Dimeric complex

Oxidative cleavage of the complex 549 with CuCri affords 2,3-bis(chloro-methyl)-1,3-butadiene (550) and regenerates PdCri. Thus the preparation of this interesting dimerization product 550 can be carried out with a catalytic amount of PdCl2 and two equivalents of CuCb in MeCN[495], Similarly, treatment of allene with PdBr2 affords the dimeric complex 551. Treatment of this complex with 2 equiv, of bromine yields the dibromide 552. The tetra-bromide 553 is obtained by the reaction of an excess of bromine[496]. Similarly,... 

Carbonylation of the complex 548 proceeds in ethanol gives ethyl 3-chloro-3-butenoate (554), The lactone 555 and the two esters 556 and 557 are obtained by carbonylation of the dimeric complex 549. The oxidative carbonylation of allene in ethanol with PdCl2 gives ethyl itacoante (558), although the yield is low[498]. 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Substituted derivatives of nickelocene, where one ring has been replaced, include the complex cyclopentadienyl nitrosyl nickel [12071 -73-7], (7T-C3H3)NiNO, a red Hquid, mp -41°C. A review of nitrosyl complexes with nickel is available (89). The dimer complex... 

The kinetics of this process is strongly affected by an association phenomenon. It has been known that the active center is the silanolate ion pair, which is in equUibrium with dormant ion pair complexes (99,100). The polymerization of cyclosiloxanes in the presence of potassium silanolate shows the kinetic order 0.5 with respect to the initiator, which suggests the principal role of dimer complexes (101). 

Rhodacarborane catalysts have been immobilized by attachment to polystyrene beads with appreciable retention of catalytic activity (227). A 13-vertex /oj iJ-hydridorhodacarborane has also been synthesized and demonstrated to possess catalytic activity similar to that of the icosahedral species (228). Ak-oxidation of closo- >(2- P((Z [) 2 - i- > l[l-Bih(Z, results in a brilliant purple dimer. This compound contains two formal Rh " centers linked by a sigma bond and a pak of Rh—H—B bridge bonds. A number of similar dimer complexes have been characterized and the mechanism of dimer formation in these rhodacarborane clusters have been studied in detail (229). 

Figure 17.12 Ribbon diagram of EMPl bound to the extracellular domain of the erythropoietin receptor (EBP). Binding of EMPl causes dimerization of erythropoietin receptor. The x-ray crystal structure of the EMPl-EBP complex shows a nearly symmetrical dimer complex in which both peptide monomers interact with both copies of EBP. Recognition between the EMPl peptides and EBP utilizes more than 60% of the EMPl surface and four of six loops in the erythropoietin-binding pocket of EBP.

Chromium(II) phthalocyanine (PcCr) is prepared from phthalonitrile and hexacarbonylchro-mium(O) in 1-chlornaphthalene.234 PcCr(OAc) is prepared from phthalonitrile and chro-mium(III) acetate without solvent235 or in nitrobenzene starting from chromium(II) acetate236 under reflux. Chromium(lll) phthalocyanine also forms /t-oxo dimeric complexes,237 which are more common with iron phthalocyanines. 

Dimeric complexes like [Cl(NH3)Pt H2N(CH2)4NH2 Pt(NH3)Cl]Cl2 are also being investigated as they bind to DNA in a different way to that involved in cisplatin binding and are active in cisplatin-resistant human tumour cells. They are more potent than cisplatin in lung cancer models in vivo and are likely to go on clinical trials in the near future [204],... 

Even if the peak behavior fits well for a given apparent desorption order, the real kinetic situation may be a different one. As a rate controlling step in a second-order desorption, random recombination of two particles is assumed most frequently. However, should the desorption proceed via a nonrandom recombination of neighboring particle pairs into an ordered structure, the resulting apparent first-order desorption kinetics is claimed to be possible (36). The term pseudo-first-order kinetics is used in this instance. Vice versa, second-order kinetics of desorption can appear for a nondissociative adsorption, if the existence of a dimer complex is necessary before the actual desorption step can take place (99). A possibility of switching between the apparent second-order and first-order kinetics by changing the surface coverage has also been claimed (60, 99, 100). 

The activation of silylene complexes is induced both photochemically or by addition of a base, e.g. pyridine. A similar base-induced cleavage is known from the chemistry of carbene complexes however, in this case the carbenes so formed dimerize to give alkenes. Finally, a silylene cleavage can also be achieved thermally. Melting of the compounds 4-7 in high vacuum yields the dimeric complexes 48-51 with loss of HMPA. The dimers, on the other hand, can be transformed into polysilanes and iron carbonyl clusters above 120 °C. In all cases, the resulting polymers have been identified by spectroscopic methods. 

Other amidinate anions normally form dinuclear copper(I) complexes with bridging amidinate ligands, although tetracopper(l) complexes have also been reported Silver(1) forms dimeric complexes with functionalized N,N -... 

Cp derivatives (Scheme 185) to form -oxo-bridged dimeric complexes. The stabilities of the Af,0-bound carbamate intermediates depend mainly on the cyclopentadienyl ring substituents, but there is also a small dependence on the nature of the length of the (dimethylamino)alkyl chain for the C5H4Me systems. ... 

Co2(CO)8 has also been studied in low-temperature matrices (19,20), the photochemical behavior of which led to the identification of three isomeric forms of the dimer complex (19). Two of these are the accepted forms, 1 and 2, whereas the third has no bridging, CO ligands. The structure most... 

Fig. 16. Salicylideneamino alcohols react with arylboronic acids to form monomeric (45-49) or dimeric complexes (50-59)...

Usually, C-mercury substituted phosphorus ylides are monomers and in order to stabilize these complexes the presence of a second substituent on the carbon is necessary to balance the electron-donating effect of the metal. However a dimeric complex 85 has been obtained by the reaction of mercuric halides HgX2... 

The polymeric [NCCH2Co(salen)] is a variant of the octahedral structure, in which the organo-ligand of one molecule also serves as the second axial ligand of the next in the polymeric chain. Solution studies have revealed other examples of five coordinated and dimeric complexes (see below). 

UV visible spectrophotometer. A1 (N03)3.9H20 monomer was prepared in same manner. In case of synthesis of dimer complex, 2 equivalent of the Co(salen) was taken with respect to AlX3.nH20. 

The formation of monomer and dimer of (salen)Co AIX3 complex can be confirmed by Al NMR. Monomer complex la show Al NMR chemical shift on 5=43.1 ppm line width =30.2 Hz and dimer complex lb 5=37.7 ppm line width =12.7 Hz. Further instrumental evidence may be viewed by UV-Vis spectrophotometer. The new synthesized complex showed absorption band at 370 nm. The characteristic absorption band of the precatalyst Co(salen) at 420 nm disappeared (Figure 1). It has long been known that oxygen atoms of the metal complexes of the SchifT bases are able to coordinate to the transition and group 13 metals to form bi- and trinuclear complex [9]. On these proofs the possible structure is shown in Scheme 1. 

Fig. 1. UV-Vis absorption spectra of the precatalyst Scheme 2. Possible working model for the HKR chiral Co(salen) and monomer and dimer complex. of terminal epoxides catalyzed by C0-AIX3...

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