Alkene Hydrosilation by a Cationic Hydrogen-Substituted Iridium Silylene Complex

Abstract

A cationic hydrogen-substituted iridium silylene complex [(PNP)(H)Ir Si(Mes)H][B(C6F5)4] (2) was synthesized via hydride abstraction from the corresponding neutral iridium silyl hydride complex. DFT calculations for 2 indicate that the cationic charge is localized at the silicon center and depict a LUMO with predominant silicon p-orbital character. Notably, complex 2 reacts rapidly with unhindered alkenes at ambient temperatures to afford disubstituted silylene complexes via Si-C bond formation. Complex 2 is also the catalyst for alkene hydrosilation of primary silanes with a high degree of anti-Markovnikov selectivity.

Multiple Reaction Pathways in Rhodium‐Catalyzed Hydrosilylations of Ketones

“…More recently, this reaction type has been extended to iridium. [76] Finally, the iridium silylene complex [Cp*A C H T U N G T R E N N U N G (PMe 3 ) 2 Ir- 4 ] was found to catalyze the hydrosilylation of ketones, even though the involvement of a metalmediated or of a Lewis acid mechanism could not be clearly distinguished. [77] Comparison of the three mechanistic pathways: The energetics of the three computationally established catalytic cycles have been depicted in Figures 6, 8, and 10, in the preceding sections.…”

Silver‐Catalyzed Silylene Transfer

“…In addition to ruthenium, Tilley and coworkers also reported that cationic iridium silylenoid complexes were efficient olefin hydrosilation catalysts [reaction (7.6)]. 56 This silylene complex catalyzes the hydrosilation of unhindered mono-or disubstituted olefins with primary silanes to produce secondary silanes with anti Markovnikov selectivity. Iridium catalyst 32 exhibited reactivity patterns similar to those of ruthenium 30; only primary silanes were allowed as substrates.…”

Oxygen Atom “Cut and Paste” from Carbon Dioxide to a Fischer Carbene Complex

“…[15] This system is a relatively poor s donor but a good p donor and readily forms well-defined rhodium, iridium, and other metal complexes that exhibit interesting reactivity, coordination chemistry, and catalytic activity with a variety of substrates. [15][16][17][18][19][20][21][22][23][24] For example, complex 1 is also successful in activating various substrates by C À H and aryl-halide oxidative addition, [14,25,26] regioselective alkyne dimerization, and Heck olefin arylation. [15] Calimano and Tilley very recently used this popular complex (1) to generate an iridium-silylene complex that efficiently catalyzes the anti-Markovnikov hydrosilylation of alkenes by direct addition of the silicon-hydrogen bond of both aryl and alkyl-substituted primary silanes to carboncarbon double bonds.…”

“…[15] Calimano and Tilley very recently used this popular complex (1) to generate an iridium-silylene complex that efficiently catalyzes the anti-Markovnikov hydrosilylation of alkenes by direct addition of the silicon-hydrogen bond of both aryl and alkyl-substituted primary silanes to carboncarbon double bonds. [26] The mechanism underlying the remarkable carbon dioxide reduction coupled with oxygen atom transfer to a Fischer carbene has been elucidated in much detail by Whited and Grubbs (Scheme 2). [9,27] The reaction pathway includes some interesting intermediates that were observed by NMR spectroscopy.…”

“…Is it possible to achieve selective oxygen-atom transfer from carbon dioxide to a carbene in a catalytic fashion under mild homogeneous reaction conditions? Pincer-based complexes are known to catalyze various reactions, [26,[31][32][33][34][35][36][37] including alkane dehydrogenation, [35] cross-coupling reactions, [38] and Milsteins direct coupling of alcohols with amines to form amides. [33] As pointed out by the authors, the system highlighted here has one drawback: the formation of the iridium-carbonyl moiety 2 makes the overall process thermodynamically favorable, but at the same time, unfortunately, it also destroys the catalytic process.…”