Ligands bipyrimidine

Homogeneous catalysts have been reported, which can oxidize methane to other functionalized products via C-H activation, involving an electrophilic substitution process. The conversion of methane into methyl bisulfate, using a platinum catalyst, in sulfuric acid, has been described. The researchers found that a bipyrimidine-based ligand could both stabilize and solubilize the cationic platinum species under the strong acidic conditions and TONs of >500 were observed (Equation (5)).13... 

Rate and equilibrium constant data, including substituent and isotope effects, for the reaction of [Pt(bpy)2]2+ with hydroxide, are all consistent with, and interpreted in terms of, reversible addition of the hydroxide to the coordinated 2,2 -bipyridyl (397). Equilibrium constants for addition of hydroxide to a series of platinum(II)-diimine cations [Pt(diimine)2]2+, the diimines being 2,2 -bipyridyl, 2,2 -bipyrazine, 3,3 -bipyridazine, and 2,2 -bipyrimidine, suggest that hydroxide adds at the 6 position of the coordinated ligand (398). Support for this covalent hydration mechanism for hydroxide attack at coordinated diimines comes from crystal structure determinations of binuclear mixed valence copper(I)/copper(II) complexes of 2-hydroxylated 1,10-phenanthroline and 2,2 -bipyridyl (399). 

It is also noteworthy that complexes containing ligands such as TAP, HAT, bpz (2,2 -bipyrazine) or bipym (2,2 -bipyrimidine) (Fig. 2), have free non-chelated nitrogen atoms. It has been shown that all these compounds are all more basic in the excited state than the ground state [75,93,94], so that the excited states are already protonated at pH 5-6 on the non-chelated nitrogen atoms. 

Gabrielsson et al. reported the aerobic oxidation of alcohols catalyzed by a cationic Cp Ir complexes bearing diamine ligands such as bipyrimidine 10 (Scheme 5.8) [35], the mechanism of which is closely related to the Oppenauer-type oxidation mentioned above. In this reaction, the deprotonation of Ir hydrido species to afford Ir species, and the reoxidation of Ir to Ir by O2, are crucial. 

Ligands such as 2,2 -bipyrimidine, bipym (110), or 2,3-bis(2-pyridyl)pyrazine, bppz (111), can act as bridging ligands, giving ternary binuclear anions such as [(NC)4Fe (bipym)Fe (H20)4] and [(NC)4Fe LFe (CN)4] with L = bipym or bppz. These and the corresponding... 

The emission from [Ru(bpz)3] is quenched by carboxylic acids the observed rate constants for the process can be rationalized in terms of the protonation of the non-coordinated N atoms on the bpz ligands. The effects of concentration of carboxylate ion on the absorption and emission intensity of [Ru(bpz)3] have been examined. The absorption spectrum of [Ru(bpz)(bpy)2] " shows a strong dependence on [H+] because of protonation of the free N sites the protonated species exhibits no emission. Phosphorescence is partly quenched by HsO" " even in solutions where [H+] is so low that protonation is not evidenced from the absorption spectrum. The lifetime of the excited state of the nonemissive [Ru(Hbpz)(bpy)2] " is 1.1ns, much shorter than that of [Ru(bpz)(bpy)2] (88 nm). The effects of complex formation between [Ru(bpz)(bpy)2] and Ag on electronic spectroscopic properties have also been studied. Like bpz, coordinated 2,2 -bipyrimidine and 2-(2 -pyridyl)pyrimidine also have the... 

Both pyrimidine and quinazoline derivatives have been investigated as ligands for palladium-mediated reactions. Examples of ligands prepared include the phosphine-free bipyrimidine 1181, which gave the isolable palladium dichloride catalyst 1182 <2001JOM(634)39>, and the chiral oxazolinyl-quinazoline BINAP analogs 1183 and 1184 <20060L5109>. 

Palladium- and platinum compounds have been successfully used for the functionalization of alkanes [110-112], An efficient and highly selective catalytic system is a platinum complex with a bipyrimidine ligand [Pt(bpym)Cl2], which provides up to 72% yield of methanol. The major drawback of the system is the reaction mediiun. Oleum leads to a large amount of diluted sulfuric acid when the formed ester is hydrolized. 

Figure 8-24. The reaction of the ruthenium(ii) complex [Ru(bpym)3]2+ with hydroxide ion results in a degradation of one of the ligands. This might be a consequence of initial attack of the hydroxide ion upon the 2,2 -bipyrimidine, although other possibilities cannot be ruled out.

In Table 1, the diimine ligands were either 2,2/-bipyridine or 1,10-phenanthroline, or one of their derivatives, although 2,2,-bipyrazinc and derivatives of 2,2 -bipyrimidine are also listed. Some monodentate chelating ligands contained one or more pyridine functionality and could bind an... 

Transition-metal ions are employed as nodes and bifunctional ligands as spacers. Commonly used spacer ligands are pseudohalides such as cyanide, thiocyanate, and azide, and N-donor ligands such as pyrazine, 4,4 -bipyridine, and 2,2/-bipyrimidine. Besides discrete supermolecules, some one-, two-, and three-dimensional architectural motifs generated from this strategy are shown in Fig. 20.3.9. 

The ligand 2,2-bipyrimidine (bpm) has been used to form terminal and bridging complexes with osmium. Reaction of s-Os(bipy)2Cl2 and the ligand yields [Os(bpm)bipy2]2+, and with cis-... 

Fig. 3. The monodentate coordination of the squarate ligand to Cu(II) in the structure of [Cu(2,2 -bipyrimidine)(C404)(H20)3] 2H2O reported by Castro et al. (66).

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