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International audience; The reaction of [Re(CO)3(THF)(μ-Br)]2 or [Re(CO)5X] (X = Cl, Br, I) with the diaryl-2-azabutadienes [(RS)2C[double bond, length as m-dash]C(H)–N[double bond, length as m-dash]CAr2] containing two thioether arms at the 4,4-position forms the luminescent S,N-chelate complexes fac-[(OC)3ReX{(RS)2C[double bond, length as m-dash]C(H)–N[double bond, length as m-dash]CAr2}] (1a–h). The halide abstraction by silver triflate converts [(OC)3ReCl{(PhS)2C[double bond, length as m-dash]C(H)–N[double bond, length as m-dash]CPh2}] (1c) to [(OC)3Re(OS([double bond, length as m-dash]O)2CF3){(PhS)2C[double bond, length as m-dash]C(H)–N[double bond, length as m-dash]CPh2}] (1j) bearing a covalently bound triflate ligand. The cyclic voltammograms reveal reversible S^N ligand-centred reduction and irreversible oxidation waves for all complexes. The crystal structures of nine octahedral complexes have been determined along with that of (NaphtylS)2C[double bond, length as m-dash]C(H)–N[double bond, length as m-dash]CPh2 (L6). A rich system of weak non-covalent intermolecular secondary interactions through CH⋯X(Cl, Br)Re, CH⋯O, CO⋯π(Ph), CH⋯πCO, CH⋯O and CH⋯S contacts has been evidenced. The photophysical properties have been investigated by steady-state and time-resolved absorption (fs transient absorption, fs-TAS) and emission (ns-TCSPC and ps-Streak camera) spectroscopy in 2-MeTHF solution at 298 and 77 K. The emission bands are composed of either singlet (450 < λmax < 535 nm) and/or triplet emissions (at 77 K only, λmax < 640 nm, or appearing as a tail at λ > 600 nm), which decay in a multiexponential manner for the fluorescence (short ps (i.e.

The reaction of [Re(CO)3(THF)(μ-Br)]2 or [Re(CO)5X] (X = Cl, Br, I) with the diaryl-2-azabutadienes [(RS)2C[double bond, length as m-dash]C(H)-N[double bond, length as m-dash]CAr2] containing two thioether arms at the 4,4-position forms the luminescent S,N-chelate complexes fac-[(OC)3ReX{(RS)2C[double bond, length as m-dash]C(H)-N[double bond, length as m-dash]CAr2}] (1a-h). The halide abstraction by silver triflate converts [(OC)3ReCl{(PhS)2C[double bond, length as m-dash]C(H)-N[double bond, length as m-dash]CPh2}] (1c) to [(OC)3Re(OS([double bond, length as m-dash]O)2CF3){(PhS)2C[double bond, length as m-dash]C(H)-N[double bond, length as m-dash]CPh2}] (1j) bearing a covalently bound triflate ligand. The cyclic voltammograms reveal reversible S^N ligand-centred reduction and irreversible oxidation waves for all complexes. The crystal structures of nine octahedral complexes have been determined along with that of (NaphtylS)2C[double bond, length as m-dash]C(H)-N[double bond, length as m-dash]CPh2 (L6). A rich system of weak non-covalent intermolecular secondary interactions through CHX(Cl, Br)Re, CHO, COπ(Ph), CHπCO, CHO and CHS contacts has been evidenced. The photophysical properties have been investigated by steady-state and time-resolved absorption (fs transient absorption, fs-TAS) and emission (ns-TCSPC and ps-Streak camera) spectroscopy in 2-MeTHF solution at 298 and 77 K. The emission bands are composed of either singlet (450λmax535 nm) and/or triplet emissions (at 77 K only, λmax640 nm, or appearing as a tail at λ600 nm), which decay in a multiexponential manner for the fluorescence (short ps (i.e.IRF)τF1.9 ns at 298 and 77 K) and monoexponentially for the phosphorescence (4.0τP7.0 ns at 77 K). The fs-TAS data reveal the presence of 2 to 4 transient species decaying in four narrow time windows (generally 125-165 fs, 370-685 fs, 3-6 ps, 30-45 ps). The complexity of these kinetics was explained by studying the photophysical behaviour of ligand L6. Its behaviour is the same as the complexes thus indicating that the ligand dictates the kinetic traits of the Re-species, except for the triplet emission as L6 is not phosphorescent. The triplet lifetime (4.0τP7.0 ns) is considered very short but not unprecedented. Furthermore, the nature of the lowest energy excited states of these chelate compounds and L6 has been addressed using DFT and TDDFT calculations and been assigned to metal-to-ligand (MLCT) and/or intraligand charge-transfer (ILCT).

The 1,3-dipolar cycloaddition reaction of (E,E)-1,3-bis(arylidene)indan-2-one with diarylnitrilimines, generated in situ via dehydrohalogenation of the corresponding hydrazonoyl chlorides , affords predominantly monospiropyrazolines and as a mixture of diastereoisomers. Also dispiropyrazolines are formed in moderate yields. The structure and stereochemistry of cycloadducts were confirmed by 1H and 13C-NMR spectroscopy, elemental analyses data, and single-crystal X-ray diffraction studies of and .

