This study describes the use of a silicon(II) complex, namely, the NHC-silyliumylidene cation complex [(I Me ) 2 SiH]I (1, I Me = :C{N(Me)C(Me)} 2 ), to catalyze the chemoselective N-formylation of primary and secondary amines using CO 2 and PhSiH 3 under mild conditions to afford the corresponding formamides as a sole product (average reaction time: 4.5 h; primary amines, average yield: 95%, average TOF: 8 h −1 ; secondary amines, average yield: 98%, average TOF: 17 h −1 ). The activity of 1 and product yields outperform the currently available non-transition-metal catalysts used for this catalysis. Mechanistic studies show that the silicon(II) center in complex 1 catalyzes the C−N bond formation via a different pathway in comparison with non-transitionmetal catalysts. It sequentially activates CO 2 , PhSiH 3 , and amines, which proceeds via a dihydrogen elimination mechanism, to form formamides, siloxanes, and dihydrogen gas.

This study describes the first use of a bis(phosphoranyl)methanido aluminum hydride, [ClC(PPh 2 NMes) 2 AlH 2 ] (2, Mes = Me 3 C 6 H 2 ) for the catalytic hydroboration of CO 2 . Complex 2 was synthesized by the reaction of a lithium carbenoid [Li(Cl)C(PPh 2 NMes) 2 ] with two equivalents of AlH 3 •NEtMe 2 in toluene at -78 o C. 10 mol % of 2 was able to catalyze the reduction of CO 2 with HBpin in C 6 D 6 at 110 o C for 2 days to afford a mixture of methoxyborane [MeOBpin] (3a; yield: 78 %, TOF: 0.16 h -1 ) and bis(boryl)oxide [pinBOBpin] (3b). When more potent [BH 3 •SMe 2 ] was used instead of HBpin, the catalytic reaction was extremely pure, resulting in the formation of trimethyl borate [B(OMe) 3 ] (3e) [catalytic loading: 1 mol % (10 mol %); reaction time: 60 min (5 min); yield: 97.6 % (>99 %); TOF: 292.8 h -1 (356.4 h -1 )] and B 2 O 3 (3f). Mechanistic studies show that the Al-H bond in complex 2 activated CO 2 to form [ClC(PPh 2 NMes) 2 Al(H){OC(O)H}] (4), which was subsequently reacted with BH 3 •SMe 2 to form 3e and 3f, along with the regeneration of complex 2. Complex 2 also shows good catalytic activity towards hydroboration of carbonyl, nitrile and alkyne derivatives. ASSOCIATED CONTENTSupporting Information. The Supporting Information is available free of charge on the ACS Publications website.Experimental procedures (PDF), theoretical studies (XYZ) X-ray crystallographic data (CIF)

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