Synthesis of spiro[bicyclo[2.2.1]heptane-2,2′-furan]-3-amines via stereoselective cycloadditions of trimethylenemethane to (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones

Stereoselective [3+2] cycloadditions of trimethylenemethane (TMM) to the exocyclic CO and CN double bonds of (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones gave the corresponding spiro[bicyclo[2.2.1]heptane-2,2′-furan] and spiro[bicyclo[2.2.1]heptane-3,2′-pyrrolidine] derivatives. Further stereoselective reductions of the CN or CO bond in these cycloadducts furnished new chiral amines, diamines, and a new aminoalcohol. All cycloadditions and reductions of the CN double bonds took place from the less hindered endo-face of the (1S,3EZ,4R)-3-arylimino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones, exclusively, thus giving the corresponding products in 100% de. The structures were determined by NMR, NOESY spectroscopy, and by X-ray diffraction.     

In silico quest for stable phosphastannaallenes

A computational study at different levels of theory was performed for the not yet synthesized phosphastannaallenes >SnCP– in order to evaluate the strength of the SnC bond, the main postulated factor to stabilize such species, and the geometry in R₂SnCPR derivatives. The influence of the substituents with various electronic effects (H, Me, Ph, F, Cl, OMe, SiMe₃) at the Sn or P atoms of the SnCP unit on the SnC bond order was evaluated in the quest for a substituent that would stabilize the phosphastannaallenic unit. PC bond orders have also been calculated.     

A theoretical study on the alkene insertion step in Rh-Yanphos catalyzed hydroformylation

This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation （AHF） catalyzed by RhH（CO）2[（R,S）-Yanphos] using four alkene substrates （CH2=CH- Ph, CH2=CH-Ph-（p）-Me, CH2=CH-C（==O）OCH3 and CH2=CH-OC（=O）-Ph, abbreviated as A1-A4）. Interestingly, the equatorial vertical coordination mode （A mode） with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode （E mode） was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.     

Nitrogen- and oxygen-bridged bidentate phosphaalkene ligands

An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe₂Si)₂CP]₂E (E = O, NR, N^?) and (RMe₂Si)₂CPN(R′)PR′′₂. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe₂Si)₂CP]₂NSiMe₃ with Au^I and Rh^I chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe₂Si)₂CP]₂N^?, and (ii) the chlorotropic formation of molecular 1:2 Pd^II and Pt^II metallochloroylid complexes with novel ylid-type ligands [(RMe₂Si)₂CP(Cl)N(R)PR₂]^?, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe₂Si)₂CP]₂E (E = S, Se, Te, PR, P^?, As^?) and (RMe₂Si)₂CPEPR′′₂ (E = S, Se, Te) are also described.     

Reaction of the RuTp(PR3)Cl fragment with alkynols: Formation of carbene,vinylidene, allenylidene,and carbyne complexes

The reaction of RuTp(COD)Cl (1) with PR₃ (PR₃ = PPh₂ⁱPr, PⁱPr₃, PPh₃) and propargylic alcohols HCCCPh₂OH, HCCCFc₂OH (Fc = ferrocenyl), and HCCC(Ph)MeOH has been studied.In the case of PR₃ = PPh₂ⁱPr, PⁱPr₃ and HCCCPh₂OH, the 3-hydroxyvinylidene complexes RuTp(PPh₂ⁱPr)(CCHC(Ph)₂OH)Cl (2a) and RuTp(PⁱPr₃)(CCHC(Ph₂)OH)Cl (2b) were isolated.With PR₃ = PPh₂ⁱPr and HCCCFc₂OH as well as with PR₃ = PPh₃ and HCCCPh₂OH dehydration takes place affording the allenylidene complexes RuTp(PPh₂ⁱPr)(CCCFc₂)Cl (3b) and RuTp(PPh₃)(CCCPh₂)Cl (3c).Similarly, with PPh₂ⁱPr and HCCC(Ph)MeOH rapid elimination of water results in the formation of the vinylvinylidene complex RuTp(PPh₂ⁱPr)(CCHC(Ph)CH₂)Cl (4).In contrast to the reactions of the RuTp(PR₃)Cl fragment with propargylic alcohols, with HCC(CH₂)_nOH (n = 2, 3, 4, 5) six-, and seven-membered cyclic oxycarbene complexes RuTp(PR₃)(C₄H₆O)Cl (5), RuTp(PR₃)(C₅H₈O)Cl (6), and RuTp(PR₃)(C₆H₁₀O)Cl (7) are obtained. On the other hand, with 1-ethynylcyclohexanol the vinylvinylidene complex RuTp(PPh₂ⁱPr)(CCHC₆H₉)Cl (8) is formed. The reaction of the allenylidene complexes 3a–c with acid has been investigated. Addition of CF₃COOH to a solution of 3a–c resulted in the reversible formation of the novel RuTp vinylcarbyne complexes [RuTp(PPh₂ⁱPr)(C–CHCPh₂)Cl]⁺ (9a), [RuTp(PPh₂ⁱPr)(C–CHCFc₂)Cl]⁺ (9b), and [RuTp(PPh₃)(C–CHCPh₂)Cl]⁺ (9c). The structures of 3a, 3b, and 5b have been determined by X-ray crystallography.     

