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The title compound was made by the reaction of the CpCo-complex of 2,3,7,8-tetrakis(trimethylsilyl) linear [3]phenylene, in which the metal coordinates one of the cyclobutadiene rings, with CpCo(C2H4)2. Because of its relative stability, a syn-dicobalt-bound configuration is indicated rather than its anti alternative.

The mechanisms by which the complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages are probed by DFT methods. The outcomes corroborate experimental results and provide energetic and structural details of the trajectories leading to 3-(oxacyclopentyl or cycloalkyl)furans via the intermediacy of isolable CpCo-η 4-dienes. They comprise initial stereoselective complexation of one of the double bonds and the triple bond, rate-determining oxidative coupling to a triplet 16e cobalta-2-cyclopentene, and terminal double bond docking, followed by stereocontrolled insertion to assemble intermediate cis- and trans-fused triplet cobalta-4-cycloheptenes. A common indicator of the energetic facility of the latter is the extent of parallel alignment of the alkene moiety and its target Co–Cα bond. The cobalta-4-cycloheptenes transform further by β-hydride elimination–reductive elimination to furnish CpCo-η 4-dienes, which are sufficiently kinetically protected to allow for their experimental observation. The cascade continues through cobalt-mediated hydride shifts and dissociation of the aromatic furan ring. The findings in silico with respect to the stereo-, regio-, and chemoselectivity are in consonance with those obtained in vitro.

1,7-Octadiyne underwent [2+2+2] cycloaddition to acetone in the presence of η5-cyclopentadienylcobalt(L)(L′) complexes to give (η5-cyclopentadienyl)[(1,4,4a,8a-η4)-5,6,7,8-tetrahydro-3,3-dimethyl-3H-2-benzopyran]cobalt, in which the two triple bonds and the carbonyl moiety have combined to engender a 2H-pyran ring complexed to CpCo. The scope of this reaction was explored, including cocyclizations of ynals and ynones with bis(trimethylsilyl)acetylene, as well as all-intramolecular reorganizations of α,ω-diynals and -diynones. Two major trajectories were observed in the case of aldehydes, the (often minor) [2+2+2] pathway and a competing trail featuring a formal 1,5-hydride shift that results in CpCo–dienones. The latter is obviated for ketone substrates. Preliminary chemistry of selected complexes uncovered unprecedented reactions, such as acid-catalyzed ring openings and additions of amines, the latter providing access to novel carbon frames.

The title compounds, in which the terminal alkyne functions are adorned with -CH2OCH2CH2OCH2CH2OCH2CH3 or -p-C6H4OCH2CH2 OCH2CH2OCH3 substituents, were synthesized. The strategies for their preparation relied on prior art and involved the use of Sonogashira alkynylations of appropriate haloarenes, Stephens–Castro cyclizations of 1,2,4-trialkynyl-3-iodobenzenes, and Hay oxidative couplings of 1,2,3,4-tetralkynylbenzenes. The targets form yellow materials, exhibiting yellow-green fluorescence, and they are very soluble in polar solvents, but only sparingly so in nonpolar media. Attempts to convert them into the antikekulene frame through CpCo(CO)2-catalyzed (co)-cyclizations failed.

The complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages to 3-(oxacyclopentyl or cycloalkyl)furans via the intermediacy of isolable CpCo-η 4-dienes. A suggested mechanism comprises initial complexation of the triple bond and one of the double bonds, then oxidative coupling to a cobalt-2-cyclopentene, terminal double bond insertion to assemble a cobalta-4-cycloheptene, β-hydride elimination, and reductive elimination to furnish a CpCo-η 4-diene. When possible, the cascade continues through cobalt-mediated hydride shifts and dissociation of the aromatic furan ring. The outcome of a deuterium labeling experiment supports this hypothesis. The reaction exhibits variable stereoselectivity with a preference for the trans-product (or, when arrested, its syn-Me CpCo-η 4-diene precursor), but is completely regioselective in cases in which the two alkyne substituents are differentiated electronically by the presence or absence of an embedded oxygen. Regioselectivity is also attained by steric discrimination or blocking one of the two possible β-hydride elimination pathways. When furan formation is obviated by such regiocontrol, the sequence terminates in a stable CpCo-η 4-diene complex. The conversion of the cyclohexane-fused substrate methylidene-2-[5-(2-propenyloxy)-3-pentynyl]cyclohexane into mainly 1-[(1R*,3aS*,7aS*)-7a-methyloctahydroinden-1-yl]-1-ethanone demonstrates the potential utility of the method in complex synthesis.

