Hydrosilylation Of Carbon Dioxide Research Articles

Stepwise carbon dioxide hydrosilylation catalyzed by bimetallic complexes [CpM(CO)2(μ-CO)···Pd([formula omitted])

The interaction of bimetallic (ButPCP)Pd···(OC)M(CO)2 Cp (M = Mo, W) complexes with PhSiH3 leads to an efficient heterolytic splitting of Si–H bond that is a primary step in catalytic hydrosilylation of CO2. The reaction can be stopped at the formate level in the presence of the above complexes while proceeds further when catalyzed by (ButPCP)PdH.

Hydrosilylative Reduction of CO2 to Formate and Methanol Using a Cobalt Porphyrin‐Based Porous Organic Polymer

AbstractThe hydrosilylation of carbon dioxide (CO2) has become a useful strategy for selectively producing fine chemicals and alternative fuels sources. However, the development of heterogeneous catalysts that complete this chemical transformation with high catalytic efficiencies are rare. Herein, the synthesis and characterization of a benzobisthiazole‐linked (BBT) Co(II)‐porphyrin‐based porous organic polymer (Co‐BBT‐POP) for hydrosilylative reduction of CO2 to potassium formate and methanol is reported. Co‐BBT‐POP can reduce CO2 to potassium formate in the presence of diphenylsilane (Ph2SiH2) and KF with a turnover number (TON) of 1627. In the presence of tris(pentafluorophenyl)borane (B(C6F5)3) and Ph2SiH2, Co‐BBT‐POP can convert CO2 to methanol with a TON of 4531. Co‐BBT‐POP exhibits great recyclability up to five cycles for both catalytic systems.

Cobalt-Catalyzed Hydrosilylation of Carbon Dioxide to the Formic Acid, Formaldehyde, and Methanol Level─How to Control the Catalytic Network?

The selective hydrosilylation of carbon dioxide (CO2) to either the formic acid, formaldehyde, or methanol level using a molecular cobalt(II) triazine complex can be controlled based on reaction parameters such as temperature, CO2 pressure, and concentration. Here, we rationalize the catalytic mechanism that enables the selective arrival at each product platform. Key reactive intermediates were prepared and spectroscopically characterized, while the catalytic mechanism and the energy profile were analyzed with density functional theory (DFT) methods and microkinetic modeling. It transpired that the stepwise reduction of CO2 involves three consecutive catalytic cycles, including the same cobalt(I) triazine hydride complex as the active species. The increasing kinetic barriers associated with each reduction step and the competing hydride transfer steps in the three cycles corroborate the strong influence of the catalyst environment on the product selectivity. The fundamental mechanistic insights provide a consistent description of the catalytic system and rationalize, in particular, the experimentally verified opportunity to steer the reaction toward the formaldehyde product as the chemically most challenging reduction level.

Catalytic CO2 hydrosilylation with [Mn(CO)5Br] under mild reaction conditions

Carbon dioxide hydrosilylation with earth-abundant transition-metal catalysts is an attractive alternative for the design of greener and cost-effective synthetic strategies. Herein, simple [Mn(CO)5Br] is an efficient precatalyst in the hydrosilylation of carbon dioxide with Et3SiH under mild reaction conditions. Using THF as a solvent, triethylsilylformate Et3SiCH(O)O was obtained in 67% yield after 1 h at 50 °C and 4 bar of CO2 pressure. The selectivity of the reaction was tuned by changing the solvent to a mixture of THF and toluene producing bis(triethylsilyl)acetal (Et3SiO)2CH2 in 86% yield. The CO2 hydrosilylation was also effective at room temperature and atmospheric pressure using either THF or the mixture THF/toluene as the solvent resulting in high Et3SiH conversion (92%–99%) but with a decrease in the selectivity. Radical trapping experiments indicated the participation of radical species in the catalytic mechanism. To the best of our knowledge, this is the first report on CO2 hydrosilylation catalyzed by transition-metal radical intermediates.