1,3-dipolar cycloaddition of diaryldiazomethanes Ar2C N2 across Cl3C–CH N–CO2Et 1 yields Δ3-1,2,4-triazolines 2. Thermolysis of 2 leads, via transient azomethine ylides 3, to diaryldichloroazabutadienes [Ar(Ar')C N–CH CCl2] 4. Treatment of 4a (Ar = Ar' = C6H5) and 4c (Ar = Ar' = p-ClC6H4) with NaSR in DMF yields 2-azabutadienes [Ar2C N–C(H) C(SR)2] 5. In contrast, nucleophilic attack of NaStBu on 4 affords azadienic dithioethers [Ar2C N–C(StBu) C(H)(StBu)] (7a Ar = C6H5; 7b Ar' = p-ClC6H4). The reaction of 4a with NaSEt conducted in neat EtSH produces [Ph2C N–C(H)(SEt)–CCl2H] 8, which after dehydrochloration by NaOMe and subsequent addition of NaSEt is converted to [Ph2C N–C(SEt) C(H)(SEt)] 7c. Upon the reaction of 4c with NaSiPr, the intermediate dithioether [(p-ClC6H4)2C N–CH C(SiPr)2] 5k is converted to tetrakisthioether [(p-iPrSC6H4)2C N–CH C(SiPr)2] 6. Treatment of 4a with the sodium salt of piperidine leads to [Ph2C N–CH C(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.

CuI reacts with E-PhS(CH2CH═CHCH2)SPh, L1, to afford the coordination polymer (CP) [Cu2I2{μ-E-PhS(CH2CH═CHCH2)SPh}2]n (1a). The unprecedented square-grid network of 1 is built upon alternating two-dimensional (2D) layers with an ABAB sequence and contains rhomboid Cu2(μ2-I)2 clusters as secondary building units (SBUs). Notably, layer A, interconnected by bridging L1 ligands, contains exclusively dinuclear units with short Cu···Cu separations [2.6485(7) A; 115 K]. In contrast, layer B exhibits Cu···Cu distances of 2.8133(8) A. The same network is observed when CuBr reacts with L1. In the 2D network of [Cu2Br2{μ-E-PhS(CH2CH═CHCH2)SPh}2]n (1b), isotype to 1a, one square-grid-type layer contains Cu2(μ2-Br)2 SBUs with short Cu···Cu contacts [2.7422(6) A at 115K], whereas the next layer incorporates exclusively Cu2(μ2-Br)2 SBUs with a significantly longer Cu···Cu separation [2.9008(10) A]. The evolution of the crystallographic parameters of 1a and 1b was monitored between 115 and 275 K. Conversely, the isomeric...

In an on-going effort to develop novel anti-tubercular agents, a series of original dispiropyrrolothiazole derivatives have been synthesized by three-component 1,3-dipolar cycloaddition of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, 1,3-thiazolane-4-carboxylic acid and cyclic diketones. The stereochemistry of the spiranic adducts has been confirmed by an X-ray diffraction analysis. Theoretical calculations have been carried out using DFT approach at the B3LYP/6-31G(d,p) level allowing an explanation for the observed regio- and stereoselectivity. The newly synthesized compounds were screened in vitro against Mycobacterium tuberculosis H37Rv and the most active compounds were tested for cytotoxicity studies. Some compounds exhibited significant activity, in particular dispiropyrrolothiazole derivatives 15c and 15f emerged as the most promising antitubercular agents.

The title compound belongs to the large family of heterodinuclear phosphide-bridged complexes. The Fe—Pt bond is of 2.7738 (4) Å and there is an unprecedented arrangement of the silyl ligand in a trans-position with respect to the metal–metal vector in the family of phosphide-bridged iron–platinum heterobimetallics., The title compound, [FePt(C12H10P)(C13H13Si)(C18H15P)2(CO)3]·0.5CH2Cl2, represents an example of a phosphido-bridged heterobimetallic silyl complex; these are inter­esting precursors for the coordination and activation of small unsaturated organic mol­ecules. The μ2-PPh2 ligand spans the iron and platinum atoms, which are connected via a metal–metal bond of 2.7738 (4) Å. In contrast to most other complexes of the [(OC)3Fe(SiR 3)(μ-PR 2)PtL 2] family, where the iron-bound SiR 3 group is trans-arranged with respect to the μ2-PPh2 ligand, the SiPh2Me ligand is roughly collinear with the Fe–Pt vector [Si—Fe—Pt = 169.07 (3)°].

Synthesis of a series of cyclic fused-isoxazolines has been accomplished by regioselective and diastereoselective 1,3-dipolar cycloaddition of 3-methylindan-1-one enamines (1a, 1b, 1c) and 3-phenylindan-1-one enamines (2a, 2b, 2c) to arylnitrile oxides (3d, 3e, 3f, 3g, 3h). The structure of the cycloadducts was elucidated by 1H and 13C NMR spectroscopy. The proposed regio- and stereochemistry of fused-compounds (4) and (5) has also been corroborated by two single-crystal X-ray diffraction studies carried out on 4-methyl-8b-morpholinyl-3-(p-tolyl)-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (4be) and 3-(p-anisyl)-4-phenyl-8b-pyrrolidinyl-4H-3a,8b-dihydroindeno[2,3-d]isoxazoline (5af) and by means of density functional theory calculations.

Two equivalents of CuI react with p-MeC6H4SCH2C≡CCH2SC6H4-p-Me (L2) to form the 2D network [(Cu4I4)(p-MeC6H4SCH2C≡CCH2SC6H4-p-Me)2] n (polymer 2) contrasting with the previously reported reaction with C6H5SCH2C≡CCH2SC6H5 (L1) which makes a 3D network [(Cu6I6)(C6H5SCH2C≡CCH2SC6H5)3] n (polymer 1) (2009, Dalton Trans. 948). The crystal structure of the latter polymer has been re-determined at 115, 155, 195, 235 and 275 K to study the impact of the recording temperature on the metric parameters, notably the Cu···Cu distances within the hexagonal prism Cu6I6 cluster. Steric hindrance between a 2D/(Cu4I4) versus 3D/(Cu6I6) appears to drive the selectivity. Upon using the ligand o-MeC6H4SCH2C≡CCH2SC6H4-o-Me (L3) with CuI, a new material (polymer 3) is formed but no X-ray structure determination was possible. From obvious steric considerations and the presence of a high energy emission characteristic of the well-known Cu4I4 cluster (absent in the Cu6I6 one), and the similarity in emission lifetime for both high and low energy emission of polymers 2 and 3, the nature of this polymer was proposed to be [(Cu4I4)(o-MeC6H4SCH2C≡CCH2SC6H4-o-Me)2] n .

