TRANSITION-METAL-DIRECTED THREADING OF MOLECULAR STRINGS INTO COORDINATING RINGS - SYNTHETIC ASPECTS AND KINETIC-STUDY OF THE DETHREADING PROCESS

Copper(I) has been used as a template species to thread a molecular st ring containing one, two or three chelating phenanthroline units into a coordinating macrocycle (m-30). Whereas any of the bis-phenanthrolin e molecular strings (T1, T2 and T3) can be threaded into two macrocycl es, the case of the tris-phenanthroline chelate (T4) is less simple. T wo of the neighboring three binding sites complex one Cu+ ion intramol ecularly and the third phenanthroline pendant coordination site is ava ilable for Cu+-directed threading of the macrocycle m-30. This particu lar behavior is probably related to the nature of the bridge linking t he phenanthroline chelates (-(CH2)(6)-). Dethreading experiments were run using the cyanide anion as a decomplexing reagent. In all cases, d issociation takes place via two-step mechanisms. In the case of the bi s-phenanthroline threads, the rates depend on the nature of the bridge s linking the phenanthroline chelates. For Cu-2[T1(m-30)(2)](2+) and C u-2[T2(m-30)(2)](2+) (rigid aromatic bridges), the rate constants are ca. 10 M(-1) s(-1) for the faster step and ca. 2.5 M(-1) s(-1) for the slower step. For Cu-2[T3(m-30)(2)](2+) (-(CH2)(4)-), the rate constan ts are much higher: 1120 and 354 M(-1) s(-1) respectively. Finally, wh en the tris-phenanthroline-containing thread is involved (the case of Cu-2[T4(m-30)](2+)), the rate constants are 1790 and 324 M(-1) s(-1) f or the faster and slower steps, respectively. In the latter case, the fast process probably corresponds to an unfolding of the thread with d emetallation of the first copper site, whereas the slower step Is a re al dethreading reaction, analogous to the second dissociation step of the other dicopper(I) complexes.