Hydrosilylation Of Ketones Research Articles

Synthesis and Characterization of Air‐Stable Palladium(II) and Copper(I) Ph‐Garphos Complexes and their Applications to Asymmetric Catalysis

AbstractAir‐stable palladium(II) and copper(I) complexes containing the 4,4′,6,6′‐tetramethoxybiphenyl‐2,2′‐diyl)bis(diphenylphosphine) ligands, (R)‐Ph‐Garphos ((R)‐L1) and ((S)‐Ph‐Garphos ((S)‐L1), were synthesized and characterized by 1H‐, 13C‐, and 31P{1H} NMR spectroscopy and elemental analyses. The PdCl2((R)‐Ph‐Garphos) ((R)‐1) and PdCl2((S)‐Ph‐Garphos) ((S)‐1) complexes were assessed for the Suzuki‐Miyaura cross‐coupling of aryl halides with phenylboronic acid under ambient conditions, or naphthyl substrates under reflux. X‐ray crystal structures of the copper complexes revealed that [Cu((R)‐Ph‐Garphos)I] ((R)‐2) crystallized as a three‐coordinate monomer in the orthorhombic space group P212121 whereas [Cu((S)‐Ph‐Garphos)I] ((S)‐2) crystallized as a tetrahedral (μ‐I) dimer in the same crystal system. The synthesis of the analogous [Cu((R)‐Ph‐Garphos)OAc] ((R)‐3) is also described. Complexes (R)‐2 and (R)‐3 were evaluated for the asymmetric hydrosilylation of ketones wherein enantioselectivities of up to 83 % ee were achieved.

Terphenyl Amido Stannylene‐NHC Adduct: A Catalyst for the Hydrosilylation of Aldehydes and Ketones

The terphenyl amido stannylene‐NHC adducts, HMDS(MesTer)Sn(NHC), (MesTer = 2,6‐Mes2C6H3, Mes = 2,4,6‐Me3‐C6H2, HMDS = N(SiMe3)2, NHC = IMe4, IEt, IMe4 = 1,3,4,5‐tetramethylimidazol‐2‐ylidene, IEt = 1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene), were reacted with benzaldehyde resulting forming HMDS(MesTer)Sn(OCH(Ph)NHC). In the presence of acetophenone, deprotonation occurs to afford the tin enolate, (MesTer)Sn(NHC)(OPhC=CH2), via the release of hexamethyldisilamine. This stannylene‐NHC adduct is a catalyst for the homogeneous hydrosilylation of aldehydes and ketones under ambient conditions.

Unveiling the Reactivity of Part Per Million Levels of Cobalt-Salen Complexes in Hydrosilylation of Ketones.

A series of air-stable cobalt(III)salen complexes Co-1 to Co-4 have been synthesized and employed in the hydrosilylation of ketones. Notably, the most intricately tailored Co-3 pre-catalyst exhibited exceptional catalytic activity under mild reaction conditions. The developed catalytic hydrosilylation protocol proceeded with an unusual ppm level (5 ppm) catalyst loading of Co-3 and achieved a maximum turnover number (TON) of 200,000. A wide variety of aromatic, aliphatic, and heterocyclic ketones encompassing both electron-donating and electron-withdrawing substituents were successfully transformed into the desired silyl ethers or secondary alcohols in moderate to excellent yields.

Palladium Nano-Dispersed and Stabilized in Organically Modified Silicate as a Heterogeneous Catalyst for the Conversion of Aldehydes into O-Silyl Ether Derivatives under Neat Conditions

AbstractPalladium nanoparticles are dispersed and stabilized in organically modified silicate (Pd@MTES), and characterized by a number of spectroscopic techniques, including FTIR, TEM, SEM, and XPS. The catalytic effect of this material toward the hydrosilylation of aldehydes and ketones is explored, and the scope of the reaction investigated, with 26 examples provided. This reaction proceeds under neat conditions via heterogeneous catalysis, and a mechanistic pathway supported by DFT calculations is proposed.

