Radicals dinuclear compounds

A particularly interesting question which remains unanswered is whether dinuclear photoproducts are produced directly from the photoexcited parent molecule or whether they are formed by reaction of free radicals within the solvent cage. In principle this question can be answered by making time-resolved IR measurements on the molecules in the gas phase, where no solvent cage can interfere. Thus, it may transpire that a full understanding of the photolysis of these dinuclear compounds will require complementary experiments in solution and in the gas phase. 

The central atom names are listed after the ligand names. The multiplicative prefix di is used where the central atoms are the same element. Otherwise, the order of the central atom names is obtained using Table VI. The order of the central atom names is reflected in the numbering employed with the K symbols. The ending ate is added if the dinuclear compound is an anion, and a radical dot may be added for radicals. In the case of two different central atoms, the two names are cited inside parentheses and ate is added outside the parentheses. 

Unfortunately, as a quadruple decker was obtained (which contained however only iron), no further results in this potentially very interesting area were published until then. A somewhat related dinuclear compound has been obtained while attempting the synthesis of l-formyl-l, 2, 3, 4, 5 -pentamethylcobaltocene. This compound was only made in situ as it rearranged into dimeric species 362 by redox disproportionation with radical coupling (Equation (62)). ... 

Manganese is used by nature to catalyze a number of important biological reactions that include the dismutation of superoxide radicals, the decomposition of hydrogen peroxide, and the oxidation of water to dioxygen. The dinuclear manganese centers that occur in Lactobacillus plantar-aum catalase and Thermus thermophilus catalase have attracted considerable attention and many model compounds have now been synthesized that attempt to mimic aspects of these biological systems.The catalases have at least four accessible oxidation states (Mn Mn , Mn°Mn , Mn" Mn", and Mn Mn ) it is believed that the Mn"Mn"/Mn"Mn" redox couple is effective in catalyzing the disproportionation of water. 

The short-lived [MH2(Cp)2] and [TaH4(dmpe)2] have been obtained from the Mv hydrides using photogenerated r-butoxy radicals, and were characterized by low temperature ESR.575 On the other hand, thermally stable, well-defined dinuclear or mononuclear MIV hydrides have been prepared by oxidative addition of H2 to dinuclear Mm or mononuclear Mn halide phosphine adducts, respectively. They constitute attractive entries to lower oxidation state compounds, and will be reviewed in Sections 34.4.3.l.i and 34.6.1.2.i. 

Fig. 5. Mechanism of action of dinuclear non-haem iron enzymes utilising ferryl intermediates. Mechanisms for ribonucleotide reductase and methane mono-oxygenase adapted from that of Que [72]. Compound I and compound II define intermediates at the same oxidation state as the equivalent peroxidase intermediate (see Fig. 2). X is an unknown group suggested to bridge between the two iron atoms and form a cation radical. The nature of the electron required for the reduction of ribonucleotide reductase compound II is not clear - it is possible that this intermediate can also oxidise tyrosine [72].

Together with dinuclear molybdenum dialkyldithiocarbamates, trinuclear dialkyldithiocarbamates have recently been introduced for lubricant applications, specifically for use in engine oils [48]. These molecules are based upon [Mo3S4]" and [MosSy] cores complexed by four dialkyldithiocarbamate ligands. It has been reported that these products decompose hydroperoxides more effectively than do dinuclear molybdenum dialkyldithiocarbamates. The patent literature discloses trinuclear molybdenum dialkyldithiocarbamates that are most effective as antioxidants when combined with radical scavengers such as organocopper compounds and diphenylamines [49]. 

An example of a diastereoselective reaction is the radical coupling of dinuclear acetylenic cobalt complexes. This coupling leads to the compound of relative configuration (R, / ) (2.52) with a diastereoselectivity of 0.9 ° (Figure 2.71). (Hi) Enzymatic reactions... 

---