Microwave-assisted 1,3-dipolar cycloaddition of (E,E)-1,3-bisarylidenetetral-2-ones with nitrilimines, generated in situ by dehydrohalogenation of the corresponding hydrazonoyl chlorides, affords a series of spiropyrazolines in good to excellent yields. The presence of a second exocyclic CC bond also allows the preparation of dispiropyrazolines. The cycloaddition proceeds with high chemo-, regio- and diastereoselectivity. The structure of the spiranic adducts has been established on the basis of their spectroscopic data and elemental analyses. The stereochemistry of these N-heterocycles has been confirmed by two X-ray diffraction studies. The luminescence properties and fluorescence quantum yields of these heterocyclic compounds have been investigated revealing that some of them are fluorescent in solution.

International audience; The CuI-or Ag 2 CO 3-catalyzed [3+2] cycloaddition of propargyl-substituted dihydroisoindolin-1-one (3) with arylnitrile oxides 1a-d (Ar = Ph, p-MeC 6 H 4 , p-MeOC 6 H 4 , p-ClC 6 H 4) produces in good yields novel 3,5-disubstituted isoxazoles 4 of the ethyl-2-benzyl-3-oxo-1-((3-arylisoxazol-5yl)methyl)-2,3-dihydro-1H-isoindole-1-carboxylate type. With aryl azides 2a-d (Ar = Ph, p-MeC 6 H 4 , p-OMeC 6 H 4 , p-ClC 6 H 4), a series of 1,4-disubstituted 1,2,3-triazoles 6 (ethyl-2-benzyl-3-oxo-1-((1-aryl-1H-1,2,3-triazol-4-yl)methyl)-2,3-dihydro-1H-isoindole-1-carboxylates) was obtained. The reactions proceed in a regioselective manner affording exclusively racemic adducts 4 and 6. Compared to the uncatalyzed cycloaddition, the yields are significantly improved in the presence of CuI as catalyst, without alteration of the selectivity. The regio-and stereochemistry of the cycloadducts has been corroborated by an X-ray diffraction study of 4a, and in the case of 6a by XH-correlation and HMBC spectra.

Microwave-assisted 1,3-dipolar cycloaddition of (E,E)-1,3-bisarylidenetetral-2-ones with nitrilimines, generated in situ by dehydrohalogenation of the corresponding hydrazonoyl chlorides, affords a series of spiropyrazolines in good to excellent yields. The presence of a second exocyclic CC bond also allows the preparation of dispiropyrazolines. The cycloaddition proceeds with high chemo-, regio- and diastereoselectivity. The structure of the spiranic adducts has been established on the basis of their spectroscopic data and elemental analyses. The stereochemistry of these N-heterocycles has been confirmed by two X-ray diffraction studies. The luminescence properties and fluorescence quantum yields of these heterocyclic compounds have been investigated revealing that some of them are fluorescent in solution.

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused piperazines through a stepwise [3 + 3] cycloaddition pathway is observed. The stereochemistry of these N-heterocycles has been confirmed by several X-ray diffraction studies. Some of these compounds exhibit extensive hydrogen bonding in the crystalline state. To enlighten the observed regio- and stereoselectivity of the [3...

International audience; The novel 1D coordination polymer (CP) [{Cu(mu(2)-Br)(2)Cu}(mu-L2)(2)] CP2 has been obtained by reaction of the tetrakisthioether p-MeSC6H4SCH2SC6H4SMe-p (L2) with CuBr in a 1: 2 metal-to ligand ratio. In contrast to the previously described CP [{Cu(mu(2)-Br)(2)Cu}(mu-L1)(2)] CP1 obtained by reaction of the tetrakisthioether p-MeOC6H4SCH2SC6H4OMe-p (L1) with CuBr, the two independent extended 1D ribbons contain bent Cu(mu(2)-Br)(2)Cu units of the butterfly-type with short Cu center dot center dot center dot Cu separations of 2.679(1) and 2.613(1) angstrom. In contrast to the common planar rhomboid Cu(mu(2)-Br)(2)Cu cluster, this butterfly-shaped geometry of the core is without precedent. A luminescent material of composition [(Cu4I4)(mu-L2)](n) CP3 is formed by reaction of L2 with CuI in a 1: 4 ratio. The two-dimensional CP of stoichiometry [Hg2Br4(L2)](n) CP4 results from treatment of HgBr2 with this tetradentate thioether L2. The structure is of the adduct type with two crystallographically different covalently bound HgBr2 bars assembled in the first step into the chains through the weak Hg-S interactions involving one Hg atom and two S atoms. The chains thus constructed are further brought together through a supplementary Hg1-S1 inter-chain interactions leading to the 2D layered structure. Consequently the Hg1 atom may be considered as pentacoordinated, while the second Hg2 atom has a formal coordination number of 4. The nature of bonding in these CPs has been studied by the Quantum Theory of Atoms in Molecules (QT-AIM) approach allowing a clear classification of metal-ligand bonds and detection of pi-pi stacking interactions. (C) 2016 Elsevier B.V. All rights reserved.

