摘要:

Two essential facets of transition metal organometallic compounds are (i) their ability to undergo transformations of organic and inorganic species at the metal and (ii) the ease of redox changes induced by the metal. This Comment indicates the potential of this second aspect and how organometallics may be designed and used to promote electron transfer (ET). Inexpensive, easily available organometallic electron-reservoirs can conveniently effect a variety of stoichiometric and catalytic ET processes. The salt effect and the activation of dioxygen are especially under our scrutiny in stoichiometric reactions. Catalytic ET involves redox catalysis of electrochemical reactions (the catalyst lowers the overpotential) and electro-catalysis of organometallic reactions (ligand substitution, decomplexation, isomerization, chelation, insertion). These processes can be effected using (instead of an electrode) iron sandwich compounds: the electron-deficient ferricinium Cp2Fe+(17 valence electrons) for oxidations and the electron-reservoir compound CpFeIC6Me6(19 valence electrons) for reductions.

ISSN:0260-3594    

DOI:10.1080/02603598708081853

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The efficiency of an asymmetric synthetic reaction is measured by what is called the enantiomeric excess (e.e.). It is commonly assumed that this is a unique quantity for a given asymmetric reaction under specified conditions. The purpose of this Comment is to show that this is not necessxily so, and that, under certain circumstances, e.e. is an elusive quantity which continuously changes with the extent of reaction.

ISSN:0260-3594    

DOI:10.1080/02603598708081854

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Mechanistic interpretation of observed pressure-dependent photochemical Φ(X) and photophysical (τ) parameters can be very complicated when more than one photoactive electronic state must be considered. The4T2gand2Egstates of Cr(NH3)3+6differ by (4–5) × 103cm−1and are both photoactive. Proposed models either postulate a single channel for deactivation of the2Egstate or several competing channels. Systematic approaches for the mechanistic evolution of pressure-dependent quantum yields and lifetimes are presented. The implications of the published pressure dependencies depend on the mechanistic model proposed. For example, the single channel, back intersystem crossing model (4T2g←2Eg) requires a volume of activation for NH3aquation from the4T2gstate, δV‡NH3≃ −13 ± 2 cm3mol−1, while a model assuming multiple competing channels for doublet decay results in δV‡NH3= −4 cm3mol−1. Both of these models imply a strongly associative pathway for (4T2g) Cr(NH3)3+6equation. Other models are considered, and photo substitution in the most plausible of these also appears to be associative. Thus prevailing theories, based on dissociative photoreaction pathways, are probably inconsistent with the published pressure effects.

ISSN:0260-3594    

DOI:10.1080/02603598708081855

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0260-3594    

DOI:10.1080/02603598708081856

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor