Stereo- and Regioselective Pt(DVDS)/P(iBuNCH2CH2)3N-Catalyzed Hydrosilylation of Terminal Alkynes

Transition-Metal-Free Synthesis of Enantioenriched Tertiary and Quaternary α-Chiral Allylsilanes

Access to enantioenriched tertiary and quaternary α-chiral allysilanes without any transition-metal catalyst is reported. This was achieved by enantioselective allylic displacement of γ-silylated allylic bromides through Lewis base activation of Grignard reagents by a bidentate chiral NHC ligand. The process afforded both high γ-regio- and enantioselectivity and is compatible with a wide range of silyl groups on the substrates.

Hydrosilylation of Terminal Alkynes Catalyzed by an Air-Stable Manganese-NHC Complex

In recent years, catalysis with base metal manganese has received a significant amount of interest. Catalysis with manganese complexes having N-heterocyclic carbenes (NHCs) is relatively underdeveloped in comparison to the extensively investigated manganese catalysts possessing pincer ligands (particularly phosphine-based ligands). Herein, we describe the synthesis of two imidazolium salts decorated with picolyl arms (L₁ and L₂) as NHC precursors. Facile coordination of L₁ and L₂ with MnBr(CO)₅ in the presence of a base resulted in the formation manganese(I)-NHC complexes (1 and 2) as an air-stable solid in good isolated yield. Single-crystal X-ray analysis revealed the structure of the cationic complexes [Mn(CO)₃(NHC)][PF₆] with tridentate N,C,N binding of the NHC ligand in a facile fashion. Along with a few known manganese(I) complexes, these Mn(I)-NHC complexes 1 and 2 were tested for the hydrosilylation of terminal alkynes. Complex 1 was proved to be an effective catalyst for the hydrosilylation of terminal alkynes with good selectivity toward the less thermodynamically stable β-(Z)-vinylsilanes. This method provided good regioselectivity (anti-Markovnikov addition) and stereoselectivity (β-(Z)-product). Experimental evidence suggested that the present hydrosilylation pathway involved an organometallic mechanism with manganese(I)-silyl species as a possible reactive intermediate.

Transition-Metal-Catalyzed Stereo- and Regioselective Hydrosilylation of Unsymmetrical Alkynes

Alkyne hydrosilylation is one of the most efficient methods for the synthesis of alkenyl silicon derivatives and has been a hot topic of research for decades. This short review summarizes the progress in transition-metal-catalyzed stereo- and regioselective hydrosilylation of unsymmetrical alkynes. Topics are discussed based on different types of alkynes and the selectivities.

1 Introduction

2 Terminal Alkyne Hydrosilylation

2.1 β-E Selectivity

2.2 β-Z Selectivity

2.3 α-selectivity

3 Internal Alkyne Hydrosilylation

3.1 Aryl–Alkyl Acetylenes

3.2 Alkyl–Alkyl Acetylenes

3.3 Internal Alkynes with Polarized Substituents

4 Summary and Outlook

Regioselective Synthesis of Multifunctional Allylic Amines; Access to Ambiphilic Aziridine Scaffolds

We describe, for the first time, a highly regioselective hydrosilylation of propargylic amines. The reaction utilizes a PtCl₂/XantPhos catalyst system to deliver hydrosilanes across the alkyne to afford multifunctional allylic amines in high yields. The reaction is tolerant to a wide variety of functional groups and provides high value intermediates with two distinct functional handles. The synthetic applicability of the reaction has been shown through the synthesis of diverse ambiphilic aziridines.