Cationic Zinc Hydride Catalyzed Carbon Dioxide Reduction to Formate: Deciphering Elementary Reactions, Isolation of Intermediates, and Computational Investigations.

Zinc has been an element of choice for carbon dioxide reduction in recent years. Zinc compounds have been showcased as catalysts for carbon dioxide hydrosilylation and hydroboration. The extent of carbon dioxide reduction can depend on various factors, including electrophilicity at the zinc center and the denticity of the ancillary ligands. In a few cases, the addition of Lewis acids to zinc hydride catalysts markedly influences carbon dioxide reduction. These factors have been investigated by exploring elementary reactions of carbon dioxide hydrosilylation and hydroboration by using cationic zinc hydrides bearing tetradentate tris[2-(dimethylamino)ethyl]amine and tridentate N,N,N',N'',N''-pentamethyldiethylenetriamine in the presence of triphenylborane and tris(pentafluorophenyl)borane.

Bis(alkyl) scandium and yttrium complexes coordinated by an amidopyridinate ligand: synthesis, characterization and catalytic performance in isoprene polymerization, hydroelementation and carbon dioxide hydrosilylation.

New neutral bis(alkyl) Sc and Y complexes [N,Npy,N-]Ln(CH2SiMe3)2(THF)n [n = 0, Ln = Sc (1Sc), Y (1Y); n = 1, Ln = Y (1YTHF)] stabilized by a tridentate monoanionic amidopyridinate ligand were straightforwardly prepared by alkane elimination, upon mixing ligand [N,Npy,N-]H and metal precursor Ln(CH2SiMe3)3(THF)2 in toluene at 0 °C. Depending on the work-up conditions, yttrium bis(alkyl)s were isolated as either a pentacoordinate Lewis base free complex [N,Npy,N-]Y(CH2SiMe3)2 (1Y) or as a hexacoordinate THF adduct [N,Npy,N-]Y(CH2SiMe3)2THF (1YTHF). For the smaller Sc ion the only solvent-free complex [N,Npy,N-]Y(CH2SiMe3)2 (1Sc) was isolated as a pentacoordinate species irrespective of the reaction/work-up/crystallization conditions applied. Complexes 1Ln (Ln = Y, Sc) and 1YTHF were scrutinized as pre-catalysts in ternary catalytic systems Ln/borate/AliBu3 (borate = [HNMe2Ph][B(C6F5)4] or [Ph3C][B(C6F5)4]), applied to isoprene (IP) polymerization, providing moderate activity albeit high selectivity with predominant formation of 1,4-cis polyisoprene (up to 99%). The same complexes proved to be effcient catalysts also for the intermolecular hydrolelementation of styrene with various EH sustrates (pyrrolidine, morpholine, Ph2PH, PhPH2, PhSH) affording linear anti-Markovnikov addition products exclusively. After a preliminary activation by B(C6F5)3, selected bis(alkyl) complexes from this series have been finally used as valuable pre-catalysts for the CO2 hydrosylilation to CH4 in the presence of organosilanes as reducing agents (PhMe2SiH, PhSiH3, Et2MeSiH).

Synthesis of silyl formates, formamides, and aldehydes via solvent-free organocatalytic hydrosilylation of CO2.

Carbon dioxide (CO2) was used as a C1 source to prepare silyl formates, formamides, and aldehydes. Tetrabutylammonium acetate (TBAA) catalyzed the solvent-free N-formylation of amines with CO2 and hydrosilane to give formamides including Weinreb formamide, Me(MeO)NCHO, which was successively converted into aldehydes by one-pot reactions with Grignard reagents.

Silica-supported Alkylammonium Formate Catalyst for Hydrosilylation of Carbon Dioxide

An amorphous silica-supported alkylammonium formate catalyst for the reductive transformation of carbon dioxide using silane as a reductant was developed. Alkylammonium iodide was grafted on amorph...

