Tertiary Hydrosilanes Research Articles

White-Light initiated Mn2(CO)10/HFIP-Catalyzed anti-Markovnikov hydrosilylation of alkenes

This study presents a highly efficient and mild method for radical hydrosilylation of alkenes. The reaction proceeds under white-light, in the presence of Mn2(CO)10 pre-catalyst and HFIP as an additive, at r.t. and under air. Under white-light, [Mn]• is generated, which activates the Si–H-group to form Si• and trigger the autocatalytic process. HFIP acts as a unique activator which enables synthesis of the products with yields close to quantitative and with anti-Markovnikov selectivity. The method is applicable to terminal alkenes, including those with O-, N- and halogen-containing functional groups, styrene and allylbenzene derivatives, etc., as well as to a wide range of alkyl-, phenyl-, siloxy- and alkoxy-containing tertiary hydrosilanes. These conditions turned out to be most efficient for hydrosilylation of gaseous reagents such as ethylene and acetylene. In both cases the products showed quantitative yield at 1 atm and at r.t. The method is easily up-scalable in batch- and flow-modes.

Breaking Conventional Site Selectivity in C-H Bond Activation: Selective sp3 versus sp2 Silylation by a Pincer-Based Pocket.

A deeply ingrained assumption in the conventional understanding and practice of organometallic chemistry is that an unactivated aliphatic C(sp3)-H bond is less reactive than an aromatic C(sp2)-H bond within the same molecule given that they are at positions unbiasedly accessible for activation. Herein, we demonstrate that a pincer-ligated iridium complex catalyzes intramolecular dehydrogenative silylation of the unactivated δ-C(sp3)-H (δ to the Si atom) with exclusive site selectivity over typically more reactive ortho δ-C(sp2)-H bonds. A variety of tertiary hydrosilanes undergo δ-C(sp3)-H silylation to form 5-membered silolanes, including chiral silolanes, which can undergo further oxidation to produce enantiopure β-aryl-substituted 1,4-diols. Combined computational and experimental studies reveal that the silylation occurs via the Si-H addition to a 14-electron Ir(I) fragment to give an Ir(III) silyl hydride complex, which then activates the C(sp3)-H bond to form a 7-coordinate, 18-electron Ir(V) dihydride silyl intermediate, followed by sequential reductive elimination of H2 and silolane. The unprecedented site selectivity is governed by the distortion energy difference between the rate-determining δ-C(sp3)-H and δ-C(sp2)-H activation, although the activation at sp2 sites is much more favorable than sp3 sites by the interaction energy.

Rhodium-Catalyzed Enantioselective Intramolecular Hydrosilylation to Access Silicon-Stereogenic Tertiary Hydrosilanes

Rhodium-Catalyzed Enantioselective Intramolecular Hydrosilylation to Access Silicon-Stereogenic Tertiary Hydrosilanes

Asymmetric Cobalt‐Catalyzed Regioselective Hydrosilylation/Cyclization of 1,6‐Enynes

AbstractWe report an enantioselective cobalt‐catalyzed hydrosilylation/cyclization reaction of 1,6‐enynes with secondary and tertiary hydrosilanes employing a catalyst generated in situ from the combination of Co(acac)2 and (R,Sp)‐Josiphos. A wide range of oxygen‐, nitrogen‐, and carbon‐tethered 1,6‐enynes reacted with Ph2SiH2, (EtO)3SiH, or (RO)2MeSiH to afford the corresponding chiral organosilane products in high yields and up to >99 % ee. This cobalt‐catalyzed hydrosilylation/cyclization also occurred with prochiral secondary hydrosilane PhMeSiH2 to yield chiral alkylsilanes containing both carbon‐ and silicon‐stereogenic centers with excellent enantioselectivity, albeit with modest diastereoselectivity. The chiral organosilane products from this cobalt‐catalyzed asymmetric hydrosilylation/cyclization could be converted to a variety of chiral five‐membered heterocyclic compounds by stereospecific conversion of their C−Si and Si−H bonds without loss of enantiopurity.

