Lanthanide aryloxides catalyzed hydroboration of aldehydes and ketones

Rare‐earth metal‐catalyzed hydroboration of unsaturated compounds

“…Likewise, the group also investigated a series of rare‐earth metal complexes bearing aryloxide ligands Ln(OAr) 3 (THF) 2 [Ar = Ar 1 = 2,6‐ t Bu 2 –4‐MeC 6 H 2 , Ln = Yb ( 11a ), Y ( 11b ), Sm ( 11c ), Nd ( 11d ); Ar = Ar 2 = 2,6‐ i Pr 2 C 6 H 3 , Ln = Y ( 11e ); Ar = Ar 3 = 2,6‐Me 2 C 6 H 3 , Ln = Y ( 11f )] in the hydroboration of carbonyl compounds (Figure 2). [ 23 ] The rare‐earth aryloxides are generally believed to be stable to air, which also, in turn, inhibit their performance in catalysis; the presented results, though, showed the comparable activity of these complexes in promoting hydroboration as Cp 3 La complex. [ 21 ] Also, the order of different metals regarding their performance followed the general trend that larger radius offers better catalytic activity, namely, Y and Yb < Sm < Nd, in this study.…”

“…[43] In this regard, Huang's group also examined the capability of the catalysts in promoting hydroboration of nitriles, and various nitriles could be smoothly converted, including substrates bearing electron-withdrawing and aliphatic substituents. It is worth noting that the authors also studied the competition between substrates bearing different unsaturated groups, and the results revealed an order of reactivity as C═O ) C═N > C≡N > CO 2 Et > C═C, although F I G U R E 5 Rare-earth complexes used in hydroboration of imines, nitriles, and amides S C H E M E 2 1 1,2-Hydroboration of pyridines catalyzed by (Cp 0 2 LaH) 2 (23) the authors believed that the active species in the catalytic cycle is shared metal hydride in other transformations. [21,22] Interestingly, the substrate possessing pyridyl group could afford product in high yield with selectively reduced nitrile and untouched pyridine under the conditions while Marks et al have demonstrated the La-H species actually is involved in the 1,2-dearomatization of pyridines.…”

Organo-f-Complexes for Efficient and Selective Hydroborations

“…Lanthanide aryloxides 33-38 ( Figure 4) were evaluated as catalysts by Xue, Bao, and co-workers in the hydroboration of carbonyl compounds with HBpin. 40 It was found that the complexes containing bulkier ligands have superior activities compared to their sterically less hindered counterparts. For instance, reducing the steric hindrance of orthosubstituents from tert-butyl (34) to isopropyl (35) and methyl (36) resulted in a reduction in alcohol conversions from 77% to 58%.…”

Hydroboration of Aldehydes, Ketones, and Carbodiimides Promoted by Mono(imidazolin‐2‐iminato) Hafnium Complexes

“…The hydroboration of C=O bonds is particularly impressive and it is strengthening its prestige as one of the utmost useful and most widely used reactions for the pharmaceutical industry . Carbonyl hydroboration catalysts include alkaline earth metals,, transition metals, group 13 metal catalysts, lanthanide, actinides, and other unique and sophisticated systems . In addition to the hydroboration of C=O bonds, the selective monohydroboration of carbodiimides to produce amidinates is also of great interest, since these systems play an important role in coordination chemistry …”