Site Selectivity of [RuCp*]⁺ Complexation in Cyclopenta[def]triphenylenes

Abstract

A series of new cyclopenta-fused triphenylenes has been synthesized in high yield and reacted with [Ru(μ 3 -Cl)Cp*] 4 to form [RuCp*(η 6 -arene)]PF 6 complexes. Systematic variation of the cyclopenta[def ]triphenylene allowed the site of complexation to be probed and the influence of the electronic and steric properties of the substituents in directing complexation to be assessed. As determined by NMR spectroscopy and X-ray crystallography, in all cases the [RuCp*] + fragment complexes at a peripheral arene ring, rather than at the central arene ring or as a neutral η 5 -cyclopentadienyl metallocene adduct. It was shown that electronic influences are minimal, while steric effects afford selective complexations. The electronic properties of the ligands and complexes were probed with electrochemistry, along with electronic absorption and emission spectroscopies. ■ INTRODUCTIONCyclopentadienyl (Cp, η 5 -C 5 H 5 ) and pentamethylcyclopentadienyl (Cp*, η 5 -C 5 Me 5 ) ruthenium complexes with arene ligands have been extensively studied, forming η 6 -sandwich complexes of the type [RuCp(η 6 -arene)] + and [RuCp*(η 6 -arene)] + that are generally stable under atmospheric conditions. 1−7 The [RuCp*] + fragment is known to strongly interact with aromatic hydrocarbons with a high tolerance to functional groups. 3 The resulting ruthenium sandwich complexes have been studied for their interesting electrochemical and spectroscopic properties, as well as their catalytic activity. 8,9 The most popular synthetic route toward simple [RuCp*(η 6 -arene)] + complexes involves the formation of a [RuCp*-(CH 3 CN) 3 ] + complex, which is reacted with the appropriate arene ligand with heating or UV irradiation. 2,5,10 These methods are generally useful and robust; however, the need for toxic or expensive Sn and Ag reagents leaves room for improvement. In 2007 Fairchild et al. 5 proposed a slightly altered route to these target [RuCp*(η 6 -arene)] + complexes that involves the direct reaction of [Ru(μ 3 -Cl)Cp*] 4 , a precursor in previous pathways, with the arene and the aid of microwave irradiation. The water-soluble chloride salt of the resultant complex was obtained after short reaction times in high yields, and the reaction was shown to be reliable for a wide range of arene ligands. However, the arene ligands studied were mostly single ring benzene derivatives, naphthalene and quinoline being the exceptions, with the [RuCp*] + forced to bind to the only arene ring present.Site selectivity for complexation of [RuCp*] + to substituted polyaromatic systems has been little studied. Previous work 1,6,11,12 gives some precious insight into the affinity of the [RuCp*] + fragment for a range of mostly monosubstituted simple arene systems. Larger polycyclic aromatic hydrocarbon (PAH) ligands that complex [RuCp*] + have all been unsubstituted. 13,14 To the best of our knowledge, no reports to date describe the site selectivity of [RuCp*] + for PAHs with a range of substitution patterns and types. Furthermore, the presence of a peripheral cyc...

Synthesis of Cyclopenta‐HBCs and their Regioselective Chlorination During Oxidative Cyclodehydrogenation

“…[18] However,t he in-plane geometricalp arameters in the region adjacent to the cyclopentaring are distorted:a nalysis of 2c shows that the peripheral bondsa re mostly elongated and the internal bonds shortened. Similarly,b ond angles involvingt he benzenoid rings of 2c are also distorted in this region when compared to HBC(tBu) 6 ,b ecomingl ess so toward the centre of the core. Both 10 b and 2c crystallise as offset dimer pairs.…”

“…Additionally, the benzylic methylene carbon offers a new reactive site, allowing for further modification, such as the formation of cyclopentadienyl‐type ligands able to form metallocenes, of importance as Ziegler–Natta catalysts, or for tuning of the electronic/supramolecular properties, such as the modification of polyfluorenes to yield more photochemically stable polymers . Our group has reported the synthesis of cyclopentatriphenylene, and as an expansion of this, our sights were set on annulation to the larger PAH, hexa‐ peri ‐hexabenzocoronene (HBC), an extensively studied, well‐defined ‘nanographene“ which participates in robust π‐stacking interactions leading to long‐range order as applied in organic electronics . Although a cyclopentadiene bis‐ ortho ‐annulated by two HBCs with the trivial name ”superfluorene“ has been reported, we endeavoured to ”bridge“ a bay region with a methylene group to give a cyclopenta‐HBC (CpHBC, 2 a , Figure ) as a step toward systematically modulating the structure and reactivity of the HBC core.…”

“…The incorporation of ac yclopenta-ring at the periphery of HBC is expected to distort the geometry of the aromatic core. The X-ray crystal structures of 10 b and 2c (Figure 2a nd SI) reveal that, although the core shows ad eviation from planarity,t he curvature is no greater than that seen for other all-benzenoid HBCs, such as HBC(tBu) 6 . [18] However,t he in-plane geometricalp arameters in the region adjacent to the cyclopentaring are distorted:a nalysis of 2c shows that the peripheral bondsa re mostly elongated and the internal bonds shortened.…”

Regioselective Coordination toward Silver(I) Ions by Bis- and Tris(Tetra-Armed Cyclen)s via Differential Electron Density of Aromatic Side Arms

“…Regioselectivity plays an important role in many areas of organic chemistry, including synthesizing pharmaceuticals and elucidating their mechanisms of action. − In other words, regioselectivity in organic chemistry is important for controlling reactions, improving synthetic efficiency, and advancing fields such as pharmaceuticals and organic electronics. While there are examples of regioselective reactions in inorganic and coordination chemistry, they are less common than in organic chemistry . Conventional regioselective coordination refers to a ligand with multiple binding sites in a molecule, each of which binds a different type of metal ion that prefers a particular site.…”

“…While there are examples of regioselective reactions in inorganic and coordination chemistry, they are less common than in organic chemistry. 7 Conventional regioselective coordination refers to a ligand with multiple binding sites in a molecule, each of which binds a different type of metal ion that prefers a particular site. For example, Lehn et al reported that simple molecular systems with heterocyclic ligands exhibit regioselectivity.…”