Novel stereocontrolled synthesis of the tricyclic lactone (1R,3R,6R,9S)-6,9-dimethyl-8-oxo-7-oxatricyclo[4.3.0.03,9]nonane

The stereocontrolled synthesis of (1R,3R,6R,9S)-6,9-dimethyl-8-oxo-7-oxatricyclo[4.3.0.0^3,9]nonane 1 from (R)-(−)-carvone has been accomplished by application of a 13-step sequence with 12% overall yield. The absolute stereochemistry of the unsaturated acid 8a has been established by X-ray analysis of the chiral amide 8c.     

Substitution reactions in ionic liquids. A kinetic study

The rate of the substitution reaction of (R)-3-chloro-3,7-dimethyloctane (1) with either methanol or benzyl alcohol in mixtures containing the ionic liquid [Bmim][N(CF₃SO₂)₂] was monitored using ³⁵Cl NMR spectroscopy. The enantiomeric excess of the product, (S)-3-methoxy-3,7-dimethyloctane (2a), was analyzed using chiral gas chromatography. This product showed a decreasing enantiomeric excess with increasing concentration of ionic liquid. The rate of reaction of substrate 1 in each case varied with the concentration of the ionic liquid. Polarity measurements of the solvent mixtures were undertaken by standard methods, which are compared both to each other and to the observed rates. Solvent reorganization and selective solvation are also each proposed as contributing to the difference in the observed rates of reaction.     

Azabrendanes. II. Chemo-, regio- and stereoselective transformation of 3-oxatricyclo[3.2.1.02,4]octane-endo-6-carbonitrile in reaction with lithium aluminum hydride

The reduction of 3-oxatricyclo[3.2.1.0^2,4]octane-endo-6-carbonitrile by lithium aluminum hydride is completed by the formation of exo-2-hydroxy-4-azatricyclo[4.2.1.0^3,7]nonane with the structure confirmed (1) by the analysis of ¹H, ¹³C, ¹⁴N, and ¹⁷O NMR spectra and the two-dimensional spectra (COSY-experiment); (2) by comparison with ¹H and ¹³C NMR spectra of the corresponding oxygen analog of heterobrendane; (3) by the calculation of the vicinal constants for the spin-spin interaction in the molecules of both analogs by the MMX program; and (4) by transformation into N-(p-bromophenylsulfonyl)-exo-2-hydroxy-4-azatricyclo[4.2.1.0^3,7]nonane prepared by an alternative synthesis, viz., epoxidation of N-(p-bromophenylsulfonyl)bicyclo-[2.2.1]hept-2-en-endo-5-methylamine. The reduction of 3-oxatricyclo [3.2.1.0^2,4]octane-exo-6-carbonitrile affords the epoxide, 3-oxatricyclo[3.2.1.0^2,4]octane-exo-6-methylamine. Different behaviors of stereoisomers are discussed; analysis of the coefficients of the atomic orbitals in the MO LCAO equation (AM1 method) has been made, and the strengths of the C(SINGLE BOND)O bonds in the epoxy ring has been analyzed. © 1997 John Wiley & Sons, Inc.     

Trichloro- and methyldichlorogermyl monochelates and dibromo- and dichlorogermyl bischelates derived from N,N-disubstituted amides of 2-hydroxycarboxylic acids