The synthesis and spectroscopic characterization of [Cp*2Mo2P2Se3] (1; Cp* = C5Me5) and its use as a molecular building block in the formation of copper(I) halide polymers is described. The reaction of 1 in CH2Cl2 with 2 equiv. of CuBr and CuI in CH3CN under diffusion conditions gave [(Cp*2Mo2P2Se3)2(CuBr)2] (2) and [(Cp*2Mo2P2Se3)(CuX)3(CH3CN)]n (X = I; 3/4), respectively. The structure of 2 is distinguished by a central Cu2Br2 ring coordinated on each side by a tripledecker complex through one of its P atoms. A 2D network is formed by weak interactions between Se atoms of neighboring molecules. Compound [(Cp*2Mo2P2Se3)(CuI)3(CH3CN)]n exists in two isomeric forms 3 and 4. The crystal structure of 3 can be described as a two-dimensional polymer that is formed by ribbons containing looped chains of three Cu2I2 rings and attached [Cp*2Mo2P2Se3] molecules. The structure of 4 contains a ribbon in which tripledecker molecules are linked through their P atoms to (CuI)6 clusters. The ribbons are connected by weak Se···Se interactions. The reaction of a mixture of 1 and P4Se3 with CuI gave [(Cp*2Mo2P2Se3)(P4Se3)(CuI)2]n. The crystal structure analysis of 5 reveals a new type of organometallic–inorganic framework in which 1 and P4Se3 are linked by Cu2I2 rings.

The reactivity of the trinuclear palladium cluster [Pd3(dppm)3(CO)] n+ (dppm = bis(diphenylphosphinomethane); n = 2, 1) towards F− was investigated by electrochemical and spectroscopic methods. The reaction depends on the charge of the cluster. The chemical reduction of the cluster dication is observed in the presence of F− generating the paramagnetic monocationic cluster. Spin-trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) provided evidence for the radical F• as an intermediate. In a similar manner to the dication, the monocationic cluster [Pd3(dppm)3(CO)]+ is also reduced, but in a slower process, by the F− ion to produce [Pd3(dppm)3(CO)]0. Additionally, the alkyne cluster adducts [Pd3(dppm)3(CO)(RCCR)] n+ (n = 2, 1; R = CO2Me) are also reactive towards F−. Particularly, the dication adduct leads to a metastable fluoride adduct [Pd3(dppm)3(CO)(RCCR)(F)]+. The electroreductive behavior of this adduct involves electron-transfer steps and F− exchange equilibriums, for which digital simulation enables the extraction of the thermodynamic parameters (standard potentials and equilibrium constants). Concurrently, the monocation adduct [Pd3(dppm)3(CO)(RCCR)]+ with F−, leads to a disproponation generating 0.5 equiv. of [Pd3(dppm)3(CO)(RCCR)(F)]+ and 0.5 equiv. of [Pd3(dppm)3(CO)(RCCR)]0. The former slowly evolves to [Pd3(dppm)3(RCCR)(F)]+, which was described by X-ray diffraction method. [Pd3(ddpm)3(CO)] n+ (n = 2, 1) are reduced by F− to form [Pd3(dppm)3(CO)](n+)−1. Concurrently, [Pd3(dppm)3(CO)(RCCR)] n+ (n = 2, 1) with F− generate the corresponding adducts [Pd3(dppm)3(CO)(RCCR)(F)](n+)−1, but, in the case of n = 1, disproponation is observed into [Pd3(dppm)3(CO)(RCCR)(F)]+ and [Pd3(dppm)3(CO)(RCCR)]0.

The molecular structure of [Cp*2Mo2P2S3] (1; Cp* = η5-C5Me5) has been reinvestigated. In DFT studies a series of various positional isomers A−E have been calculated for the model complex [(C5H5)2Mo2P2S3]. The energetically favored isomer [Cp*2Mo2(μ,η2:2-PS)2(μ-S)] (1B) reacts with W(CO)5THF to give [Cp*2Mo2P2S3·W(CO)5] (2). X-ray diffraction analysis of 2 confirms the presence of two η2:2-PS dumbbells and one singly bridging sulfur ligand, the W(CO)5 fragment being coordinated at one of the P atoms. Arrangement B is also found in the structure of the diadduct [Cp°2Mo2P2S3{W(CO)5}2] (3; Cp° = t-BuMe2C5H2), which is more stable than its Cp* analogue. 31P solid-state MAS NMR spectroscopic studies of 1 and 2 confirm the existence of only one isomer, but reveal disorder phenomena in the solid state within the cyclo-P2S3 middle deck. Addition of excess W(CO)5THF to 1 proceeds via elusive [Cp*2Mo2P2S3{W(CO)5}2] to give the cluster [{Cp*2Mo2W(CO)3(μ2,η2:2-PS)(μ3,η1:1:2-PS)(μ3-S)}{W(CO)5}2] (5). The molecular stru...

Treatment of [Re(CO)3(THF)(μ-Br)]2 with 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl2C C(H)–N CPh2] (1a) yields the di-nuclear benzophenone azine-bridged compound [(OC)3Re(μ-Ph2C N–N CPh2)(μ-Br)2Re(CO)3] (2a), albeit in low yield. Alternatively, compounds [(OC)3Re(μ-Ph2C N–N CPh2)(μ-X)2Re(CO)3] (2a,b) (X = Br, Cl) are obtained in high yields by direct reaction of [Re(CO)3(THF)(μ-Br)]2 or [Re(CO)5Cl] with benzophenone azine. Nucleophilic attack of NaSPh on 1a affords the 2-azabutadiene derivative [(PhS)(Cl)C C(H)–N CPh2] (1b), which upon reaction with [Re(CO)3(THF)(μ-Br)]2 forms the S,N-chelate complex fac-[(OC)3ReBr{(PhS)(Cl)C C(H)–N CPh2}] (3). The crystal structures of 1b, 2a and 3 have been determined and the luminescence properties of 2 and 3 have been investigated.