The fulvalene diiridium platform was scrutinized for its potential to effect double vicinal C–H activation of C6H6 and C6H12, respectively. For this purpose, an improved preparation of Fv[Ir(CO)2]2 was developed, and the syntheses of the new complexes FvIr(CO)2Ir(CO)(η 2-C6F6), Fv[Ir(CO)(η 2-C6F6)]2, Fv[Ir(CH2=CH2)2]2 (X-ray), Fv[Ir(PMe3)(H)2]2 (X-ray), and (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)2]2 were accomplished. When irradiated in C6H6, these molecules succeeded to varying degrees, and best for (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)2]2, in the double metalation of the aromatic ring to engender ligating Ir2(ortho-μ-C6H4)(CO)2 (Ir–Ir) moieties, in addition to their precursor mono(phenyliridium hydride) constructs. A competing photochemical pathway is evident by the formation of diastereomers of Fv (or 2,2’,3,3’-tetra-tert-butylFv) [Ir(CO)(Ph)(H)]2 and the resulting dehydrogenated ligated [Ir(CO)(Ph)]2 (Ir–Ir). The structures of FvIr2(ortho-µ-C6H4)(CO)2 (Ir–Ir) and trans-Fv[Ir(CO)(Ph)]2 (Ir–Ir) were corroborated by X-ray analyses. Efforts to realize C–H bond activations with C6H12 generally failed or fared very poorly, with the exception of the tert-butylFv system, which enabled single, but not further, insertion to give (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)(Cy)(H)][Ir(CO)2] in 34% yield. To explore the relevant chemistry of phenyl- and alkyliridium species attached to Fv, several such derivatives were made by independent routes, adding knowledge to the fundamental behavior of this category of molecules. Where appropriate and for comparative purposes, similar reactions were performed on the corresponding Cp- and 1,2-di-tert-butylCpIr(CO)2 relatives.

Exploratory studies of the CpCo-mediated [2+2+2] cycloaddition of alkynes to the 2,3-double bond of benzo[b]furans (and some benzo[b]thiophenes) are presented, with the general aim to access morphinan substructures. The basic feasibility of constructing Co-complexed tetrahydrophenanthro[4,5-bcd]furans (and -thiophenes) in moderate to good yields is demonstrated, with complete to extensive diastereoselectivity. Limitations are the apparent necessity for bulky (silylated) monoalkynes, the lack of regioselectivity in the cocyclization with unsymmetrical alkynes, and the sensitivity of the ligands, both complexed and uncomplexed, with respect to ring opening and rearrangement.

Understanding the mechanisms involved in the covalent attachment of organic molecules to surfaces is a major challenge for nanotechnology and surface science. On the basis of classical organic chemistry mechanistic considerations, key issues such as selectivity and reactivity of the organic adsorbates could be rationalized and exploited for the design of molecular-scale circuits and devices. Here we use tris(benzocyclobutadieno)triphenylene, a singular Y-shaped hydrocarbon containing antiaromatic cyclobutadienoid rings, as a molecular probe to study the reaction of polycyclic conjugated molecules with atomic scale moieties, dangling-bond (DB) dimers on a hydrogen-passivated Ge(001):H surface. By combining molecular design, synthesis, scanning tunneling microscopy and spectroscopy (STM/STS) and computational modeling, we show that the attachment involves a concerted [4+2] cycloaddition reaction that is completely site-selective and fully reversible. This selectivity, governed by the bond alternation induced by the presence of the cyclobutadienoid rings, allows for the control of the orientation of the molecules with respect to the surface DB-patterning. We also demonstrate that by judicious modification of the electronic levels of the polycyclic benzenoid through substituents, the reaction barrier height can be modified. Finally, we show that after deliberate tip-induced covalent bond cleavage, adsorbed molecules can be used to fine tune the electronic states of the DB dimer. This power to engineer deliberately the bonding configuration and electronic properties opens new perspectives for creating prototypical nanoscale circuitry., This work was supported by the FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (funded by the European Commission under contract no. 610446), by the Polish Ministry for Science and Higher Education from financial resources for science in 2013–2017 granted for an international co-financed project (contract no. 2913/7.PR/2013/2) and by projects CTQ2016-78157-R, MAT2016-78293-C6-3R and MAT2016-78293-C6-4R (AEI/FEDER, UE). EG, DP and DP are grateful for financial support from the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09) and the European Union (European Regional Development Fund-ERDF).