Cr(II) and Cr(III) NCN pincer complexes: synthesis, structure, and catalytic reactivity

The synthesis, characterization, and reactivity of several new Cr(II) and Cr(III) complexes featuring an NCN pincer ligand with an arene backbone connected to amine donors NEt2 and NiPr2 via CH2-linkers is described. Reacting the in situ lithiated ligand precursor N(C–Br)NCH2-Et with [CrCl3(THF)3] resulted in the formation of the Cr(III) complex trans-[Cr(κ3NCN-NCNCH2-Et)(Cl)2(THF)]. Upon reaction of lithiated N(C–Br)NCH2-iPr with a suspension of anhydrous CrCl2, the Cr(II) complex [Cr(κ2NC-NCNCH2-iPr)2] is formed featuring two NCN ligands bound in κ2NC-fashion. In contrast, when lithiated N(C–Br)NCH2-iPr is reacted with a homogeneous solution of anhydrous CrX2 (X = Cl, Br), complexes [Cr(κ3NCN-NCNCH2-iPr)X] are obtained. Treatment of [Cr(κ3NCN-NCNCH2-iPr)Cl] with 1 equiv of PhCH2MgCl and LiCH2SiMe3 afforded the alkyl complexes [Cr(κ3NCN-NCNCH2-iPr)(CH2Ph)] and [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)]. All Cr(II) complexes exhibit effective magnetic moments in the range of 4.7–4.9 µB which is indicative for d4 high spin systems. If a solution of lithiated N(C–Br)NCH2-iPr is treated with CrCl2, followed by addition of an excess of Na[HB(Et)3], the dimeric complex [Cr(κ2NC-NCNCH2-iPr)(μ2-H)]2 is obtained bearing two bridging hydride ligands. [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)] turned out to be catalytically active for the hydrosilylation of ketones at room temperature with a catalyst loading of 1 mol%. X-ray structures of all complexes are presented.Graphical abstract

Nickel(II) complexes bearing 8-hydroxyquinoline-imine ligands: Synthesis and catalysis in hydrosilylation of aldehydes and ketones

Treatment of Ni(OAc)2⋅4H2O with 8-hydroxylquinoline-imine ligands [2-(ArN=HC)-8-OH]C9H5N (Ar = 2,6- iPr2C6H3, L1H; Ar = 2,4,6-(Me)3C6H2, L2H; Ar = 4-MeC6H4, L3H and Ar = 4-ClC6H4, L4H) in refluxing EtOH afforded the dual-ligand coordinated nickel complexes [L2Ni] 1-4, respectively. All the four nickel complexes were characterized by IR, elemental analysis and high-resolution mass spectrometry. Furthermore, the molecular structures of complexes 3 and 4 were confirmed by X-ray diffraction analysis. Complexes 1-4 were found to be efficient catalysts for hydrosilylation of aldehydes and ketones with PhSiH3 as the hydrogen source. Various aromatic and aliphatic ketones and aldehydes were proven to be suitable substrates for such catalytic property, affording the corresponding alcohols in good to excellent yields.

Bis‐Dianionic β‐Ketoiminato Octalithium Complex Catalyzed Hydrosilylation and Cyanosilylation of Carbonyl Compounds

AbstractA well‐defined bis‐dianionic β‐ketoiminato octalithium complex was employed as an efficient catalyst for the hydrosilylation of aldehydes and ketones. Various corresponding alcohols were obtained in high yields with functional group tolerance. In addition, the catalytic system can also be applied to the cyanosilylation of a broad range of aldehydes and ketones with down to 0.05 mol % catalyst loadings.

