Phosphato complexes

The preparation of aV[Co(cyclen)P04] has been described and its reactivity in acidic and basic solution studied/This complex undergoes rapid ring opening in acidic or basic solution to give the monodentate phosphato species. Loss of monodentate phosphate in acidic solution follows a rate expression of the form feobs = where fco = 

Sargeson and co-workers initially reported that 4-nitrophenyl phosphate in (38) underwent base hydrolysis some 10 -fold faster than the uncoordinated ester. Subsequent X-ray work has now shown that (38) and the analogous ethylenediamine derivative do not contain chelated 

The factors influencing cobalt-alkyl bond dissociation energies are of considerable interest in view of coenzyme Bi2-dependent enzymatic processes which are triggered by such bond dissociation. Steric influences on cobalt-alkyl bond dissociation energies have now been considered. For reactions of the type in equation (9), where L is an axial tertiary phosphine 

The kinetics of oxidation of [Co(CysOS)(en)2] (41) by peroxodisul-fate has been investigated and activation parameters obtained. Gibbs 

Substitution Reactions of Inert-Metal Complexes— Coordination Numbers 6 and Above Other Inert Centers 

Tracer 0 studies have established that base hydrolysis of coordinated acetyl phosphate in the complex [(NH3)5Co-OP03COCH3] [ifcoH = 0.53 M s at 25°C and I = l.OM (NaC104)] occurs by exclusive carbon-oxygen bond fission. The hydrolysis of the acetyl phenyl phosphate monoanion is significantly catalyzed by the exchange-inert hydroxo complex [(NH3)sCoOH] ( MOH = 2.9 X 10 M s at 25 C) which operates by 

The hydrolysis of /3,-y-[Co(NH3)4H2P30io], in which the triphosphate ion is coordinated as a bidentate ligand, has been studied in the presence of [Co(cyclen)(OH)OH2] (cyclen = 1,4,7,10-tetraazacyclododecane). In the presence of the macrocyclic complex, the rate of hydrolysis of triphosphate to pyrophosphate is increased by a factor of 5 x 10 over the rate for the free ion. The pH rate profile for the reaction indicates that a deprotonation step with a pisT of 7.9 was required for the accelerated hydrolysis to occur. The results are consistent with the formation of the binuclear complex 24, followed by internal nucleophilic attack on phosphorus by coordinated hydroxide. 

There is considerable scope for much interesting kinetic and mechanistic work on cobalt(III) complexes of phosphate ligands. The early work of Lincoln and Stranks on the hydrolysis of c -[Co(en)2P04] in acidic and basic solution has indicated some of the complexities to be expected in this area. 

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The solubility of Tc02 nH20 in an aqueous solution was investigated by Meyer et al, [55-58], Paquette and Laurence [59] reported that carbonato- and phosphato-complex formation was likely to occur. The precipitation of Tc02-H20 is prevented in solution if the ratio... 

Phosphato complexes may have PO3-, HPO , or H2P04 coordinated.142 In Comen2(P04) there is a bidentate chelate, whereas the pyrophosphate Comen2(HP207) has a six-membered ring ... 

The major product of the hydrolysis of cis-[(en)2lr(OH)(BNPP)] (10) the corresponding monoester, is also hydrolyzed by attack of the cis coordinated hydroxide ion with a rate constant of 8 x 10 s at 40 C, or 2 X 10 S at 25 °C in the pH independent region. The product of this reaction is the ring opened monodentate phosphato complex cis-[(en)2lr(0H)(0P03)j. Thus, unlike the corresponding Co(III) complex, the chelate is not thermodynamically stable even at pH 9. The rate of attack of the cis coordinated hydroxide ion on the P center is also —500-fold slower than that reported for the analogous Co(III) reaction. 

The chelation of phosphate ion itself needs some discussion. Lincoln and Stranks (102) have published an extensive series of papers on the phosphato complexes of a series of Co(III) complexes. They showed that the chelate is the thermodynamically favored species in the pH range 5-... 

The 0x0 (0 ) ligand is dominant in the coordination chemistry of osmium, participating in the VIII to IV oxidation states inclusive. The tetroxide OSO4 is the single most important compound of osmium OSO4 and the recently discovered [0s04] ion arc tetrahedral. The /ra 5-[0=0s —O] osmyl moiety displays an extensive chemistry, comparable with that of the uranyl 0=U=0 unit, and there is an extensive and unique cyclic oxo-ester chemistry (p. 584). There is surprisingly little information on hydroxo, aqua, sulfato, nitrato or phosphato complexes, but much recent work has been carried out on carboxylato species, and clearly much work remains to be done on the O-donor chemistry of the element. There are a reasonable number of sulfur-donor complexes but few with selenium or tellurium. 

The and PtNMR spectra of the binuclear /i-sulfato and ju-hydrogen phosphato complexes of platinum(III) show values of V(PtP) in the range 40-100 Hz, and V(PtPt) between 3500 and 5400 Hz. The V(PtPt) values for the hydrogen phosphato complexes are significantly larger than those of complexes with bridging sulfato ligands. 

The synthesis and structure determination of a number of pyrophosphito complexes has been carried out. Typical of these is K4 Pt2(H2P205)4) 2H2O, which forms dark green crystals solnble in water to produce an intensely fluorescent solution. The complex anion has a paddle-wheel -type structure in which the P atoms are directly linked to the Pt atoms (8.224a) (cf. phosphato complexes (5.370)) and the pyrophosphinito complex (8.224b) [10]. 

The kinetic pattern for aquation of the newly characterized iU-amido-At-selenato-dicobalt complex (11) is similar to that established for its / -amido-A -sulphato-analogue. In both cases the product is (12), and there is strong kinetic evidence for transient intermediates of the type (13). A rate law of the form shown in equation (4) above operates kinetic parameters for aquation of the Ai-amido-jM-selenato-complex are included in Table 6. A preliminary report on the kinetics of aquation of the closely related acetato-complex (14) indicates that the rate law of equation (4) also applies here, but the rate law for aquation of the yU-amido-/ -phosphato-complex (15) is more complicated. 

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