The oxidative addition of (2,2-dibromovinyl)ferrocene [Br2C=C(H)–Fc] (1) to [Pd(PPh3)4] yields the heterodinuclear σ-alkenyl complex trans-[{Pd(Br)(PPh3)2}–C(Br)=C(H)–Fc] (2). Nucleophilic attack of sodium thiolates on 1 unexpectedly affords the vinyl thioether derivatives (Z)-[(RS)(H)C=C(H)–Fc] (4a: R = Ph; 4b: R = tBu; 4c: R = Et). Complexes 4a and 4c can also be prepared by addition of NaSR across the triple bond of Fc–C≡C–H (3). Addition of an excess of NaSR to 1 affords the dithioether derivatives (Z)-[(RS)(H)C=C(SR)–Fc] (5a: R = Ph; 5b: R = p-tolyl; 5c: R = Et). An addition/elimination sequence is suggested to account for this surprising result. The yield of 5c is very low due to a competing formation of ethynylferrocene (3). Reaction of 5b with [Re(thf)(CO)3(μ-Br)]2 and [PtCl2(PhCN)2] leads to the heterodinuclear chelate complexes [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}Re(Br)(CO)3] (6) and [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}PtCl2] (7a), respectively. Metathesis of the fluxional compound 7a in the presence of NaI affords [Fc{C(S–p-tolyl)=C(H)(S–p-tolyl)}PtI2] (7b). The electrochemical properties of some of these complexes have been studied by means of cyclic voltammetry, and the molecular structures of 1, 2, 3, 4b, 4c and 6 have been determined by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The reaction of [ Cp 2 ∗ Nb ( Te 2 H ) ] (Cp∗ = η5-C5Me5) with [Pd(DBA)2] (DBA = dibenzylidenacetone) and dppm (bis(diphenylphosphanyl)methane) gave the new tetratelluropalladate cluster [ ( Cp 2 ∗ Nb ) 2 PdTe 4 ] (1), which has been characterised by means of elemental analysis, FD-MS and X-ray crystallography. The structure of compound 1 contains a planar PdTe4 rectangle to which two niobocene groups are coordinated. DFT calculations on the hypothetical [PdTe4]2− anion and comparison of the results with those of the W and Ni homologues show that the planar arrangement of Te ligands in 1 is due to the intrinsic property of the central Pd atom.

The reaction of [Ni(COD) 2 ] with [Cp* 2 NbTe 2 H] (1; Cp * = η-C 5 Me 5 ) in the presence of Ph 2 PCH 2 PPh 2 (dppm) in boiling toluene gives black-violet [(Cp * 2 Nb) 2 NiTe 4 ] (3). If [Cp' 2 NbTe 2 H] (2; Cp' = tBuC 5 H 4 ) is used under similar conditions dark-brown [(Cp'Nb)2Ni5Te7(dppm)2] (4) is formed. The structures of 3 and 4 have been determined crystallographically. Complex 3 contains a severely distorted NiTe 4 tetrahedron to which two niobocene groups are coordinated. Density functional analysis of the electronic structure of the NiTe 4 building block shows that it is best described as an [Ni(η 2 -Te 2 ) 2 ] 2- fragment. The structure of 4 reveals the presence of two Ni 5 and Te 5 tetragonal pyramids stacked into each other in an opposite way. Six of the Te bridges form two triangular faces, each of which is capped by a Cp'Nb fragment. Additionally, two dppm ligands bridge the long Ni-Ni edges of the Ni 4 bases. Oxidation of 3 with [(C 5 H 5 ) 2 Fe]BPh 4 gives paramagnetic [(Cp* 2 Nb) 2 NiTe 4 ]BPh 4 (6), whereas oxidation with [(C 5 H 5 ) 2 Fe]PF 6 proceeds with fluoride transfer to give [Cp* 2 NbF 2 ]PF 6 (5). Electrochemical studies of 3 reveal the existence of the redox couples [3]2+/[3]+/[3]°/[3] - /[3] 2- . Density functional calculations carried out on the different oxidation states of 3 reveal the following main features: the persistent presence of Nb-Ni bonds and the retention of Te-Te bonds in cationic and neutral species and their breaking off in reduced forms. Irrespective of the initial site of electrochemical attack, the Te atoms and Cp rings are principally affected in the final products.

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused piperazines through a stepwise [3 + 3] cycloaddition pathway is observed. The stereochemistry of these N-heterocycles has been confirmed by several X-ray diffraction studies. Some of these compounds exhibit extensive hydrogen bonding in the crystalline state. To enlighten the observed regio- and stereoselectivity of the [3 + 2] cycloaddition, calculations using the DFT approach at the B3LYP/6-31G(d,p) level were carried out. It was found that this reaction is under kinetic control.

Novel dispiropyrrolothiazole derivatives (IV) and (VI) are synthesized under mild reaction conditions in a complete regio- and stereoselective manner using three-component 1,3-dipolar cycloaddition reactions of cyclic diketones (I) or (V) with thiazolanecarboxylic acid (II) and arylidenepyrolidinedione (III) The dispiropyrrolothiazole derivatives (IVf) and (IVg) are found to exhibit significant antimycobacterial activity and emerge as the most promising antitubercular agents.

