Advances in the chemistry of bis-cyclopentadienyl hydride derivatives of niobium and tantalum

✍ Scribed by Antonio Antiñolo; Fernando Carrillo-Hermosilla; Mariano Fajardo; Juan Fernández-Baeza; Santiago Garcı́a-Yuste; Antonio Otero

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 296 KB
• Volume: 193-195
• Category: Article
• ISSN: 0010-8545
• DOI: 10.1016/s0010-8545(99)00164-2

✦ Synopsis

The bis-cyclopentadienyl hydride chemistry of the elements niobium and tantalum has been dominated by the family of trihydride complexes, namely Cp 2 MH 3 (M= Nb, Ta, Cp = C 5 H 5 , C 5 Me 5 , C 5 H 4 SiMe 3 , C 5 H 3 (SiMe 3 ) 2 and related substituted cyclopentadienyl rings). The chemical and spectroscopic properties of these complexes are strongly influenced by both the nature of the Cp ring and the metal center. In some cases, anomalous NMR spectroscopic behavior has been observed, and values of J HH that are largely dependent on the temperature have been found. This behavior can be modulated by means of the interaction of the trihydride complexes with Group 11 metal fragments, and in some cases HH interactions in the molecules can be observed. Several X-ray crystal structure determinations of this kind of complex, as well as different theoretical calculations, have been performed in order to gain a deeper insight into these systems. The reactivity of the trihydride metallocene complexes has been extensively considered. Thus, the easy elimination of H 2 from the Cp 2 MH 3 species, giving rise to the unsaturated species Cp 2 MH, has been used to study the activation processes of several kinds of H X bond, in hydrosilanes, hydrogermananes, etc., which allows the synthesis of complexes such as Cp 2 MH 2 X. This type of complex has been extensively studied, especially when X = SiR 3 , because in several cases these complexes exhibit a special hypervalence behavior. A large family of complexes of stoichiometry Cp 2 MHL was prepared from the reaction of the Cp 2 MH 3 complexes with different classes of p-acid ligands, L. The Cp 2 MHL complexes can undergo insertion reactions into the M H bond with several classes of unsaturated molecules, and such processes are of interest in the field of organic synthesis. Furthermore, the protonation processes of the Cp 2 MHL complexes give rise to a new family of h 2 -H 2 -containing cationic species, Cp 2 M(h 2 -H 2 )L + , which are stable at low temperatures. The NMR data of such compounds indicate that it is possible to block the rotation of the H 2 molecule at low temperatures. Of particular interest are the Cp 2 MH(olefin) complexes, and these have been widely studied because they can be considered as excellent models for the study of the b-elimination reaction and the reverse olefin insertion process. Finally, from the trihydride derivatives Cp 2 MH 3 and related species, several heterometallic complexes have been prepared and characterized.