is 1.7739(12) ?, the Fe-O-Fe bond angle is 180.0° and the two porphyrin rings are parallel. Crystal data: triclinic crystal system, a = 10.915(4) ?, b = 12.951(4) ?, c = 13.403(4) ?, α = 118.06(1)°, β = 100.33(1)°, Γ = 102.43°, space group, V = 1144.5(1) ?³, Z = 1.     

Redetermination of Na3TaF8

The crystal structure of trisodium octafluoridotantalate, Na₃TaF₈, has been redetermined using diffractometer data collected at 153 K, resulting in more accurate bond distances and angles than obtained from a previous structure determination based on film data. The structure is built from layers running along [101], which are formed by distorted [TaF₈] antiprisms and [NaF₆] rectangular bipyramids sharing edges and corners. The individual layers are separated by eight‐coordinated Na ions. Two atoms in the asymmetric unit are in special positions: the Ta atom is on a twofold axis in Wyckoff position 4e and one of the Na ions lies on an inversion centre in Wyckoff site 4d.     

A lithium ethyl­ene­diphos­phon­ate containing lithium chains and symmetric hydrogen bonds

In the title compound, catena‐poly[lithium‐μ₃‐ethyl­ene­diphos­phon­ato], [Li(C₂H₇O₆P₂)]_n, the supra­molecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethyl­ene­diphosphon­ate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand.     

Two new thiophosphoramide structures: N,N′,N′′‐tricyclohexylphosphorothioic triamide and O,O′‐diethyl (2‐phenylhydrazin‐1‐yl)thiophosphonate

The compound N,N′,N′′‐tricyclohexylphosphorothioic triamide, C₁₈H₃₆N₃PS or P(S)[NHC₆H₁₁]₃, (I), crystallizes in the space group Pnma with the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond‐angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to an anti orientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]₃ skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N—H...S=P hydrogen bonds. In O,O′‐diethyl (2‐phenylhydrazin‐1‐yl)thiophosphonate, C₁₀H₁₇N₂O₂PS or P(S)[OC₂H₅]₂[NHNHC₆H₅], (II), the bond‐angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, for the N atom bonded to the P atom, a practically planar environment is observed, with a bond‐angle sum of 359.1°. A Cambridge Structural Database [CSD; Allen (2002). Acta Cryst. B 58 , 380–388] analysis shows a shift of the maximum population of P=S bond lengths in compounds with a P(S)[O]₂[N] skeleton to the shorter bond lengths relative to compounds with a P(S)[N]₃ skeleton. The influence of this difference on the collective tendencies of N...S distances in N—H...S hydrogen bonds for structures with P(S)[N]₃ and P(S)[O]₂[N] segments were studied through a CSD analysis.     

Kinetics of the Conformer Reactions: II. Significance of Media in the Electrophilic addition Reactions

The kinetics of electrophilic addition reaction of bromine to a multiple bond in a series of con-formationally unhomogenous 2-substituted 1'3-dioxa-5-cycloheptenes was studied. We found that the com-pounds with trans structure are formed. The partial reaction rate constant for chair, twist forms, thereaction susceptibility parameters to the substituent electronic effect at the ^C2atom are obtained. Relativereactivity of the alternative steric structures is defined by the specific solvation of the substrate. The result obtained are compared with those achieved without accounting for conformational term.     

Doppelkomplexsalze des Thioharnstoffs und der Thiocyanat-Ionen mit den Übergangsmetallen Cd(II), Cu(II) und Co(II)

Three new double complex compounds with the following compositions were obtained:[Cd(thio)₄]·[Cd(SCN)₄],[Cd(thio)₄]·[Co(SCN)₄], [Cu(thio)₄] [Cd₂(SCN)₆].Some of their physical properties including melting points and electric conductivity have been determined. The study of their IR-spectra shows that the metal-thiourea bond in the complex cation is formed via the sulphur atom. The Co-SCN bond in the complex anion [Co(SCN)₄]^2– is formed through the nitrogen atom, and in [Cd(SCN)₄]^2– the cadnium-thiocyanate bond is probably formed with some groups through the sulphur atom, and with others through the nitrogen.In the complex anion [Cd₂(SCN)₆]^2– the IR spectral data show that a bridging bond is also formed.     

