Simultaneous synthesis, separation and characterization of metal complexes with monomeric lacunar ligands and dimeric ligands capable of bimetallic coordination
“…These splittings indicate the presence of dynamic isomerism influencing the unsaturated chelate rings and adjacent vinyl-like groups. Although isomerism at the bridgehead nitrogens has been previously observed in long-chain cyclidenes (lid-on−lid-off isomers), this does not explain the present observations. 5 Temperature dependencies of 1 H and 13 C NMR spectra of [Ni(C 6 MeHH[16]cyclidene)](PF 6 ) 2 ·CH 3 OH in acetonitrile.…”
Section: Resultscontrasting
confidence: 89%
“…The so-called “lid-on−lid-off” isomerism is very common for long-bridged cyclidenes, involving two different orientations of bridge R 1 and substituent R 2 (Figure a,b). It is associated with the planar configuration of the vinyl exocyclic nitrogen atom . The carbon−nitrogen bond to the bridging group R 1 is directed away from the cavity in the lid-off isomer, while that same C−N bond directs the bridge upward in the lid-on isomer, in the latter case positioning the bridge more nearly above the O 2 binding site.…”
A new type of isomerism has been detected in the cyclidene family of lacunar dioxygen carriers, providing an additional structural variable for the control of their oxygen affinity. In those rare complexes that do not have methyl substituents on the primary macrocycle, NMR and X-ray crystallographic data indicate that, in addition to their usual cis orientation, the bridges can also adopt a trans orientation. In the crystal structure of [Co(C(8)MeHH[16]cyclidene)](PF(6))(2).3CH(3)OH, the bridge has this trans orientation with one end in the "lid-on" configuration while the other end is "lid-off". The trans orientation of the bridge is identified as the principal cause of the decreased dioxygen affinity of such unsubstituted cyclidenes.
“…These splittings indicate the presence of dynamic isomerism influencing the unsaturated chelate rings and adjacent vinyl-like groups. Although isomerism at the bridgehead nitrogens has been previously observed in long-chain cyclidenes (lid-on−lid-off isomers), this does not explain the present observations. 5 Temperature dependencies of 1 H and 13 C NMR spectra of [Ni(C 6 MeHH[16]cyclidene)](PF 6 ) 2 ·CH 3 OH in acetonitrile.…”
Section: Resultscontrasting
confidence: 89%
“…The so-called “lid-on−lid-off” isomerism is very common for long-bridged cyclidenes, involving two different orientations of bridge R 1 and substituent R 2 (Figure a,b). It is associated with the planar configuration of the vinyl exocyclic nitrogen atom . The carbon−nitrogen bond to the bridging group R 1 is directed away from the cavity in the lid-off isomer, while that same C−N bond directs the bridge upward in the lid-on isomer, in the latter case positioning the bridge more nearly above the O 2 binding site.…”
A new type of isomerism has been detected in the cyclidene family of lacunar dioxygen carriers, providing an additional structural variable for the control of their oxygen affinity. In those rare complexes that do not have methyl substituents on the primary macrocycle, NMR and X-ray crystallographic data indicate that, in addition to their usual cis orientation, the bridges can also adopt a trans orientation. In the crystal structure of [Co(C(8)MeHH[16]cyclidene)](PF(6))(2).3CH(3)OH, the bridge has this trans orientation with one end in the "lid-on" configuration while the other end is "lid-off". The trans orientation of the bridge is identified as the principal cause of the decreased dioxygen affinity of such unsubstituted cyclidenes.
“…Newly prepared materials were routinely characterized and identified by analysis, 13 C and 1 H NMR, FAB MS, and IR (Table and procedures). In general, the synthetic route to unsubstituted cyclidenes was patterned after that for the substituted analogs, ,, (Scheme ), but differences abound, and they start with a change in the initial starting material. 3-(Ethoxymethylene)-2, 4-pentanedione ( I ) (Scheme ) used for all previous cyclidene syntheses necessarily gives products with R 3 = R 4 = CH 3 .…”
Section: Resultsmentioning
confidence: 99%
“…The first ligand produced by condensation, 2,2‘-[propylenebis(iminomethylidyne)]-1,3-propanedione ( IIIa ), prepared in analogy to its well-known counterpart, 3,3‘-[ethylenebis(iminomethylidene)]di-2,4-pentanedione ( IIIc ),15a was found by FAB/TG-G mass-spectra ([M + H] peak m / z = 239) to contain the macrocyclic byproduct VIII ( m / z = 279). Conveniently, both IIIa and its impurity VIII give the desired macrocyclic complex VIa via transformations 3, 5, and 6 (Scheme ).…”
A major advance has been made in the incremental
molecular design of long-lived cobalt(II) dioxygen
carriers. Preceding mechanistic studies revealed that ionizable
methyl groups trigger the autoxidation of the
O2
adduct of the cobalt(II) cyclidene. Two members of a new
family of unsubstituted (no methyl groups) lacunar
cyclidene dioxygen carriers have been prepared in an eight-step
synthesis, and a complex with a hexamethylene
bridge has been structurally characterized. In contrast to
previously studied cyclidenes, these materials bear no
substituents on the chelated macrocyclic platform. As anticipated,
the rates of autoxidation of these unsubstituted
cyclidene complexes were found to be 5−8 times slower than those for
the most stable previously known cyclidene
derivatives. Because of the absence of Me−Me vicinal repulsion,
the C6 bridge assumes a zig-zag conformation
directly across the cavity. The accompanying, relatively low,
dioxygen affinity is explained on the basis of electronic
and steric factors. The rates of dioxygen binding to these newly
prepared cobalt(II) unsubstituted cyclidenes are fast
and approximately equal to the corresponding values for their
Me-substituted analogs. Consequently, differences in
dissociation rates are responsible for the differences in
O2 affinities. This is a clear example of an unusual
steric
effect for O2 adducts.
“…[4,5] The saddle-shaped [16]cylidenes react with a,w-diamines at high dilution, closing the bridge between the meso carbon atoms of the macrocycle. This leads to lacunar ligands [6][7][8][9][10] A similar procedure for bridge closure can be applied in the case of [15]cyclidenes. The coordinated nickel(II) ion can easily be removed from the cyclidene moiety and substituted with an another transition metal ion.…”
Multicenter (bi-, tri-, and tetranuclear) tetraazamacrocyclic complexes were self-assembled from Ni and Cu tetraazamacrocyclic mononuclear units and α,ω-diamines as building blocks. The structures of all compounds studied were proved by spectroscopic methods (ESI MS and NMR spectroscopy). Electrochemical experiments revealed reversible one-electron electrode processes at each of the Ni(2+) and Cu(2+) centers with formation of metal cations in oxidation state +3. Long linkers allow bi- and trinuclear complexes with noninteracting metal centers to be obtained. In the case of the short linkers (e.g. ethylenediamine) higher, trinuclear species are formed as major product. The structures of the bis- and tris-macrocyclic systems were confirmed by single-crystal X-ray diffraction. The tris-macrocyclic systems form cations in the shape of triangles partially filled with counterions and solvent molecules. The cations form positively charged layers, which interact in the crystal lattice with the neighboring negatively charged layers of anions. In solution, the trinuclear complexes exhibit strong host-guest interactions with 9,10-dimethyltriptycene due to complementarity of shape and size of this guest molecule. The association constants were determined by NMR spectroscopy and voltammetry, and very good agreement was obtained. The structural flexibility of the tetranuclear complex with long linkers allows for attractive interactions between the metal-complexing macrocycles that result in folding of the molecule. On the contrary, no folding is possible in the case of short linkers consisting of two CH(2) groups.
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