Rhenium complexes tris

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

Rhenium(III) tris-chelates are formed by the reaction of 2-(diphenylphosphinomethyl)-4-methylphenol, PpOH (258a), or 2-diphenylphosphinophenol, P2-OH (258b) with [ReCl3(PPh3)2(CH3CN)] in a 1 3 ratio. [Re(Pi-0)3] is stable as solid and in solutions while [Re(P2-0)3] is easily oxidized in air giving the rhenium(V) 0x0 complex [Re0(P2-0)2(0P2-0]. This behavior is also reflected in the electrochemical behavior of the compounds, where each one well-defined redox couple for one-electron oxidation and reduction steps are observed for both compounds. A second oxidative wave (Re /Re ) is only reversible for [Re(Pi-0)3]. 

Rhenium displays an unusual array of oxidation states and coordination numbers that make it the subject of much current research. The following preparation, adapted from one developed by Chatt and coworkers, provides a convenient synthesis of trichlorooxobis(triphenylphosphine)rhenium(V)1 based on either rhenium(VII) oxide or perrhenate salts. The trichlorooxo compound is a versatile intermediate for the synthesis of other rhenium complexes such as wer-trichlorotris(dimethylphenylphosphine)rhenium-(III),2 as described below. The rhenium(III) complex, in turn, provides a starting point for synthesis of other compounds such as frans-tetrachloro-bis(dimethylphenylphosphine)rhenium(IV)3 and tris(dimethylphenylphos-phinepentahydrido)rhenium(V).4 An alternative synthesis of the trichloro-complex is described in the accompanying preparation by Douglas and Shaw.4... 

One important example of this class of rearrangement was reported for a rhenium complex in 199367 and, in retrospect, took advantage of the lower barrier of hydrogen migrations as compared to alkyl migrations. Mayer and co-workers prepared the tris-acetylene hydroxide complex 11, as well as the oxo hydride 12. Upon standing at room temperature for 5 days in benzene solution, the hydroxide spontaneously forms the oxo hydride with loss of one equivalent of acetylene, as shown in Eq. (8). 

Experiments in which introduction of bulky pseudofluorides to try to understand the way they might influence the chemistry of low-valent metals was described in Section 3.6 in respect of rhenium complexes. The same thinking has been applied in the case of osmium and the reaction of cf.v-[Os(CO)4Me2] with on the one hand, HF and on the other, HOTeF5 have resulted in methane elimination and the formation of m-[OsF2(CO)4] and c/.v-[Os(OTeF5)(CO)4Me] respectively [44]. This offers the promise that methane elimination from hydrides will be a useful route into other low-valent fluoro derivatives. 

Finally, insertion of alkynes into dihydrogen mononuclear cationic rhenium complexes, stabilized by the triphos (= l,l,l-tris(diphenylphosphinomethyl)ethane) ligand, leads to vinylidene derivatives which react with water or ethanol eliminating silanols or methane, Fig. 18. Solvents were acetone or THF no chromatography was used. 

The reactions of rhenium(V) oxo-alkyl-phosphine complexes with various alkynes were studied and the X-ray crystal structure of [Re(=0)Mc3(PhC>CPh)] was reported OO. The synthesis of a number of ibenium(I) tris-alkyne complexes was reported and [Re(OSiMe3)(MeCjCMe)3] characterised by X-ray diffraction Oi. The synthesis of a series of bis-imido alkyne and imido bis-alkyne rhenium complexes of the type [Re(NAr)2Cl(RCSCR)] and [ReCl(NAr)(NpGCNp)2] has been reported302 and the electrtxiic structures of the compounds investigated by Extended Huckel molecular mbital calculations. 

Scheme 25 Carbonyl manganese and rhenium complexes with tris(oxazolinyl)...

Tris(dioxime) complexes that are capped with a boryl group BR at only one end of the molecule are also known, e.g., with technetium(III) [227, 228] and rhenium(III) [229]. 

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