On Transannulation in Azaphosphatranes: Synthesis and Theoretical Analysis

A combined synthetic-theoretical study has been undertaken to determine the factors that influence transannulation in azaphosphatranes. The commonly used proazaphosphatrane P(i-BuNCH₂CH₂)₃N and several of its oxidized congeners are used as model systems. The haloazaphosphatranes of P(i-BuNCH₂CH₂)₃N were synthesized, including a rare fluoroazaphopshatrane, and used as references for computational investigations. Comparisons of the experimental and theoretical observations highlight the flexibility observed in transannulated atranes and the potential for multiple local energetic minima depending on the identity of the equatorial substituents for a given azaphosphatrane. Theoretical calculations also identify the role of the ethylene linker in azaphosphatrane bonding, the influence of transannulation on P-electrophile interactions, and the contribution of electrostatic interactions to transannulation.

Construction of highly sterically hindered 1,1-disilylated terminal alkenes

One direct and efficient procedure for the synthesis of 1,1-disilylated terminal alkenes is demonstrated in this paper. To overcome and rationally utilize the steric hindrance of silyl units, the cationic ruthenium catalyst [CpRu(MeCN)3]+ was found to be effective for Markovnikov hydrosilylation of 1-silyl terminal alkynes with high yields and excellent regioselectivity. Dissimilarities between alkyl and alkoxy silyl units lead to versatile product derivatizations toward a variety of useful building blocks.

Regiocontrol in the cobalt-catalyzed hydrosilylation of alkynes

A highly versatile cobalt-catalyzed hydrosilylations of alkynes is reported. Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Hydrofunctionalizations of unsaturated hydrocarbons are key strategies for the synthesis of functionalized building blocks. Here, we report highly versatile cobalt-catalyzed hydrosilylations of alkynes that operate with minute amounts of the inexpensive, bench-stable pre-catalyst Co(OAc)₂·4H₂O under mild conditions (0.1–1 mol%, THF, r.t., 1 h). Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Highly β( Z)-Selective Hydrosilylation of Terminal Alkynes Catalyzed by Thiolate-Bridged Dirhodium Complexes

A series of novel monothiolate-bridged dirhodium complexes, [Cp*Rh(μ-SR)(μ-Cl)₂RhCp*][BF₄] {Cp* = η⁵-C₅Me₅, R = tertiary butyl ( ^tBu), 1a; R = ferrocenyl (Fc), 1b; R = adamantyl (Ad), 1c} were designed and successfully synthesized, which can smoothly facilitate highly regioselective and stereoselective hydrosilylation of terminal alkynes to afford β( Z) vinylsilanes with good functional group compatibility. Furthermore, the hydride bridged dirhodium complex [Cp*Rh(μ-S ^tBu)(μ-Cl)(μ-H)RhCp*][BF₄] (5) as a potential intermediate was obtained by the reaction of 1a with excess HSiEt₃.

Functionalized vinylsilanes via highly efficient and recyclable Pt-nanoparticle catalysed hydrosilylation of alkynes

A mild, selective and facile synthesis of vinylsilanes via a recyclable platinum nanoparticle catalysed hydrosilylation of alkynes is reported. Various functionalized alkynes are selectively hydrosilylated to furnish functional β-E vinylsilanes in high yields. The catalytic effectiveness, ease of catalyst recovery and recyclability of the polysiloxane stabilized Pt-nanoparticle catalyst are the major achievements of this work. Detailed in situ characterization using Electron Microscopy and controlled poisoning experiments supports the participation of Pt-nanoparticles as active catalysts.

Synthesis of Monofunctionalized Silsesquioxanes (RSiMe2 O)(iBu)7 Si8 O12 via Alkene Hydrosilylation

The research presented in this work comprehensively describes hydrosilylation of a wide spectrum of alkenes which contain one or more reactive groups with (HSiMe₂ O)(iBu)₇ Si₈ O₁₂ , in the presence of different types of catalysts. Special attention is paid to the influence of alkene, catalyst, and reaction conditions on process effectiveness and selectivity by the precise monitoring of the experiments with in situ FTIR and NMR spectroscopies. More than twenty silsesquioxanes bearing reactive groups (OH, Br, NR₂ , CO, COOR, NCO, epoxy, SiR₃ ) commonly used in organic and polymer chemistry, were obtained, isolated and characterized by ¹ H, ¹³ C, ²⁹ Si NMR and MALDI TOF. Importantly, in the presented syntheses, commercially available reagents and catalysts were used, meaning that the presented methods could be easily repeated, rapidly scaled up, and widely applied.

