Rhenium imido complexes

Compounds of the composition [ReOCl3(N N)] have also been isolated with pyridine-2-aldi-mine and rr-acidic arylazopyridine and arylazoimidazole ligands." The products (101) are readily reduced by oxygen atom transfer reactions from Re to phosphorus atoms of phosphines which results in the formation of rhenium(III) complexes. Depending on the reaction condition and the phosphines used either mononuclear or binuclear compounds are formed." " Azo splitting reactions with arylazopyridines give access to arylimido and binuclear oxo/imido com-plexes. "" ... 

The reactivity of terminal nitrido ligands towards acidic fragments has been used for the synthesis of imido derivatives starting from the neutral rhenium(V) complex... 

The one example of an imido complex of rhenium(lV) is Re(NPh)Cl2(PMe3)3 which has been prepared by the reduction of Re(NPh)Cl3(PMe3)2 in THF using one equivalent of Na/Hg in the presence of an excess of trimethylphosphine. This air sensitive, dark red crystalline complex is paramagnetic with a magnetic moment of 1.66 BM at room temperature, and is further characterized by a broad ESR signal centered at g = 1.74 for a frozen benzene solution.34 These observations have been interpreted in terms of a low-spin ReIV species with a ligand field of low symmetry. 

FIGURE 3.24 Oxo imido rhenium(VII) complexes and their mechanism of OAT. 

Studies of the chemistry of phenylimido rhenium complexes have normally employed Re(NPh)Cl3(PPh3)2 as the starting material because of its easy preparation from aniline and the readily available compound ReOClj(PPh3)2. Tungsten imido complexes cannot be prepared similarly. The lack of good preparative methods leading to suitable starting materials has limited studies with this metal. 

The first rhenium dithiocarbamate complexes, [ReClaCSaCNRa)], were not reported until 1960 (1181), and even then, it was not until the 1970s that substantial inroads were made. Now, dithiocarbamates are known to stabilize rhenium in oxidation states +1 to +5, with the latter being the most common, and the chemistry is dominated by strong jt-donor ligands such as oxo and imido, and especially prevalent are nitride complexes. 

Rhenium imido-dithiocarbamate complexes were first prepared by Rowbot-tom and Wilkinson in 1972 (1182) and considerable recent progress has been made in this area. Reaction of [ReCl3(NAr)(PPh3)2] (Ar = Ph, p-tol. Me) (240) with either Me3SiS2CNR2 or TIS2CNR2 (R = Me, Et) gives [Re(NAr)-... 

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