Diverse Catalytic Systems and Mechanistic Pathways for Hydrosilylative Reduction of CO2.

Catalytic hydrosilylation of carbon dioxide has emerged as a promising approach for carbon dioxide utilization. It allows the reductive transformation of carbon dioxide into value-added products at the levels of formate, formaldehyde, methanol, and methane. Tremendous progress has been made in the area of carbon dioxide hydrosilylation since the first reports in 1981. This focus review describes recent advances in the design and catalytic performance of leading catalyst systems, including transition-metal, main-group, and transition-metal/main-group and main-group/main-group tandem catalysts. Emphasis is placed on discussions of key mechanistic features of these systems and efforts towards the development of more selective, efficient, and sustainable carbon dioxide hydrosilylation processes.

Carbon Dioxide Hydrosilylation to Methane Catalyzed by Zinc and Other First-Row Transition Metal Salts

Abstract We accomplished zinc catalyzed hydrosilylation of carbon dioxide (CO2) to silyl formate (C+II), bis(silyl)acetal (C0), methoxysilane (C−II), and finally methane (C−IV). Among several zinc salts, we found that Zn(OAc)2 with ligand 1,10-phenanthroline was the best. A turnover number of 815000 was achieved using the zinc catalyst to yield C+II. Unexpectedly, we observed the generation of CO from CO2 and hydrosilane for the first time. In addition to Zn, other first-row transition metals (Mn, Fe, Co, Ni, and Cu) also served as Lewis acid catalysts for CO2 hydrosilylation, regardless of the nature of the metal.

Highly efficient palladium-catalysed carbon dioxide hydrosilylation employing PMP ligands.

A series of zero-valent palladium complexes featuring diphosphinometal ligands is reported. The metalloligand in the PMP-type framework (M = LiI, CuI, ZnII) acts as a weak to medium acceptor ligand for palladium. A Pd0→ZnII bond was observed in the solid state and further confirmed by NBO analysis. The heterobimetallic Pd/Zn complex 2-Zn displayed excellent activity in chemoselective CO2 hydrosilylation producing silyl formate (TOF1/2 = 3000 h-1).

Benzoimidazole‐Pyridylamido Zirconium and Hafnium Alkyl Complexes as Homogeneous Catalysts for Tandem Carbon Dioxide Hydrosilylation to Methane

AbstractNeutral ZrIV and HfIV alkyl/amido complexes stabilized by a tridentate N ligand that contains a “rolling” heterodentate benzoimidazole fragment have been prepared and characterized. The ultimate nature of the ligand denticity, the electronic properties of the ligand binding pocket and the metal coordination environment are controlled by the protection/deprotection of the benzoimidazole NH group. The metal precursor used [MIV(Bn)4 or MIV(NMe2)4] also has an influence on the final coordination sphere of the complex; indeed, a permanent central pyridine dearomatization occurs in the presence of dimethylamido ancillary groups. DFT calculations on the real system have been used to elucidate the mechanism. Selected alkyl species from this series have been scrutinized for the tandem hydrosilylation of CO2 to CH4 in combination with the strong Lewis acid B(C6F5)3 using a variety of hydrosilanes. A positive effect of the hardness modification of the ligand donor atom set is observed in the catalytic outcomes. Indeed, κ3{N−,N,N−}ZrIV(Bn)2 catalyzes the process to methane selectively with a turnover frequency as high as 272 h−1 (at 96 % substrate conversion) almost twice as much as that claimed for the benchmark κ3{O−,O,O−}ZrIV(Bn)2 complex under similar experimental conditions.

