Aluminium‐Catalyzed Selective Reduction of Heteroallenes Through Hydroboration: Amide/Thioamide/Selenoamide Bond Construction and C=X (X=O, S, Se) Bond Activation**

Abstract

An unprecedented conjugated bis-guanidinate (CBG) stabilized aluminium dihydride, [LAlH 2 ; (L={(ArNH)(ArN)À C=NÀ C=(NAr)(NHAr)}; Ar=2,6-Et 2 -C 6 H 3 )] (I) catalyzed chemoselective hydroboration of heteroallenes such as carbodiimide (CDI)s, isocyanates, isothiocyanates, and isoselenocyanates is reported. A wide range of heteroallenes, including electron-donating and withdrawing groups, experience hydroboration to obtain selectively N-boryl amide, N-borylaminal, and N-boryl methyl amine products. More importantly, a single sustainable molecular aluminium-based catalyst effectively catalyzes CDIs, isocyanates, isothiocyanates, and isoselenocyanates into formamidines, formamides, thioformamides, and selenoformamides, respectively. Further, heteroallene substrates undergo hydrodeoxygenation (HDO), hydrodesulfurization (HDS), and hydrodeselenization (HDSe) reactions leading to Nboryl methyl amines. In addition, a series of control and kinetic experiments indicate that the aluminium hydride species are essential for all partial and complete reduction steps and breaking the C=X (X=O, S, and Se) bonds in heteroallenes.

NHC-Silyliumylidene Cation-Catalyzed Hydroboration of Isocyanates with Pinacolborane

“…In these catalysis reactions, the activity of catalyst 1 in terms of TOF and product yield are better than that of other metal catalysts such as β-diketiminato magnesium, bis­(guanidinate) aluminum and zinc dihydride complexes, , AgSbF 6 , and Co­(acac) 2 (for example, 4m , [Zn]: yield = > 99%, TOF = 4.17 h –1 ; [Al]: yield = > 99%, TOF = 4.17 h –1 ; [Co]: yield = 91%, TOF = 0.95 h –1 ; see Table S4).…”

Magnesium halide-catalyzed hydroboration of isocyanates and ketones

“…11–27 Compared with alkene (CC), alkyne (CC) and nitrile (CN) unsaturated bonds, reports on metal-catalyzed hydroboration of isocyanates are very few. 28–35 In 2021, Nembenna et al . reported that a remarkable conjugated bis-guanidinate supported zinc hydride was employed as an efficient catalyst in the hydroboration of a range of aryl and alkyl isocyanates to afford selectively N -boryl formamide, bis(boryl) hemiaminal and N -boryl methyl amine products, respectively.…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Compared with alkene (CvC), alkyne (CuC) and nitrile (CuN) unsaturated bonds, reports on metal-catalyzed hydroboration of isocyanates are very few. [28][29][30][31][32][33][34][35] In 2021, Nembenna et al reported that a remarkable conjugated bisguanidinate supported zinc hydride was employed as an efficient catalyst in the hydroboration of a range of aryl and alkyl isocyanates to afford selectively N-boryl formamide, bis (boryl) hemiaminal and N-boryl methyl amine products, respectively. 28 Nevertheless, to the best of our knowledge, there have been only three examples of Mg-catalyzed hydroboration of isocyanates so far.…”

Carbodiimide and Isocyanate Hydroboration by a Cyclic Carbodiphosphorane Catalyst**

“…Catalytic carbodiimide hydroboration reactions were first reported in 2016 using magnesium catalysts. [8,9] Since then, catalysts for carbodiimide hydroboration using pinacolborane (HBpin) have been reported from across the periodic table, including transition metal, [10][11][12] main group, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and actinide [28] catalysts. Most carbodiimide hydroboration catalysts operate at elevated temperatures (50-80 °C).…”

“…Most carbodiimide hydroboration catalysts operate at elevated temperatures (50-80 °C). [8][9][10][16][17][18][19][20][21][22][23][24]27,28] Exceptions that operate at room temperature include a carbatrane magnesium hydride complex, [14] the 9-borabicyclo[3.3.1]nonane dimer, [15] manganese(II) bis(hexamethyldisilazide), [11] a boron-functionalized heptaphosphide Zintl cluster, [25] 9,10-dihydro-9,10-diboraanthracene dianions, [26] and an N-heterocyclic carbene-supported copper alkoxide complex. [12] Initial studies of catalytic isocyanate hydroboration reactions in 2016 and 2017 reported magnesium catalysts for the dihydroboration of isocyanates to form N,O-bis(boryl) hemiaminal products or hydrodeoxygenation reactions to generate N-methyl amines.…”