Dihydrogen Formation in a Trihydride Metallocene and Its Elimination, Both Assisted by Lewis Acids: The [Cp₂NbH₃]+BH₃ System

Theoretical Study of the Effect of Lewis Acids on Dihydrogen Elimination from Niobocene Trihydrides

“…[12] On the other hand, the formation of a strong adduct between BF 3 and the hydride ligand when BF 3 is added to a solution of [Cp 2 Nb(CO)H] has been reported. [19] For comparative purposes, our previous results [10] with the parent BH 3 species are also presented. It should be noted that the strength of the Lewis acid increases from the less acidic catecholborane model to the nonexistent BH 3 , which was used as a theoretical model of a very strong Lewis acid.…”

“…Moreover, for TS 2 the H 2 molecule is much farther away from the metal (NbÀH distances of 3.60, 4.03 ) than in the cases of TS 3 and TS 4. Thus, it is not surprising to find an energy barrier for this system very similar to that of the system without Lewis acid (29.3 vs. 30.8 kcal mol À1 ) [10] . Finally, if we consider the process as a whole, we see that, from a static point of view, a stronger Lewis acid favors both the formation of adducts and the process of losing dihydrogen, so that starting from the original 1 Lewis acid structures the hydrogen elimination process requires a lower energy as long as the Lewis acid is stronger.…”

“…[10] The effect of the presence of BH 3 on the energetics of the process of dihydrogen elimination was spectacular. The Lewis acid formed a trihydride adduct with [Cp 2 NbH 3 ], an adduct that was only 3.3 kcal mol À1 below the corresponding dihydrogen complex.…”

Nickel(ii) hydride and fluoride pincer complexes and their reactivity with Lewis acids BX3·L (X = H, L = thf; X = F, L = Et2O)

“…The same kind of geometry has been reported in the theoretical analysis of the reaction between BH 3 and the niobium polyhydride Cp 2 Nb(H) 3 (Cp = h 5 -C 5 H 5 ). 12 The BH 3 fragment is not planar, showing a tetrahedral distortion typical of the BH 4 anion. Interestingly, the PES analysis for this system also led to another structure, where the BH 4…”

Direct Hydride/Silyl Exchange — Synthesis and X‐ray Study of the Bis(silyl) Complex [Cp2NbH(SiCl3)2]

“…It is therefore reasonable to assume that this direct silyl/hydride exchange mechanism is general even for d n ( n > 0) systems, like the Ru and Mo complexes cited above. Complications can arise from the substitution of the silane in 10 by the chloride anion, leading (possibly) to the transient [Cp 2 Nb(H) 2 Cl] and eventually to [Cp 2 NbCl] 2 (as in the reaction with SiCl 3 Me), and, in the case of bulkier or less acidic silanes [such as SiCl 2 Et 2 , SiCl 2 i Pr 2 , SiCl(OMe)Me 2 and SiClMe 3 ], when Lewis acid induced dihydrogen elimination35 occurs faster than deprotonation.…”