The reactions of GeCl₄, GeBr₄, and MeGeCl₃ with O-trimethylsilyl derivatives of N,N-disubstituted amides of 2-hydroxycarboxylic acids afforded pentacoordinate and hexacoordinate neutral (O,O)-mono- and (O,O)-bischelates. The reactions of glycolic acid derivatives with GeX₄ produced bischelates X₂Ge[OCH₂C(O)NR²R³]₂ 7a,c,d (X = Cl, R² = R³ = Me (a), (CH₂)₅ (c), (CH₂CH₂)₂O (d)) and 8a (X = Br). By contrast, the reactions of lactic and mandelic acid derivatives with GeCl₄ and MeGeCl₃ gave monochelates Cl₃Ge[OCH(R¹)C(O)NR²R³] (S)-9a–c (R¹ = Me) and Cl₂MeGe[OCH(R¹)C(O)NR²R³] 10a (R¹ = H), (S)-11a,b (R¹ = Me), and (S)-12a (R¹ = Ph) (R²R³ = (CH₂)₄ (b)), respectively. According to the X-ray diffraction data, the Ge atom in bischelates 7c,d and 8a has a coordination number 6, and its coordination polyhedron can be described as a slightly distorted octahedron. In monochelates (S)-9a-c, 10a, (S)-11a,b, and (S)-12a, the Ge atom has a coordination number 5, and its coordination polyhedron can be described as a trigonal bipyramid with two halogen atoms or one halogen atom and one ethereal oxygen atom in equatorial positions and the halogen atom and the amide oxygen atom in the axial positions. The bonds in the axial positions are somewhat longer than the corresponding bonds in tetracoordinate Ge compounds.     

Lactonization of epoxyendic anhydride in reactions with amines

Reactions of exo-5,6-epoxybicyclo[2.2.1]hept-5-ene-endo-2,endo-3-dicarboxylic anhydride (epoxyendic anhydride) with acyclic, aromatic, heteroaromatic, and nonaromatic heterocyclic amines afforded the corresponding heterocyclization products, substituted exo-2-hydroxy-5-oxo-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxamides (oxabrendanes), whose structure was confirmed by the IR and ¹H and ¹³C NMR (including two-dimensional) spectra. Other approaches to the tricyclic compounds were also examined, in particular via reactions of organic peroxy acids with amido acids obtained by aminolysis of endic anhydride.     

Amido acids of norbornene series in reactions with sulfonyl azides

In reaction of amido acids from the norbornene series with arenesunfonyl azides alongside the expected N,N-dialkyl-5-oxo-exo-2-arylsulfonylamino-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxamides (oxabrendanones) the formation of zwitter-ions with a structure of 5-(N,N-dialkyliminio)-exo-2-arylsulfonylamino-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxylates came as a surprise. The structure of compounds obtained was confirmed by the analysis of their IR and ¹H NMR spectra. The molecular structure of one among the zwitterions was established by XRD analysis.     

Intramolekulare Diels-Alder-Additionen in 6-(But-3-enyl)-6-methyl-cyclohexa-2,4-dien-1-on-Systemen; eine neue Synthese von Twistanderivaten

Alkylation of the sodium salt of mesitol with 2-bromomethyl-buta-1,3-diene ( 7 ) in benzene and subsequent refluxing of the reaction mixture gave 7% 2-methylene-3-butenyl-mesitylether ( 8 ), 12% 5-methylene-1,3,8-trimethyl-tricyclo[4,3,1,0^3,7]-8-decen-2-one ( 9 ) and 44% 9-methylene-1,3,5-trimethyl-tricyclo[4,4,0,0^3,8]-4-decen-2-one ( 10 ), a twistane derivative. The same procedure, when applied to the sodium salt of 2,6-dimethyl-4-methoxyphenol, gave in 73% yield a 26:18:54 mixture of 2,6-dimethyl-4-methoxyphenyl-(2-methylene-3-butenyl)-ether ( 11 ), 1,3-dimethyl-8-methoxy-5-methylene-tricyclo[4,3,1,0^{3, 7}]-8-decen-2-one ( 12 ), and 1,3-dimethyl-5-methoxy-9-methylene-tricyclo[4,4,0,0^{3, 8}]-4-decen-2-one ( 13 ). The tricyclic ketones 9 and 10 , or 12 and 13 , were also obtained on heating 8 or 11 respectively at 176° in decane solution. Alkylation of the sodium salt of 2,6-dimethylphenol with 3-butenylbromide in boiling toluene gave 1,3-dimethyl-tricyclo[4,3,1,0^3,7]-8-decen-2-one ( 17 ) as the only tricyclic product in 8% yield. The structures of the twistane derivatives 10 and 13 as well as those of the ketones 9, 12 and 17 were mainly deduced from spectroscopic data. Furthermore, the ketones 10 and 13 could be converted to the twistane derivatives 20 and 22 , possessing C₂-symmetry. On the other hand, compounds 9 and 17 gave only the asymmetric derivatives 18 and 21 .     