Co‐Catalyzed Hydrosilylation of Ketones under Base‐Free Conditions: A Convenient Route to Silyl Ethers or Secondary Alcohols

AbstractA cobalt‐catalyzed addition of hydrosilanes to unsaturated carbon‐oxygen bonds has been developed, relying on complexes featuring easily accessible and inexpensive PNP‐type pincer ligands. A wide range of heterocyclic, aliphatic, and aromatic ketones, including those containing both electron‐donating and electron‐withdrawing substituents, were transformed into silyl ethers or secondary alcohols with high yields. An important feature of this protocol is that silanes can act as both the substrates and activators, eliminating the need for external additives such as strong bases.

PCP Pincer Carbene Nickel(II) Chloride, Hydride, and Thiolate Complexes: Hydrosilylation of Aldehyde, Ketone, and Nitroarene by the Thiolate Complex

The one-pot reaction between ethylenediamine, paraformaldehyde, and Ph2PH or tBu2PH gave a new diphosphine compound 1,3-bis((diphenylphosphaneyl)methyl)imidazolidine L1 or 1,3-bis((di-tert-butylphosphaneyl)methyl)imidazolidine L2, respectively, in excellent yields. Metalation with [NiCl2(DME)] in the presence of KPF6 afforded pincer carbene nickel chloride complexes [(PhPCP)NiCl]PF6, 1, and [(tBuPCP)NiCl]PF6, 2, by the simultaneous double C–H bond activations of the methylene protons. The reaction of 1 and 2 with PhSNa gave both neutral five- and ionic four-coordinate thiolate complexes [(PhPCP)Ni(SPh)2], 3, and [(PhPCP)NiSPh]PF6, 4, and [(tBuPCP)NiSPh]PF6, 5, depending upon the reaction stoichiometry. Interestingly, the reaction of 2 with an excess of NaBH4 gave the new hydride complex [(tBuPCP)NiH]PF6, 6. Their structures were confirmed by the X-ray diffraction method. Of these, only the thiolate complexes 3 and 4 are efficient catalysts for the hydrosilylation of aldehydes, ketones, and nitroarenes to give primary, secondary alcohols, and aromatic amines using PhSiH3 after hydrolysis. Aldehydes containing different substituents and conjugated double bonds, aliphatic, and heterocyclic aldehydes are converted to alcohols in excellent isolated yields with 0.5 mol % complex 3 in 2 h under neat conditions at room temperature. The hydrosilylation of ketones requires heating conditions in toluene to give products in moderate yields. Eight nitroarenes were converted to their aromatic amines in very good yields including chemoselective reductions. The poor performance of the nickel hydride suggests that the bound thiolate group in 3 or 4 plays a key role in mediating these reactions possibly via metal–ligand cooperation. Preliminary mechanistic studies indicated the formation of a nickel silyl complex detected by the 19Si NMR method with H2 evolution among others. For the nitroarene reduction, the detection of intermediates followed by the catalytic reduction of N-phenylhydroxylamine to give aniline indicated the direct method mechanism.

Manganese Salan Complexes as Catalysts for Hydrosilylation of Aldehydes and Ketones

Manganese has attracted significant recent attention due to its abundance, low toxicity, and versatility in catalysis. In the present study, a series of manganese (III) complexes supported by salan ligands have been synthesized and characterized, and their activity as catalysts in the hydrosilylation of carbonyl compounds was examined. While manganese (III) chloride complexes exhibited minimal catalytic efficacy without activation of silver perchlorate, manganese (III) azide complexes showed good activity in the hydrosilylation of carbonyl compounds. Under optimized reaction conditions, several types of aldehydes and ketones could be reduced with good yields and tolerance to a variety of functional groups. The possible mechanisms of silane activation and hydrosilylation were discussed in light of relevant experimental observations.

Cobalt-Catalyzed Asymmetric Hydrosilylation of α-Oxygenated Ketones.

An asymmetric hydrosilylation of α-oxygenated ketones was developed under the catalysis of Co(OAc)2 in combination with a chiral phosphine-amido-oxazoline (PAO) ligand, providing a mild, efficient, and enantioselective access to a variety of synthetically useful 1,2-diol derivatives. This protocol can be carried out at the gram scale with a catalyst loading of 1 mol %, and its synthetic utility was demonstrated by efficient conversion of the optically enriched products into chiral α-hydroxy acid, 1,3-dioxolan-2-one, ethylene oxide, and 1,2,3-1H-triazole.

