Cyclidene vaulted

The lacunar cyclidenes are synthesized from a precursor tetraaza macrocycle containing a pendant vinyl carbon attached to a methoxy group, which readily undergoes addition-elimination reactions with diamines to give the vaulted bridge bicycle.36... 

Figure 1. Structures of cydidene complexes 1) lacunar cyclidene comply 2) vaulted cyclidene...

RESULTS AND DISCUSSION Iron Vaulted Cyclidene Complexes... 

The vaulted iron(II) cyclidene complexes were easily isolated as orange to red crystalline bis(hexafluorophosphate) salts or chloro hexafluorophosphate salts. The extreme air sensitivity and proclivity toward capturing varying numbers of molecules of solvent led to difficulties in obtaining simply definable and reliable elemental analyses. However, careful work led to pure samples and elemental analysis was an important part of the characterization of these compounds (see Experimental Section). Magnetic moments were determined by the Evans method at 25°C in acetonitrile solution [Fe VMe(3,6-durene) Cl]PF6, 5.0BM [Fe VC5H (3,6-durene) ](PF6)2, 4.87BM [Fe VPh(9,10-... 

Electrochemical data for one unbridged and four vaulted cyclidene complexes of iron(II) appear in Table 2. The most obvious feature is the dependence of redox potential on the axial ligand. For mixed chloride/bromide derivatives, the potential is much more negative than that for complexes having neutral acetonitrile as the axial ligand. The potentials are generally consistent with values reported for lacunar iron(II) cyclidene... 

Table 2. Electrochemical data for the first oxidation reaction of vaulted and unbridged iron(II) cyclidene complexes. ... 

Attempts were made to observe stoichiometric reaction between the [Fe VMe(3,6-durene) (H02 )] (or rather its equilibrium partner) and a variety of substrates in 311APW, acetonitrile, or acetone solutions. Reducing agents were also varied and included ascorbic acid and dithionite, but no substrate oxidation was detected. The possibility of vaulted iron cyclidene promoted reaction of substrates with O2 was also explored in the absence of reducing agents but, again, with no evidence for reaction. 

The vaulted cyclidenes were designed to facilitate selective oxidation of organic substrates through mimicing the action of the ternary complex of cytochrome P450. Because... 

Figure 12. Variations in the superstructures and substituents in cyclidene complexes a) general cyclidene structure b) lacunar [16]cyclidene c) retro-bridged lacunar [1 cyclidene d) vaulted [16]cyclidene e) dinuclear [16]cyclidene.

Table II. Calculated distances for various protons in several alcohols for vaulted cyclidene hosts ( H NMR V = 300 MHz [Host] = 6.48 x 10-= M [guest] = 10 M).

Here we consider a rare example of a quaternary complex in which four separate, distinctly different molecular species reside simultaneously within a single complex [74]. The general concept, shown in Figure 14, is a model for the so-called ternary complex of cytochromes P450 [75]. This is a misnomer since the complex is actually quaternary i.e., it involves the enzyme protein, the heme prosthetic group, the substrate, and the O2 cofactor. Our complex involves the vaulted cyclidene ligand, the cobalt ion, the O2 molecule and a guest molecule [74]. 

Additional problems that had to be confronted derived from the stability of the O2 adduct. The great stability of the cobalt/cyclidene/02 adducts depends on the presence of a reasonably small lacuna in the structure [25, 53]. The vaulted complexes have very large cavities and the resulting cobalt/02 adducts autoxidize relatively rapidly. Consequently, it was necessary to study the quaternary complex at the lowest possible temperature 1°C for the solvent D2O. This assured the saturation of the O2 forming equilibrium so that only a single NMR relaxing agent was present in the solvent. At the same time, the lower temperature reduced the quality of the measurement to some extent. 

Busch and coworkers have synthesized a series of remarkable vaulted and lacunar cobalt(II) cyclidene complexes, which reversibly bind dioxygen and undergo autoxidation to cobalt(III) species. In some cases they exhibit catalytic properties in the oxidation of phenol derivatives. 

The totally synthetic superstmctured cobalt(II) cyclidene complexes (Figure 61) CoA (vaulted), CoB (unbridged) and CoC (lacunar), function as both oxidase and oxygenase models in oxygenation of substituted phenols . 

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