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Linker units complexes

Advantage Transition metal complexes with chelating bis-carbenes featuring acidic methylene protons in the linker unit can be readily prepared, when the isolation of the free carbene using strong bases would be far more difficult. [Pg.14]

A third structural motif for silver(l) pincer carbene complexes is the dimer observed by Nielsen et al. [490] (see Figure 3.169). This dimeric structure becomes possible because of the flexibility introduced into the pincer structure by the linker unit, which acts as a hinge. It makes it possible for the NHC donor ligands to align themselves parallel to each other and perpendicular to the C-Ag-C vector of the silver coordination sphere. The dimer is considered to possess no argentophilic interactions as the Ag-Ag distance is 31 pm longer than the sum of the van der Waal s radii (340 pm) [20]. [Pg.176]

Figure 3.167 Transition metal pincer carbene complexes of Ag(l), Pd(ll) and Rh(l) featuring a pincer carbene ligand with a methylene linker unit. Figure 3.167 Transition metal pincer carbene complexes of Ag(l), Pd(ll) and Rh(l) featuring a pincer carbene ligand with a methylene linker unit.
The flexibility of the pincer carbene ligand system can be seen from the crystal structures of their palladium complexes. The ligand without linker units features the central pyridine ring and the flanking NHC units strictly coplanar [431] whereas the linker unit introduces twisting of these three ring systems [490]. The flanking NHC units are now... [Pg.177]

The method of preparation is seemingly irrelevant as demonstrated by Danopoulos et al. [504]. They used three different routes to synthesise the same C,C,C palladium(II) pincer carbene complexes and showed in the process that all three methods can be applied to the linker unit free ligand as well (see Figure 3.174). [Pg.182]

Figure 4.57 Transition metal complexes of Fc functionalised NFiC ligands without linker units. Figure 4.57 Transition metal complexes of Fc functionalised NFiC ligands without linker units.
Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. [Pg.304]

The basic structure of the mycobacterial cell wall is shown in O Fig. 1 (O Sect. 1). The major component of the cell wall is the mycolyl-arabinogalactan-peptidoglycan (mAGP) complex [21]. This consists of an inner peptidoglycan layer attached through a linker unit to an ara-binogalactan polysaccharide, which is in turn esterified to mycolic acids. The mycolic acids are branched hydroxy fatty acids that form the inner leaflet of the lipid bilayer. The outer leaflet... [Pg.1571]

One direction for the development in this area is looking for more active and stable complex. In 2011, Hapke and coworkers prepared CpCo(H2C = CHSiMc3)2 complex and was found active in [2 + 2 + 2] cycloaddition reactions [26], The other direction is the exploration of applications. In 2005, Maryanoflf and coworkers applied [2 + 2 + 2] cycloaddition reaction in the preparation of macrocycles [27]. In the presence of CpCo(CO)2, pyridine containing macrocycles were prepared from long-chain a,cr-diyne and nitriles, cyanamides, or isocyanates (Scheme 3.11). The regioselectivity of these reactions was affected by the length and type of linker unit between the alkyne groups, as well as by certain stereoelectronic factors. [Pg.25]

Analysis of the 1H and 13C NMR spectra of the tin complexes, being derivatives of various di-Schiff bases, [46] has revealed the dependence of the position of tin centre on the type of linker between the two imine units and the metal coordination number.110... [Pg.172]

To evaluate the influence of structural parameters governed by the cyclophosphazene core concerning the valency and the spatial orientation of epitopes, as well as the nature of linkers directly related to the ligation technique used for the mannoside incorporation, the authors performed preliminary kinetic turbidimetric assays with Con A. Insoluble cross-linked complexes formed rapidly for all compounds, without marked difference for the hexavalent analogues. On the other hand, the incorporation of additional mannosyl units led merely to statistical binding-affinity enhancements, notably for the less-dense decamer 194, which presents favorable extended intersugar distances. [Pg.236]

The synthesis of the bis-P-cyclodextrin 35 is outlined in Fig. 14. Interestingly, however, the X-ray structure of 36, the de-tosylated 35, revealed that P-carotene would not be incorporated into both CD units due to the unfavorable orientation of the diamide linker which blocks the entrance to the second P-CD. In agreement with this result are experiments with the target Ru complex 37 which displayed central cleavage on P-carotene 1 5delding retinal 2 as the major product (Fig. 15) (19). [Pg.42]


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See also in sourсe #XX -- [ Pg.255 ]




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