Synthesis and Complexation of Multiarmed Cycloveratrylene‐Type Ligands: Observation of the “Boat” and “Distorted‐Cup” Conformations of a Cyclotetraveratrylene Derivative

Abstract

Investigations of a previously reported ligand, hexakis(2-pyridylmethyl)cyclotricatechylene (1), and a new tetrameric bridging ligand, octakis(2-pyridylmethyl)cyclotetracatechylene (2), the latter constructed on a larger cyclotetraveratrylene (CTTV) scaffold, are described. Variable-temperature NMR studies support a "sofa" conformation for 2, akin to studies on the parent compound. The coordination chemistry of 2 and its smaller trimeric homologue have also been investigated with silver(I), copper(II) and palladium(II) salts. An unexpected chelating mode was observed for 1 in the structure of DMF subset[Pd(3)Cl(6)(1)] x DMF, whereby the palladium cations bridge two veratrole subunits rather than chelating within a single subunit. In the structure of [Ag(4)(2)][Co(C(2)B(9)H(11))(2)](4) x 2.8 CH(3)CN x H(2)O, ligand 2 adopts a "boat" conformation, whereas in [Pd(4)Cl(8)(2)] x 4 H(2)O, (1)H NMR spectroscopic studies and calculations indicate that the ligand is present in a previously unobserved "distorted-cup" conformation. This conformation was calculated to be approximately 90 kJ mol(-1) lower in energy than the alternative "sofa" conformation. Thus, coordination-induced conformational control over CTTV derivatives offers new routes to exploit the host-guest chemistry of these compounds.

The Dimeric “Hand‐Shake” Motif in Complexes and Metallo–Supramolecular Assemblies of Cyclotriveratrylene‐Based Ligands

“…A handful of discrete coordination and organometallic complexes of CTV-or aCTG-based ligands have been previously reported, [25][26][27] [26,27] There are only two crystal structures of prior examples of simple trinuclear coordination complexes, [26] and in both cases the extended metalled arms of the complexes point outwards from the CTG-bowl in a symmetric or near symmetric fashion. This is not the case in complex 7 in which the asymmetric conformation produces an extended host with a C-shaped cavity or cleft in the solid state.…”

Tris(rhenium fac-tricarbonyl) Polypyridine Functionalized Cyclotriguaiacylene Ligands with Rich and Varied Emission

“…complexes of salicylaldiminato derivatives of CTV, 6 a CuCl2 complex of tris(4-[2,2',6',2"-terpyridyl]benzyl)cyclotriguaiacylene (ligand L3 in this study), 7 Pd(II) and Cu(II) complexes of hexakis(2-pyridylmethyl)cyclotriveratrylene, 8 and a Cu(I) complex of a tris(2-pyridylmethyl)-amine decorated CTG which forms adducts with O2 and other small molecules. 9 CTV itself can also behave as an organometallic ligand to form trinuclear complexes by binding metals through its arene faces.…”

“…CTG can be functionalized at the upper rim through its hydroxyl substituents to give tripodal bowl-shaped ligands capable of binding three metal centers . Examples of such trinuclear transition-metal complexes of CTV-type ligands include Cu­(II/I) complexes of hexakis­(2,2′-bipyridylmethyl)­cyclotriveratrylene which act as conformational switches, anion-binding ferrocene-appended derivatives of CTV, Ni­(II) complexes of salicylaldiminato derivatives of CTV, a CuCl 2 complex of tris­(4-[2,2′,6′,2″-terpyridyl]­benzyl)­cyclotriguaiacylene (ligand L3 in this study), Pd­(II) and Cu­(II) complexes of hexakis­(2-pyridylmethyl)­cyclotriveratrylene, and a Cu­(I) complex of a tris­(2-pyridylmethyl)­amine-decorated CTG which forms adducts with O 2 and other small molecules . CTV itself can also behave as an organometallic ligand to form trinuclear complexes by binding metals through its arene faces …”

Tribenzotriquinacene‐Based Triscyclophanes: Intra‐ and Inter‐Wing C3v‐Symmetrical Extension of the Bowl‐Shaped Tribenzotriquinacene Core

“…One of the major differences between tribenzotriquinacene (TBTQ, 1 ; Figure 1) and its derivatives,1–4 on the one hand, and cyclotribenzylene ( 2 )5–10 and its derivatives, on the other, is the conformational rigidity of the former, giving rise to an almost perfect orthogonal orientation of the three indane wings, as compared with the conformational flexibility of the latter. The C 3 v ‐symmetrical, bowl‐shaped structure11,12 and the “Cartesian” geometry1b of the TBTQ scaffold and the diverse and well controllable chemical reactivity of the TBTQ hydrocarbons [1,4,11,13,14] enables a large range of intriguing extensions, which may lead to novel applications as nanoscaled building blocks and supramolecular hosts.…”