Supramolecular organometallic complex

The photocatalytic reduction of CO2 to CO using supramolecular organometallic complexes has been described. In particular, irradiation of [(dmb)2Ru"(bpyC3bpy)Re (CO)3Cl] (dmb =4,4 -dimethyl-2,2 -bipyridine) in DMF/ TEOA solution (DMF = N,N-dimethylformamide TEOA = triethanol amine) containing a sacrificial electron source gave CO. The mechanism (Scheme 16) was proposed to involve initial excitation to an MLCT excited state of the Re moiety. Electron transfer then occurs from the reduced bpy ligand bonded to the Re center to the bpy ligand bonded to the Re center. The latter species is the catalyst for the CO2 reduction reaction. 

There are very few examples of MOFs that have organometallic complexes as metalloligands, or so-called organometalloligands . However, Sweigart and co-workers (139-144) studied a number of such compounds. Their organo-metalloligand of choice was the piano stool complex [(Tj -benzoquinone)Mn (CO)3] , or /i-QMTC (Fig. 33). The C=0 moieties of the quinones can associate to secondary metal centers to form supramolecular networks with a rich diversity of... 

We have seen before that functionalized ferrocenyl complexes form a large family portion of the organometallic complexes investigated for their supramolecular bonding capacity. This popularity extends also to the use of ferrocenyl complexes for the preparation of coordination networks and complexes and complexes in which the ferrocenyl derivative is used as a ligand. Some recent results are summarized in Table 4. 

As presented in the previous section, the chiral self-assembled M4L6 supramolecular tetrahedron can encapsulate a variety of tetra-alkyl ammonium guests and presents high configurational stability. Raymond, Bergman and coworkers, used the tetrahedral [Ga4(23)6] (5.32) (H4(23) = l,5-bis(2,3-dihydroxybenzamido)naphthalene) (Figure 5.11) as a host to encapsulate reactive cationic organometallic complexes and studied some catalytic transformations within the chiral environment of the cavity of the supramolecular tetrahedron. 

Nickel and platinum complexes of alkynols and alkynediols are an interesting class of organometallic complex self-associated by O-H- -O hydrogen-bond interactions. Their solid-state supramolecular assembly has been the subject of thorough studies [127]. 

Cyclophanes or 7r-spherands have played a central role in the development of supramolecular chemistry forming an important class of organic host molecules for the inclusion of metal ions or organic molecules via n-n interactions. Particular examples are provided by their applications in synthesis [80], in the development of molecular sensors [81], and the development of cavities adequate for molecular reactions with possible applications in catalysis [82]. The classical organic synthesis of cyclophanes can be quite complex [83], so that the preparation of structurally related molecules via coordination or organometallic chemistry might be an interesting alternative. 

By employing coordination complexes as branch points, dendrimers can be synthesized that contain metal ions throughout their structure. The repetitive unit of such dendrimers contains M-C, M-N, M-P, or M-S bonds [53,62]. The metal ions act as supramolecular glue [63], in which the complexation chemistry directs the assembly and structure of the dendrimer [53]. One of the synthetic procedures used to prepare organometallic dendrimers with coordination centers in every layer is based on a protection/deprotection procedure in which two complexes are used as dendritic building blocks wherein one acts as a metal and the other as a ligand [64,76]. 

The development of chemistry in the last 20 years has revealed a significant shift of interest on the part of theoreticians and experimentalists [1,2]. Earlier, chemists attention was concentrated on atoms and atom-atom bonds. This strategy has been very successful in the creation of new molecules with unusual structures and with new chemical and physical properties. However, two decades ago, the primary objects of chemical studies become intermolecular interactions leading to complex molecular assemblies that exhibit unusual and often unique macro properties. This situation has dominated in all areas of modem chemical science from physical, organic, inorganic, and organometallic chemistry to material science and biochemistry, and has resulted in the formulation of new chemical disciplines supramolecular chemistry and crystal engineering. 

The same organometallic zwitterion [Co" (ri -C5H4COOH)(tx -C5H4COO)] used successfully in the solid-solid reactions described above has also been used in solid-sohd reactions with crystalhne alkaU salts MX (M=K+, Rb+, Cs+, NHJ X=C1", Br", T, PFg though not in all permutations of cations and anions) yielding supramolecular complexes of formula [Co (ri -C5H4COOH)-(tx=-C5H4COO)]2 M+X- [67]. 

Fig. 9 The organometallic zwitterion [Co (r -C5H4COOH)(ri -C5H4COO)] reacts quantitatively as a solid polycrystalline phase with a number of crystalline alkali salts MX (M= K+, Rb+, Cs+, NHJ X=Ch, Br, h, PF ) forming supramolecular complexes of formula [Co -(q -C5H4COOH)(q -C5H4COO)]2 M+X. The example shows the adduct obtained from the reaction with KBr...

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