New iminophosphorane-mediated synthesis of thieno[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-ones and 5H-2,3-dithia-5,7-diaza-cyclopenta[c,d]indenes

Mono(iminophosphorane) 4 was selectively prepared from the reaction of 3,4-diaminothieno[2,3-b]thiophene 3 with excess triphenylphosphine, C₂Cl₆, and Et₃N due to intramolecular double hydrogen bond formation. Mono(iminophosphorane) 4 reacted with aromatic isocyanates to give stable carbodiimides 8, which were further treated with aliphatic secondary or primary amines to give 2-amino substituted thieno[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-ones 10 or 12 in the presence of a catalytic amounts of EtO⁻Na⁺. However, in the presence of a catalytic amounts of potassium carbonate, the carbodiimides 8 were transformed into previously unreported 5H-2,3-dithia-5,7-diaza-cyclopenta[c,d]indenes 13 via direct cyclization in high yields. The reaction of carbodiimides 8 with phenols in the presence of a catalytic amounts of potassium carbonate gave a mixture of 2-aryloxy substituted thieno[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-ones 14 and 13. X-ray structure analysis of 10m supported the structure and the proposed reactivity of amino group.     

A practical one-pot procedure for the synthesis of pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinones by a tandem aza-Wittig/heterocumulene-mediated annulation strategy

A simple one-pot and efficient method is described for the synthesis of pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinone derivatives 6 via a tandem aza-Wittig/heterocumulene-mediated annulation process. The iminophosphorane 3 reacted with aryl isocyanates, followed by heterocyclization on addition of secondary amines to give the corresponding guanidine intermediates 5, which were cyclized in the presence of a catalytic amount of potassium carbonate to tricyclic compounds 6. Similarly, iminophosphorane 3 reacts with phenols, thiophenol, or ROH to give 2-aryl(alkyl)oxy(thio)pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinone derivatives 7 in good yields. The corresponding carbodiimide 4c and guanidine-type intermediate compounds 5 could be isolated and characterized, thus confirming the suggested reaction pathway. However, two isomeric pyrazinothienopyrimidinones 8 and 9 may be produced in the reaction of iminophosphorane 3 with aromatic isocyanates and subsequent reaction with primary amines in the presence of a catalytic amount of potassium carbonate. The effects of the nucleophiles and isocyanates on the regioselectivity of the cyclization have been investigated.     

Efficient one-pot preparation of bis(pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidin-4-yl)benzenes based on an aza-Wittig/mediated annulation strategy

Aza-Wittig mediated annulation provides a highly facile and straightforward one-pot strategy for the synthesis of bis(pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidin-4-yl)benzenes 5 and 7. A tandem aza-Wittig reaction of iminophosphorane 2 with 1,4- or 1,3-phenylene diisocyanate, followed by intramolecular heteroconjugate addition annulation after addition of a nucleophilic reagent (amine, phenol, thiophenol or ROH), in presence of catalytic K₂CO₃ or NaOR, gives selectively the functionalized bis(pyrazinothienopyrimidinones) 5 and 7.     

New efficient synthesis of 2,3,4-trisubstituted 3,4-dihydroquinazolines by a Ugi 4CC/Staudinger/aza-Wittig sequence

A series of 2,3,4-trisubstituted 3,4-dihydroquinazoline 3 was prepared by intramolecular aza-Wittig reaction of amide carbonyl groups with methyldiphenyl iminophosphorane, which was obtained from a Ugi 4CC/Staudinger sequence. Further intramolecular Heck reaction of 3d′-g′ in the presence of catalytic amount of Pd(OAc)₂ gave 6,12-dihydroindolo[2,1-b]quinazolines 4a-d in good yields.     

Palladium complexes of N-aryl-2-pyridylamines

Palladium complexes of N-phenyl-2-pyridylamine (4) and dipyridylamine substrates (7, 11) have been studied. Due to the coordination ability of the pyridine-nitrogen atoms, the pyridyl substrates, 4, 7, 11 were subjected to Pd(OAc)₂ complexations and a number of N-aryl-2-pyridylamine Pd complexes (13-17) were isolated and characterised, in particular by NMR and ESI-MS. A new method for the preparation of the acetato-bridged six-membered ring palladacycle complex (13) of 4 is reported. The dipyridyl amines 7, 11 formed cis/trans bis-dentate acetato-bridged dimeric Pd₂Lig₂(OAc)₂ (14a,b/16a,b) and Pd₃Lig₂(OAc)₄ complexes (15a,b/17a,b). The N-aryl-2-pyridylamine substrates (4, 7, 11) were prepared by oxidative nucleophilic substitution, by 1,3-cycloaddition reaction or by Buchwald amination.     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Synthesis and reactivity of para-substituted benzoylmethyltellurium(II and IV) compounds: observation of intermolecular C-H-O hydrogen bonding in the crystal structure of (p-MeOC6H4COCH2)2TeBr2

Bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC₆H₄COCH₂)₂TeBr₂, (Y=H (1a), Me (1b), MeO (1c)) can be prepared either by direct insertion of elemental Te across C_Rf-Br bonds (where C_Rf refers to α-carbon of a functionalized organic moiety) or by the oxidative addition of bromine to (p-YC₆H₄COCH₂)₂Te (Y=H (2a), Me (2b), MeO (2c)). Bis(p-substituted benzoylmethyl)tellurium dichlorides, (p-YC₆H₄COCH₂)₂TeCl₂ (Y=H (3a), Me (3b), MeO (3c)), are prepared by the reaction of the bis(p-substituted benzoylmethyl)tellurides 2a-c with SO₂Cl₂, whereas the corresponding diiodides (p-YC₆H₄COCH₂)₂TeI₂ (Y=H (4a), Me (4b), MeO (4c)) can be obtained by the metathetical reaction of 1a-c with KI, or alternatively, by the oxidative addition of iodine to 2a-c. The reaction of 2a-c with allyl bromide affords the diorganotellurium dibromides 1a-c, rather than the expected triorganotelluronium bromides. Compounds 1-4 were characterized by elemental analyses, IR spectroscopy, ¹H, ¹³C and ¹²⁵Te NMR spectroscopy (solution and solid-state) and in case of 1c also by X-ray crystallography. (p-MeOC₆H₄COCH₂)₂TeBr₂ (1c) provides, a rare example, among organotellurium compounds, of a supramolecular architecture, where C-H-O hydrogen bonds appear to be the non-covalent intermolecular associative force that dominates the crystal packing.     

The first entry to pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones

Wittig olefination of 3-aminoquinoline-2,4(1H,3H)-diones 1 with ethyl (triphenylphosphoranylidene)acetate (Ph₃PCHCO₂Et) afforded (E)-3-amino-4-ethoxycarbonylmethylene-1,2,3,4-tetrahydro-2-quinolones (E)-2 and pyrrolo[2,3-c]quinoline-2,4(3aH,5H)-diones 3. An alternative approach for the synthesis of 3 via 3-bromoacetamidoquinoline-2,4(1H,3H)-diones 7, their corresponding triphenylphosphonium salts 8, and ylides A that undergo intramolecular Wittig reaction, was investigated. Under the applied reaction conditions, the phosphonium salts 8 and ylides A are so unstable that they partly decompose to 3-acetamidoquinoline-2,4(1H,3H)-diones 9 during the synthesis of 3.     

Steric course of some cyclopropanation reactions of L-threo-hex-4-enopyranosides

Completely protected 4-deoxy-α-L-threo-hex-4-enopyranosides 1c,d undergo the dichlorocarbene addition affording exclusively diastereomeric adducts 5c,d with the cyclopropane ring anti to the C-3 alkyloxy substituent, while the reaction with 3-unprotected derivatives 1a,b affords a mixture of syn and anti derivatives. Under the Simmons-Smith cyclopropanation adducts 2a-d with a syn stereochemistry are obtained. Starting from 5b, the cyclopropanated sugar 3b is obtained by reduction with LiAlH₄, thus the two diastereomers 2b and 3b can be stereoselectively obtained through the two different pathways. For a useful comparison, 4-deoxy-β-L-threo-hex-4-enopyranoside 1e was also subjected to the above two cyclopropanation methods affording the expected cycloadduct 2e and a diastereomeric mixture of dichlorocycloadducts 4e and 5e (4e/5e=2.8:1).     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

A facile approach for the synthesis of novel substituted 4H-chromenes and condensation reactions of 4H-chromenes leading to chromenopyrrolones and triazolylchromenopyrrolones

A facile method has been developed for the synthesis of 4H-chromene-3-carboxylates 3a–d by the nucleophilic substitution reaction of 2-hydroxy-2H-chromene-3-carboxylates 2a–d with triethylsilane in the presence of BF₃·O(C₂H₅)₂. Cyclocondensation of 4H-chromene-3-carboxylates 3a–d with benzylamines 4a–d afforded a series of 2,3-dihydrochromenopyrrolones 5a–p and with propargylamine afforded 2-propynyl-2,3-dihydrochromenopyrrolones 6a–d. Click reaction of 6a–d with benzyl azides 7a–d provided a series of 1H-1,2,3-triazolylmethyl-2,3-dihydrochromenopyrrolones 8a–p. Thus synthesized compounds 3a–d, 5a–p, 6a–d, and 8a–p are novel heterocyclic compounds and being reported for the first time.     

Solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes under high-speed vibration milling

The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a-e under high-speed vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a-e (C₆₀(CH₂N(CH₃)CHR), R=H (4a), C₆H₅ (4b), p-NO₂-C₆H₄ (4c), p-CH₃O-C₆H₄ (4d), p-(CH₃)₂N-C₆H₄ (4e)) were obtained in moderate yields from reactions of C₆₀ with aldehydes 2a-e and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b-e, indicating that fullerenes can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the reagent ratio for the reaction of C₆₀ with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The reaction of C₇₀ with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the positional isomers of [70]fulleropyrrolidines.     

Polyhedral monocarbaborane chemistry : Reactions of the [6-Ph-nido-6-CB9H11] anion with two-electron donors to yield a series of neutral arachno and closo ten-vertex monocarbaborane derivatives

Reaction of the ten-vertex [6-Ph-nido-6-CB₉H₁₁]⁻ anion (1) with two-electron donor ligands L, where L is SMe₂, NH₂Ph, NC₅H₅, NC₅H₄-para-CH₂Ph, NC₅H₄-para-Ph or NC₉H₇ (where NC₉H₇ is quinoline) in the presence of {FeCl₃(OH₂)₆} gives the six neutral arachno ten-vertex monocarbaboranes [6-Ph-9-L-arachno-6-CB₉H₁₂], compounds 2, 3, 4, 7, 9 and 11, respectively, isolatable in yields of up to 63%. On prolonged treatment with {FeCl₃(OH₂)₆} oxidative cluster closure of the four compounds 4, 7, 9 and 11 that have pyridine-type ligands gives the neutral closo ten-vertex monocarbaboranes [1-Ph-6-L-closo-1-CB₉H₈], compounds 6, 8, 10 and 12, respectively, in yields of 49-92%. All new species 2, 3, 4, 6, 7, 8, 9, 10, 11 and 12 are characterised by single-crystal X-ray diffraction analysis and NMR spectroscopy. [This paper is an annotated exposition of parts of an oral presentation at the Third Pan-European Meeting of Boron Chemists, EUROBORON-3, Pruhonice, The Czech Republic, September 2004, of which the proceedings constitute this volume of Journal of Organometallic Chemistry.]     

Cyclopalladated complexes with N-(benzoyl)-N-(2,4-dimethoxybenzylidene)hydrazine: syntheses, characterization and structural studies

Cyclopalladated complexes with the Schiff base N-(benzoyl)-N^′-(2,4-dimethoxybenzylidene)hydrazine (H₂L, 1) have been described. The reaction of 1 with Li₂[PdCl₄] in methanol yields the complex [Pd(HL)Cl] (2). [Pd(HL)(CH₃CN)Cl] (3) has been prepared by dissolving 2 in acetonitrile. In methanol-acetonitrile mixture, treatment of 2 with two mole equivalents of PPh₃ produces [PdL(PPh₃)] (4) and that with one mole equivalent of PPh₃ produces [Pd(HL)(PPh₃)Cl] (5). Crystallization of 2 from dmso-d₆ results into isolation of [Pd(HL)((CD₃)₂SO)Cl] (6). In 2, the monoanionic ligand (HL⁻) is C,N,O-donor and the Cl-atom is trans to the azomethine N-atom. In 3, 5 and 6, HL⁻ is C,N-donor and the Cl-atom is trans to the metallated C-atom. The remaining fourth coordination site is occupied by the N-atom of CH₃CN, the P-atom of PPh₃ and the S-atom of (CD₃)₂SO in 3, 5 and 6, respectively. Thus on dissolution in acetonitrile and dmso and in reaction with stoichiometric PPh₃ the incoming ligand imposes a rearrangement of the coordinating atoms on the palladium centre. On the other hand, in presence of excess PPh₃ deprotonation of the amide functionality in 2 occurs and the Cl-atom is replaced by the P-atom of PPh₃ to form 4. Here the dianionic ligand (L²⁻) remains C,N,O-donor as in 2. The compounds have been characterized with the help of elemental analysis (C, H, N), infrared, ¹H NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography.     

