Mono complexes niobium

Mono(cyclopentadienyl) complexes alkenes and tantalum, 5, 157 alkyne and niobium, 5, 80 calcium, strontium, barium, 2, 133... 

The cocondensation of Nb atoms with toluene has yielded bis( -toluene)niobium, which serves as a useful intermediate for the preparation of a wide series of mono- and bis-arene derivatives. While Ti, V, Nb, Cr, Mo, and W form (Ar)2M sandwich complexes, Mn, Tc, and Re appear less promising, because Mn-arene complexes have already been shown to be unstable, Tc is radioactive, and Re remains to be investigated. As already mentioned, Ti forms fairly labile bis(arene)Ti complexes. The unstable 16-electron sandwich complexes from elements of group 4 can be stabilized with phosphine ancillary ligands, yielding bis-arene derivatives as in Table 6. 

Although group 5 organometallic systems have been found to be of relevance in transition-metal catalyzed hydroboration reactions, structurally authenticated group 5 boryl complexes remain relatively few in number. Smith and co-workers, for example, have probed the mechanisms for the formation of niobium and tantalum mono- and bis(boryls) from propylene complex precursors, with concomitant formation of propyl boronate esters [31,32]. Of particular interest from a structural viewpoint are the relative merits of alternative bonding descriptions for metal(V) boryl bis(hydrides) as borohydride complexes or as mono(hydride) a-borane systems [31-34]. 

Vanadium, Niobium and Tantalum An entry into Cp 2Ta chemistry has been developed with the reaction of Cp TaCl3PMe3 with LiCp. The complex Cp 2Nb(BH4) provides an appropriate entry into Cp 2NbH3 chemistry,A study of the electrochemistry of Cp2NbCl2 has led to the identification of the one-electron reduction product (Cp2NbCl3NbCp2l and (Cp2NbCl]2 on the way to niobocene. Reactions of mono and dihydrides of Cp2TaH(C0)... 

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