An experimental foray into the potential of oxazoles and thiazoles to enter into CpCo-mediated [2+2+2] cycloadditions is described. α,ω-Diynes failed to engage the heterocycles productively, as illustrated by the behavior of the unique cobaltacyclopentadiene(oxazole) complex 10 , the isolation and X-ray structural determination of which is recorded. Alkyne-tethered systems gave moderate yields to products resulting from [2+2+2] cycloaddition and C–H activation. The azaenol ether bridge in the cycloaddition products appears sensitive to oxidation, elimination, and rearrangement, depending on the system and reaction conditions.

Optimized procedures to [7]heliphene are described that allowed the synthesis of (η6-[7]heliphene)tricarbonylchromium and a preliminary exploration of its chemical behavior. DFT calculations provide structural and energetic information on this complex and its haptomeric isomers. Attempts to prepare the corresponding ([7]heliphene)chromium sandwich failed so far, but DFT evidence is presented to indicate that the target should be accessible.

A study of the scope and limitations of varying the ligand framework around the dinuclear core of FvRu(2) in its function as a molecular solar thermal energy storage framework is presented. It includes DFT calculations probing the effect of substituents, other metals, and CO exchange for other ligands on Delta H-storage. Experimentally, the system is shown to be robust in as much as it tolerates a number of variations, except for the identity of the metal and certain substitution patterns. Failures include 1,1',3,3'-tetra-tert-butyl (4), 1,2,2',3'-tetraphenyl (9), diiron (28), diosmium (24), mixed iron-ruthenium (27), dimolybdenum (29), and di-tungsten (30) derivatives. An extensive screen of potential catalysts for the thermal reversal identified AgNO3-SiO2 as a good candidate, although catalyst decomposition remains a challenge.

Forty-five years after their first preparation, nitroalkynes retain interest for their unique chemical behavior and their potential as energetic materials. This review encompasses the physical and spectral properties, synthesis, reactivity, metal complexes, and theoretical studies of nitroalkynes not previously reviewed, and those prepared after 1973. 1 Introduction 2 Physical Properties of Nitroalkynes 3 Spectral Properties of Nitroalkynes 4 Syntheses of Nitroalkynes 4.1 Unsuccessful Attempts 4.1.1 Nitration 4.1.2 Elimination 4.1.3 Retrocycloaddition 4.2 Successful Strategies 4.2.1 Nitration 4.2.2 Elimination 4.2.3 Nucleophilic Displacement 4.2.4 From Triazoles 4.3 Attempts at the Synthesis of Dinitroacetylene 5 Reactions of Nitroalkynes 5.1 Thermal Decomposition 5.2 Nucleophilic Addition 5.3 Cycloaddition 6 Metal Complexes 7 Theoretical Studies 8 Conclusion

Ni(COD)(PMe3)2 catalyzes the cycloaddition of diphenylacetylene to the four-membered rings of linear [3]phenylene and its 2,3,7,8-tetrakis(trimethylsilyl) derivative. The reaction proceeds via initial formation of the 5,6-diphenylbenzo[3,4]cyclobuta[1,2-b]phenanthrene frame, followed by a competitive second, nonregio­selective alkyne insertion to furnish the corresponding phenyl-­substituted benzo[k]- and -[m]tetraphenes.

