Multimetallic complexes

Ag2C2 AgF 4AgCF3S03 RCN (R = Me, Et) have been prepared and structurally characterised the compounds display a honeycomb-like layered structure.  

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Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

The presence of multiple C=C moieties affords the potential to assemble novel arrays of metal centers by combinations of a- and tt-bonding interactions. " However, examples of multimetallic complexes containing poly-yne and poly-yndiyl ligands are limited, although preliminary reports suggest that there is much scope for the preparation of new structural types. 

In addition to the monoadducts, there are a growing number of multimetallic complexes, of which some are illustrated in Fig. 11. These can be subdivided into those that involve metals binding to adjacent and to more distant C=C bonds. 

The ability of the boron atom of 59 to engage in a donor-acceptor interaction was illustrated with DMAP and DABCO (DABCO = diazabi-cyclo-[2.2.2]-octane) that readily formed the corresponding Lewis adducts. Interestingly, a similar behavior was retained after coordination of the phosphorus atom to palladium. The formation of the Lewis base adducts 66a and 66b of complex 65 (Scheme 38) was supported by solid-state 31P and nB CP/MAS-NMR spectroscopy (<5 1 B = 5-6 ppm), although the occurrence of decomposition and/or dissociation processes impeded spectroscopic characterization in solution and recrystallization to obtain X-ray quality crystals. Compounds 66a and 66b substantiate the ability of ambiphilic compounds to engage concomitantly into the coordination of donor and acceptor moieties. Such a dual behavior opens interesting perspectives for the preparation of metallo-polymers and multimetallic complexes. 

Molybdenocene dihalides, associated chemistry, 5, 573 Molybdenocene dihydrides monomeric complexes, 5, 568 multimetallic complexes, 5, 570 protonation studies, 5, 570 Molybdenocenes... 

Multimetallic complexes, molybdenocene dihydrides, 5, 570 Multimetallic nickel-alkynes, synthesis and reactivity, 8, 145 Multinuclear chromium(II) complexes, with halides, alkyls,... 

Multimetallic complexes (tetranuclear and pentanuclear with complicated structures) of these ligands which could have unique magnetic properties were prepared and studied. It is noted [125a] that, in the copper complex with H2L, Cu5(0H)2(L)2(N03)4, all magnetic interactions within the complex unit H2L appear to be antiferromagnetic, as well as in copper complexes with two other ligands, [Cu(HL1)(N03)]4 and [Cu2(L2)(OAc)2]2 [187,188],... 

In a nice illustration of the impact of metal coordination upon the reactivity of phospholes, a methodology for the functionalization of these heterocycles in the /3-position has been described (see also Scheme 22) <2001JOM105>. Here, coordination of both the P-lone pair and the cyclic diene system was undertaken. The resulting multimetallic complex 79 was treated with lithium diisopropylamide (LDA) to afford the lithium salt 350 (Scheme 118). This readily undergoes nucleophilic substitution with a variety of electrophiles to afford the corresponding substituted phosphole complexes 351-353. The free phospholes can be isolated following decomplexation with cerium(iv) ammonium nitrate (CAN). 

A considerable amount of work has been done in this area, which has been spurred in part by interest in the synthesis of multimetallic complexes in which the metal atoms are connected by unsaturated chains of several carbon atoms that may serve as molecular wires. The initial and still most widely employed synthetic route to vinylidene complexes involves addition of four equivalents of a triaUcylphosphine (T = PPrj hereafter unless otherwise... 

Suzuki et al. reported an interesting example of a C-C bond cleavage of an ordinary non-strained diene substrate with a multimetallic complex [62]. The Csp2-Csp3 bond of cyclopentadiene is cleaved by trinuclear ruthenium pentahydride complex 40 to afford ruthenacyclohexadiene 41, which then rearranges to 2-methylruthenacyclopentadiene complex 42. The three metal centers cooperate for cleavage two of the three centers act as coordination sites for the diene moiety and the third is inserted into the C-C bond. 

Calixarenes as platforms for the construction of multimetallic complexes 04JOM(689)4125. 

Sleiman. H. Baxter. P. Lehn, J.-M. Rissansen. K. Self-assembly of rigid-rack multimetallic complexes of rotax-ane type. J. Chem. Soc., Chem. Commun. 1995. 715-716. 

Multimetallic complexes are also of interest. Ru complexes (30 and 31, Chart 5.7) in which the two metals are bridged via oligothiophene ligands of varying lengths have been prepared and their electrochemical and spectroscopic behaviors characterized [44]. In these complexes, the first reduction is bpy-based and the first oxidation is thiophene-based. The metals are weakly interacting and transient absorption and photophysical studies reveal that the lowest excited state is an oligothiophene-based state. The Ru,... 

Yamamoto has shown that 1 mol% of tr/s(pentafluorophenyl)borane (40) or of 4-(trifluoromethyl)phenylboroxin (41), dramatically improve the reaction yields and enantiomeric excesses (Table 2). Yamamoto postulated that the accelerating effect may be due to an enhancement of the Lewis acidity of the titanium center via multimetallic complex 42. ... 

DIAMINOCATECHOL A USEFUL BUILDING BLOCK IN SYNTHESIS OF MULTIMETALLIC COMPLEXES... 

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