Asymmetric Cobalt‐Catalyzed Regioselective Hydrosilylation/Cyclization of 1,6‐Enynes

We report an enantioselective cobalt-catalyzed hydrosilylation/cyclization reaction of 1,6-enynes with secondary and tertiary hydrosilanes with a catalyst generated in situ from the combination of Co(acac) 2 and ( R , S p )-Josiphos. Under identified conditions, a wide range of oxygen-, nitrogen-, and carbon-tethered 1,6-enynes reacted with Ph 2 SiH 2 , (EtO) 3 SiH, or (RO) 2 MeSiH to afford the corresponding chiral organosilane products in high yields with excellent enantioselectivity (up to >99% ee). In addition, this cobalt-catalyzed hydrosilylation/cyclization also occurred with prochiral secondary hydrosilane PhMeSiH 2 to yield chiral alkylsilanes containing both carbon- and silicon-stereogenic centers with excellent enantioselectivity, albeit with modest diastereoselectivity. The chiral organosilane products from this cobalt-catalyzed asymmetric hydrosilylation/cyclization could be converted to a variety of chiral five-membered heterocyclic compounds by stereospecific conversion of their C-Si and Si-H bonds without loss of enantiopurity. Mechanistic studies including deuterium-labeling, control, and competition experiments suggest a chiral cobalt hydride intermediate [( L* )Co-H], the chelation of 1,6-enynes to cobalt catalysts, and the regioselectivity controlled by the relative reactivity of the alkyne and alkene moieties toward hydrocobaltation.

Di-tert-butyl Peroxide (DTBP)-Mediated Oxysilylation of Unsaturated Carboxylic Acids for the Synthesis of Silyl Lactones.

Herein, we describe the first oxysilylation of unsaturated carboxylic acids mediated by di-tert-butyl peroxide (DTBP), which enables the rapid and efficient preparation of silyl lactone compounds. This process tolerates functional groups, such as methyl, methoxy, halogen (fluoride and chloride), and cyano moieties. Furthermore, the strategy allows the application of a wide range of primary, secondary, and tertiary hydrosilanes for functionalization.

Molecular Zinc Hydride Cations [ZnH]+ : Synthesis, Structure, and CO2 Hydrosilylation Catalysis.

Protonolysis of [ZnH2]n with the conjugated Brønsted acid of the bidentate diamine TMEDA (N,N,N′,N′‐tetramethylethane‐1,2‐diamine) and TEEDA (N,N,N′,N′‐tetraethylethane‐1,2‐diamine) gave the zinc hydride cation [(L2)ZnH]+, isolable either as the mononuclear THF adduct [(L2)ZnH(thf)]+[BArF 4]− (L2=TMEDA; BArF 4 −=[B(3,5‐(CF3)2‐C6H3)4]−) or as the dimer [{(L2)Zn)}2(μ‐H)2]2+[BArF 4]− 2 (L2=TEEDA). In contrast to [ZnH2]n, the cationic zinc hydrides are thermally stable and soluble in THF. [(L2)ZnH]+ was also shown to form di‐ and trinuclear adducts of the elusive neutral [(L2)ZnH2]. All hydride‐containing cations readily inserted CO2 to give the corresponding formate complexes. [(TMEDA)ZnH]+[BArF 4]− catalyzed the hydrosilylation of CO2 with tertiary hydrosilanes to give stepwise formoxy silane, methyl formate, and methoxy silane. The unexpected formation of methyl formate was shown to result from the zinc‐catalyzed transesterification of methoxy silane with formoxy silane, which was eventually converted into methoxy silane as well.

Si-H Bond Activation with Bullock's Cationic Tungsten(II) Catalyst: CO as Cooperating Ligand.

An in-depth investigation of the reaction of tertiary hydrosilanes with [CpW(CO)2(IMes)]+[B(C6F5)4]- reveals a fundamentally new Si-H bond activation mode. Unlike the originally proposed oxidative addition of the Si-H bond to the tungsten(II) center, there is strong experimental and NMR spectroscopic evidence for the involvement of one of the CO ligands of the cationic complex in the Si-H bond breaking event. The Si-H bond is heterolytically cleaved to form a tungsten(II) hydride and a silylium ion, which is stabilized by one of the CO ligands. This reactive hydrosilane adduct was eventually isolated and characterized by X-ray diffraction analysis. Quantum-chemical calculations support a cooperative mechanism, but a stepwise process consisting of oxidative addition and subsequent tungsten-to-oxygen silyl migration in the tungsten(IV) silyl hydride is also energetically feasible. However, our combined spectroscopic and computational analysis favors the cooperative pathway. The newly identified hydrosilane adduct is the key intermediate of Bullock's ionic carbonyl hydrosilylation.

Interconversion and reactivity of manganese silyl, silylene, and silene complexes.