The 1D coordination polymer (CP) [(Me2S)3{Cu2(μ-I)2}]n (1) is formed when CuI reacts with SMe2 in n-heptane, whereas in acetonitrile (MeCN), the reaction forms exclusively the 2D CP [(Me2S)3{Cu4(μ-I)4}]n (2) containing "flower-basket" Cu4I4 units. The reaction product of CuI with MeSEt is also solvent-dependent, where the 1D polymer [(MeSEt)2{Cu4(μ3-I)2(μ2-I)2}(MeCN)2]n (3) containing "stepped-cubane" Cu4I4 units is isolated in MeCN. In contrast, the reaction in n-heptane affords the 1D CP [(MeSEt)3{Cu4(μ3-I)4}]n (4) containing "closed-cubane" Cu4I4 clusters. The reaction of MeSPr with CuI provides the structurally related 1D CP [(MeSPr)3{Cu4(μ3-I)4}]n (5), for which the X-ray structure has been determined at 115, 155, 195, 235, and 275 K, addressing the evolution of the metric parameters. Similarly to 4 and the previously reported CP [(Et2S)3{Cu4(μ3-I)4}]n (Inorg. Chem. 2010, 49, 5834), the 1D chain is built upon closed cubanes Cu4(μ3-I)4 as secondary building units (SBUs) interconnected via μ-MeSPr ligands. The 0D tetranuclear clusters [(L)4{Cu4(μ3-I)4}] [L = EtSPr (6), Pr2S (7)] respectively result from the reaction of CuI with EtSPr and n-Pr2S. With i-Pr2S, the octanuclear cluster [(i-Pr2S)6{Cu8(μ3-I)3}(μ4-I)2}] (8) is formed. An X-ray study has also been performed at five different temperatures for the 2D polymer [(Cu3Br3)(MeSEt)3]n (9) formed from the reaction between CuBr and MeSEt in heptane. The unprecedented framework of 9 consists of layers with alternating Cu(μ2-Br)2Cu rhomboids, which are connected through two μ-MeSEt ligands to tetranuclear open-cubane Cu4Br4 SBUs. MeSPr forms with CuBr in heptane the 1D CP [(Cu3Br3)(MeSPr)3]n (10), which is converted to a 2D metal-organic framework [(Cu5Br5)(μ2-MeSPr)3]n (11) incorporating pentanuclear [(Cu5(μ4-Br)(μ2-Br)] SBUs when recrystallized in MeCN. The thermal stability and photophysical properties of these materials are also reported.

1,3-dipolar cycloaddition of (E)-arylidene-(2H)-indanones 1 (Ar = Ph, p-MeC6H4, p-MeOC6H4, p-ClC6H4) and (E)-2-arylidene-(2H)-tetralones 2 (Ar = Ph, p-MeC6H4, p-MeOC6H4, p-ClC6H4) to N-metalated azomethine ylides 3 generated from methyl N-arylideneglycinate in the presence of silver acetate produces in good yields novel spiro[3,5-(diaryl)-2-carbomethoxypyrrolidine-4:2’-indanones] 4 and spiro[3,5-(diaryl)-2-carbomethoxypyrrolidine-4:2’-tetral-1-ones] 5. The cycloaddition proceeds in regio- and stereoselective manner (100%) at room temperature to afford respectively the syn-endo cycloadducts 4 and 5 via metallo-azomethine ylides. The regio- and stereochemistry of the spiranic adducts has been established on the basis of spectroscopic data and elemental analyses, corroborated by single-crystal X-ray crystallographic analysis of the heterocycles 4cd, 4bb and 5bd. The endo-pyrrolidines 4 were brominated by N-bromosuccinimide to give finally the dehydrobrominated 3,4-dihydro-2H-pyrrole derivatives 6. The spiro-adducts 4 and their corresponding oxidation products 6 are fluorescent in solution.

Treatment of 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl2C=C(H)-N=CPh2] (1) with excess sodium isopropylthiolate or sodium thiophenolate in DMF yielded the 2-azabutadiene derivatives (RS)2C=C(H)–N=CPh2 (2) (2a R = iPr; 2b R = Ph). Nucleophilic attack of the sodium salt of ethyl thioglycolate on 1 afforded as the sole product the six-membered heterocyclic compound ethyl 2-ethoxycarbonylmethylthio-5,5-diphenyl-5,6-dihydro-4H-1,4-thiazine-6-carboxylate (5). The reaction is initiated by substitution of the two vinyl-bound chloro substituents to give {EtO(O=)CCH2S}2C=C(H)–N=CPh2 (2c) as intermediate. A mechanism that accounts for the subsequent cyclisation reaction is proposed. The 2-azabutadiene derivative (PhO)2C=C(H)–N=CPh2 (7) was obtained by the reaction of 1 with sodium phenolate. The regioselectivity of the incoming nucleophile is roughly correlated with its hardness/softness in accord with Pearson’s HSAB principle. The molecular structures of 2a,b, 5 and 7 were determined by single-crystal X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reaction of [1,4-{SiMe3(H)N}2C6Me4] (1) with 2 equivalents of LiBun followed by the addition of SiMe3Cl gave the diamine compound [1,4-{(SiMe3)2N}2C6Me4] (2). [Ta(η5-C5H4SiMe3)Cl4] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η5-C5H4SiMe3)Cl2}2(μ-1,4-NC6Me4N)] (3), and mononuclear, [Ta(η5-C5H4SiMe3)Cl2{ NC6Me4-4-(N(SiMe3)2)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η5-C5H4SiMe3)Cl4] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl3(CH3CN)2{ NC6Me4-4-(N(SiMe3)2)}] (5) has been prepared by the reaction of one molar equivalent of TaCl5 with 2 in a CH3CN/CH2Cl2 solvent mixture. The synthesis of the niobium complexes, [{Nb(η5-C5H4SiMe3)Cl2}2(μ-1,4-NC6Me4N)] (6) and [Nb(η5-C5H4SiMe3)Cl2{ NC6Me4-4-(N(SiMe3)2)}] (7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η5-C5H4SiMe3)RCl{ NC6Me4-4-(N(SiMe3)2)}] (R = η5-C5H4SiMe3 (8), PhC(NSiMe3)2 (9), NMe2 (10)). In an attempt to form the hetero bimetallic complex, [{Nb(η5-C5H4SiMe3)Cl2}(μ-1,4-NC6Me4N){Ta(η5-C5H4SiMe3)Cl2}] (11), the reaction of 7 with [Ta(η5-C5H4SiMe3)Cl4] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.

