Deprotonation complexes

The deprotonated complex is a nucleophilic synthon which reacts smoothly with a large variety of organic and inorganic electrophiles forming a carbon-element bond Eq. (14) and Scheme IX ... 

Figure 3-9. The structure of the deprotonated complex formed between one Cu2+ and one ethylenediamine.

Bis-iV-alkylated complexes of Me2-9 and Me2-ll, as well as the tetra-methylated Ni(II)cyclam (NinTMC) derivatives, have been synthesized by the deprotonation of secondary amines followed by alkylation (34, 47,48). When EtI or other alkyl halide with /3-hydrogen was added to the deprotonated Ni(II) complex of cyclam or 11, HX elimination occurred instead of SN2 reaction. Therefore, ethylene gas was produced instead of -ethylated complex formation when EtI was added to the deprotonated complex of cyclam or 11. However, in the case of 8, bis- -ethylated Ni(II) complex was isolated. This may be because HX elimination is slower than SN2 reaction. The - -alkylated Ni(II) complexes of 9 (Me2-9 and Et2 9) and Me2-ll were stable against ligand dissociation in acidic aqueous solutions. The -alkylated complexes were dealkylated when the complexes were heated in aqueous solutions (34, 47). 

The tetraza macrocycle (150 LH4), with four ethanoate groups, is readily prepared by treatment of the cyclic tetramine with bromoethanoic acid.1101 Its complex [ZnLH2j utilizes two amino N atoms and two carboxylates as ligands. The fully deprotonated complex may be prepared in solution by treatment with NaOH. 

The above studies indicate that metal ions catalyze the hydrolysis of amides and peptides at pH values where the carbonyl-bonded species (25) is present. At higher pH values where deprotonated complexes (26) can be formed the hydrolysis is inhibited. These conclusions have been amply confirmed in subsequent studies involving inert cobalt(III) complexes (Section 61.4.2.2.2). Zinc(II)-promoted amide ionization is uncommon, and the first example of such a reaction was only reported in 1981.103 Zinc(II) does not inhibit the hydrolysis of glycylglycine at high pH, and amide deprotonation does not appear to occur at quite high pH values. Presumably this is one important reason for the widespread occurrence of zinc(Il) in metallopeptidases. Other metal ions such as copper(II) would induce amide deprotonation at relatively low pH values leading to catalytically inactive complexes. 

The interaction of 2-pyridinecarbaldehyde with Cu(II) has been studied by potentiometric and spectrophotometric methods,522 and formation constants have been determined. The neutral deprotonated complex (167) was characterized in the solid state. 

The enhancement of the acidity of the amine is not limited to sites which are directly co-ordinated to the metal, but may also be transmitted for considerable distances through the molecule. For example, the complex bis(di-2-pyridylamine)palladium(ii) undergoes a facile deprotonation (Fig. 5-28). This reaction also serves to exemplify the importance of charge control over the level of protonation. The deprotonation yields the neutral doubly deprotonated complex. 

The incident monochromatic photon-to-current conversion efficiency (IPCE) is plotted as a function of excitation wavelength. The IPCE value in the plateau region is 80% for complex 2, while for complex 25 it is only about 66%. In the red region, the difference is even more pronounced. Thus, at 700 nm the IPCE value is twice as high for the fully protonated complex 2 as compared to the deprotonated complex 25. As a consequence, the short circuit photocurrent is 18-19 mAcrn-2 for complex 2, while it is only about 12-13 mA cm-2 for complex 25. However, there is a trade-off in photovoltage, which is 0.9 V for complex 25, as compared to 0.65 V for complex 2. Nevertheless, this is insufficient to compensate for the current loss. Hence, the... 

Although other deprotonated complexes are sometimes not as stable as [CpFe( 5-QMesCF )], they can be generated and used at low temperature to form the desired bonds [27e]. Using the base and electrophile in excess, the reactions can be carried out at room temperature because the deprotonated species immediately reacts with the electrophile in situ. This kind of deprotonation/alkylation sequence underpins the star and dendrimer construction described herein (vide infra). In this way, the complexes [FeCp( s-arene)][PF6] also act as proton reservoirs [33]. 

The total charge of the system containing beta-cluster, two cations [H2OHOH2]+, the deprotonated complex of phosphatydic acid and phos-phatydilcholine is zero. The initial spatial structure placed the distances between the periphery atoms of the cluster and of [H2OHOH2]+ particles, as well as those between cations and the deprotonated complex of phospholipids, was somewhat greater than at equilibrium to reconstruct a situation excluding an immediate contact between SiC>2 nanoparticles and the cell membrane. 

The presence of L-histidine as the third amino acid residue in tripeptide complexes of Cu(II) drastically decreases their susceptibility to both nucleophilic attack and acid attack (11, 12). Thus, the doubly deprotonated complex of glycylglycyl-L-histidine (Cu(H 2gly-gly-his) shown in Structure I is relatively slow to react with the nucleophilic tri-ethylenetetramine (trien) since this reaction is seven orders of magnitude slower than the corresponding reaction with Cu(H 2gly-gly-gly). The... 

It seems strange that no hydroxylamine complexes of osmium are established. There is a brief report of a deprotonated complex Os(NO)(NHOH)Cl2(PPh3)2, made from Os(NO)2(PPh3)2 and HC1. The vNO band is at 1860 cm-1.247... 

The final neutral palladium(II) complex with the amide functionalised carbene hgand features two six membered metallacycles, just as the cationic not yet deprotonated one does. The amine nitrogen atom has four substituents (H, Pd and two C). Since the two metallacycles can adopt two distinct conformations that slowly flip into each other for steric reasons, the nitrogen atom appears chiral due to atropisomerism despite its overall C -symmetry. The deprotonated complex lacks this feature, clearly visible in the respective NMR spectra. 

Cobalt(III) hexaammine is quite inert to hydrolysis. In strongly basic media ([OH ] = 0.1 to 2.1 M) the reaction rate increases and [OH ] apparently reaches a limiting value around 1 M, where the reaction becomes independent of [OH ], 3 x 10 s at 61.8°, (i = 2.0 (157). The mechanism of the reaction involves the SnI(CB) pathway. The limiting rate observed at high pH is thought to refiect a pre-equilibrium ion pair formation between the complex ion and OH , rather than the first-order reaction of the fuly deprotonated complex ion. The rate of... 

Other bases have been employed to deprotonate these complexes 63). The singly deprotonated complex [Os(en-H)(en)2]l2 can be obtained by reaction of [Os(en)3]l3 with one molar equivalent of potassium or potassium amide in liquid ammonia, with a six-fold molar excess of KOC2H5 in ethanol, or with a four-fold molar excess of KOH in ethanol. However,... 

In the case of a cobalt(III) N Ss-nitrosarcophaginate, the rearrangement of the deprotonated complex with the loss of a... 

When the irradiated solutions are exposed to air, the initial solution spectra for the cobalt(III) complexes are re-established. A slight increase in the intensity and the appearance of a longwave band in the UV range were attributed to the formation of a deprotonated complex [383]. 

The deprotonated complex [Co H20)5(OH)] will undergo loss of H2O faster than the starting complex [Co(H20)fi] because the anionic OH" ligand is both better ct and tt donor than H2O. As a consequence the bond trans to Co-OH bond is going to be weaker, and substitution is going to proceed faster. The implication is that a complex without protic ligands will not undergo anomalously fast substitution reaction in the presence of OH". 

Equilibrium Constants for Acid Dissociation and Complex Formation. An Increased Index Number Reflects a Higher Deprotonation/Complexation State... 

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