Trimer–dimer equilibrium studies of alkylaluminum alkoxides

The aluminum alkoxides [MeClAlOEt]₃ (1), [Et₂AlOMe]₃ (2), [Me₂AlOEt]₃ (3), and [EtClAlOEt]₃ (4) were investigated by ¹H NMR spectroscopy to study the o-dichlorobenzene solution equilibrium: 2 [R₂AlOR′]₃⇌3 [R₂AlOR′]₂. The complexes are shown to exist primarily as trimers at room temperature, but increasing concentrations of the dimeric form are observed at higher temperatures. Equilibrium constants, ΔH, and ΔS were determined for the trimer–dimer equilibrium. Values of ΔH for the conversion of 2 moles of trimer are 63(4), 78(1), 85.0(8), and 99(6) kJ for 1, 2, 3, and 4, respectively. The corresponding values of ΔS are 142(7), 184(3), 218(2), and 265(17) J/K, respectively. Thermodynamic parameters are compared with those reported for [Me₂AlOPrⁿ]₃ and [Me₂AlOPh]₃. The characterization of [EtClAlOMe]₃ is also reported.     

Baseninduzierte umlagerungen von 3,9 dioxatricyclo[3.3.1.02,4]nonan-7-onen zu m-hydroxyphenylcarbonyl-verbindungen

8-Oxabicyclo[3.2.1]oct-6-en-3-ones (5), easily available by [4+3]cycloaddition, were epoxidised at the CC double bond. The 3,9-dioxatricyclo[3.3.1.0^2,4]nonan-7-ones (6) thus obtained are rearranged on treatment with sodium ethoxide in ethanol to form 3-hydroxybenzaldehydes (8a-d) and 3-hydroxy-2,4,5-trimethylacetophenone (8e) in good yields. As intermediates of these rearrangements, 8-hydroxy-6-oxatricyclo [3.2.1.0^2,7]octan-3-ones are postulated ; the trimethyl derivative 7g and the 6-carba-derivatives 4a,b could be isolated.     

Synthesis,crystal structures,spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H₂L¹), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂L²); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H₂L³), namely [Co^III(L¹)(N-MeIm)₃]PF₆ (1), [Co^III(L¹)(py)₃]ClO₄ (2), [Co(L¹)(py)₃][Co(L¹)₂] (3) and [Co^III(L²)(N-MeIm)₃]PF₆ (4) and [Co(L³)(N-MeIm)₂]PF₆ (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.     

New nitro-benzo[c]phenanthridine and indolopyridoquinazoline alkaloids from Zanthoxylum atchoum

The first phytochemical investigation of the roots of Zanthoxylum atchoum has led to the isolation of two new nitro-benzo[c]phenanthridine alkaloids 6-nitronitidine (1) and 6-nitro-8-methoxy-7,8-dihydronitidine (2), two new salts of indolopyridoquinazoline alkaloids 3-hydroxy-8,13-dihydro-14-methyl-5-oxo-7H-indolo[2’,3’:3,4]pyrido[2,1-b]quinazolin-14-ium (3) and its zwitterionic form 3-phenolate-8,13-dihydro-14-methyl-5-oxo-7H-indolo[2’,3’:3,4]pyrido[2,1-b]quinazolin-14-ium (4) along with 18 (5–22) known compounds. Their chemical structures were elucidated by spectroscopic analysis including 1D and 2D NMR and MS techniques. This is the first report of the nitro group on the biosynthesis of the natural benzo[c]phenantridine alkaloids. Compound 2 exhibited potent antibacterial activity against Staphylococcus aureus of MIC₅₀ = 4 μg·mL⁻¹.     