Highly selective hydrosilylation of olefins and acetylenes by platinum(0) complexes bearing bulky N-heterocyclic carbene ligands

Platinum(0) complexes bearing bulky N-heterocyclic carbene ligands, catalyse selective hydrosilylation of terminal olefins as well as terminal and internal acetylenes.

Adaptable ligand donor strength: tracking transannular bond interactions in tris(2-pyridylmethyl)-azaphosphatrane (TPAP)

Flexible ligands that can adapt their donor strength have enabled unique reactivity in a wide range of inorganic complexes.

Pincer cobalt complex-catalyzed Z-selective hydrosilylation of terminal alkynes

Co-Catalyzed Z-selective hydrosilylation of terminal alkynes produces (Z)-β-vinylsilanes, which are further converted to (Z)-disubstituted alkenes by Pd-catalyzed cross couplings.

Electronic and steric Tolman parameters for proazaphosphatranes, the superbase core of the tri(pyridylmethyl)azaphosphatrane (TPAP) ligand

The Tolman electronic parameters (TEP) and cone angles were experimentally measured for a series of substituted proazaphosphatranes ligands by synthesizing their respective Ni(L^R)(CO)₃ complexes, where L = P(RNCH₂CH₂)₃N and R = Me, iPr, iBu and Bz.

One-step preparation of functionalized (E)-vinylsilanes from aldehydes

Functionalized (E)-vinylsilanes have been prepared in one step from a wide range of aldehydes, via a chromium(II)-mediated olefination with novel dihalomethylsilane reagents, in moderate to excellent yields and with excellent stereoselectivity.

Rh(I) and Ir(I) Derivatives of a P(S),N-Substituted Indene Ligand: Synthetic, Structural, and Catalytic Alkene Hydrosilylation Studies

Treatment of 1-PiPr2-indene or 1-PiPr2-2-NMe2-indene (1a) with elemental sulfur afforded 3-iPr2P(S)-indene or 1-iPr2P(S)-2-NMe2-indene (4a) in 81% and 85% isolated yield, respectively. Addition of 4a to [(COD)M(THF)2]+BF4- afforded the corresponding [(COD)M(kappa2-N,S-4a)]+BF4- complexes (M = Rh, 5a, 76%; M = Ir, 5b, 59%; COD = eta4-1,5-cyclooctadiene), which were found to exhibit temperature-dependent NMR spectral features that were rationalized in terms of a dynamic process involving M-NMe2 dissociation, rotation about the indenyl-NMe2 bond, inversion at nitrogen, and re-coordination to M. Analysis of variable-temperature NMR data collected for 5a and 5b each yielded a value for DeltaG(double dagger) of ca. 14 kcal/mol for this process. Exposure of 5a or 5b to NaN(SiMe3)2 generated the corresponding (COD)M(kappa2-C,S-1-iPr2P(S)-2-NMe2-(C1-indenyl)) complex (M = Rh, 6a, 70%; M = Ir, 6b, 86%) in which the metal is incorporated into an M-C-P-S ring via coordination to the indenyl ring in an eta1-fashion, as well as to sulfur. Alternatively, complex 6b was prepared cleanly via lithiation of 4a followed by treatment with 0.5 equiv of [(COD)IrCl]2. The ability of 5a,b and 6a,b to mediate the addition of triethylsilane to styrene was also explored, and their performance was compared with that of Wilkinson's Catalyst ((PPh3)3RhCl) and Crabtree's catalyst ([(COD)Ir(PCy3)(Py)]+PF6-; Cy = cyclohexyl; Py = pyridine). Single-crystal X-ray diffraction data are provided for 4a, 2-NMe2-3-iPr2P(S)-indene (4b), 6a, and 6b.