Sphere Reactions Scheme

The oligomerization of the ethylene proceeds as a ligand reaction in the coordination sphere of the catalyst complex, as the following reaction scheme shows. The reaction course corresponds with the Ziegler process for ethylene polymerization. 

Set up a reaction scheme in which Ru(bpy)3+ forms an outer-sphere complex with Co(en)j+. Both electron transfer and energy transfer can occur within this complex to produce Ru(bpy)j [Co(en)3 and/or Ru(bpy)3 Co(en)3. The breakdown of these lead to Co(Il) and/or Co(lll) respectively. The relative values of the various rate constants linking these species will determine the value of N p. 

The hydrogenation reaction mechanisms may be classified according to the role played by the substrate in the coordination sphere of the metal catalyst. Thus, those mechanisms proceeding with coordination of the substrate to the metal center can be labeled as inner-sphere mechanisms, whereas those with no direct coordination of the substrate to the metal center can be labeled as outer-sphere reaction mechanism (see Scheme 4). Hydrogenation reactions belonging to the so-called hydrogen transfer reactions (where the hydrogen source is usually an alcohol) can be also classified within these two families of reaction... 

The series of elementary steps which constitute the overall electron transfer mechanisms for outer-sphere and inner-sphere reactions are illustrated in Schemes 1 and 2. 

For an inner-sphere reaction there are necessarily more steps since both association and substitution must precede electron transfer. Intermediates like (H20)5CruClCoUI(NH3)54+ and (H20)5CrinClCoII(NH3)54 shown in Scheme 2 are often referred to as the precursor and successor complexes since they precede or follow the electron transfer step. 

In contrast to outer-sphere reactions, the simple observation that a reaction occurs by an inner-sphere mechanism necessarily introduces an element of structural definition. The relative dispositions of the oxidizing and reducing agents are immediately established and, except for structurally flexible bridging ligands such as NC5H4(CH2) C5H4N, the internuclear separation between redox sites can be inferred from known bond distances. Even so, bimolecular inner-sphere reactions necessarily occur by a sequence of elementary steps (Scheme 2) and the observed rate constant may include contributions from any of the series of steps. 

By following the reaction scheme proposed by dos Santos Afonso and Stumm (22) for the reductive dissolution of hematite surface sites (Scheme 1), we were able to explain perfectly the observed pH pattern of the oxidation rate of H2S. The rate is proportional to the concentration of inner-sphere surface complexes of HS" formed with either the neutral (>FeOH) or the protonated (>FeOH2+) ferric oxide surface sites. 

Autoxidadon of Bare ruthenium( II) and osmium(II) porphyrins - A resonance Raman study of the intermediates formed during the reaction of Ru(TPP) (which was obtained according Scheme 1, paths — f, — j, — k) in toluene [258] proved the anticipated [205] reaction scheme of the inner-sphere autoxidation, the first step of which is the formation of a p-peroxobis[porphyrinato-ruthenium(III)] complex which is split into two oxoruthenium (IV) fragments. These species precede the formation of /r-oxobisruthenium(IV) porphyrins (reaction 16) for P = TPP, OEP for P = TMP, a disproportionation (17) is indicated, the resulting Ru(P) itself is further autoxidized. 

Few monomeric d4 bisalkyne complexes with only monodentate ligands in the coordination sphere have been reported. The only molybdenum(II) complex in this category is Mo(PhC=CR)2(CO)(NCMe)I2 (R = Ph, Me), which was included in a reaction scheme illustrating products accessible from cleavage of the iodide bridges in dimeric [Mo(PhC=CR)(/r-I)-(I)(CO)(CNMe)]2 reagents (51). Efforts to convert Mo(RC=CR)(CO)-L2X2 complexes to bisalkyne derivatives were not successful (46). 

Now that we have data for water exchange rates, the complex formation reactions of lanthanides in aqueous media can be considered. Complex formation reactions of lanthanides usually involve initial formation of an outer-sphere complex followed by a loss of water molecule and the ligand taking the position of the leaving water molecule. The reaction scheme is as follows ... 

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