Manganese disilyl hydride complexes [(dmpe)2MnH(SiH2R)2] (4Ph : R = Ph, 4Bu : R = n Bu) reacted with ethylene to form silene hydride complexes [(dmpe)2MnH(RHSi[double bond, length as m-dash]CHMe)] (6Ph,H : R = Ph, 6Bu,H : R = n Bu). Compounds 6R,H reacted with a second equivalent of ethylene to generate [(dmpe)2MnH(REtSi[double bond, length as m-dash]CHMe)] (6Ph,Et : R = Ph, 6Bu,Et : R = n Bu), resulting from apparent ethylene insertion into the silene Si-H bond. Furthermore, in the absence of ethylene, silene complex 6Bu,H slowly isomerized to the silylene hydride complex [(dmpe)2MnH([double bond, length as m-dash]SiEt n Bu)] (3Bu,Et ). Reactions of 4R with ethylene likely proceed via low-coordinate silyl {[(dmpe)2Mn(SiH2R)] (2Ph : R = Ph, 2Bu : R = n Bu)} or silylene hydride {[(dmpe)2MnH([double bond, length as m-dash]SiHR)] (3Ph,H : R = Ph, 3Bu,H : R = n Bu)} intermediates accessed from 4R by H3SiR elimination. DFT calculations and high temperature NMR spectra support the accessibility of these intermediates, and reactions of 4R with isonitriles or N-heterocyclic carbenes yielded the silyl isonitrile complexes [(dmpe)2Mn(SiH2R)(CNR')] (7a-d: R = Ph or n Bu; R' = o-xylyl or t Bu), and NHC-stabilized silylene hydride complexes [(dmpe)2MnH{[double bond, length as m-dash]SiHR(NHC)}] (8a-d: R = Ph or n Bu; NHC = 1,3-diisopropylimidazolin-2-ylidene or 1,3,4,5-tetramethyl-4-imidazolin-2-ylidene), respectively, all of which were crystallographically characterized. Silyl, silylene and silene complexes in this work were accessed via reactions of [(dmpe)2MnH(C2H4)] (1) with hydrosilanes, in some cases followed by ethylene. Therefore, ethylene (C2H4 and C2D4) hydrosilylation was investigated using [(dmpe)2MnH(C2H4)] (1) as a pre-catalyst, resulting in stepwise conversion of primary to secondary to tertiary hydrosilanes. Various catalytically active manganese-containing species were observed during catalysis, including silylene and silene complexes, and a catalytic cycle is proposed.

Synthesis and Reactivity of Thiolate‐Bridged NiIIMI Heterodinuclear Complexes (M = Rh, Ir) with an S‐Bidentate NiP2S2 Metalloligand

The mononuclear complex [Ni(meppp)] {H2meppp = meso‐1,3‐bis[(2‐mercaptoethyl)(phenyl)phosphino]propane} was used as an S‐bidentate NiP2S2 metalloligand to prepare a series of NiIIMI complexes with various neutral ligands, namely, [Ni(µ‐meppp)ML2]PF6 [M = Rh, L = 1/2cod (1a; cod = 1,5‐cycloocatadiene), CO (1b), XylNC (1c; Xyl = 2,6‐dimethylphenyl), P(OPh)3 (1d); M = Ir, L = 1/2cod (2a), CO (2b), XylNC (2c)]. The reactivities of 1 and 2 toward methyl iodide and tertiary hydrosilanes were examined. Complexes 1c, 2a, and 2b reacted with MeI to afford the oxidative addition products [Ni(µ‐meppp)M(L)2(Me)(I)]PF6 [M = Rh, L = XylNC (3c); M = Ir, L = 1/2cod (4a)] and [Ni(µ‐meppp)Ir(CO)(Me)(I)2] (5). In the reactions with hydrosilanes, only 2c exhibited an interesting reactivity to afford the NiII(µ‐H)IrIII silyl complexes [Ni(µ‐meppp)(µ‐H)Ir(XylNC)2(Si)]PF6 [Si = SiEt3 (6a), SiMe2Ph (6b), SiMePh2 (6c), SiPh3 (6d)]. The reaction proceeded via the intermediate isomers [Ni(meppp)(µ‐H)Ir(XylNC)2(Si)]PF6 (7); intermediate 7d (Si = SiPh3) was characterized and has an NiII(µ‐H)IrIII silyl structure with the hydrido ligand nesting in the reverse side of the Ni(µ‐S)2Ir pocket to that of 6d. These results demonstrated that the reactivities of the bis(thiolate)‐bridged NiIIMI heterodinuclear complexes can be tuned by changing the metal ions and ancillary ligands. In addition, the S‐bidentate NiP2S2 metalloligand [Ni(meppp)] plays an important role in the stabilization of the bridging hydrido ligand in both pockets of the NiII(µ‐H)IrIII core owing to the flexibility of the hinged Ni(µ‐SR)2Ir structure.