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL¹Cl] (1), [CuL¹NO₃]₂ (2), [CuL¹N₃]₂ · 2/3H₂O (3), [CuL¹]₂(ClO₄)₂ · 2H₂O (4), [CuL²Cl]₂ (5), [CuL²N₃] (6), [Cu(HL²)SO₄]₂ · 4H₂O (7), [Cu(HL²)₂] (ClO₄)₂ · 1/2EtOH (8), [CuL³Cl]₂ (9), [CuL³NCS] · 1/2H₂O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL¹], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL²] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL³]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.     

Synthesis and structural studies of some titanium and zirconium complexes with chiral bis(amide), amidinate or bis(amidinate) ligands

Reaction of bis(amide) sodium Na₂[(1R,2R)-(−)-1,2-(NSiMe₃)₂-C₆H₁₀] (Na₂[L¹]) with Ti(OiPr)₂Cl₂ in different conditions gave mixed-ligand complexes [Ti(OiPr)Cl][L¹] (1) or [Ti(OiPr)₂Cl]₂[L¹] (2); 2 is a dinuclear titanium example in which Ti atoms are bridged by nitrogen and oxygen atoms simultaneously forming a distorted rhombic core. Reaction of the amine-amidinate ligand (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-(NHSiMe₃)-C₆H₁₀(Li[L²]) or rarely linked bis(amidinate) ligand Li₂[(1R,2R)-(−)-1,2-{NC(Ph)N(SiMe₃)}₂-C₆H₁₀](Li₂[L³]) with ZrCl₄ yielded the unbridged and bridged bis(amidinate) complexes ZrCl₂[L²]₂ (3) and [ZrCl₂(THF)][L³] (4), respectively; Moreover, the reaction of (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-Li(NSiMe₃)C₆H₁₀(Li₂[L²]) with Ti(OiPr)₂Cl₂ gave a new type of tridentate amido-amidinate product [Ti(OiPr)₂][L²] (6), which is a distinct model compared to [Ti(OiPr)₂Cl][L²] (5) yielded from Li[L²]. All the products have been characterized by X-ray crystallography and the structural studies are presented detailedly comparing with relevant compounds.     

Linked bis(β-diketiminato) yttrium and lanthanum complexes as catalysts in asymmetric hydroamination/cyclization of aminoalkenes (AHA)

Linked bis(β-diketiminato) rare-earth metal complexes based on the ethylene-bridged ligand [C₂H₄(BDI^DClP)₂]H₂ [DClP = 2,6-Cl₂C₆H₃] and the cyclohexyl-bridged ligands [Cy(BDI^Ar)₂]H₂ [Ar = PMP (= p-MeOC₆H₄), Mes (= 2,4,6-Me₃C₆H₂), DIPP (= 2,6-iPr₂C₆H₃)] were prepared via amine elimination starting from [Ln{N(SiMe₃)₂}₃] (Ln = La, Y). The three cyclohexyl-bridged complexes [{(R,R)-Cy(BDI^Mes)₂}YN(SiMe₃)₂] ((R,R)-3), [{(R,R)-Cy(BDI^Mes)₂}LaN(SiMe₃)₂] ((R,R)-4), and [{(R,R)-Cy(BDI^DIPP)₂}LaN(SiMe₃)₂] ((R,R)-5) were obtained enantiomerically pure. The X-ray crystal structure analysis of the racemic variants of 3 and 4 revealed a distorted square pyramidal coordination geometry around the rare-earth metal, in which the amido ligand occupies the apical position and the two linked β-diketiminato moieties form the basis. The two aromatic substituents adopt a transoid arrangement and both β-diketiminato moieties are bound in a η⁵ coordination mode with close Ln?C contacts. Due to the smaller ionic radius of yttrium vs. lanthanum, the front side of the yttrium complex 3 is sterically more hindered than in the lanthanum complex 4, but there is much more empty coordination space on the rear side, which may rationalize the observed differences in selectivity of 3 in comparison to 4. The catalytic efficiency of the β-diketiminato complexes was strongly affected by steric factors such as ionic radius of the metal and the steric bulk of the aryl substituents, which is an indication for highly steric encumbered catalytic species. The complexes displayed good to moderate catalytic activity in the hydroamination/cyclization of aminoalkenes depending on the steric hindrance around the metal center. The sterically most demanding diisopropylphenyl-substituted complex (R,R)-5 displayed significantly higher enantioselectivities (up to 76% ee), but lower catalytic activity in comparison to the sterically more open mesityl-substituted complex (R,R)-4. The smaller yttrium metal center in complex (R,R)-3 led to reduced activity as well as a reversal in enantioselectivity, which may be rationalized by a change of the approach of the alkene moiety to the Ln-amido bond in the cyclization transition state.     

