Macrocyclic ligand ring size effects on complex stabilities and kinetics. Copper(II) complexes of cyclic polythiaethers

Abstract

34% yield. An increase in the diene concentration resulted in a decrease in the yield of the silacyclopentene, and none of this product was obtained when the hexamethylsilirane-2,3-dimethyl-l,3-butadiene reaction was carried out (1 5 hr at 70°) in the absence of a diluent, although the tetramethylethylene yield was 40%. With some other dienes (e.g., trans,trans-2,4-hexadiene) no dimethylsilylene adducts were obtained under the conditions found to be successful with 2,3-dimethyl-1,3-butadiene. One may speculate that the unconverted 1,3 diene present in these reactions intercepts either a diradical intermediate'2a,b of the rearrangement of the vinylsilacyclopropane or reacts (by cycloaddition?) with the product of the rearrangement. Further experiments are required on this point.This new, mild route to dimethylsilylene may allow the development of new silylene chemistry, and experiments directed toward this goal are in progress. However, it should be recognized that the scope of the application of hexamethylsilirane will be limited by the extremely high reactivity of the silacyclopropane ring system toward many classes of corn pound^,^^^^-'^ among which are some which might react with silylenes. In those cases reactions with the silirane starting material would preclude observation of the desired silylene reactions.This thermal dimethylsilylene extrusion from hexamethylsilirane finds parallels in some known cases of sulfur extrusion from thiiranes" and in thermal difluorocarbene extrusion from gem-difluorocyclopropanes.'* The other known silacycl~propanes'~ are much more thermally stable than hexamethylsilirane and do not serve as sources of dimethylsilylene at these low temperatures. Thus when 2 2 was heated in triethylsilane solution at reflux for 17 hr, no Et3SiSiMe2H was obtained, Instead, a 20% yield of a dimer of 2, presumably 3, was formed, along with nonvolatile polymeric material. 3No information concerning the mechanism of dimethylsilylene extrusion from hexamethylsilirane is available at present. A concerted process, the reverse of singlet state silylene addition to the C-C bond,I2 seems a good possibility, but a stepwise process proceeding via the diradical -Si-MezCMezCMe2-also must be considered.

Electrochemical Extraction of Cu(I) and Cu(II) Ions Assisted by 1,4,7,10-Tetrathiacyclododecane

“…36 Without being able to quantify it exactly, the association constant for the [Cu(II)-TTCD] complex is estimated as being very low in view of the forward wave position situated at the extreme right of the cyclic voltammogram (Figure 5). This result is consistent with literature data, 17,37 where values of log K 1 o ) 2.5 (in a methanol/water (4:1) mixture at 25 °C) are reported. Nevertheless, numerous authors showed that cyclic thioether ligands complex Cu + ions very strongly.…”

Structure of the 14-membered macrocyclic tetrathia ether complex of copper(II). Evidence for undistorted geometries in blue copper protein models

“…Recently, however, we have shown that the cyclic tetrathia ethers2•' represent an excellent series of ligands for the systematic investigation of the dependence of kinetic parameters on ligand ring size, presumably reflecting the influence of ligand structure upon bond formation and rupture processes. 4 Of even greater interest is the very recent discovery that the copper(II) thia ether complexes exhibit unusual spectral and redox properties similar to those found in the blue copper proteins.5™7 Since the blue copper protein phenomena have frequently been ascribed to the presence of tetrahedral or five-coordinate copper(II),8™10 a rigorous determination of the structural features inherent in the copper(II) thia ether complexes was deemed a matter of the utmost importance.…”

Comparative study of donor atom effects on the thermodynamic and electron-transfer kinetic properties of copper(ii/i) complexes with sexadentate macrocyclic ligands. [CuII/I([18]aneS4N2)] and [CuII/I([18]aneS4O2)]

“…The copper(II) complexes formed with both [18]aneS 4 N 2 and [18]aneS 4 O 2 exhibit a strong S-to-Cu charge-transfer band around 390 nm and a somewhat weaker band around 580 nm, consistent with the absorption bands found previously for similar copperpolythioether complexes. [33][34][35] The molar absorptivity values for all complexes were determined using solutions of known concentration as shown in Table 1.…”