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Hemilability and nonrigidity in a series of mixed P,PS donor ligands has been studied in the complexes [Pd(P,PS)Cl₂], [Pd(η³-C₃H₅)(P,PS)][SbF₆], and [Rh(cod)(P,PS)][SbF₆] (P,PS = Ph₂P-Q-P(S)Ph₂). The effect of bite angle, the rigidity of the ligand backbone, and the role of the ancillary ligands are discussed.     

Understanding the reactivity of [WNAr(CH2tBu)2(CHtBu)] (Ar = 2,6-iPrC6H3) with silica partially dehydroxylated at low temperatures through a combined use of molecular and surface organometallic chemistry

Reaction of [WNAr(CH₂tBu)₂(CHtBu)] (Ar = 2,6-iPrC₆H₃) with silica partially dehydoxylated at 200 °C does not lead only to the expected bisgrafted [(SiO)₂WNAr(CHtBu)] species, but also surface reaction intermediates such as [(SiO)₂WNAr(CH₂tBu)₂]. All these species were characterized by infrared spectroscopy, 1D and 2D solid state NMR, elemental analysis and molecular models obtained by using silsesquioxanes. While a mixture of several surface species, the resulting material displays high activity in the olefin metathesis.     

Two-dimensional correlation infrared spectroscopy studies on the thermal-induced mesophase of 4-nitrobenzohydrazide derivative

Two-dimensional (2D) correlation infrared (IR) spectroscopy has been applied to explore the effect of hydrogen bondings (HBs) on the structure of mesophase in the dissymmetrical 4-nitrobenzohydrazide derivative, N-(4-cetyloxybenzoyl)-N′-(4′-nitrobenzoyl) hydrazine (C16-NO₂). The strength and species of HBs as well as the heat-induced structural variations in mesophase have been investigated. It has been found from 2D correlation IR spectroscopy that the sequential order of changes in the different functionalities in the course of liquid crystalline formation is that, firstly, the alkyl chain changes from the significant population of the trans conformation to the significant population of gauche conformation; then, the intermolecular HB between CO and NH groups is weakened, some even being broken, and consequently, the intermolecular distance is enlarged; finally, the skeleton of phenyl ring has enough space to change their conformation to weaken the π–π stacking interaction. In addition, besides a few free and some medium bonded NH and CO groups, strongly bonded NH and CO groups still predominantly exist in the mesophase.     

1,3-Dipolar cycloaddition of diaryldiazomethanes across N-ethoxy-carbonyl-N-(2,2,2-trichloroethylidene)amine and reactivity of the resulting 2-azabutadienes towards thiolates and cyclic amides

1,3-dipolar cycloaddition of diaryldiazomethanes Ar₂CN₂ across Cl₃C–CHN–CO₂Et 1 yields Δ³-1,2,4-triazolines 2. Thermolysis of 2 leads, via transient azomethine ylides 3, to diaryldichloroazabutadienes [Ar(Ar')CN–CHCCl₂] 4. Treatment of 4a (Ar = Ar' = C₆H₅) and 4c (Ar = Ar' = p-ClC₆H₄) with NaSR in DMF yields 2-azabutadienes [Ar₂CN–C(H)C(SR)₂] 5. In contrast, nucleophilic attack of NaStBu on 4 affords azadienic dithioethers [Ar₂CN–C(S^tBu)C(H)(S^tBu)] (7a Ar = C₆H₅; 7b Ar' = p-ClC₆H₄). The reaction of 4a with NaSEt conducted in neat EtSH produces [Ph₂CN–C(H)(SEt)–CCl₂H] 8, which after dehydrochloration by NaOMe and subsequent addition of NaSEt is converted to [Ph₂CN–C(SEt)C(H)(SEt)] 7c. Upon the reaction of 4c with NaSⁱPr, the intermediate dithioether [(p-ClC₆H₄)₂CN–CHC(SⁱPr)₂] 5k is converted to tetrakisthioether [(p-ⁱPrSC₆H₄)₂CN–CHC(SⁱPr)₂] 6. Treatment of 4a with the sodium salt of piperidine leads to [Ph₂CN–CHC(NC₅H₁₀)₂] 10. The coordination of 6 on CuBr affords the macrocyclic dinuclear Cu(I) complex 11. The crystal structures of 5i, 7a,b, 10 and 11 have been determined by X-ray diffraction.     