Ruthenium-catalyzed hydrosilylation of C=N bond in benzothiazole

Various tertiary hydrosilanes are shown to be compatible with ruthenium-catalyzed hydrosilylation of carbon-nitrogen double bond in benzothiazole. The addition reaction was successfully performed by using a catalytic amount of Ru3(CO)12. The products were isolated and characterized by IR, 1H NMR, 13C NMR, 29Si NMR, HRMS and MS analysis. This is the first example for the catalytic hydrosilylation of benzothiazole.

H/D Exchange Processes Catalyzed by an Iridium-Pincer Complex

A PNP-pincer iridium dihydride performs the H/D exchange between aromatic substrates and tertiary hydrosilanes and D_(2)O or C_(6)D_(6). Complete incorporation of deuterium into sterically accessible C_(ar)–H and Si–H bonds was observed at a moderate temperature of 80 °C.

Synthesis, Structure, and Catalytic Activity of Bimetallic PtII–IrIII Complexes Bridged by Cyclooctane‐1,2‐dithiolato Ligands

AbstractCationic PtII–IrIII heterobimetallic complexes bridged by cyclooctane‐1,2‐dithiolato ligands [(PPh3)2Pt(μ2‐SRS)IrCl(η5‐Cp*)][SbF6] [R = cis‐C8H14 (5), trans‐C8H14 (6), Cp* = C5Me5] were synthesized by reaction of (cyclooctane‐1,2‐dithiolato)PtII complexes [Pt(SRS)(PPh3)2] [R = cis‐C8H14 (3), trans‐C8H14 (4)] with [IrCl(μ‐Cl)(η5‐Cp*)]2 in thf in the presence of AgSbF6. The structures of complexes 5 and 6 were fully characterized by their NMR spectroscopic data. Moreover, X‐ray crystallographic analysis of 5 revealed that the PtS2Ir core exhibits a hinged arrangement, in which the cis‐cyclooctane‐1,2‐dithiolate acts as a bridging ligand between the platinum and iridium metals. Complexes 5 and 6 served as a catalyst in the hydrosilylation of terminal alkynes R′CCH (R′ = Ph, Bu, CO2Me) with tertiary hydrosilanes such as Et3SiH and Ph3SiH to afford selectively β‐(Z)‐vinylsilanes 8 in high yields.

Cationic Iridium(I) Complexes as Catalysts for the Alcoholysis of Silanes

The syntheses of five cationic iridium(I) complexes, containing the bidentate ligands bis(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM), {[Ir(BPM)(COD)]+(BPh4)-} (1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4), {[Ir(BPM)(CO)2]+(BPh4)-} (3), and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5), are reported. The complexes were characterized by NMR spectroscopy, and the solid-state structure of {[Ir(BPM)(CO)2]+(BPh4)-} (3) was determined by single-crystal X-ray crystallographic analysis. The complexes {[Ir(BPM)(CO)2]+(BPh4)-} (3) and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5) are effective catalysts for the alcoholysis of a range of alcohols and hydrosilanes, including secondary and tertiary hydrosilanes, under mild conditions.

Cyclization/Hydrosilylation of Functionalized Dienes Catalyzed by a Cationic Palladium Phenanthroline Complex

Mixtures of (phen)PdMe2 (2a) and HBAr‘4 (3a) or (phen)PdMe(Cl) (2b) and NaBAr‘4 (3b) [phen = 1,10-phenanthroline; Ar‘ = 3,5-C6H3(CF3)2] catalyzed the cyclization/hydrosilylation of functionalized 1,6-dienes to form silylated cyclopentanes in good yield and with excellent trans selectivity about the newly formed C−C bond (typically >50:1). A range of tertiary hydrosilanes were employed in the procedure although unhindered trialkylsilanes provided the most consistent results. The protocol tolerated a range of polar functionality including esters, ethers, amides, sulfones, and cyano groups. 4,4-Disubstitution on the diene backbone promoted cyclization, and a homoallylic ester, ketone, or ether directing group was required for efficient cyclization. The procedure tolerated dienes which possessed a single trans-substituted olefin and also tolerated allylic substitution. These substituted dienes underwent cyclization/hydrosilylation to form carbocycles resulting from transfer of the silyl group to the less hind...

Conversion of Hydrosilanes to Silanols and Silyl Esters Catalyzed by [Ph(3)PCuH](6).

[Ph3PCuH]6 is an efficient catalyst for the dehydrogenative coupling between the tertiary hydrosilanes Ph3SiH, Ph2MeSiH, Me2PhSiH, or Et3SiH and water or acetic acid to give silanols or silyl acetates.