Cavitands bearing both eight (5) and two (13) metal-ligating carboxymethylphosphonate groups on their rims were synthesized by Arbuzov reaction of the corresponding bromoacetamido cavitands with trialkyl phosphites. These exist in the vase conformation in CDCl(3) and are stabilized by a cyclic seam of hydrogen bonds. This structure was also found in the solid state for the octabromoacetamide 4a and diphosphonate cavitand 13 by single-crystal X-ray analysis. Cavitands 5 and 13 form caviplexes in CDCl(3), CD(2)Cl(2), and alcohol solutions with adamantane derivatives 15a,b, quinuclidine 15d, ammonium and phosphonium salts 14, and drugs like ibuprofen 15c, all of which are stable on the NMR time scale at 295 K. NMR spectroscopy reveals that at 223 K octaphosphonate 5b exists in two forms: the major C(4)-symmetrical compound is filled with solvent while the minor species shows intramolecular inclusion of a dialkoxyphosphoryl group. In methanol-d(4) 5 and 13 exist in a lower symmetry vase conformation with self-inclusion of one alkyl group. Interaction of these complexes with La(OTf)(3) results in a change in the conformation of the cavitand from vase to kite with concomitant and quantitative release of the encapsulated guests. Two to three equivalents of the lanthanide salt per equivalent of cavitand 5a-d is necessary for the complete decomplexation of the included guest. The kite and the vase conformers equilibrate slowly on the NMR time scale at 295 K. The addition of good ligands for metal cations (nitrate or CMPO calixarene 16) shifts the equilibrium to the vase-shaped caviplex and allows quantitative control of the binding and release of the guest. The lanthanide complexes of octaphosphonates 5 in methanol-d(4) are velcraplex-like dimers held together by four metal cations.
The ancillary ligands in trans-[FeH(CN)L2] control whether protonation occurs at hydride to produce a dihydrogen complex or at cyanide to produce a hydrogen isocyanide complex.
This review provides applications of organoiron compounds in organic synthesis, focusing on [(η 5 -C 5 H 5 )(CO) 2 Fe]-substituted complexes. Covering recent work the preparation of representative compounds, their reactivity and some details of selected reaction mechanisms are discussed.
Fe(TIM)(CNBPh3)2 (TIM =
2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene)
was isolated from the reaction of a solution of FeCl2 in
methanol, TIM, and acetic acid with NaCN and then NaBPh4.
The CNBPh3
- ligand is generated from an
unexpected transformation of
BPh4
-.
A self-folding cavitand binds quinuclidinium cation in its vase conformation and lanthanum ions in its kite conformation. Metal coordination provides a novel switching mechanism for the uptake and release of guests.
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