Cruciaromaticity in organometallic compounds

Dewar, Michael J. S.; Healy, Eamonn F.; Ruiz, Jaimé

doi:10.1351/pac198658010067

Cited by 9 publications

(1 citation statement)

References 3 publications

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“…Since the original work of Woodward and Hoffmann, describing suprafacial or antarafacial orbital overlap in concerted reactions, only three additional orbital topologies have been proposed: pseudopericyclic, cruciaromatic, and coarctate. , In Herges' seminal paper, the formal definition of a coarctate reaction was one “that proceeds by breaking and making two bonds at one or more atoms at a time.” The term “coarctate” is derived from the Latin “to compress”, and his operational topological definition is that such reactions can be analyzed as a “compressed” loop of interacting orbitals. It is this topological definition that will be assumed in the discussions below.…”

Section: Introductionmentioning

confidence: 99%

Electrocyclic Ring Openings of 2-Furylcarbene and Related Carbenes: A Comparison between Pseudopericyclic and Coarctate Reactions

Birney

2000

J. Am. Chem. Soc.

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Ring openings of 2-furylcarbene (5a), 2-pyrrolylcarbene (5b), 1-cyclopenta-1,3-dienylcarbene (5c), and of 11, as well as of the 3-and five-membered ring vinylogs (7a, 7c, 9a, 9c) were investigated at the B3LYP/6-31G(d,p) level of theory. The reactions of 5a, 5c, and 11 were also studied at the G2(MP2) level. This work provides the first comparison of pseudopericyclic and coarctate orbital topologies in concerted reactions. The ring openings of 5a, 5b, 11 and their vinylogs have pseudopericyclic (but not coarctate) topologies, while the ring openings of 5c and vinylogs are pericyclic and can be described as coarctate. The transition structure geometry for the ring opening of 5c is not well described by MP2 theory. The G2(MP2) barrier for this ring opening is estimated to be 6.4 kcal/mol, significantly higher than that calculated by Sun and Wong. The ring opening is an eight-electron, Mo ¨bius, conrotatory process, not the six-electron, Huckel process described by Herges in his original work describing coarctate orbital topology. The vinylogous reactions of 7c and 9c are disrotatory. The triplet photochemistry of 3a and 3b, as studied by Nakatani et al., was modeled by 6a and 12, respectively. The difference between the two is attributed to the greater stability of the triplet carbene 3 11 as compared to 3 syn-5.

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Section: Introductionmentioning

confidence: 99%

Electrocyclic Ring Openings of 2-Furylcarbene and Related Carbenes: A Comparison between Pseudopericyclic and Coarctate Reactions

Birney

2000

J. Am. Chem. Soc.

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Die Porphyrin‐Homologen: [22]Porphyrin (2.2.2.2), ein „gestrecktes Porphycen”︁

et al. 1990

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Atome von der mittleren Ringebene: 0.07 A). Aus der Symmetrie folgt, dab die einander gegeniiberliegenden C,,2C,,C,,C,p,-Struktureinheiten aquivalent sind und somit 12 als Resonanzhybrid zu formulieren ist. Was die geometrischen Parameter der genannten c,-Einheiten betrifft, so besteht sowohl hinsichtlich der Bindungswinkel an den sp-hybridisierten Kohlenstoffatomen (178.8 und 177.1") als auch in Bezug auf die Langen von C,,,C,,-und C,,C,-Bindungen (1.385 und 1.387 8, bzw. 1.21 7 A) vorziigliche Ubereinstimmung rnit den Verhaltnissen in 1 sowie in 3,9,12,18-Tetratert-butyl-tetradehydro[18]ann~len['~! Im Grunde kann der Makrocyclus 12 als ein ,,gestrecktes Porphycen" betrachtet werden. Anders als bei 2 sind bei 12 die NH-Wasserstoffatome nicht fehlgeordnet, so dab eine Zuordnung zu bestimmten Stickstoffatomen (symmetriebedingt zu N-Atomen in diagonaler Position) moglich ist. Der Hohlraum in 12 weist mit NlN2'-und NlN2-Abstanden von 2.62 bzw. 5.39 A eine fur Metallkomplexbildung sehr ungiinstige Abmessung auf, doch erscheint denkbar, daD die C,,C,,-Bindungen fur manche Metall-Ionen koordinationsfordernd sind. 15 Die bei der reduktiven Kupplung von 10 zu 12 in geringen Anteilen auftretenden Nebenprodukte wurden als die acetylenische Dihydroverbindung 14 und die Tetrahydroverbindung 15 erkannt. Bei 15 handelt es sich um das erste [22]Porphyrin(2.2.2.2), das in der direkt folgenden Zuschrift beschrieben wird [I6]. Arbeitsvorschrifr 12: 650 mg (10 mmol) aktiviertes Zink und 65 mg (0.7 mmol) wasserfreies Kupfer(1)-chlorid werden in 40 mL absolutem Tetrahydrofuran (THF) suspendiert und langsam rnit 0.54 mL (5 mmol) Titantetrachlorid versetzt. Die Mischung wird 3 h unter RuckfluB erhitzt, ehe man in kleinen Portionen 162 mg (0.5 mmol) Dialdehyd 10 eintragt. Nach 10 min weiterem Erhitzen wird rnit 40 mL Ammoniakwasser hydrolysiert und das Gemisch rnit Chloroform extrahiert. Chromatographie an Silicagel mit Kohlenstoffdisulfid und anschlieBende Umkristallisation aus Benzol liefern 26 mg (28%) 12 in blauen. metallisch glanzenden Nadeln (Zers. oberhalb 300 'C), Als Nebenprodukte isoliert man bis zu 5 % partiell hydrierte Verbindungen. Eingegangen am 13. Dezember 1989 [Z 36851 Auf Wunsch der Autoren erst jetzt veroffentlicht.