Addition of 2-tert-butyldimethylsilyloxythiophene to activated quinones: an approach to thia analogues of kalafungin

The uncatalyzed reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-quinones bearing either an electron withdrawing acetyl or a carbomethoxy group at C-2, was investigated. No reaction was observed using 1,4-quinones 8 and 9 bearing an ester group at C-2 whereas use of 1,4-quinones 10 and 11 bearing an acetyl group at C-2 only provided low yields of the silyloxythiophenes 15 and 16 resulting from electrophilic substitution of the silyloxythiophene by the 1,4-quinone. Use of the Lewis acids InCl₃, Cu(OTf)₂ and BF₃·Et₂O were investigated in an effort to improve the yield of the desired annulation reaction. BF₃·Et₂O proved to be the optimum catalyst for the synthesis of thiolactone naphthofuran adducts 14 and 18 from 1,4-naphthoquinones 9 and 11, respectively. Reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-benzoquinones 8 and 10 bearing a carbomethoxy or an acetyl group at C-2, respectively, afforded thiolactone benzofuran adducts 13 and 17, respectively, catalyzed by either InCl₃ or Cu(OTf)₂. Addition of 2-tert-butyldimethylsilyloxythiophene 2 to 3-acetyl-5-methoxy-1,4-naphthoquinone 12 afforded adduct 19 that underwent oxidative rearrangement to thiolactone pyranonaphthoquinone 20 using ceric ammonium nitrate in acetonitrile, thus providing a novel approach for the synthesis of a thia analogue of the pyranonaphthoquinone antibiotic kalafungin.     

A convenient one-pot synthesis of 2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives and their further transformations

The trifluoromethyl containing heterocycles, 2-hydroxy-4-aryl-3-(thien-2-oyl)-2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives 4, were synthesized via a one-pot three-component reaction of aldehyde 1 with 1,3-cyclohexanedione 2 and 4,4,4-trifluoro-1-(thien-2-yl)butane-1,3-dione 3 in the presence of a catalytic amount of Et₃N. The effect of bases and solvents on the reaction efficiency and yield was briefly investigated. Treatment of 4 with an excess amount of NH₄OAc in ethanol afforded 2-trifluoromethyl-1H-quinolin-5-one derivatives 5. Refluxing of 4 with TsOH in CHCl₃ gave the corresponding dehydrated products 8.     

Wittig reaction with ion-supported Ph3P

Ion-supported Ph₃P, 4-(diphenylphosphino)benzyltrimethylammonium bromide A and N-methyl-N-[4-(diphenylphosphino)benzyl]pyrrolidinium bromide B, were used for the Wittig reaction. Ion-supported phosphonium salts A1 and B1, which were prepared from the reactions of ion-supported Ph₃P A and B with ethyl bromoacetate, respectively, reacted with aromatic and aliphatic aldehydes in the presence of K₂CO₃ to give the corresponding α,β-unsaturated ethyl esters in good yields with high purity by simple filtration of the reaction mixture and subsequent removal of the solvent from the filtrate. Similarly, ion-supported phosphonium salts A2 and B2, which were prepared from the reactions of ion-supported Ph₃P A and B with p-methylbenzyl bromide, respectively, reacted with aromatic and aliphatic aldehydes in the presence of NaH to provide the corresponding p-methylstyrene derivatives in good yields with high purity by simple filtration of the reaction mixture and the subsequent removal of the solvent from the filtrate. In both reactions, the co-product, ion-supported Ph₃PO, could be obtained quantitatively by simple filtration, and was converted into the corresponding ion-supported Ph₃P A and B again in high yields using dimethyl sulfate, followed by the reduction with LiAlH₄. Recovered and regenerated ion-supported Ph₃P A and B could be reused for the same Wittig reaction while maintaining good yields of ethyl (E)-3-(4′-chlorophenyl)-2-propenoate and 1-(4′-chlorophenyl)-2-(4″-methylphenyl)ethene with high purity by simple filtration and removal of the solvent from the filtrate.     

Thermal rearrangements of tetrahydroimidazo[1,5-b]isoxazole-2,3-dicarboxylates. Synthesis of 3H-imidazol-1-ium ylides and their silver derivatives

Isoxazolines 2 from the cycloaddition of imidazoline 3-oxides 1 with DMAD undergo rearrangement to 3,4-dihydro-2H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 3, which spontaneously undergo elimination to give 3H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 5 or 1H-imidazoles 6 when heated in toluene at reflux. The presence of the aromatic ring at C-6 decelerated the conversion and enhanced the yield of 5. Solvents more polar than toluene (e.g., DMSO) provided quantitative conversion of 2 into 6 in mild conditions, while in less polar solvents such as CCl₄, the reaction rate was lowered and the yield of 5 enhanced. C-2 unsubstituted ylides 5 were treated with Ag₂O or AgNO₃ in the presence of Et₃N at room temperature to give C-2 metallated derivatives 9 in excellent yields.     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.