The use of opto-thermal molecular energy storage at the nanoscale creates new opportunities for powering future microdevices with flexible synthetic tailorability. Practical application of these molecular materials, however, requires a deeper microscopic understanding of how their behavior is altered by the presence of different types of substrates. Here we present single-molecule resolved scanning tunneling microscopy imaging of thermally- and optically-induced structural transitions in (fulvalene)tetracarbonyldiruthenium molecules adsorbed onto a Ag(100) surface as a prototype system. Both the parent complex and the photoisomer display distinct thermally-driven phase transformations when they are in contact with a Ag(100) surface. This behavior is consistent with the loss of carbonyl ligands due to strong molecule-surface coupling. Ultraviolet radiation induces marked structural changes only in the intact parent complex, thus indicating a photoisomerization reaction. These results demonstrate how stimuli-induced structural transitions in this class of molecule depend on the nature of the underlying substrate., Comment: 4 figures

Caught in the light: The fulvalene diruthenium complex shown on the left side of the picture captures sun light, causing initial Ru-Ru bond rupture to furnish a long-lived triplet biradical of syn configuration. This species requires thermal activation to reach a crossing point (middle) into the singlet manifold on route to its thermal storage isomer on the right through the anti biradical.

Dinitroacetylene and other nitroacetylenes are attractive stoichiometric precursors to high energy-density materials, but suffer from high reactivity and thermal instability. Herein, we report that nitroacetylenes can be dramatically stabilized in the form of their dicobalt hexacarbonyl complexes. In particular, we describe the syntheses and characterization of the first two transition-metal complexes of nitroalkynes, [μ-1-nitro-2-(trimethylsilyl)ethyne-1,2-diyl]bis(tricarbonylcobalt)(Co-Co) and [μ-1-nitroethyne-1,2-diyl]bis(tricarbonylcobalt)(Co-Co). The chemistry of these compounds reveals their potential as reaction partners in [2+2+2] cyclotrimerizations, furnishing nitroindane, nitrotetralin, and trinitrobenzene products. The X-ray crystal structure of 1,3,5-trinitro-2,4,6-tris(trimethylsilyl)benzene presents a distorted, yet planar, aromatic ring.

This review discusses from a qualitative viewpoint three-dimensional structures (hydrocarbons and carbon allo- tropes) that can be obtained from the 4,6,12-archimedean tiling of the Euclidean plane (graphenylene net) or that are re- lated to subgraphs derived from the graphenylene net, insisting on helical structures called (n)heliphenes with alternating 4- and 6-membered conjugated rings. Analogies with benzenoid (n)helicenes allow proposals for non-planar heliphene- related structures that have yet to be explored.

Oligoaryls were prepared through transition-metal-catalyzed [2+2+2] cycloadditions of borylated alkynes, followed by Suzuki cross-couplings with aryl halides. Ethynylboryl pinacolate took part in cobalt-catalyzed [2+2+2] cycloadditions of all types investigated (i.e., all-intermolecular cyclotrimerization, diyne-yne cocyclization, and all-intramolecular triyne cycloisomerization). The resulting platforms gave rise to linear and angular ter- and quateraryls after Pd-catalyzed cross-coupling. In addition, the first [2+2+2] cycloadditions involving alkynyl naphthaloboramides were developed. These derivatives could be cocyclized with diynes in the presence of a rhodium complex as catalyst. Because the boramide group is inactive under Suzuki coupling conditions, but can be readily deprotected to afford an active one, an iterative functionalization of a boronate-/boramide-substituted benzene could be achieved.

Radial (tetracyclopentadienyl)cyclobutadiene pentametals have been synthesized by the Pd-catalyzed coupling of cyclopentadienyltin or of (CpM)zinc reagents with (tetraiodocyclobutadiene)iron(tricabonyl). X-ray structural and NMR data reveal that, while these arrays are crowded, the substituents enjoy considerable rotational freedom. The method constitutes a significant complement to currently existing strategies for the construction of persubstituted cyclobutadiene complexes.

CpCo(CO) 2 catalyzes the cocyclization of ortho-diethynylthiophenes and -pyridines with alkynes to construct the corresponding thia- and azaphenylenes. This strategy is applied to the synthesis of linear 1-aza[3]phenylene, the first higher heterophenylene.