Effect of substituants on the structure of dioxouranium(VI) complexes of 7-carboxaldehyde-8-hydroxyquinoline and some of its Schiff bases

Summary A series of dioxouranium(VI) complexes with 7-carboxaldehyde-8hydroxyquinoline (oxine) and with some of its Schiff bases, LH, have been prepared and characterized by elemental analyses, electronic and vibrational spectral studies. All complexes except those of the oxine have the [UO₂L₂] · EtOH, stoichiometry (n=0, 1, 2 or 4). The uranyl complexes of the oxine have the formula [UO₂L₂(LH)]. The i.r. spectra reveal all ligands to be monobasic bidentate chelating agents coordinated to the uranium(VI)via the enolized phenolic OH and aldehydic oxygen or azomethine nitrogen atom. The force constant f_U-o (mdyn Å) and the bond length r_U-o (Å) of the U-O bond are also calculated and related to the electronic properties of thep-substituents.     

An Experimental Evidence of a Metal−Metal Bond in μ‐Carbonylhexacarbonyl[μ‐(5‐oxofuran‐2(5H)‐ylidene‐κC,κC)]‐dicobalt(Co−Co)[Co2(CO)6(μ‐CO)(μ‐C4O2H2)]

The orthorhombic crystal structure of [Co₂(CO)₆(μ‐CO)(μ‐C₄O₂H₂)] ( 1 ) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical‐atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn₂(CO)₁₀], confirming our previously established bonding classification for organometallic and coordination compounds.     

The structures of the isomorphous potassium and rubidium salts of 4‐nitrobenzoic acid and an overview of the metal complex stereochemistries of the alkali metal salt series with this ligand

4‐Nitrobenzoic acid (PNBA) has proved to be a useful ligand for the preparation of metal complexes but the known structures of the alkali metal salts of PNBA do not include the rubidium salt. The structures of the isomorphous potassium and rubidium polymeric coordination complexes with PNBA, namely poly[μ₂‐aqua‐aqua‐μ₃‐(4‐nitrobenzoato)‐potassium], [K(C₇H₄N₂O₂)(H₂O)₂]_n, (I), and poly[μ₃‐aqua‐aqua‐μ₅‐(4‐nitrobenzoato)‐rubidium], [Rb(C₇H₄N₂O₂)(H₂O)₂]_n, (II), have been determined. In (I), the very distorted KO₆ coordination sphere about the K⁺ centres in the repeat unit comprise two bridging nitro O‐atom donors, a single bridging carboxylate O‐atom donor and two water molecules, one of which is bridging. In Rb complex (II), the same basic MO₆ coordination is found in the repeat unit, but it is expanded to RbO₉ through a slight increase in the accepted Rb—O bond‐length range and includes an additional Rb—O_carboxylate bond, completing a bidentate O,O′‐chelate interaction, and additional bridging Rb—O_nitro and Rb—O_water bonds. The comparative K—O and Rb—O bond‐length ranges are 2.7352 (14)–3.0051 (14) and 2.884 (2)–3.182 (2) Å, respectively. The structure of (II) is also isomorphous, as well as isostructural, with the known structure of the nine‐coordinate caesium 4‐nitrobenzoate analogue, (III), in which the Cs—O bond‐length range is 3.047 (4)–3.338 (4) Å. In all three complexes, common basic polymeric extensions are found, including two different centrosymmetric bridging interactions through both water and nitro groups, as well as extensions along c through the para‐related carboxylate group, giving a two‐dimensional structure in (I). In (II) and (III), three‐dimensional structures are generated through additional bridges involving the nitro and water O atoms. In all three structures, the two water molecules are involved in similar intra‐polymer O—H...O hydrogen‐bonding interactions to both carboxylate and water O‐atom acceptors. A comparison of the varied coordination behaviour of the full set of Li–Cs salts with 4‐nitrobenzoic acid is also made.