Dinuclear ruthenium(I) complexes of the type [Ru2(CO)4L2] with carboxylate or 2-pyridonate ligands: Evaluation as catalysts for olefin cyclopropanation with diazoacetates

Dinuclear ruthenium(I,I) carboxylate complexes [Ru₂(CO)₄(μ-OOCR)₂]_n (R = CH₃ (1a), C₃H₇ (1b), H (1c), CF₃ (1d)) and 2-pyridonate complex [Ru₂(CO)₄(μ-2-pyridonate)₂]_n (3) catalyze efficiently the cyclopropanation of alkenes with methyl diazoacetate. High yields are obtained with terminal nucleophilic alkenes (styrene, ethyl vinyl ether, α-methylstyrene), medium yields with 1-hexene, cyclohexene, 4,5-dihydrofuran and 2-methyl-2-butene. The E-selectivity of the cyclopropanes obtained from the monosubstituted alkenes and the cycloalkenes decreases in the order 1b > 1a > 1d > 1c. The cyclopropanation of 2-methyl-2-butene is highly syn-selective. Several complexes of the type [Ru₂(CO)₄(μ-L¹)₂]₂ (4) and (5), [Ru₂(CO)₄(μ-L¹)₂L²] (L² = CH₃OH, PPh₃) (6)–(9) and [Ru₂(CO)₄(CH₃CN)₂(μ-L¹)₂] (10) and (11), where L¹ is a 6-chloro- or 6-bromo-2-pyridonate ligand, are also efficient catalysts. Compared with catalyst 3, a halogen substituent at the pyridonate ligand affects the diastereoselectivity of cyclopropanation only slightly.     

Reaction of N-substituted <Emphasis Type="Italic">exo</Emphasis>-2-hydroxy-5-oxo-4-oxatricyclo[4.2.1.0<Superscript>3,7</Superscript>]nonane-<Emphasis Type="Italic">endo</Emphasis>-9-carboxamides with acetic acid

Acylation of N-substituted exo-2-hydroxy-5-oxo-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxamides on heating in boiling glacial acetic acid gave the corresponding trans-diacetoxy imides of the norbornane series. The effect of the reaction time on the product composition was studied in the reaction with exo-2-hydroxy-N-(4-methylphenyl)-5-oxo-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxamide. The structure of the resulting norbornane-2,3-dicarboximides was confirmed by IR, ¹H NMR, and mass spectra, and the structure of N-(2,5-dimethylphenyl)-exo-2,endo-3-diacetoxybicyclo[2.2.1]heptan-endo-5,endo-6-dicarboximide was additionally proved by X-ray analysis.     

Neat total synthesis of six monoterpenic alkaloids of the actinidine series

A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[c]pyridine skeleton, (+)-deoxyrhexifoline (4), (+)-boschniakinic acid (5), (+)-boschniakine (6), (−)-plantagonine (7), (−)-indicaine (8) and (−)-tecostidine (9) is reported starting with the chiral precursor 3-bromo-5-((4R)-phenyloxazolin-2-yl)pyridine (10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5-exo-trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3R)- and (3S)-7-((4R)-phenyloxazolin-2-yl)cyclopenta[c]pyridines was separated by HPLC before being transformed into enantiopure natural products (4-9) by modification of the oxazoline group.     

