Borohydride half-sandwich

This synthesis is complicated, however, by the need to remove the LiCl formed in the reaction. In addition, metathesis of 1 with LiBHit gives the borohydride half-sandwich. 

Metathesis of the borohydride ligand for cyclopentadienyl in a reaction with KCp or diorganomagnesium compounds gives half sandwich borohydride complexes [Mg(THF)6][Cp Ln(BH4)3] (Cp =Cp, Cp C5H2Ph3, Ln — La, Nd) that are stable to redistribution. Combined with dia-lkylmagnesium, the Nd complexes provide useful catalysts for stereospecific isoprene polymerization.62... 

Tardif reported recently that the cationic half-sandwich lanthanide amido complexes [(Ind)Ln N(SiMe3)2 ][B(C6Fs)4] (29, Fig. 3) were also highly efficient and c/x-l,4-selective for butadiene polymerization [115]. Meanwhile, Visseaux demonstrated that the half-sandwich scandium borohydride complex Cp Sc(BH4)2(THF) (30, Fig. 3) combined with [Ph3C][B(C6Fs)4] and TIBA led to the very active and highly stereoselective isoprene polymerization (>90% c/x-1,4. Table 11) as well as styrene (>99.9% syndio, Table 12). Improvement of the control of the polymerization was performed at lower temperature at — 10°C that the cm-1,4-ratio increased up to 97.2% followed by the decrease of PDI down to 1.7 [116]. This... 

The bimetallic complex 6 containing half-sandwich RhCp fragments (where Cp = 1,2,3,4,5-pentamethylcyclopentadienyl) bridged by a borohydride scaffold also showed moderate catalytic activity for the cyclotrimerisation of several alkynes (Scheme 4) [18,19]. 6 was recovered from the reaction mixture unchanged. 

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