Organic and organometallic derivatives of pentaphenylbenzene, C₆Ph₅X: correlation of peripheral phenyl ring orientations with the steric bulk of “X”

Abstract

A series of C 6 Ph 5 X compounds, including X = H, Br, CO 2 H, CO 2 R, C'CPh, cis-BrC=C(Br)Ph, 2-bornenyl, and ferrocenyl, have been characterized by use of X-ray crystallography. Also, the first organometallic complexes of pentaphenylbenzene have been prepared by reaction with chromium hexacarbonyl to yield ( 6 -C 6 Ph 5 H)Cr(CO) 3 complexes in which the metal tripod is attached either to an ortho peripheral ring or to the central ring. Crystalline pentaphenylbenzoic acid exists as a hydrogenbonded dimer; however, the steric bulk of the substituents does not allow the carboxylic acid moieties to be linked directly but instead via two bridging methanol molecules. In the solid state, the orientation of the peripheral rings in bulky C 6 Ph 5 X systems is very sensitive to the size of the "X" substituents, such that the twist angle of the para ring responds inversely with increasing bulk of "X", which drives the ortho rings farther out of the plane of the central ring. The relevance of these observations to correlated motion in molecular propellers, and ultimately to molecular machines, is discussed.Résumé : À l'aide de la cristallographie aux rayons X, on a caractérisé une série de composés de formule C 6 Ph 5 X, où X = H, Br, CO 2 H, CO 2 R, C'CPh, cis-BrC=C(Br)Ph, 2-bornényl et ferrocényl. En outre, on a préparé les premiers complexes organométal-liques du pentaphénylbenzène en le faisant réagir avec de l'hexacarbonyle de chrome pour obtenir les complexes ( 6 -C 6 Ph 5 H)Cr(CO) 3 dans lesquels le tripode métallique est attaché à un noyau périphérique en ortho ou au noyau central. L'acide pentaphénylbenzoïque existe à l'état de dimère formé par liaisons hydrogènes; toutefois, l'encombrement stérique des substituants ne permet pas la liaison directe des groupements carboxyliques qui sont plutôt reliés par un pont constitué de deux molécules de méthanol. À l'état solide, l'orientation des noyaux périphériques dans les volumineux systèmes C 6 Ph 5 X est très sensible à la taille des substituants « X », de sorte que l'angle de torsion du noyau en para répond inversement à l'encombrement croissant de « X » qui repousse de plus en plus les noyaux en ortho hors du plan du noyau central. Une discussion de l'intérêt de ces observations en ce qui concerne le mouvement corrélé dans les hélices moléculaires, et en bout de ligne les machines moléculaires, est offerte. [Traduit par la Rédaction]

The Pursuit of Perphenylterphenyls

“…[4] This synthesis undoubtedly proceeds via the intermediate alkyne 7, and we would expect to form terphenyl 2 by treating diyne 12 in a similar manner. Unfortunately, our initial attempts to prepare 12 via the Sonogashira coupling of 2,3,5,6tetraphenyl-1,4-dibromobenzene [6] (10) and phenylacetylene failed completely.…”

Diels–Alder Cycloaddition with CO, CO2, SO2, or N2 Extrusion: A Powerful Tool for Material Chemistry

“…Pentaphenylbenzene obtained via DA cycloaddition with CO extrusion and used as a ligand for synthesising the (CO) 3 chromium(0)-η 6 -arene complex ( Scheme 99 ) was described by Brydges and colleagues in 2013 [ 154 ].…”

“… Ph 5 Ph obtained via DA cycloaddition as a ligand in the [Cr(CO) 3 L] complex; L = η 6 –P–(PhPh 4 ) [ 154 ]. Reagents and conditions: a = Ph 2 O, 210 °C; b = next step.…”

Diels-Alder Additions as Mechanistic Probes–Interception of Silyl-Isoindenes: Organometallic Derivatives of Polyphenylated Cycloheptatrienes and Related Seven-Membered Rings

“…In the somewhat less sterically hindered system, pentaphenylbenzene (the Diels-Alder adduct of tetracyclone and phenylacetylene) the reaction with chromium hexacarbonyl yielded two π-bonded Cr(CO) 3 derivatives ( Figure 15 ): the centrally bonded isomer, 33 , and the peripherally complexed molecule, 34 , in which the metal tripod is bonded to the least hindered phenyl adjacent to the ring hydrogen [ 50 ].…”