A 1,2,3-triazole-derived pincer-type mesoionic carbene complex of iron(II): carbonyl elimination and hydrosilylation of aromatic aldehydes via the concerted reaction with hydrosilane and a base.

Iron complexes bearing 1,2,3-triazol-5-ylidene were synthesized and applied to the reaction with hydrosilane and homogeneous catalytic hydrosilylation of aromatic ketones and aldehydes. Addition of a free carbene to a solution of Fe(CO)4Br2 yielded an octahedral, diamagnetic and cationic iron(II) complex [Fe(1,2,3-triazolylidene)(CO)2Br]+. Pyrolysis of the dicarbonyl complex eliminated the two CO ligands to form a paramagnetic four-coordinate complex. A theoretical study using DFT calculations indicated that the spin state changed from singlet to quintet during ligand elimination. Investigations of the successful hydrosilylation of acetophenone and benzaldehyde derivatives using MIC-iron(II) bromide suggested the importance of the base for efficient conversion in the catalytic process. The bromide-to-hydride exchange reaction, transmetallation, of MIC-iron(II) bromide in the presence of KOtBu and HSi(OEt)3 which could occur in the initial process of hydrosilylation was proposed, and supported by a theoretical study.

Synthesis of [CNN] pincer nickel(ii) NHC chlorides and their catalytic effects on the hydrosilylation of aldehydes and ketones under mild conditions

Eight pincer nickel chlorides, [RCcarbeneNamidoR′2Namine–Ni–Cl] (R/R′2 = quinolinyl/nBu (3a); quinolinyl/Me (3b); quinolinyl/PhCH2 (3c); (CH2)4/nBu (5a); (CH2)4/iPr (5b); Me2/nBu (5c); Me2/iPr (5d); Me2/PhCH2 (5e)), were obtained.

Cobalt Nanoparticles Formed upon Reaction of Cp*Co(III) Metallacycles with Na[BHEt3] Show Catalytic Activity in the Hydrosilylation of Aryl Ketones, Aldehydes and Nitriles

AbstractThe reactivity of the 2‐phenylpyridine‐derived [Cp*CoI(phpy‐κC,N)] metallacycle towards Et3SiH and hydrides was evaluated. The treatment of the same Co(III) complex with Na[BHEt3] resulted in its decomposition into cobalt nanoparticles. The hydride‐promoted decomposition of the metallacycle involves the transient formation of an elusive hydrido‐cobalt(III) intermediate, the traces of which were detected by 1H NMR spectroscopy at sub‐ambient temperature. The Co nanoparticles produced from a 5 mol% and 10 mol% load of cobaltacycle and Na[BHEt3] respectively contain Co(0) that is responsible for the hydrosilylation by Et3SiH of arylketones into silylalkyl ethers. To minimize the residual side reduction of carbonyls by Na[BHEt3], a mixture of 5 mol% of the latter with 5 mol% of BEt3 was found to produce optimal hydrosilylation yields at 40 °C in 2 h. Under similar conditions, several arylnitriles were mono‐hydrosilylated into N‐silyl‐imines in yields ranging from 68 to 100 %.