The reactions between the copper (II) salts [CuXL]PF6 (L: 2,6-[1-(2,6-diisopropylphenylimino)ethyl]pyridine) (X = Cl 1, X = Br 2) and LiTCNQ, in a DMF/water mixture, or Et3NH(TCNQ)2, in acetone, produced the new complexes [CuXL(TCNQ)] (X = Cl 3, X = Br 4). For both compounds, crystallographic studies have clearly evidenced the existence of dimeric complexes [{CuClL}(TCNQ)]2 owing to π–π overlap between two adjacent TCNQ − radical anions. Compound 1 reacted with Et4N(C10N7) to afford the mononuclear derivative [CuClL(C10N7)] (5), while its reaction with K2C10N6 produced the dinuclear complex [(CuClL)2(C10N6)] (6). The crystal structures of complexes 5 and 6 have been determined by X-ray crystallography. Magnetic studies have revealed that compound 6 displays weak antiferromagnetic interactions between the two metal centres, conversely compounds 3 and 5 exhibit purely paramagnetic behaviours.

The preparation of a family of dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, i = 4 (1); Cp′ = η5-C5H4SiMe3, M = Nb, i = 3 (2); Cp′ = η5-C5H4SiMe3, M = Nb, i = 2 (3); Cp′ = η5-C5Me5, M = Nb, i = 4 (4); Cp′ = η5-C5Me5, M = Nb, i = 3 (5); Cp′ = η5-C5H4SiMe3, M = Ta, i = 4 (6); Cp′ = η5-C5H4SiMe3, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl3}2(μ-1,i-NC6H4N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C5H4(SiMe3)2 or C5Me5(SiMe3). Complexes 1−7 can also be prepared by the reaction of two equivalents of [MCp′Cl4] (Cp′ = η5-C5H4SiMe3, M = Nb, Ta; Cp′ = η5-C5Me5, M = Nb, Ta) with one equivalent of the corresponding aniline compound, N,N,N′,N′-tetrakis(trimethylsilyl)-1,4-, -1,3-, or -1,2-phenylenediamine, respectively. The synthesis of [{Ta(Cp′)Cl2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5Me5, i = 4 (8); Cp′ = η5-C5Me5, i = 3 (9)] was only successful with the second preparative method. The reaction of 1, 2 and 8 with alkylating reagents gave the corresponding tetraalkyl derivatives, [{M(Cp′)R2}2(μ-1,i-NC6H4N)] [Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 4 (10); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 4 (11); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 4 (12); Cp′ = η5-C5H4SiMe3, M = Nb, R = Me, i = 3 (13); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 3 (14); Cp′ = η5-C5H4SiMe3, M = Nb, R = CH2Ph, i = 3 (15); Cp′ = η5-C5Me5, M = Ta, R = Me, i = 4 (16); Cp′ = η5-C5Me5, M = Ta, R = CH2SiMe3, i = 4 (17); Cp′ = η5-C5Me5, M = Ta, R = CH2Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp′)(Me)(X)}2(μ-1,4-NC6H4N)] [Cp = η5-C5H4SiMe3, M = Nb, X = Cl (19); Cp = η5-C5H4SiMe3, M = Nb, X = NMe2 (20); Cp = η5-C5Me5, M = Ta, X = Cl (21)], were also prepared. The molecular structures of complexes 1, 8 and 17 were determined by single-crystal X-ray diffraction studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The complex [Cp*{C5H4(CH2CH2NMe2)}TaCl2] (1) was synthesised by reaction of the lithium salt LiC5H4(CH2CH2NMe2) with the tantalum compound [Cp*TaCl3(PMe3)]. Reduction of 1 with NaAl(H)2(OCH2CH2OMe)2 leads to the trihydride derivative [Cp*{C5H4(CH2CH2NMe2)}TaH3] (2). The oxidation of 2 in THF with ferrocenium ion leads to a cationic dihydride intermediate [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) with an intramolecular stabilization by the aminoethyl side-chain of the cyclopentadienyl ligand. The hemilabile character of the functionalised cyclopentadienyl ligand was checked by treating 3 with electron-donating ligands (e.g. phosphanes, sulfides, anions); in all cases, no displacement of the amino group was observed. When treated with HBF4, 2 undergoes a loss of the hydride and the resulting cation can be isolated as a solvento adduct by carrying out the reaction in dimethyl sulfide. Acidolysis of 2 in the presence of an excess of trifluoroacetic acid affords the compound [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). Microanalytical and NMR spectroscopic data for these complexes are given. The X-ray crystal structures are reported for [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) and [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

4,4-Dichloro-1,1-diphenyl-2-azabuta-1,3-diene (1) oxidatively adds to [Pd(PPh3)4] and [Pt(C2H4)(PPh3)2] giving rise to the σ-alkenyl complexes trans-[MCl{[C(Cl)=C(H)−N=CPh2]}(PPh3)2] (2a: M = Pd; 2b: M = Pt). When 1 is treated with [Pd(PPh3)4] in a 1:2 ratio in refluxing toluene, the dimetallic μ-vinylidene complex [(PPh3)ClPd{μ-[C=C(H)−N=CPh2]}PdCl(PPh3)2] (3) is formed. In this fluxional compound, a PPh3 ligands migrates in a reversible manner between the two Pd centers. Substitution of the PPh3 ligands of 3 by 2 equiv. of Ph2PCH2PPh2 affords the A-frame complex [ClPd(μ-dppm)2{μ-[C=C(H)−N=CPh2]}PdCl] (4). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Reaction of various neutral LXH bidentate ligands (2-aminobenzoic acid, acetylacetone, dibenzoylmethan and 2-aminobenzenethiol) with [Cp′2TaH2]+, obtained in situ from Cp′2TaH3 treated with triphenylmethan cation, affords after dihydrogen elimination the corresponding cationic species [Cp′2Ta(H)(LX)]+ in BF4 or PF6 salts. Complexes [Cp′2TaH(η2-O2CC6H4-o-NH2O,O′)]PF6 (3), {Cp′2Ta[η2-OC(Me)CHC(Me)OO,O′]}BF4 (4a), {Cp′2TaH[η2-OC(Ph)CHC(Ph)OO,O′]}BF4 (4b) and [Cp′2TaH(η2-SC6H4-o-NH2S,N)]PF6 (5) are characterised by analytical and spectroscopic methods. With thiopyridine, the kinetic (6) and the thermodynamic (6′) isomers [Cp′2TaH(η2-2-SC5H4NS,N)]PF6 are identified. Crystal structures are reported for complexes 3, 5 and 6′.

