Heterogeneous‐Gold‐Catalyzed Acceptorless Cross‐Dehydrogenative Coupling of Hydrosilanes and Isocyanic Acid Generated in situ from Urea

Abstract

Cross-coupling reactions (e.g., Suzuki, Negishi, Heck, Stille, Kumada, and Buchwald-Hartwig reactions) are of paramount importance and have proven useful for the design of molecules. [1] Although cross-coupling reactions can precisely construct new C À C, C À X, and X À X bonds (X = heteroatom), they usually utilize preactivated substrates (e.g., halides, tosylates, and triflates) and require transmetalation steps, which concurrently generate at least stoichiometric amounts of metal salts as waste. [1] Recently, cross-dehydrogenative coupling reactions by direct activation of CÀH or XÀH bonds have been emerging as synthetic tools because they are more atom efficient and environmentally benign than classical cross-coupling reactions. [2] To date, several efficient crossdehydrogenative coupling reactions using hydrogen acceptors (oxidants) such as tert-butyl hydroperoxide, [3] hydrogen peroxide, [4] and molecular oxygen [5] have been developed. Acceptorless cross-dehydrogenative coupling reactions have also been developed. [6] Quite recently, we have also reported C À N (terminal alkynes and amides), [7] P À N (H-phosphonates and amides), [8] SiÀN (hydrosilanes and indoles), [9] and SiÀC (hydrosilanes and terminal alkynes) [10] bond-forming reactions by cross-dehydrogenative coupling strategy. Herein, we successfully developed a novel green synthetic route to silyl isocyanates through heterogeneous-gold-catalyzed, acceptorless cross-dehydrogenative coupling of hydrosilanes and isocyanic acid (generated by in situ thermolysis of urea [11] ) [Eq. (1)].

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N‐Silylation

“…Gold supported on Al 2 O 3 was used by Mizuno in the coupling of tertiary silanes with urea, producing silyl isocyanates under somewhat forcing conditions [48] . Silane was hypothesized to engage in a σ‐coordination to gold which, after reaction with NH 3 , reacts with the gold σ‐complex to liberate H 2 and silyl isocyanates (Scheme 15).…”

Catalytic Cyanation Using CO2 and NH3

“…trimethylsilyl isocyanate (TMS-NCO) as the CN source gave the desired product omethylbenzonitrile (19% yield). Considering the ease with which urea can decompose to isocyanic acid and ammonia at elevated temperatures, 33 the formation of silyl isocyanate intermediates was reasonable. Meanwhile, to better understand the active copper species involved, we performed reactions by using organocopper reagents with different valencies.…”

Gold nanoparticle (AuNPs) and gold nanopore (AuNPore) catalysts in organic synthesis

“…Other supported AuNPs studied for these reactions also led to good yields of the desired products, but Au/HAP proved to be best (Scheme 40). Mizuno and co-workers 102 presented a novel AuNPs promoted dehydrogenative coupling of hydrosilane and isocyanic acid (generated in situ from urea), which resulted in silyl isocyanates. To realize this, they used various metals (Au, Pd, Rh, Ag, Pt, Ru, and Cu) supported on Al 2 O 3 , additionally, other supported gold catalysts (Au/CeO 2 , Au/SiO 2 , Au/TiO 2 , etc.)…”