Heterometallic Complexes with Re−Bi Metal Bonds

Abstract

The reaction of rhenocene hydride with bismuth alkoxides leads to complexes containing Re-Bi metal bonds with concomitant formation of the corresponding alcohols. Hence, compounds of the type [Cp 2 Re-BiR 2 ] can be obtained from the monoalkoxide [(MeO)Bi(o-tol) 2 ] n and also from the trialkoxide [Bi{OCH(CF 3 ) 2 } 3 (thf)] 2 , for which in principle also multiple substitution reactions would have been possible, but are prohibited by the electron-withdrawing character of the hexafluoroisopropyl groups. Correspondingly, the trialkoxide [Bi(O t Bu) 3 ] containing electron-rich tert-butyl groups does lead to multiple substitution events: First of all it reacts with two equivalents of [Cp 2 ReH] to give the intermediate [(Cp 2 Re) 2 Bi(O t Bu)], which could not be isolated, since it undergoes an intramolecular alcohol elimination via Cp C-H bond cleavage. This results in the complex [CpRe(μ-η 5 ,η 1 -C 5 H 4 )Bi-ReCp 2 ], featuring a bent Bi-C bond so that one deprotonated Cp ligand bridges a Bi-Re metal bond. All compounds have been fully characterized, and their crystal structures are discussed.

Heterometallic Complexes with Rhenium- and Iron-Bismuth Bonds

“…1 is readily soluble in all common solvents. A proton nuclear resonance measurement of the yellow crystals dissolved in C 6 D 6 confirmed the 1 H NMR data of 1 derived before from the spectrum of a reaction mixture [13]. A singlet resonance can be observed for all Cp protons at 4.24 ppm and a further one for the tert-butoxide moieties at 1.45 ppm.…”

“…1. It is very similar to that of [Cp 2 Re-Bi{OCH(CF 3 ) 2 } 2 ], I [13]. A rhenocene fragment is connected to a bismuth alkoxide moiety through a Re-Bi single bond, the distance .…”

“…We have also shown that this "hydride alkoxide" approach can be successfully extended to Re-Bi compounds [13].…”

“…This indicates that the two Cp 2 Re units are chemically equivalent, that the Cp ligands are able to rotate freely around their Cp-Re axis, and that in turn the Cp 2 Re fragments can rotate along the Re-Bi bonds with no significant barrier. The single proton at the hexafluoroiso-propoxide moiety gives rise to a septet at 4.44 ppm, which is shifted to higher field compared to that of the precursor I (C 7 D 8 : 5.04 ppm) [13]. Slow concentration of a diethyl ether solution of the dark-green solid at room temperature led within 2 weeks to black plates of 4, which were investigated by single-crystal X-ray diffraction (Fig.…”

“…Monitoring the reaction by NMR provided evidence for the occurrence of two intermediates, which we assigned as [Cp 2 ReBi(O t Bu) 2 ], 1, and [(Cp 2 Re) 2 Bi(O t Bu)], 2, but these compounds eluded isolation due to fast subsequent reactions [13]. Analogs of 1, [Cp 2 Re-BiR 2 ], could be prepared for R = OCH(CF 3 ) 2 , I, and R=o-tol, II, as the electron-withdrawing alkoxide ligands slow down further reactions and as Bi-C bonds are relatively inert, respectively.…”