International audience; The reactions of the copper(I) derivative [CuL(THF)(CH3CN)]PF6 (1), in which L is the di-imine/pyridine ligand 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine, with different β-diketones (2,4-pentanedione (acacH), 1,3-diphenyl-1,3-propanedione (dbm)) yielded the new Cu(I) salt [CuL′2]PF6 (2) (L′: 2-[acetyl]-6-[1-(2,6-diisopropylphenylimino)ethyl]pyridine). These reactions of β-diketones with a di-imine/pyridine ligand co-ordinated to a Cu(I) centre constitute the first example of a partial hydrolysis of such a Schiff base within the inner sphere of a Cu centre. Compound 2·acaH has been characterised by X-ray crystallography. © 2002 Elsevier Science B.V. All rights reserved.

The aim of this paper is to look for a better knowledge of the behaviour of bent tantalocenes that bear hydrides, phosphorus PR2X (R=Me, Ph; X=H, lone pair) and cyclopentadienyl (Cp=C5H5, Cp′=C5H2tBu(Me)2, Cp*=C5Me5) ligands. An orbital control of regioselectivity of insertion of the PR2 phosphide fragment of chlorophosphines PR2Cl into the central TaH bond of trihydrides Cp2TaH3 leading to the formation of metallophosphonium cations is discussed. Neutralisation of cationic complexes with strong bases leads either to the Ta(V)–phosphide or to the Ta(III)–phosphine species depending on the nature of the cyclopentadienyl ligand; good electron donor Cp′ and Cp* rings favour the formation of Ta(V)–phosphide species, while C5H5 orients neutralisation towards Ta(III)–phosphine ones. These trends are roughly confirmed by DFT calculations. The X-ray structure of the first tantalocene phosphonium ionic compound [CpCp′TaH2(PMe2H)]PF6 (Cp′=C5H2tBu(Me)2) as well as that of the bimetallic complex Cp2Ta(H)(μ-PPh2,H)Fe(CO)3 are also reported.

A series of cyclic fused-isoxazolines is obtained by regioselective and diastereoselective 1,3-dipolar cycloaddition of enamines (I) and (IV) to arylnitrile oxides.

Bis(phenylthio)methane (L1) reacts with CuI to yield the 1D-coordination polymer [{Cu4(μ3-I)4}(μ-L1)2]n (1) bearing cubane Cu4I4 clusters as connecting nodes. The crystal structures at 115, 155, 195, and 235 K provided evidence for a phase transition changing from the monoclinic space group C2/c to P21/c. The self-assembly process of CuI with bis(p-tolylthio)methane (L2), bis(4-methoxyphenylthio)methane (L3), and bis(4-bromo-phenylthio)methane (L4) affords the 1D-coordination polymers [{Cu4(μ3-I)4}(μ-Lx)2]n (x = 2, 3, or 4). Compounds 2 and 4 are isostructural with C2/c low temperature polymorph of 1, whereas the inversion centers and 2-fold axes are lost in 3 (space group Cc). The use of bis(m-tolylthio)methane (L5) has no impact on the composition and overall topology of the resulting 1D ribbon of [{Cu4(μ3-I)4}(μ-L5)2]n (5). Even the coordination of the sterically crowded dithioether bis(5-tert-butyl-2-methylphenylthio)methane (L8) does not alter the network topology generating the 1D polymer [{Cu4(μ3-I...

SamariumIII monoalkoxides bearing two, one, or no cyclopentadienyl type spectator ligands are easily synthesized by monoelectronic oxidation with tert-butylperoxide of the corresponding samariumII precursors. These monoalkoxides are single-site initiators for ring-opening polymerization.

The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(O)H] (1), the new compound [Cp*2Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the NbO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*2Nb(O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.

Lactols are compounds of increasing interest in the synthesis of active pharmaceutical derivatives. Nevertheless, the product obtained by the reduction of the carbonyl group of coumarin has been described only twice, and without definition of its precise chemical structure. Since these studies, doubts have been raised about the existence of a monomeric or dimeric form. Our study has led us to conclude definitely that the single dimeric form exists and to precisely define the spectral properties of the two diastereoisomers.

The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Huckel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: significant shortening of the Fe-Fe distance (deltad(Fe-Fe)> 0.3 A) and weakening of the As-As bond length ((deltad(As-As) > 0.3 A) suggests the formal presence of two diatomic AsSe ligands and a Fe-Fe bond. DFT and EHMO calculations confirm that an electron is removed from an occupied Fe-Fe orbital of antibonding character during oxidation. All molecular orbitals lower their energies upon oxidation, but the energy drop is relatively small for those involving the As-As bond. An additional structural feature in 4 consists of an electronic interaction of the iodide with both As atoms which suggests a formally neutral ion pair. Electrochemical studies confirm that the oxidation of 1 is a reversible one-electron process with E(1/2)= +0.07 V (in THF). These studies also reveal that 4 dissociates in polar solvents, such as THF, into [1]+ and I-, which is followed by transformation into 1 and I3.