Metal oxidation state formalism

Method (i) is a route commonly utilized in monometal nitrosyl complexes. The nitrosyl ligand may function as (formally) a three-electrop donor (NO+) with a linear bonding mode, or as (formally) a one-electron donor (NO ) with a bent (—120°) M-N-0 arrangement. Conversion of the M-NO system to a M-NO system has two effects. First, it increases the metal oxidation state by two second, it generates a vacant coordination site. The dinitrosyl cluster Os3(CO)8(NO)2, which has... 

The second photochemical reaction which was studied was the reaction of CotCO NO with Lewis base ligands L (J 6 ). The observed solution phase photochemical reaction is carbonyl photosubstitution. This result initially did not appear to be related to the proposed excited state bending. Further reflection led to the idea that the bent molecule in the excited state is formally a 16 electron coordinatively unsaturated species which could readily undergo Lewis base ligand association. Thus, an associative mechanism would support the hypothesis. Detailed mechanistic studies were carried out. The quantum yield of the reaction is dependent on both the concentration of L and the type of L which was used, supporting an associative mechanism. Quantitative studies showed that plots of 1/ vs. 1/[L] Were linear supporting the mechanism where associative attack of L is followed by loss of either L or CO to produce the product. These studies support the hypothesis that the MNO bending causes a formal increase in the metal oxidation state. 

Numerous transient paramagnetic compounds are known and some of these are also shown in Table IV there is an overlap with Section V, and Table IV does not duplicate material which is more conveniently treated later. The distinction is arbitrary, but we shall defer consideration of transient transition metal-centered radicals, e.g., Pt(I), if their formation is primarily of interest in connection with an organometallic mechanistic study, e.g., the oxidative addition of an alkyl halide to a Pt(0) substrate. The designation of metal oxidation state in Table IV is somewhat formal in many cases it might be more appropriate to describe a complex as derived from a paramagnetic ligand, such as a nitroxide or ketyl. 

There are 35 Au dithiolene units with formal metal oxidation states mostly as Au(III) and some as Au(IV) . The complexes are often considered alongside isoelectronic Pt bis(dithiolene) examples. Coordination geometries for all the Au structures are square planar as is the case for the Auidmit) 1 example shown in Fig. 8. Average Au—S bond distances range from 2.263-2.344 A (Fig. 5) and the longest Au—S bonds are observed with the dithiosquarate ligand (Table IIC, Entry 52). 

Note that while oxidative addition reactions (Section 21-2) could be defined as insertions of metals into R—X bonds, the reactions under discussion here only deal with insertions into M—X bonds, without changes in the formal metal oxidation state. 

A very large series of nitrosyl complexes, [Mo(NO)Tp X Y] has been described where X and Y are halide, alkoxide, aryloxide, alkyl or arylamide, alkyl or aryl thiolate groups. These diamagnetic Mo(NO) + species are regarded as containing 16 valence electrons, with a formal metal oxidation state of 11, assuming NO+ binding, and the metal center could... 

Reaction between DNA/RNA and Mn04 or 0s04 , where the formal metal oxidation states are Mn + and Os +, results in base-specific modification of thymidine/uridine residues. These anionic metal species can oxidize the pyrimidine C5-C6 double bond, which results in formation of m-5,6-dihydroxy-5,6-dihydro-pyrimidine. This reaction is followed by opening of the pyrimidine ring and its subsequent removal from the polynucleotide chain. Permanganate can also oxidize and remove guanine residues (but not adenine) while osmium tetroxide acts much more specifically on pyrimidine residues with the following kinetic preferences (relative rates shown in parenthesis) T (45) U(4.5) > dU(2.8) >... 

---