Spectral additive properties of phosphorus-containing dendrimers

The FT-Raman and FTIR spectra of 12 generations of phosphorus-containing dendrimers:

1. Download : Download full-size image

with terminal aldehyde and PCl groups have been recorded and analyzed. Their spectral pattern is determined by the ratio T/R (T, the number of terminal groups; R, the number of repeating units). The influence of the encirclement on the band frequencies and intensity was studied and due to the predictable, controlled and reproducible structure of dendrimers the information usually inaccessible was obtained. Bands assigned to the core, repeated units and terminal groups of dendrimers were separated by the differential spectroscopy method. The strong band at 1600 cm⁻¹ show marked changes of optical density in dependence of the aldehyde (CHO) or azomethyne (CHN) substitution in aromatic ring. From the differential IR and Raman spectra of dendrimers it follows that for the generations higher than 6, the steric congestion disturbs the conformations of the terminal groups. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers up to 11 generation. FT-Raman and FTIR spectroscopy provides the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.     

The structure and two-dimensional correlation infrared spectroscopy study of a new 2D polyoxomolybdate complex containing β-octamolybdate linked up by potassium ions: (4,4′-Hbpy)2(K2Mo8O26)

A novel compound, (4,4′-Hbpy)₂(K₂Mo₈O₂₆) 1 (bpy = bipydine), was synthesized by hydrothermal method and characterized by X-ray single analysis, thermalgravimetric analysis, one-dimensional (1D) infrared spectroscopy and two-dimensional (2D) correlation infrared spectroscopy under thermal perturbation. In the compound 1, the [Mo₈O₂₆] units link to potassium ions to form layer structure, and the protonated 4,4′-bpy are linked to chains by hydrogen bonds. The 2D IR correlation spectroscopy study indicates that the intensity changes of MoO, NH and CC stretching vibration are sensitive to the temperature variation, and the intensity changes of asymmetry stretching vibration of the terminal MoO occur prior to that of terminal MoO linked by K atom. At the same time, the peaks of asymmetry stretching vibrations of the terminal MoO and the stretching vibrations of NH split into two peaks respectively in 2D IR correlation spectroscopy.     

CuLn complexes with a single μ-oximato bridge

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^IILn^IIICu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to ?1.25 cm^?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.     

A convenient route to six-membered heterocyclic carbene complexes: Reactions of aminoallenylidene complexes with 1,3-bidentate nucleophiles

Pentacarbonyl dimethylamino(methoxy)allenylidene complexes of chromium and tungsten, [(CO)₅MCCC(NMe₂)OMe] (M = Cr (1a), W (1b)), react with 1,3-bidentate nucleophiles such as amidines and guanidine, H₂N–C(NH)R (R = Ph, C₆H₄NH₂-4, C₆H₄NO₂-3, NH₂), by displacing the methoxy substituent to give exclusively dimethylamino(imino)-allenylidene complexes, [(CO)₅MCCC{NC(NH₂)R}NMe₂] (2a–5a, 2b). Treatment of the chromium complexes 2a–5a with catalytic amounts of hydrochloric acid or HBF₄ gives rise to an intramolecular cyclization. Addition of the terminal NH₂ substituent to the C_α–C_β bond of the allenylidene chain affords pyrimidinylidene complexes 6–9 in high yield. In contrast to the chromium complexes 2a–5a, the corresponding tungsten complex 2b could not be induced to cyclize due to the lower electrophilicity of the α-carbon atom in 2b. The dimethylamino(phenyl)allenylidene complex [(CO)₅CrCCC(NMe₂)Ph] (10) reacts with benzamidine or guanidine similarly to 1a. However, the second reaction step – cyclization to give pyrimidinylidene complexes – proceeds much faster. Therefore, the formation of an imino(phenyl)allenylidene complex as an intermediate is established only by IR spectroscopy. The analogous reaction of 10 with 3-amino-5-methylpyrazole affords, via a formal [3+3]-cycloaddition, a pyrazolo[1,5a]pyrimidinylidene complex 13. Compound 13 is obtained as two isomers differing in the relative position of the N-bound proton (1H or 4H). The related reaction of 10 with thioacetamide yields a thiazinylidene complex and additionally an alkenyl(amino)carbene complex.     

