C-H Borylation of arenes has been a subject of great interest recently because of its atom-economy and the wide applicability of borylated products in value-added synthesis. A new bis(silylene)cobalt(II) complex bearing a bis(N-heterocyclic silylene)-pyridine pincer ligand (SiNSi) has been synthesized and structurally characterized. It enabled the regioselective catalytic C-H borylation of pyridines, furans, and fluorinated arenes. Notably, it exhibited complementary regioselectivity for the borylation of fluorinated arenes compared to previously known catalytic systems, demonstrating that N-heterocyclic silylene donors have enormous potential in metal-catalyzed catalytic applications.

An arene-tethered silylene ligand, L (L = PhC(tBuN)2SiCH2C(tBu)NAr, Ar = 2,6-iPr2C6H3), allowed the synthesis of three-coordinate Fe(ii) silylamido and piano-stool Fe(0) dinitrogen complexes LFe[N(SiMe3)2]2 (3) and LFe-N2 (4), which not only exhibit interesting bonding but also enabled the catalytic silylation of N2 to yield N(SiMe3)3 under 1 atm of N2 at room temperature with high TONs.

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Silylenes, isoelectronic with carbenes, are a kind of key intermediates in organosilicon chemistry. They possess a lone pair and an empty orbital on the silicon center, and thus could be used as donors and acceptors. Consequently, they could form complexes with various metals to support new structures and chemistry similar to both carbenes and phosphines. Iron complexes played important roles in the development of catalysts because of the inexpensive, nontoxic and sustainable characteristics. Catalytic hydroboration of alkynes presents the most atom-economic and straightforward protocol for the synthesis of vinylboranes which are indispensable intermediates for C-C coupling reactions. For the catalytic hydroboration of alkynes with iron catalysts, Enthaler's group developed the first iron catalytic system for hydroboration of alkynes by using Fe 2 (CO) 9 (A, Chart 1) as the catalyst. Almost at the same time, Thomas's group reported the bis(imino)pyridine derived iron complexes (B) in combination with an activator for catalytic hydroboration of alkynes and alkenes. In 2017, Nishibayashi and co-workers employed an iron(II) hydride complex (C) supported by a PNP pincer ligand for catalytic E-selective hydroboration of alkynes. In 2020, Findlater et al. reported the regioselective hydroboration of alkynes and alkenes with iron complexes supported by bis(2,6-diisopropylaniline)acenaphthene ligands. However, these catalysts still suffered from limited substrate scope or harsh conditions. The development of highly selective catalysts for a wide substrate scope is still desirable. On the basis of our design on silylene ligands for iron chemistry, we are interested in the silylene-iron complexes for catalytic hydroboration reactions. In this paper, hydroborylation of terminal alkynes catalyzed by a neutral silylene-imine iron(0) dinitrogen complex D was studied. The reaction is highly regio-and stereoselective and almost exclusively gave E-hydroboration products. The optimized reaction conditions are as following: To a dried Schlenk tube were added complex D (0.006 g, 0.01 mmol), toluene (1.0 mL), alkyne (0.20 mmol), and catechol borane (0.02 g, 0.20 mmol). After the mixture was stirred at 80 ℃ for 24 h, it was cooled down to room temperature. The solvents were removed under vacuum and the residue was purified by flash chromatography on silica gel to afford the desired products.

Reaction of silaamidinate nickel bromide ate complex LSi(NAr)2NiBr2Li(thf)(OEt2) (L = PhC(NtBu)2, Ar = 2,6-iPr2C6H3, 1) with NaHBEt3 led to the intramolecular C-H activation with the formation of the -1,2-dinitrogen dinickel...