Redox‐Active BIAN‐Based Iron Complexes in Catalysis

Abstractα‐Diimine ligands have contributed extensively to the coordination chemistry of the majority of the transition metals; bis(arylimino)acenaphthene ligands (BIANs) have been widely studied and found to offer great versatility in their application as supporting ligands in catalytic transformations. In recent years, BIAN‐based iron complexes have proven effective in mediating a number of reductive transformations which includes hydrosilylation, hydroboration and hydrogenation chemistries. This review highlights the most recent contributions to the field. In our initial 2015 communication, we disclosed that the arene‐capped Fe(0) species ArBIAN−Fe(toluene) mediates aldehyde and ketone hydrosilylation with exceptional activity under solvent‐free conditions. This led us to the discovery that such systems were capable of the hydrosilylation of imines and esters, the hydroboration of imines, aldehydes, ketones, alkenes, and alkynes and even the ring‐opening polymerization of rac‐lactide. Spectroscopic and computational studies have firmly established the importance of redox non‐innocence in BIAN complexes and detailed mechanistic studies have revealed the importance of spin‐state‐crossing in catalysis. Although this work represents only a small component of advances in iron catalysis, our efforts have proven influential in Fe‐based approaches to reductive transformations and is likely to continue to inform the design of Fe‐based catalysts.

Visible light‐induced catalytic hydrosilylation of ketones mediated by manganese NHC complexes

Manganese catalysis has attracted significant attention in the last few years. In comparison with the extensively studied Mn complexes bearing phosphine‐based pincer ligands, catalysis with Mn containing N‐heterocyclic carbenes (NHC) is poorly developed. In this work, new manganese(I) complexes bearing an NHC ligand with picolyl wingtip substituents (an N,C,N ligand) have been synthesized and fully characterized. The structure of fac‐[Mn(CO)3(κ2N,C,N)Br] and fac‐[Mn(CO)3(κ3N,C,N)](OTf) complexes with a bidentate and tridentate coordination of the N,C,N ligand, respectively, has been elucidated by single crystal X‐ray diffraction studies. These Mn complexes were applied as catalysts for the visible light‐induced hydrosilylation of ketones. The mild protocol operated efficiently at room temperature under visible light irradiation (blue LED), enabling the conversion of a wide variety of aromatic ketones to their respective alcohols in high yields. Evidence for radical intermediates and the participation of Mn‐H species has been demonstrated by a series of trapping experiments.

Cobalt Complexes Supported by Phosphinoquinoline Ligands for the Catalyzed Hydrosilylation of Carbonyl Compounds.

P,N phosphinoquinoline based ligands differing by the nature of the phosphorus substituent (i Pr, Ph) were employed to synthesize a series of cobalt(II) complexes ([LCoBr2 ], [L2 CoBr](PF6 ) and [L'2 CoBr](PF6 )). The latter were obtained in high yield and characterized among others by X-ray analysis and elemental analysis. Complex [L2 CoBr](PF6 ) showed a very good catalytic activity for the hydrosilylation of various ketones. The catalysis proceeds at a low catalytic loading (1 mol %) with only 1 equivalent of Ph2 SiH2 in mild conditions and was efficient with aliphatic or aromatic ketones giving moderate to excellent yields of the corresponding silylated ether.

Hydrosilylation of ketones catalyzed by novel four-coordinate copper(I) complexes under mild conditions

Using conveniently available Cu(CH3CN)4PF6 and PxNy-type ligands as starting material, copper(I) complexes 1 and 2 could be easily prepared. Furtherly, we confirmed the structures of these novel copper(I) complexes by studying X-ray diffraction of the single crystals. The hydrosilylation of a wide range of ketones catalyzed by the well-designed copper(I) complex proceeded smoothly under mild reaction conditions, obtaining the corresponding alcohols with high yields.

Investigation of Iron Silyl Complexes as Active Species in the Catalytic Hydrosilylation of Aldehydes and Ketones

Investigation of Iron Silyl Complexes as Active Species in the Catalytic Hydrosilylation of Aldehydes and Ketones

Silyl formates as hydrosilane surrogates for the transfer hydrosilylation of ketones.

A transfer hydrosilylation of ketones employing silyl formates as hydrosilane surrogates under mild conditions is presented. A total of 24 examples of ketones have been successfully converted to their corresponding silyl ethers with 61–99% yields in the presence of a PNHP-based ruthenium catalyst and silyl formate reagent. The crucial role of the ligand for the transformation is demonstrated.