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Porphyrin Homologues: [22]Porphyrin(2.2.2.2), a “Stretched Porphycene”

Vogel

Jux

Rodriguez‐Val

et al. 1990

Angew. Chem. Int. Ed. Engl.

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tically planar ring framework (maximal distance of the C and N atoms from the mean ring plane: 0.07 A). As indicated by the symmetry, the C,,,C,,C,,C,,, structural units on opposite sides are equivalent; 12 should therefore be formulated as a resonance hybrid. The geometric parameters of these C, units are in excellent agreement with those in 1 and in 3,9,12,18-tetra-tert-butyltetradehydro[ 18lannulene[2b1 with respect to the bond angles at the sp-hybridized carbons (178.8 and 177.1") and the lengths of the CSp2C,, and C,,C,, bonds (1.385/1.387 A and 1.217 A, respectively).Basically, the macrocycle 12 may be viewed as a "stretched" porphycene. The N H hydrogens in 12, unlike those in 2, are not disordered, so that assignment to specific nitrogens (which must be N atoms in diagonal positions owing to symmetry) is possible. The cavity of 12 exhibits NlN2' and N1N2 distances of 2.62 and 5.39 A, respectively, and therefore has very unfavorable dimensions for complexation of metals. Conceivably, however, the C,,C,, bonds might assist coordination with suitable metal ions. The small amounts of byproducts formed on reductive coupling of 10 to give 12 were identified as the acetylenic dihydro compound 14 and the tetrahydro compound 15. Compound 15, described in the following communication,[l6I represents the first [22]porphyrin(2.2.2.2). 14 15Experimental Procedure 12: Activated zinc (650 mg. 10 mmol) and anhydrous copper(1)chloride (65 mg, 0.7 mmol) were suspended in 40 mL of absolute tetrahydrofuran (THF) and treated slowly with titanium tetrachloride (0.54 mL, 5 mmol). The mixture was refluxed for 3 h before dialdehyde 10 (162 mg, 0.5 mmol) was added in Small portions. After 10 min of further heating, 40 mL of aqueous ammonia was added in order to hydrolyze the reaction mixture, which was then extracted with chloroform. Chromatography on silica gel with carbon disulfide and subsequent recrystdlization from benzene afforded 26 mg (18 %) of 12 as blue needles with a metallic luster (dec. above 300°C). Compounds 14 and IS were isolated as minor products in up to 5 % combined yield.

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Cruciaromaticity in organometallic compounds

Cited by 9 publications

References 3 publications

Electrocyclic Ring Openings of 2-Furylcarbene and Related Carbenes: A Comparison between Pseudopericyclic and Coarctate Reactions

Electrocyclic Ring Openings of 2-Furylcarbene and Related Carbenes: A Comparison between Pseudopericyclic and Coarctate Reactions

Die Porphyrin‐Homologen: [22]Porphyrin (2.2.2.2), ein „gestrecktes Porphycen”︁

Porphyrin Homologues: [22]Porphyrin(2.2.2.2), a “Stretched Porphycene”

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