TpRe , ligand

TpRe(CO)(PMe3) produces a variety of stable rj complexes of the type TpRe(CO)(PMe3)() -E) (E = cyclohexene, cyclopentene, naphthalene, phenanthrene, thiophene, 2-methylthiophene, furan, or acetone). They are obtained by reduction of the Re complex TpRe(CO)(PMe3)(OTf) with Na/Hg in the presence of the unsaturated ligand. 

Schrock and co-workers have described the synthesis of a rhenium neopentyli-dyne complex containing the tris(pyrazolyl)borate ligand from Re( = C Bu) (CH2 Bu)3(OTf). Treatment of this complex with excess pyridine afforded the colourless, six-coordinate rhenium neopentylidene/neopentylidyne complex Re( = C Bu)(OTf)(CH2 Bu)( = CH Bu)(py)2], which was subsequently subject to ligand substitution by Na[Tp], producing the thermally stable, 18-electron complex TpRe( = C Bu)(CH2 Bu)( = CH Bu) (Scheme 27). Rhenium is one of the three... 

Isolable transition metal complexes containing hydride and terminal oxo ligands are rare however, Tp Re( = 0)(H)X (X = Cl, H or OTf) and TpRe( = 0)(H)Cl have been synthesized, isolated and characterized. Reactions of Tp Re( = 0)(H) OTf (12) with unsaturated substrates (e.g., ethene, propene or acetaldehyde) result in insertion of C = C or C = 0 bonds into the Re-H bond to yield Tp Re( = 0)(R) (OTf) (R = ethyl or propyl) or Tp Re( = 0)(0Et)(0Tf) (Scheme 6). Oxidation of 12 with pyridine-iV-oxide or DMSO produces Tp Re( = 0)3, acid and free pyridine or dimethylsulfide, respectively. A likely mechanism involves initial oxidation of 12 to produce [Tp Re( = 0)2H][0Tf] (13) followed by the formation of Tp Re( = 0) (OH)(OTf) (14) via a 1,2-migration of the hydride to an oxo ligand (Scheme 6). Reaction of 14 with a second equivalent of oxidant in the presence of base yields Tp Re( = 0)3 (15). Direct deprotonation of 13 is noted as less likely than the pathway shown in Scheme 6 due to the lack of precedent for acidity of related rhenium hydride systems. 

Re(V) oxo-amido complexes of the type TpRe( = 0)(NRR )Cl are formed upon reaction of 4 with several primary or secondary amines (NRR = NHEt, NH"Pr, NH Pr, NH2, NEt2, NHPh, NH-/ -tolyl or piperidyl) (Scheme 11). The Re complexes with secondary amido ligands are more robust and less reactive than the... 

Scheme 12. Ligand substitution reactions of TpRe(=NTol)(Ph)(OTf).

Complex 4 and TpRe( = 0)Br2 (27) have been prepared by reaction of 3 with PPhs in the presence of Me3SiCl or Me3SiBr (Scheme 19). The reduction of 4 requires more forcing conditions relative to the technetium analog, consistent with the fact that reduction of rhenium complexes is typically less facile than corresponding technetium complexes. Replacement of chloride ligands with bromide does not significantly alter the redox properties of TpRe( = 0)X2 (X = Cl or Br). 

A survey of available IR and CV data has revealed that relative donor properties of Cp, Cp, Tp and Tp can vary with metal identity and oxidation state. Analysis of TpRe(CO)3 and Tp Re(CO)3 shows that the two complexes are electronically similar. For example, sharp peaks at 2010 and 2020cm are assigned as the symmetric CO stretching absorption for TpRe(CO)3 and Tp Re(CO)3, respectively, while broad absorptions at 1900 and 1890cm were assigned as the asymmetric vcoj respectively. Analysis of vco fof CpRe(CO)3 and TpRe(CO)3 suggest that, for these systems, the Tp ligand is a more effective electron donor compared to... 

Scheme 28. Dihapto-coordination of various ligands upon reduction of TpRe(CO)(PMe3)OTf.

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