Synthesis and complexation of multiarmed cycloveratrylene-type ligands: observation of the "boat" and "distorted-cup" conformations of a cyclotetraveratrylene derivative.
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.
Sumby
Christopher J
CJ
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK. christopher.sumby@adelaide.edu.au
Gordon
Keith C
KC
Walsh
Tim J
TJ
Hardie
Michaele J
MJ