The synthesis of hexacyclopropylbenzene via cyclotrimerization of dicyclopropylacetylene by Fe3(CO)12

Three-Membered-Ring-Based Molecular Architectures

“…457 For comparison, in 1,2-diisopropyl-3,4,5,6-tetracyclopropylbenzene, which was prepared by cotrimerization of diisopropylacetylene and dicyclopropylacetylene (565) under catalysis with Hg[Co-(CO) 4 ] 2 , the four cyclopropyl groups adopt the same conformation with C ar -C ar -C cycl -H torsional angles close to 90°, whereas the two isopropyl groups maintain a bisected orientation. 458 Upon careful reinvestigation of the thermal reaction of 565 with Fe 3 (CO) 12 under almost the same conditions as previously reported 456 (4 h of heating), the known 455 tetracyclopropyl-p-benzoquinone (650) (3%) and the previously unknown tricarbonyl(tetracyclopropylcyclobutadiene)iron (651-H) (1%), along with the previously described products 648 (48%) and 649 (18%), were isolated (Scheme 113). 459 Under the same conditions, the reaction of bis(1-methylcyclopropyl)ethyne (621) with Fe 3 (CO) 12 yielded neither any of the peralkylated cyclopentadienone complex nor the corresponding benzene or benzoquinone derivatives.…”

“…455 The latter was prepared directly from 565 by heating with Fe 3 (CO) 12 at 180°C in 30% yield along with hexacyclopropylbenzene (649) (20% yield). 456 In the crystal, 649 disclosed an unusual conformation of D 3d symmetry in which the cyclopropyl substituents are alternatingly oriented up and down with respect to the central six-membered ring (Scheme 113); thus no conjugative interaction between the six cyclopropyl groups and the π-system of the aromatic ring is possible. 457 For comparison, in 1,2-diisopropyl-3,4,5,6-tetracyclopropylbenzene, which was prepared by cotrimerization of diisopropylacetylene and dicyclopropylacetylene (565) under catalysis with Hg[Co-(CO) 4 ] 2 , the four cyclopropyl groups adopt the same conformation with C ar -C ar -C cycl -H torsional angles close to 90°, whereas the two isopropyl groups maintain a bisected orientation.…”

“…Heating of 647 in toluene furnished tricarbonyl(tetracyclopropylcyclopentadienone)iron ( 648 ) in 45% yield . The latter was prepared directly from 565 by heating with Fe 3 (CO) 12 at 180 °C in 30% yield along with hexacyclopropylbenzene ( 649 ) (20% yield) . In the crystal, 649 disclosed an unusual conformation of D 3 d symmetry in which the cyclopropyl substituents are alternatingly oriented up and down with respect to the central six-membered ring (Scheme ); thus no conjugative interaction between the six cyclopropyl groups and the π-system of the aromatic ring is possible .…”

Syntheses, Structures and Electronic Properties of Cationic Hydroxy‐ and Methoxy‐Substituted Tricarbonyl(tetracyclopropylcyclopentadienyl)iron Complexes

“…most efficient access to oligosubstituted oligounsaturated conjugated cyclic compounds. The reaction of neat dicyclopropylacetylene (1) [2] with dodecacarbonyltriiron in a sealed tube gave a mixture of products from which, after flash chromatography on silica gel, on top of the previously described hexacyclopropylbenzene (2), [3] and tricarbonyl(tetracyclopropylcyclopentadienone)iron (3), [3] tetracyclopropyl-p-benzoquinone (4) [4] and tricarbonyl(tetracyclopropylcyclobutadiene)iron (5) [5] were isolated in 3 and 1 % yield, respectively (Scheme 1). Scheme 1. Uncomplexed cyclopentadienones are very reactive compounds, which are prone to immediately undergo [4+2] or [2+2] cyclodimerization [6] unless sufficiently sterically demanding substituents prevent it.…”

“…In the latter, the bond order of this C,O bond apparently is between that of a single and a double bond, indicating that a considerable fraction of the positive charge remains on the oxygen atom, like in protonated dicyclopropyl ketone 13, in which the C,O bond length is 129.0 pm indicating an even higher double bond character than in 11 and 12. [15] The five-membered ring in 3 is not planar with the ring carbonyl group being bent away from the Fe(CO) 3 tively, and the distance between the iron and the carbonyl carbon atom to shorten from 238.8 to 219.7 and 219.4 pm, respectively. With the other four iron to carbon distances remaining virtually the same, the coordination hapticity of the iron atom changes from η 4 to almost η 5 .…”