Low oxidation state chemistry

Amongst the consequences to be expected from the change from Werner-type behaviour to carbonyl, low oxidation state chemistry is a breakdown in the efficacy... 

The coordination chemistry of boron was reviewed some time ago and the structure and properties of compounds of the general formula BX3 L, where X and L can be one of a wide variety of substituents and electron pair donors, respectively (15). Indeed, the reactions of tricoordinate boron compounds in general are thought to proceed via addition of the reaction partner in a Lewis acid-base reaction to yield a tetracoord-inate intermediate that then undergoes further reaction. Stable tetra-coordinate boron compounds are subject to ligand displacement reactions for which a variety of mechanisms obtain (16). The coordination chemistry of transition metals is vast and includes not only structimal facts (17) but considerable information on the mechanistic behavior of these species as well (18). In our brief comparison we will restrict ourselves to low oxidation state chemistry and group 16 metals (19). 

Joseph Chatt s interests in organometallic chemistry were wide-ranging, from bonding theories to nitrogen fixation. While these areas may not seem of immediate relevance to either carbonyl cluster chemistry or to electrospray mass spectrometry (both of which play a major role in the work described herein), the chemistry that is discussed broadly overlaps with Chatt s contributions in metal hydride, metal phosphine and low-oxidation-state chemistry. 

Both our photochemical and radiation studies have focused on the chemistry of very reactive species in aqueous solution. Indeed, it is because the photochemical work involved aqueous media that radiation chemistry techniques could be so useful to us. Our pulse radiolysis work has led to a number of highly unusual mechanistic conclusions. In the area of low-oxidation-state chemistry, several of the systems violate standard organometaUic dogma. We investigated the rate of hydride formation in another cobalt(I) system, that derived from the high-spin d polypyridyl-cobalt(I) complexes (28). Remarkably, electron transfer was found to be the rate-determining step for formation of the hydride complex, and contributions from Bronsted acid pathways contribute neghgibly to the rate. Rather, the hydride formation appears to involve H-atom transfer from the protonated bpy radical. The H-atom receptor may be either Co(bpy)2 or Co(bpy) as shown in Scheme II. 

As with last year, many fundamental advances have been made in the area of low oxidation state chemistry. A simple synthesis of (Cp Al)4, by reduction of Cp AlCl2 with potassium rather than starting from AlCl, should pave the way for further derivative chemistry. Indeed, the first reactions of this species have been... 

Low Oxidation State Chemistry of the Group 2 Metals A Brief Overview... 

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