In the currently intensifying quest to harness solar energy for the powering of our planet, most efforts are centered around photoinduced generic charge separation, such as in photovoltaics, water splitting, other small molecule activation, and biologically inspired photosynthetic systems. In contrast, direct collection of heat from sunlight has received much less diversified attention, its bulk devoted to the development of concentrating solar thermal power plants, in which mirrors are used to focus the sun beam on an appropriate heat transfer material. An attractive alternative strategy would be to trap solar energy in the form of chemical bonds, ideally through the photoconversion of a suitable molecule to a higher energy isomer, which, in turn, would release the stored energy by thermal reversal. Such a system would encompass the essential elements of a rechargeable heat battery, with its inherent advantages of storage, transportability, and use on demand. The underlying concept has been explored extensively with organic molecules (such as the norbornadiene-quadricyclane cycle), often in the context of developing photoswitches. On the other hand, organometallic complexes have remained relatively obscure in this capacity, despite a number of advantages, including expanded structural tunability and generally favorable electronic absorption regimes. A highly promising organometallic system is the previously reported, robust photo-thermal fulvalene (Fv) diruthenium couple 1 {l_reversible} 2 (Scheme 1). However, although reversible and moderately efficient, lack of a full, detailed atom-scale understanding of its key conversion and storage mechanisms have limited our ability to improve on its performance or identify optimal variants, such as substituents on the Fv, ligands other than CO, and alternative metals. Here we present a theoretical investigation, in conjunction with corroborating experiments, of the mechanism for the heat releasing step of 2 {yields} 1 and its Fe (4) and Os (6) relatives. The results of the combined study has enabled a rigorous interpretation of earlier and new experimental measurements and paint a surprising picture. First-principles calculations were employed based on spin unrestricted density functional theory (DFT) with a non-empirical gradient corrected exchange-correlation functional. Ultrasoft pseudopotentials were used to describe the valence-core interactions of electrons, including scalar relativistic effects of the core. Wavefunctions and charge densities were expanded in plane waves with kinetic energies up to 25 and 200 Rydberg, respectively. Reaction pathways were delineated with the string method, as implemented within the Car-Parrinello approach. This method allows for the efficient determination of the minimum energy path (MEP) of atomistic transitions and thus also saddle points (transition states, TSs), which are the energy maxima along the MEP. All geometries were optimized until all forces on the atoms were less than 0.02 eV/{angstrom}. The calculated structures of 1 and 2 were in good agreement with their experimental counterparts.

The generality of the [CpCoL 2 ]-mediated [2+2+2] cycloaddition of α,ω-diynes to (cyclo)alkenes has been extended to include linear oligocycles as models for the one-step, A + D → ABCD construction of optically pure, novel 6,10-dihydroanthracyclinones.

The complex [CpCo(C2H4)2] facilitates the [2+2+2] cycloaddn. of borylalkynes to N-(4-pentynoyl)indole and -pyrrole to furnish heterocyclofused borylcyclohexadienes regioselectively.

Experimentally, tri-trans-[12]annulene and tris(cyclohexeno)[12]annulene exhibit differing reactivities. Whereas the former, after isomerizing to its di-trans isomer, undergoes sequential electrocyclizations, the latter follows a Diels-Alder pathway after initial electrocyclization. B3PW91/6-31+G*//B3LYP/6-31G* calculations indicate that cyclohexenofusion simultaneously hinders the second electrocyclization and facilitates Diels-Alder reaction, primarily by inducing greater puckering in the intermediate eight-membered ring.

To understand some experimental data at odds with the computed mechanism of the CpCo(L2)-catalyzed [2 + 2 + 2] cyclotrimerization of ethyne, DFT computations were carried out following the fate of methyl- and hydroxycarbonyl-substituted alkynes to give the corresponding arenes. The key intermediate in all cases is a triplet cobaltacyclopentadiene obtained by oxidative coupling of the corresponding CpCo(bisalkyne) complex and subsequent spin change via a minimum energy crossing point (MECP). From that species, two different catalytic cycles lead to an arene product, depending on the nature of the alkyne and other ligands present: either alkyne ligation to furnish a cobaltacyclopentadiene(alkyne) intermediate or trapping by a sigma-donor ligand to generate a coordinatively saturated cobaltacyclopentadiene(PR3) complex. The former leads to the CpCo-complexed arene product via intramolecular cobalt-assisted [4 + 2] cycloaddition, whereas the latter may, in the case of a reactive dienophile (butynedioic acid), undergo direct intermolecular [4 + 2] cycloaddition to generate a cobaltanorbornene. The bridgehead cobalt atom is then reductively eliminated after another change in spin state from singlet to triplet. The necessary conditions for one or the other mechanistic pathway are elaborated.

