Divalent compounds containing reactivity

A highly reactive compound containing a neutral divalent carbon with two nonbondmg electrons (ie.,. CR2 or a substitution derivative). The nonbonding electrons can have parallel spins (triplet state) or antiparallel spins (singlet state). The parent species, iCRz, is also known as methylene. A number of carbene derivatives have been used as photoaffinity labels of proteins. Irradiation of 3 -0-(4-benzoyl)benzoyl-ATP will cause 70% inactivation of mitochondrial Fi-ATPase. ... 

The other isolable molecular compoimds of uncommon divalent rare earths have been imtil now mostly organometallic complexes featuring cyclopentadienyl ligands or cyclopentadienyl "equivalents" such as pyrazolylborates. The vast majority of characterised compounds contain Tm", the less reactive of the uncommon divalent rare earths (which unfortunately is also the most expensive). Many other stable compounds seem within reach, given that a good steric protection is achieved, such as for instance amides or alkoxides. Also, it may be possible to synthesise more heteroleptic complexes such as LR°I with an open coordination sphere, which could lead to a very rich new chemistry. A pending question finally involves the possibility of finding yet other complexes of rare earths in new divalent states (for instance Y " "). 

A comparison of porphyrin and pincer activity rationalized through reactivity index Porphyrin and pincer complexes are both important categories of compounds in biological and catalytic systems. Structure, spectroscopy, and reactivity properties of porphyrin pincers are systematically studied for selection of divalent metal ions. It is reported that the porphyrin pincers are structurally and spectroscopically different from their precursors and are more reactive in electrophilic and nucleophilic reactions. These results are implicative in chemical modification of hemoproteins and understanding the chemical reactivity in heme-containing and other biologically important complexes and cofactors [45]. 

A relatively unique type of reactive metabolite is carbene, i.e., a divalent carbon, which is a proposed intermediate in the oxidation of methylene dioxy-containing compounds. A methylenedioxy group in aromatic compounds is subject to O-dealkylation, e.g., 3,4-methylenedioxyamphetamine, as shown in Figure 8.20. The process generates formic acid and the catechol metabolite as final products. However, in the course of the reaction, a... 

Carbenes, which may be formed photochemically from precursors such as diazo compounds and diazirines, are highly reactive entities containing divalent carbon. The first photogenerated reagent was a carbene, formed by irradiation of diazoacetyl chymotrypsin (Singh et al., 1962). 

In its reactivity, iodomethylzinc iodide behaves as if it were a source of H2C , a species called methylene. It is not. Methylene belongs to a class of neutral molecules called carbenes, which contain a divalent carbon plus two unshared electrons that can be either paired or unpaired. A characteristic reaction of many carbenes is cycloaddition to double bonds to form cyclopropanes, a property that is shared by iodomethylzinc iodide. Free H2C is not involved in the Simmons-Smith reaction, but the similarity in behavior of iodomethylzinc iodide toward alkenes has led to referring to it and related compounds as carbenoids. 

However, mention should be made of the use of a trimethylsilyl methyl acetal of dimethylketene as an initiator for addition polymerization " and characterization or detection of compounds with Si=Si or Si=C bonds or containing divalent silicon or interchanges between these species. The chemistry of reactive intermediates in organosilicon chemistry has been reviewed by Barton."... 

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