Reactions of the Square-Planar Compounds Ir(C₂Ph)L₂(PCy₃) (L₂ = 2 CO, TFB) with HSiR₃ (R = Et, Ph) and H_x+1SiPh_3-x (x = 1, 2):  Stoichiometric and Catalytic Formation of Si−C Bonds

Abstract

The square-planar cis-dicarbonyl complex Ir(C 2 Ph)(CO) 2 (PCy 3 ) (1) reacts with ca. 1 equiv of HSiR 3 to give, in quantitative yield, the corresponding alkynyl-hydrido-silyl derivatives Ir(C 2 Ph)(H)(SiR 3 )(CO) 2 (PCy 3 ) (SiR 3 ) SiEt 3 (2), SiPh 3 (3), SiHPh 2 (4), and SiH 2 Ph (5)). The reactivity of the related tetrafluorobenzobarrelene compound Ir(C 2 Ph)(TFB)(PCy 3 ) (6) toward HSiR 3 has been also studied by NMR spectroscopy. The addition of ca. 2 equiv of HSiEt 3 to a benzene-d 6 solution of 6 affords IrH 2 (SiEt 3 )(TFB)(PCy 3 ) (7) and PhCtCSiEt 3 in a 1:1 molar ratio, while the reaction of 6 with ca. 1 equiv of HSiPh 3 yields, after 1 h and 30 min, IrH 2 -(SiPh 3 )(TFB)(PCy 3 ) (10, 8%), Ir{C(SiPh 3 )dCHPh}(TFB)(PCy 3 ) (11, 52%), and PhCtCSiPh 3 (8%). The addition of ca. 1 equiv of H 2 SiPh 2 to a benzene-d 6 solution of 6 leads, after 1 h, to IrH 2 {Si(C 2 Ph)Ph 2 }(TFB)(PCy 3 ) ( 12) in 90% yield. The alkynyl compounds 1 and 6 have been found to be active catalysts for the addition of triethylsilane to phenylacetylene. In all experiments, PhCHdCH 2 , PhCtCSiEt 3 , cis-PhCHdCH(SiEt 3 ), trans-PhCHdCH(SiEt 3 ), and Ph(SiEt 3 )CdCH 2 were obtained. On the basis of the results from the stoichiometric reactions together those from the catalytic experiments, reaction pathways for the formation of these silylate products are discussed.

Iridium-catalyzed Markovnikov hydrosilylation of terminal alkynes achieved by using a trimethylsilyl-protected trihydroxysilane

“…Other propargyl ethers derived from quinine, estrone, testosterone, cholesterol, and vitamin E could be effectively hydrosilylated as well, providing desired products with outstanding α regioselectivity (35)(36)(37)(38)(39). It is worthwhile to note that though terminal alkynyl derivatives from nitrogenous bases, theobromine, uridine, and phenylalanine showed poor solubility in acetonitrile, this protocol is well applicable in Markovnikov hydrosilylation of them as well (40)(41)(42)(43)(44)(45)(46).…”

“…3). Considering the widespread hydroxyl and amino groups in biomolecules, propargyl derivatives from them were selected as representatives in most cases (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45). Propargyl ether analogues of menthol, carveol, prolinol, glucose and glucofuranose were successfully transformed into corresponding α-vinylsilanes in good to excellent yields (30-34).…”

“…1 H and 13 C NMR Spectra of all hydrosilylation products and unknown substrate were provided. 13 C DEPT135 NMR Spectra of products 3,4,5,6,7,9,10,12,13,15,19,20,21,26,30,31,32,36,37,38,39,40,41,42,44,45 were afford. 2D NOESY Results of products 1 and 27 are also provided.…”

“…The bulky silyl group could be easily converted into other useful silyl groups, or participate in subsequent derivatizations directly. It's noteworthy that though iridium complexes have been broadly investigated for hydrosilylation of unsaturated C-C bonds 37 , anti-Markovnikov selectivity is usually observed in their use toward terminal alkynes [38][39][40][41][42][43][44][45][46][47][48][49] . As one example of Markovnikov hydrosilylation of internal thioalkynes has been reported by Sun and Wu 50 , this is to our knowledge the first case in which α-vinylsilanes are mainly provided from terminal alkynes under iridium catalysis.…”

Square-Planar Alkylidyne–Osmium and Five-Coordinate Alkylidene–Osmium Complexes: Controlling the Transformation from Hydride-Alkylidyne to Alkylidene

“…Subsequently, the metal center slips to the C–H bond to form η 2 -(C,H)-species . Thus, the oxidative addition to square-planar complexes, such as 2 and 5 , is a diastereoselective process with specific C–H bond orientation. , At first glance, the oxidative addition of the alkyne to these compounds can take place along the i Pr 3 P–Os–IPr or X–Os–CPh axis, the latter being favored from a steric point of view. Addition along the X–Os–CPh axis can occur with the hydrogen directed toward the halide and the substituent of the alkyne on the alkylidyne ( A ) or vice versa ( B ).…”