Oxygen coordination compounds

Because of the great volume of literature on boron-oxygen coordination compounds, it has been necessary to be highly selective in the choice of material and to confine our attention predominantly to reviews. Of the metal borates only those existing in aqueous media will be briefly mentioned and of the complexes of organoboron oxygen compounds, known in a very large number, the most important types only will be included. 

Ligands Other than Oxygen and Sulfur. See Sec. 3.1.7, Coordination Compounds, for acids containing ligands other than oxygen and sulfur (selenium and tellurium). 

Reactions of the Hydroxyl Group. The hydroxyl proton of hydroxybenzaldehydes is acidic and reacts with alkahes to form salts. The lithium, sodium, potassium, and copper salts of sahcylaldehyde exist as chelates. The cobalt salt is the most simple oxygen-carrying synthetic chelate compound (33). The stabiUty constants of numerous sahcylaldehyde—metal ion coordination compounds have been measured (34). Both sahcylaldehyde and 4-hydroxybenzaldehyde are readily converted to the corresponding anisaldehyde by reaction with a methyl hahde, methyl sulfate (35—37), or methyl carbonate (38). The reaction shown produces -anisaldehyde [123-11-5] in 93.3% yield. Other ethers can also be made by the use of the appropriate reagent. 

Ternary compounds are also named by citing the more electropositive constituent first. The various oxidation states of the more electropositive element are designated by a system of prefixes and terminations added to a stem characteristic of the element, except in the case of coordination compounds (qv). Examples are as follows (see Chlorine oxygen acids and salts) ... 

Whereas this reaction was used to oxidize ethylene (qv) to acetaldehyde (qv), which in turn was oxidized to acetic acid, the direct carbonylation of methanol (qv) to acetic acid has largely replaced the Wacker process industrially (see Acetic acid and derivatives). A large number of other oxidation reactions of hydrocarbons by oxygen involve coordination compounds as detailed elsewhere (25). 

Beryllium, calcium, boron, and aluminum act in a similar manner. Malonic acid is made from monochloroacetic acid by reaction with potassium cyanide followed by hydrolysis. The acid and the intermediate cyanoacetic acid are used for the synthesis of polymethine dyes, synthetic caffeine, and for the manufacture of diethyl malonate, which is used in the synthesis of barbiturates. Most metals dissolve in aqueous potassium cyanide solutions in the presence of oxygen to form complex cyanides (see Coordination compounds). 

Oxygen bonding in coordination compounds. B. Jezowska-Trzebiatowska, Coord. Chem. Rev.,... 

Metal complexes of ligands containing a sulfur donor in conjunction with nitrogen, oxygen or a second sulfur have been reviewed in the past [11-13]. For example, reviews of the coordination compounds of dithiophosphates [14], dithiocarbamates [15, 16], dithiolates [17], dithiodiketonates [18], and xanthates [16] have appeared. The analytical aspects [19] and the spectral and structural information of transition metal complexes of thiosemicarbazones [20, 21] have been reviewed previously. Recent developments in the structural nature of metal complexes of 2-heterocyclic thiosemicarbazones and S-alkyldithiocarbazates, depicted below, are correlated to their biological activities. 

While metal-nitrogen and metal-oxygen bonded compounds dominate nucleobase coordination chemistry, examples in which metal-carbon bonds are formed have been identified. Early studies on the synthesis of metal-labeled DNA demonstrated that nucleotide-triphosphates, UTP, CTP, dUTP, and dCTP, can undergo mercury modification at C5 (82,83). The UTP derivative was also shown to act as a substrate for RNA polymerase in the presence of mercaptans (83). Later, guano-sine was shown to undergo mercury modification at C8 though, in this case, the purine was multiply substituted, 21 (84). 

The divalent Co(salen) complex (69a) is one of the most versatile and well-studied Co coordination compounds. It has a long and well-documented history and we shall not restate this here. Recent applications of (69a) as both a synthetic oxygen carrier and as a catalyst for organic transformations are described in Sections 6.1.3.1.2 and 6.1.4.1 respectively. Isotropic shifts in the HNMR spectrum of low-spin Co(salphn) (69b) were investigated in deuterated chloroform, DMF, DMSO, and pyridine.319 Solvent-dependent isotropic shifts indicate that the single unpaired electron, delocalized over the tetradentate 7r-electron system in CHCI3, is an intrinsic property of the planar four-coordinate complex. The high-spin/low-spin equilibrium of the... 

Thus it has so far proved possible to isolate stable derivatives of monomeric metaphosphoric acid and of metathio- and metaselenophosphoric acid, which, understandably, generally bear tert-butyl and/or trimethylsilyl substituents u. Specifically, we know aminobisiminophosphoranes (3, Z = NR2, X = Y = NR)2,3,4), aminoiminothio (or seleno)phosphoranes (5, Z = NR2, X = NR, Y = S or Se)5), and aminoiminomethylenephosphoranes (1, R = NR2, X = NR)6>. Conspicuously, no stable phosphorus(V) three-coordinate compounds have been synthesized with oxygen as divalent ligand. 

If you were designing a synthetic oxygen carrier, what characteristics would be required of the metal ion Suggest some alternative choices to Fe2+ and describe the characteristics of coordination compounds of the metal (s) you choose. 

The idea (50, 5/) of dual coordination of CO implies the presence of two coordination centers in a Fischer-Tropsch catalyst system, i.e., a carbonyl carbon coordinating center, Ma, and a carbonyl oxygen coordinating center, M6 (14). It is this concept which has led at least two groups to examine transition metal carbonyl cluster compounds as homogeneous Fischer-Tropsch catalysts. 

In the last few years, EPR has been widely used to study the electronic structure of four-and five-coordinated low-spin Co(II) complexes. Compounds of this class gained considerable interest because of their relation to biological oxygen carriers and to vitamin B12r. The ground state of the five-coordinated complexes is accepted to be dz2 ), in contrast to the four-coordinated compounds for which the determination of the correct ground state was quite troublesome, due to the fact that these types of Co(II) complexes have low-lying excited states. 

Figure 10.5 Quenching by oxygen affects the phosphorescence emission arising from Dj but has no effect on the photosolvation reaction that occurs from Q, Adapted from F. Scandola and V. Balzani, Energy-Transfer Processes of Excited States of Coordination Compounds , Journal of Chemical Education, Volume 60 (10), 1983. American Chemical Society...

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