Ni(I)-Hydride Catalyst for Hydrosilylation of Carbon Dioxide and Dihydrogen Generation: Theoretical Prediction and Exploration of Full Catalytic Cycle

We wish to report here the first theoretical prediction that a unique nickel(I) hydride complex NiIH(bpy) (bpy = 2,2′-bipyridine) 1 is a good catalyst for hydrosilylation of CO2 with hydrosilane (HSiR3) and dihydrogen (H2) generation via alcoholysis/hydrolysis of hydrosilane. Full catalytic cycles of these reactions were elucidated by density functional theory (DFT) calculations. In the CO2 hydrosilylation, the first step is CO2 insertion into the NiI–H bond of 1, which occurs easily to afford NiI(η1–OCOH)(bpy) species, in which charge transfer (CT) occurs from singly occupied molecular orbital (SOMO) corresponding to Ni–H antibonding orbital to LUMO of CO2. The next step is metathesis between NiI(η1–OCOH)(bpy) and HSiR3 to produce H(CO)OSiR3 and regenerate 1. This is rate-determining (ΔG°⧧ = 19.5 kcal mol–1). In the transition state of the metathesis, the Si atom takes a hypervalent trigonal-bipyramidal structure, suggesting that hydrosilane with electron-withdrawing substituents is good for this reaction. The use of 6,6′-dimethyl-2,2′-bipyridine (dmbpy), which has methyl groups at the ortho position to the N of bpy, substantially decreases the ΔG°⧧ value of the metathesis, suggesting that NiIH(dmbpy) is a better catalyst. In the dihydrogen generation via alcoholysis of hydrosilane by 1, the first step is metathesis between the O–H bond of ROH (R= Me or H) and the NiI–H bond of 1 to afford NiI(OR)(bpy) and dihydrogen molecule. Next step is the second metathesis between the NiI–OR bond and the Si–H bond of HSiR3 to yield R3Si(OR) and regenerate 1. The second metathesis occurs with a negligibly small ΔG°⧧ value, indicating that various hydrosilanes can be employed for this reaction. On the basis of these computational findings, it is predicted that 1 can catalyze two completely different reactions, CO2 hydrosilylation with hydrosilane and dihydrogen generation via alcoholysis/hydrolysis of hydrosilane.

Zinc and Magnesium Catalysts for the Hydrosilylation of Carbon Dioxide.

The terminal zinc and magnesium hydride compounds, [κ3-TismPriBenz]ZnH and [TismPriBenz]MgH, which feature the tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl ligand, react with B(C6F5)3 to afford the ion pairs, {[TismPriBenz]M}[HB(C6F5)3] (M = Zn, Mg), which are rare examples of these metals in trigonal monopyramidal coordination environments. Significantly, in combination with B(C6F5)3, {[TismPriBenz]M}-[HB(C6F5)3] generates catalytic systems for the hydrosilylation of CO2 by R3SiH to afford sequentially the bis(silyl)acetal, H2C(OSiR3)2, and CH4 (R3SiH = PhSiH3, Et3SiH, and Ph3SiH). In contrast to many other catalysts for these transformations, both the zinc and magnesium catalytic systems are active at room temperature, and the latter provides the first example of catalytic hydrosilylation of CO2 involving a magnesium compound. Also of note, the selectivity of the catalytic systems may be controlled by the nature of the silane, with PhSiH3 favoring CH4, and Ph3SiH favoring the bis(silyl)acetal, H2C(OSiPh3)2.

Zinc phthalocyanine as an efficient catalyst for halogen-free synthesis of formamides from amines via carbon dioxide hydrosilylation under mild conditions

The combination of a zinc phthalocyanine (ZnPc) catalyst and a stoichiometric amount of dimethyl formamide (DMF) provided a simple route to formamide derivatives from amines, CO2, and hydrosilanes under mild conditions. We deduced that formation of an active zinc-hydrogen (Zn-H) species promoted hydride transfer from the hydrosilane to CO2. The cooperative activation of the Lewis acidic ZnPc by strongly polar DMF, led to formation of activated amines and hydrosilanes, which promoted the chemical reduction of CO2. Consequently, the binary ZnPc/DMF catalytic system showed excellent yields and superior chemoselectivity, representing a simple and sustainable pathway for the reductive transformation of CO2 into valuable chemicals as an alternative to conventional halogen-containing process.