An approach to the synthesis of bent phenylenes is described, which features 1,2,3,4-tetraethynylbenzene as starting material. Application of this synthon in CpCo-catalyzed alkyne cocyclizations allows the total synthesis of bent [5]phenylene, the seventh isomer of the family of twelve [5]phenylenes to be isolated.

Diborylated compounds are obtained by means of CpCo-mediated cocyclization of alkynyl(pinacol)boronic esters to alkenes followed by oxidative demetalation (see scheme). This strategy for the rapid and efficient construction of highly functionalized 1,3-cyclohexadienes and arenes is compatible with various substrates.

2,2',3,3'-Tetramethylfulvalene (4) and 2,2',3,3'-tetra-tert-butylfulvalene (7) were synthesized by two different routes. The potential of these systems to function as ligands to transition metals was explored with the more readily made 7, resulting in the preparation of the dinuclear complexes (η 5 :η 5 -t-Bu 4 C 1 0 H 4 )M 2 (CO) 4 (M = Fe, Ru, Os, 8-10) and (η 5 :η 5 -t-Bu 4 C 1 0 H 4 )Mo 2 (CO) 6 (11). The molecular structures of complexes 8 and 10 were determined by X-ray diffraction. Complexes 9 and 10 rearranged on irradiation to their (μ 2 -η 1 :η 5 -cyclopentadienyl) 2 M 2 (CO) 4 isomers 12 and 13, respectively, thermally reversible for 12, while 8 was photoinert.

[structure: see text] The parent and dipropyl-substituted anti (1a,b) and syn doublebent (2a,b) [5]phenylenes have been assembled by CpCo-catalyzed double cyclization of regiospecifically constructed appropriate hexaynes. (1)H NMR, NICS, and an X-ray structural analysis of 1a reflect the aromatizing effect of double angular fusion on the central ring of the linear [3]phenylene substructure.

Under CO atmosphere, between 80 and 120 C, a glyme solution of PtCl{sub 4} forms a carbonyl compound that promotes hydration of internal as well as terminal alkynes to give aldehyde-free ketones. The catalytic process depends strongly on the electronic and steric nature of the substrates. Part of the carbonyl functions of the catalyst can be replaced by phosphine ligands. Chiral DIOP reacts with the PtCl{sub 4}-CO compound to give a catalyst that promotes partial kinetic resolution of a racemic alkyne. Replacement of part of the CO by polystyrene-bound diphenylphosphine enables to attach the catalyst to the polymeric support. Upon entrapment of the platinum compound in a silica sol-gel matrix, it reacts as a partially recyclable catalyst. A reformulated mechanism for the PdCl{sub 4}-CO catalyzed hydration is suggested on the basis of the present study.

Reaction of FvW2(H)2(CO)6 with 2/8S8 in THF results in rapid and quantitative formation of FvW2(SH)2(CO)6. The crystal structure of this complex is reported and shows that the two tungsten−hydrosul...