Polymerization of ε-caprolactone using bulky alkoxo-titanium complexes and structural analysis of [Ti(OBorneoxo)2Cl2(thf)2]

A variety of bisalkoxo titanium dichloride THF adducts [Ti(OR)₂Cl₂(thf)₂] {OR = adamantanoxo (9), (1R,2S,5R)-(−)-menthoxo (10), (1S-endo)-(−)-borneoxo (11)} have been prepared and characterized by spectroscopic techniques. The molecular structure of 11 has been determined by single-crystal X-ray diffraction studies. The parent Lewis acid bisalkoxo titanium dichloride derivatives and related alkoxo complexes [Ti(OR)₂(OPrⁱ)₂]₂ have been tested as initiators in ring-opening polymerization of ε-caprolactone and l-lactide.     

Optimisation of a key cross-coupling reaction towards the synthesis of a promising antileishmanial compound

During the course of a research program aimed at identifying novel antileishmanial compounds, a multi-gram synthesis of N-(trans-4-((4-methoxy-3-((R)-3-methylmorpholino)-1H-pyrazolo[3,4-d]pyrimidin-6-yl)amino)cyclohexyl)-2-methylpropane-1-sulfonamide ((R)-1) was required. This letter describes optimisation of the reaction conditions and protecting group strategy for a key Buchwald-Hartwig coupling, delivering the required quantities of (R)-1, as well as further compounds in the series.     

Nucleophilic substitution reactions of acetylides on substituted tricarbonyl(η6-fluoroarene)chromium and reactions of tricarbonyl[η6-(2-trimethylsilylethynyl)toluene]chromium and tricarbonyl[η6-(p-ethynyl-phenylethynyl)benzene]chromium with dicobalt octacarbonyl

Nucleophilic substitution reactions of various acetylides on substituted tricarbonyl(η⁶-fluoroarene)chromiums were pursued. The reaction presumably underwent a more complicated mechanism rather than the direct substitution on the fluorine-bearing carbon. The organometallic compounds (η⁶-C₆H₃R¹R²R³)Cr(CO)₃ (R¹: CC–C₆H₄CH₃, R²: o-Me, R³: H (5a), R¹: CC–C₆H₄CH₃, R²: o-OMe, R³: H (6a), R¹: CC–C₆H₄CH₃, R²: m-OMe, R³: H (6b), R¹: CCPh, R²: o-Me, R³: o-OMe (8b), R¹: CCPh, R²: m-Me, R³: m-OMe (8c), R¹: CCSiMe₃, R²: o-Me, R³: H (9a), R¹: CC–C₆H₄CCH, R²: H, R³: H (12), R¹: CC–C₆H₄CCH, R²: o-Me, R³: H (13)) as well as the organometallic dimmer [{(η⁶-o-Me-C₆H₄)Cr(CO)₃(di-ethynyl)] (di-ethynyl: CC–C₆H₄CC (14)) have been synthesized from nucleophilic substitution reactions of tricarbonyl(η⁶-fluoroarene)(chromium) compounds with suitable acetylides. The products have been characterized by spectroscopic means. In addition, (8b) and (8c) were characterized by X-ray diffraction studies. Further reactions of (9a) and (12) with appropriate amount of Co₂(CO)₈ yielded μ-alkyne bridged bimetallic complexes, Co₂(CO)₆{μ-Me₃SiCC–(o-tolueneCr(CO)₃} (10) and (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–(benzene)Cr(CO)₃)}(15), respectively. Both (10) and (15) were characterized by spectroscopic means as well as single crystal X-ray crystallography. The core of these molecules is quasi-tetrahedron containing a Co₂C₂ unit. A two-dicobalt-fragments coordinated di-enyls complex, (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–H} (17), was synthesized from the reaction of 1,3-diethynylbenzene with Co₂(CO)₈. Crystallographic studies of (17) also show that it exhibits a distorted Co₂C₂ quasi-tetrahedral geometry.