For reactions with Co

Olefin Product Time for reaction with CO (minutes) 20... 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

As was previously mentioned, PtRu alloys exhibit improved performance over pure Pt alloys.117,118 This is primarily a result of the ability of Ru to dissociate H20 for reaction with CO adsorbed on Pt sites.115,116 That CO oxidation on pure Ru is unfavorable indicates that on the bimetallic surface, CO is oxidized only on the Pt sites.119 Thus, CO is oxidized on Pt sites adjacent to Ru sites, where water is activated.120,121 This is known as a bifunctional mechanism. In addition, the presence of Ru atoms reduces the adsorption energy of CO on neighboring Pt atoms, lowering the activation energy of CO oxidation.122 This effect is purely electronic and is less significant than the bifunctional effect of Ru.123 One significant limitation of PtRu is the weak adsorption of methanol on Ru, particularly at room temperature.117,124 The weak adsorption severely hinders methanol decomposition, which is evident in Fig. 7 by the drop in current density for PtRu electrodes with high Ru composition.125... 

The second-order decay of the three-coordinate transient (to form a dimer, k = 2 X lO M s ) can be accelerated in the presence of substrates, Ph3P, CO etc. The second-order rate constant for reaction with CO, 1.0 x 10 M s is consistent with an early... 

Related experiments have recently been carried out in Xe (sc) and Kr (sc) with a time-resolved infrared (TRIR) spectrometer . In this system, reaction is initiated with a laser as before, but spectra are measured one frequency at a time with a continuous diode laser as the IR source. This apparatus, which has a time resolution of ca. 10 s, has been used to observe the complete set of M(CO)5Ng complexes (M = Cr, Mo, W Ng = Kr, Xe) and has provided tentative evidence for W(CO)sAr in Ar (sc). The measurements are carried out with a small pressure of added CO chosen such that the complexes have lifetimes from 100 ns to 2 qs. The rate constants for reaction with CO increase as follows Xe < Kr < Ar W < Mo Cr. The IR spectra are supplemented by UV/visible spectra of Cr(CO)sNg, which are in satisfactory agreement with matrix spectra. 

The kinetics of dioxygen consumption are described by the equation which is common for reactions with Co(III) participation... 

Particularly intensive investigations have been carried out on catalysts for reactions with CO or alkenes. These reactions, which are typical transition metal catalyzed conversions, provide the best possibility for assessing the properties of heterogenized catalysts. Examples are given in the following overview (Table 6-1). AU the examples show that the reaction mechanisms with homogeneous and heterogeneous catalysis are in many respects similar. However, care must be taken in... 

The reactions of alkali metal hydroxides (see Section 7.4) with acids and acidic oxides call for no special mention (see end-of-chapter problem 11.23), except for reactions with CO which give metal formates (methanoates), e.g. reaction 11.17. 

Recently, the in situ DRIFT studies on Pd-doped Sn02 sensors showed that in the presence of water, the reaction between CO and hydroxyl groups determines the creation of the hydrated protons, which additionally increases the sensor signal [103]. The exact role of the Pd in the reaction mechanism is still unclear but, due to the fact that for undoped sensors we record a different effect of humidity, Pd should play a determining role. It is also important to note that hydroxyl groups present at the sensor surface do not seem to react with CO in the absence of the water vapor this fact indicates that the association between OH groups and H2O is the condition necessary for reaction with CO. 

Cobalt(in) oxidizes 2-mercaptoethylamine (HMea) in [Co(en)2(Mea)] to the corresponding co-ordinated disulphide complex by pathways involving Co + and [CoOH] +. An outer-sphere mechanism is suggested by the activation entropy (—3.1 cal K mol ) for reaction with Co and the reaction with [CoOH] + is substitution controlled. Redox proceeds by formation of a co-ordinated radical complex [Co(en)2(Mea)] +,... 

Since the solubility of COS into an aqueous alkaline solution has some importance here, and the reaction takes place only in the aqueous phase, Bhave and Sharma (1983) have introduced species such as tricapryl methyl ammonium chloride (Aliquat 336) into the organic phase. This species acts as a phase-transfer catalyst, transferring OH ions into the organic phase near the interface for reaction with COS. Thus COS reacts both in the organic and the aqueous phase, and the rate of COS extraction is increased considerably. 

Reaction of cw-[MeMn(CO)4(THF)] with CO is 10 times slower. In contrast to comparable photoreactions of [M(CO)j], flash photolysis of [MeMn(CO)j] in cyclohexane under CO yields much less [MeMn(CO)4S] and the initially produced intermediate is believed to be in a triplet electronic state that is highly selective, the specific rate for reaction with CO being ca 10 times that for reaction with CgHjj. The greater nucleophilicity of THF prevents this happening in THF solution. 

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