Role of the intermolecular and intramolecular hydrogen bonding on the excited-state proton transfer behavior of 3-aminophthalimide (3AP) dimer

In this work, both the intermolecular and intramolecular hydrogen bonding of 3-aminophthalimide (3AP) dimer complex in the electronically excited state have been investigated theoretically using the time-dependent density functional theory (TDDFT) method. The calculated infrared spectrum of the hydrogen-bonded 3AP dimer complex for the S₁ state shows that the CO and H–N bonds involved in the intramolecular hydrogen bond C₃O₅?H₈–N₆ and intermolecular hydrogen bond C₁O₄?H_7′–N_2′ which are markedly red-shifted compared with those predicted for the ground state. The calculated length of the two hydrogen bonds C₃O₅?H₈–N₆ and C₁O₄?H_7′–N_2′ are significantly shorter in S₁ state than in the ground state. However, the bond lengths of the intramolecular hydrogen bond C_3′O₅?H_8′–N_6′ and intermolecular hydrogen bond C_1′O_4′?H₇–N₂ nearly unchanged upon electronic excitation to the S₁ state. Thus, the intramolecular hydrogen bond C₃O₅?H₈–N₆ and intermolecular hydrogen bond C₁O₄?H_7′–N_2′ of the hydrogen-bonded 3AP dimer complex are stronger in the electronically excited state than in the ground state. Moreover, it has been demonstrated that the excited-state proton transfer reaction is facilitated by the electronic excited-state hydrogen bond strengthening.     

Phosphorus-substituted carbene complexes: Chelates,pincers and spirocycles

The syntheses, structural characterizations and reactivity patterns of main group and late transition metal carbene complexes of the bis(phosphoranimino)methandiide, [C(Ph₂PNSiMe₃)₂]²⁻, and the carbodiphosphorane, Ph₃PCPPh₃, are described and compared to previously reviewed early transition metal analogues. Bimetallic spirocyclic aluminum complexes of the former ligand are accessed by spontaneous double deprotonation of the central carbon atom of the parent, CH₂(Ph₂PNSiMe₃)₂, by two equivalents of AlMe₃, whereas the synthesis of platinum complexes requires the intermediacy of the tetralithium dimer, [Li₂C(Ph₂PNSiMe₃)₂]₂, and elimination of LiCl from a metal chloride precursor. In contrast to the early transition metal analogues, which are N,C,N-pincer, Schrock-type alkylidenes, the C,N-chelated platinum complexes are more akin to Fischer carbenes, and their chemistry is dominated by the nucleophilicity of free nitrogen atom and insertions into labile N–Si bonds. Chelated and pincer carbene complexes of rhodium result from single and double orthometallations, respectively, of the phenyl rings in Ph₃PCPPh₃; the latter compounds represent a wholly new class of C,C,C-pincer complexes. Electronic structure calculations show that the metal–carbon interaction in these compounds may be described as a dative, two-electron, C → M σ-bond. The free bis(phosphoranimino)methandiide and carbodiphosphorane ligands, while not having formal six valence electron resonance forms, may be thought of as having “pull–pull” Fischer carbene character, but the metal to which they become coordinated ultimately dictates their chemistry.     

DFT study of the IR and Raman spectra of a fluorescent dendron built from cyclotriphosphazene core

Combined experimental and theoretical studies on molecular structure of the zero generation dendron, built from the hexafunctional cyclotriphosphazene core, with five OC₆H₄(CH₂)₂NHSO₂C₁₀H₆N(CH₃)₂ terminal groups and one oxybenzaldehyde group G₀ are reported. The Fourier transform Raman and IR spectra of G₀ have been recorded. Conformations of low energy isomers of G₀ have been studied at quantum-chemical level. The optimized geometry has been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. The theoretical geometrical parameters, harmonic vibrational frequencies, IR intensities and Raman scattering activities are predicted in a good agreement with the experimental data. It was found that dendron molecule G₀ has a concave lens structure with planar OC₆H₄CHO fragments and slightly non-planar cyclotriphosphazene core. Relying on DFT calculations the bands of the core and terminal groups were assigned. The frequencies of ν(NH) bands in the IR spectrum reveal the presence of the H-bonds in the dendron.     