Catalytic reduction of CO2 with organo-silanes using [Ru3(CO)12

The reaction of carbon dioxide with Et3SiH in the presence of catalytic amounts of [Ru3(CO)12] as a catalytic precursor was achieved to produce silyl formate (Et3SiOCOH) 1s with a TON of 9000. A similar reaction in the presence of KF yielded potassium formate (8s) in a one-pot protocol with high selectivity using water or MeCN as the solvent. In the current report the complete reduction of carbon dioxide to methane was achieved, with the use of a more reactive silane (phenylsilane). A catalytically relevant species was the ruthenium cluster [H4Ru4(CO)12]. This is the second report on the hydrosilylation of carbon dioxide catalyzed by highly active and readily available ruthenium clusters and this is the first report of hydrosilylation of CO2 to methane.

Phosphazenes: efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide.

Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h(-1) with a TON of 759. It is also shown that unexpectedly, N,N-dimethylformamide can reduce CO2 to a mixture of silyl formates, acetals and methoxides in the absence of any catalyst.

Temperature-Dependent Chemoselective Hydrosilylation of Carbon Dioxide to Formaldehyde or Methanol Oxidation State

Tethered Ru–S complexes were found to catalyze the hydrosilylation of carbon dioxide with a variety of simple monohydrosilanes selectively to bis(silyl)acetals or silylated methanol, respectively. The chemoselective conversion to either the formaldehyde or methanol oxidation state was solely dependent on the reaction temperature. This is the first example of a catalyst system that gives access to both of the intermediate oxidation states in a controlled way.

Carbon dioxide hydrosilylation promoted by cobalt pincer complexes.

The addition of carbon dioxide to ((tBu)PNP)CoH [(tBu)PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine] resulted in rapid insertion into the Co-H bond to form the corresponding κ(1)-formate complex, which has been structurally characterized. Treatment of ((tBu)PNP)CoH with PhSiH3 resulted in oxidative addition to form trans-((tBu)PNP)CoH2(SiH2Ph), which undergoes rapid exchange with excess free silane. With 0.5 mol % ((tBu)PNP)CoH, the catalytic hydrosilylation of CO2 with PhSiH3 to a mixture of oligomers containing silyl formate, bis(silyl)acetyl, and silyl ether subunits has been observed.

Generation of dihydrogen molecule and hydrosilylation of carbon dioxide catalyzed by zinc hydride complex: theoretical understanding and prediction.

Generation of H2 from methanol/water and hydrosilylation of CO2 catalyzed by [tris(2-pyridylthio)methyl]zinc hydride [κ(3)-Tptm]ZnH 1 were investigated with DFT and MP2 methods. The hydrosilylation of CO2 occurs via the CO2 insertion into the Zn-H bond of 1 followed by the metathesis of a Zn-(η(1)-OCOH) bond with hydrosilane to yield silyl formate and regenerate 1. The CO2 insertion easily occurs, but the metathesis is difficult because of the formation of a very stable Zn-(η(2)-O2CH) species before the metathesis. The ΔG°(‡) value of the metathesis with triethoxysilane is much smaller than that with phenylsilane because electronegative methoxy groups stabilize the transition state bearing hypervalent Si center, which is consistent with the experimental result that triethoxysilane is used in the hydrosilylation of CO2. It is theoretically predicted here that hydrosilane with two electronegative OEt groups or one to three F groups can be applied to this reaction. In the generation of H2 from methanol/water by 1, the first step is the metathesis of 1 with the O-H bond of methanol/water to produce [κ(3)-Tptm]Zn(OMe)/[k(3)-Tptm]Zn(OH) and dihydrogen molecule. The next step is the metathesis of the Zn-OMe/Zn-OH bond with hydrosilane to yield silyl ether and regenerate 1. The first metathesis is rate-determining but the second one occurs with very small activation energy, indicating that various hydrosilanes can be applied to this reaction.