Irradiation (λmax = 300−375 nm) of FvRu2(CO)4 (1, Fv = η5:η5-bicyclopentadienyl) or (μ2-η1:η5-cyclopentadienyl)2Ru2(CO)4 (2) with dimethyl cis- or trans-butenedioate resulted in FvRu2(η2-trans-CHRCHR)(CO)3 (3, R = CO2CH3). Prolonged irradiation of 1−3 provided FvRu2(η2-trans-CHRCHR)2(CO)2 (4a, R = CO2CH3) and FvRu2(η2-cis-CHRCHR)(η2-trans-CHRCHR)(CO)2 (4b, R = CO2CH3). Photocatalytic isomerization of cis to trans alkene occurred in the presence of 1−4. Irradiation of 1−3 with dimethyl butynedioate produced FvRu2(μ2-η2-dimethyl butynedioate)(CO)3 (5). Prolonged irradiation of 1−5 with the alkyne afforded FvRu2(μ2-η2:η4-CRCRCRCR)2(CO) (6, R = CO2CH3). Irradiation of a THF solution of 6 generated FvRu2(μ2-η2:η4-CRCRCRCR)2(THF) (7, R = CO2CH3). Photochemical alkyne cyclotrimerization was observed in the presence of 1−7. In the presence of CO, 7 reverted to 6 thermally. Heating 7 in the presence of dimethyl cis-butenedioate, thiophene, PPh3, or dimethyl sulfoxide (DMSO) afforded FvRu2(μ2-η2:η4-CRCRCRCR)2(L) (8...

An application of alkyne metathesis to 1,2-di(prop-1-ynyl)arenes, producing dehydrobenzannulenes, is described. An efficient method for selective Sonogashira couplings of bromoiodoarenes under conditions of microwave irradiation is also reported.

The X-ray structure of the parent linear [3]phenylene (benzo[3,4]cyclobuta[1,2-b]biphenylene) has been obtained and is compared with those of its angular isomer and model compounds. The terminal rings reveal a relatively large degree of bond alternation while the center distorts to a cyclic bisallyl frame.

Five synthetic approaches to racemic strychnine (1), with the cobalt-mediated [2 + 2 + 2] cycloaddition of alkynes to indoles as the key step, are described. These include the generation and attempted cyclization of macrocycle 8 and the synthesis of dihydrocarbazoles 15, 22, and 26 and their elaboration to pentacyclic structures via a conjugate addition, dipolar cycloaddition, and propellane-to-spirofused skeletal rearrangement, respectively. Finally, the successful total synthesis of 1 is discussed. The development of a short, highly convergent route (14 steps in the longest linear sequence) is highlighted by the cyclization of enynoylindole 40 with acetylene and the formal intramolecular 1,8-conjugate addition of amine 49 to form pentacycle 50. Numerous attempts toward the formation of the piperidine ring of 1 from vinyl iodide 56 were made and its successful formation via palladium-, nickel-, and radical-mediated processes is described.

Flash vacuum pyrolysis (FVP) of linear [3]phenylene affords its angular counterpart and the same mixture of polycyclic aromatic hydrocarbon isomers as that observed on FVP of angular [3]phenylene. A mechanism, supported by a 13C labeling study, is proposed to explain these results.

(Fulvalene)hexacarbonyldirhenium (1) furnishes the first silylene fulvalenedimetal complex 3 by double Si−H activation. The solid-state structure of the molecule was determined by X-ray analysis and its solution dynamics by 1H NMR spectroscopy.

The unusual solid-state nonplanarity seen in the X-ray structures of the [N]phenylenes (an example is shown here) is shown to be most likely the result of crystal-packing-induced deformations. These conclusions are based on a study of published and eight new structure determinations, comparison with data on napththalenes and anthracenes obtained from the Cambridge Structural Database, and ab initio calculations.

In Ubereinstimmung mit der Theorie weisen die Titelverbindungen 1 und 2 – durch CpCo-katalysierte Cycloisomerisierung geeigneter Oligoalkinylbenzole hergestellt – bezuglich ihrer physikalischen Eigenschaften grose Ahnlichkeiten mit den jeweiligen gewinkelten Topomeren auf. Sie unterscheiden sich dagegen stark von den entsprechenden linearen Isomeren.

The title compound [Cp 5 CpMn(CO) 3 ], 1 , has been characterized by X-ray crystallography and shown by laser-induced desorption/ionization (LDI) to undergo dissociative coalescence to fullerene C 60 and other carbon clusters.

The experimental 1H NMR chemical shift values of six benzocyclynes (benzodehydroannulenes) have been assigned and, in combination with nucleus-independent chemical shift (NICS) calculations, shown to indicate diatropic behavior for 4n+2, paratropic behavior for 4n π systems.