Catalytic Dehydrogenative Stannylation of C(sp)–H Bonds Involving Cooperative Sn–H Bond Activation of Hydrostannanes

Abstract

The catalytic generation of a stannylium-ion-like tin electrophile by heterolytic cleavage of the Sn-H bond in hydrostannanes at the Ru-S bond of Ohki-Tatsumi complexes is reported. Reacting these activated hydrostannanes with terminal acetylenes does not lead to hydrostannylation of the C-C triple bond but to dehydrogenative stannylation of the alkyne terminus. The scope of this rare direct C(sp)-H bond stannylation with hydrostannanes is broad, and a mechanism involving a β-tin-stabilized vinyl cation likely having a bridged structure is presented.

A Drastic Effect of TEMPO in Zinc‐Catalyzed Stannylation of Terminal Alkynes with Hydrostannanes via Dehydrogenation and Oxidative Dehydrogenation

“…The importance of our original zinc−pyridine−nitrile system is that all inexpensive commercial sources including the zinc Lewis acid based on an abundant metal resource in nature are available, in contrast to the general types catalyzed by rare, and thus, expensive transition metals. To date, despite the well‐studied dehydrogenative C−Si and C−B bond‐forming couplings, the stannylation thereof has only two precedents for the alkynyl C−H bond, once again, with transition metal catalysts of Rh and Ru . We herein report on the first case of non‐transition‐metal‐catalyzed stannylation of alkynes with hydrostannanes, and also clarify that a unique reaction mechanism is operative.…”

Cross‐Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

“…During studies on the rhodium‐catalyzed hydrostannylation of propargyl ethers, Mitchell and co‐workers found that when Me 3 SnH was used instead of ( n ‐Bu) 3 SnH, cross dehydrogenative coupling, rather than hydrostannylation, took place to produce the coupling products of alkynyl stannanes in 61 %–84 % yields with dihydrogen gas release. Very recently, Oestreich and co‐workers demonstrated that ( n ‐Bu) 3 SnH could also selectively undergo cross dehydrogenative coupling with terminal alkynes when catalyzed by a ruthenium catalyst (Scheme ) . Both aromatic and aliphatic terminal alkynes were applicable to this reaction, enabling synthesis of various alkynyl stannanes including those bearing functional groups.…”

Cleavage of Unactivated Si−C(sp3) Bonds with Reed's Carborane Acids: Formation of Known and Unknown Silylium Ions

“…Them ethod was also applicable to the cleavage of unactivated Sn À C(sp 3 )b onds and, hence,t ot he synthesis of trialkylstannylium ions [13,23] Density functional theory (DFT) calculations were performed at the PW6B95-D3/def2-QZVP+ +COSMO-RS-(benzene)// TPSS-D3/def2-TZVP+ +COSMO(benzene) level of theory [24] to provide insight into the mechanism of the protonation of Me 4 ' + ]°.T he former scenario proceeds with inversion of the configuration at the carbon atom and is kinetically more favorable (DDG°= 5.6 kcal mol À1 ). That step releases CH 4 and the silylium ion B + and is exergonic by 11.5 kcal mol À1 .T he same applies to the protonation of the Sn À C(sp 3 )b ond, albeit with al ower barrier of 13.2 kcal mol À1 (see the Supporting Information for details).…”