Cationic Palladium Complex-Catalyzed Cyclization-Hydrosilylation of 1,6-Heptadiyne and its Homologs

Abstract

Palladium complex (A)-catalyzed dimerization-hydrosilylation of 1-alkynes, which has previously been reported, can not be applied effectively to the intramolecular version of a,walkanediynes, while a cationic palladium complex (B) is a very effective catalyst for cyclization-hydrosilylation of functionalized a,w-diynes to give (Z)-1-methylene-2-silylmethylenecycloalkane derivatives, with 5-, 6-, and 7-membered ring, in good to moderate yields.

Cobalt-Catalyzed Cyclization/Hydrosilylation Reaction of 1,6-Diynes Enabled by an Oxidative Cyclization–Hydrosilylation Mechanism

“…This catalytic reaction exhibits a broad scope on 1,6-diynes and hydrosilanes and produces five-membered ring-fused silyl ( Z ) - dienes in good yields and excellent stereoselectivity. Mechanistic study suggested that the cobalt-catalyzed reaction likely operates in a mechanism of 1,6-diyne oxidative cyclization followed by hydrosilylation, which is distinct from the mechanistic rationale of hydrosilane oxidative addition-alkyne insertion of the reported noble metal-catalyzed reactions. − , …”

“…Moreover, stereoselectivity control on the Z-or E-geometry of the silyl dienes could also be problematic. [3][4][5]8 Intrigued by the economical and environmentally benign feature of late 3d metals, there has been great interest in late 3d metal-catalyzed cyclization/hydrosilylation reactions in recent years. The efforts have led to the development of late 3d metalcatalyzed cyclization/hydrosilylation reactions of enynes.…”

“…Transition-metal-catalyzed cyclization/hydrosilylation reactions of nonconjugated diynes are effective methods for the synthesis of silyl substituted exocyclic dienes that are useful building blocks for the synthesis of polycyclic organic molecules. , Over the years, a number of Pt, , Pd, and Rh − -catalyzed cyclization/hydrosilylation reactions of 1,6-diynes, which yield five-membered ring-fused exocyclic silyl dienes, have been reported. These catalytic systems, however, are far from ideal as side reactions, such as uncyclized hydrosilylation of diynes, ,, hydrosilylation of the resultant dienes, and/or cyclotrimerization of alkynes, ,, are always in company with the desired cyclization/hydrosilylation reaction (Scheme a).…”

“…These catalytic systems, however, are far from ideal as side reactions, such as uncyclized hydrosilylation of diynes, ,, hydrosilylation of the resultant dienes, and/or cyclotrimerization of alkynes, ,, are always in company with the desired cyclization/hydrosilylation reaction (Scheme a). Moreover, stereoselectivity control on the Z - or E -geometry of the silyl dienes could also be problematic. − , …”

“…Mechanistic study suggested that the cobalt-catalyzed reaction likely operates in a mechanism of 1,6-diyne oxidative cyclization followed by hydrosilylation, which is distinct from the mechanistic rationale of hydrosilane oxidative addition-alkyne insertion of the reported noble metal-catalyzed reactions. [3][4][5]9 ■ RESULTS AND DISCUSSION Catalytic Reaction Development. Previously, we found that low-coordinate Co(0)-NHC complexes in the form of [(NHC)Co(vtms) 2 ] (vtms = vinyltrimethylsilane) can serve as effective catalysts for the hydrosilylation of alkynes with H 2 SiPh 2 .…”