Reactions of α-phenylethynyl-trans-β-styryl complexes with isonitriles: hemi-labile alkyne coordination

Treatment of the complex [Ru{C(CCPh)CHPh}Cl(CO)(PPh₃)₂] (1) with one equivalent of CNR(R =^tBu, C₆H₃Me₂-2,6) gives [Ru{C(CCPh)CHPh}Cl(CNR)(CO)(PPh₃)₂]. Addition of a further equivalent of isonitrile and [NH₄]PF₆ leads to the salts [Ru{C(CCPh)CHPh}Cl(CNR)₂(CO)(PPh₃)₂]PF₆ and the mixed species [Ru{C(CCPh) CHPh}(CO)(CN^tBu)(CNC₆H₃Me₂-2,6)(PPh₃)₂]PF₆. The related [Ru{C(CCPh)CHPh}(CN^t(CO)₂     

1,1-Bis(trifluoromethyl)butadiene-1,3—A new fluorinated building block

Although 1,1-bis(trifluoromethyl)butadiene-1,3 (1) reacts with dimethylamine with selective formation of 1,4-adduct [trans-(CF₃)₂CHCHCHCH₂N(CH₃)₂], halogenation of 1 proceeds with predominant formation (>92%) of 1,2-adducts (CF₃)₂CCHCHXCH₂X (X = Cl or Br). Electrophilic conjugated addition of “ClF” or “BrF” to 1 proceeds exclusively with the formation of 1,2-adducts (CF₃)₂CCHCHFCH₂X (major) and (CF₃)₂CCHCHXCH₂F (X = Cl or Br). Difluorocarbene adds selectively to CHCH₂ moiety of 1 forming thermally stable vinylcyclopropane. In Diels-Alder reaction with linear or cyclic dienes (butadienes, cyclopentadiene, cyclohexadiene-1,3) and quadricyclane compound 1 behaves as dienophile providing for the reaction electron-deficient CHCH₂ bond. The relative rate of cycloaddition of 1 and other fluoroolefins to quadricyclane, measured by high temperature NMR, indicates that (CF₃)₂CCH acts as very strong electron-withdrawing substituent. Synthetic utility of products based on 1 was also demonstrated.     

Structural studies of methyl brevifolincarboxylate in solid state by means of NMR spectroscopy and DFT calculations

Methyl brevifolincarboxylate isolated from the herb of Potentilla argentea L. (Rosaceae) is a representative of the naturally occurring polyphenols. The compound is of pharmaceutical interest mainly because of its antiviral and antioxidant properties. ¹³C NMR spectra were recorded for solution and solid phase. ¹³C CPMAS spectra were assigned by comparison with solution data, dipolar dephasing and short contact time experiments. The correctness of assignments was verified by GIAO DFT calculations of shielding constants. The differences between the solution and solid state chemical shift values were explained in terms of orientation of OH groups and intramolecular hydrogen bonds. The splitting of the C1O resonance shows that there exists a polymorphism in the solid phase, which might be due to the formation of intramolecular hydrogen bond involving carbonyl or methoxy oxygen (i.e. C10OH⋯OC or C10OH⋯OCH₃).     

Theoretical calculations of the substituent effect on molecular properties of the RCN⋯HF hydrogen-bonded complexes with R = NH2, CH3O,CH3, OH,SH, H,Cl, F,CF3, CN and NO2

DFT calculations with B3LYP and PBE1PBE functionals and 6–311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the RCN?HF H-bonded complexes with R = NH₂, CH₃O, CH₃, OH, SH, H, Cl, F, CF₃, CN and NO₂. As expected, it has been verified as a red-shift of the HF stretching frequency (ν_HF), in conformity with the elongation of the bond after complexation. On the other hand, the CN stretching frequency (ν_CN) is blue-shifted and corresponds to a shortening of the bond. The binding energies (ΔE_c), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free RCN molecule (μ_RCN) has been found. This result suggests that μ_RCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed HF acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in HF using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.