Dehydrogenative Silylation Research Articles

Catalytic study of heterobimetallic rhodium complexes derived from partially alkylated s-indacene in dehydrogenative silylation of olefins

This work describes the catalytic study of heterobimetallic rhodium compounds derived from partially alkylated s-indacene in dehydrogenative silylation of olefins in order to elucidate as much as possible the effects of: solvent, temperature, chemical substrates, olefin effect, silane effect, and secondary metallic fragment. The rhodium complexes, anti-[Cp*Fe-s-Ic′-Rh(COD)] 1, anti-[Cp*Ru-s-Ic′-Rh(COD)] 2, and syn-[Cp*Ru-s-Ic′-Rh(COD)] 2′ (with s-Ic′: 2,6-diethyl-4,8-dimethyl-s-indaceneiide) were previously synthesized and characterized, and were compared with the catalytic activity of the complexes previously reported; monometallic [(COD)Rh-s-Ic′H] 3, and homobimetallic anti-[{(COD)Rh}2-s-Ic′] 4, and syn-[{(COD)Rh}2-s-Ic′] 4′.The heterobimetallic complexes show a high activity and selectivity for the dehydrogenative silylation of styrene and these complexes show also the presence of a cooperative effect between both metallic centers, which is evidenced when compared with monometallic complex.

Hemilabile N-Xylyl-N′-methylperimidine Carbene Iridium Complexes as Catalysts for C–H Activation and Dehydrogenative Silylation: Dual Role of N-Xylyl Moiety for ortho-C–H Bond Activation and Reductive Bond Cleavage

Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)Ir(cod)(X) (1) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis(cyclometalated)iridium complexes, (C(∧)C:)(C(∧)N)IrOAc (2) (C(∧)C: = a cyclometalated perimidine-carbene ligand and C(∧)N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis(cyclometalated)iridium complex ((Xy)C(∧)C:)(C(∧)N)IrOAc (2d) ((Xy)C(∧)C: = a cyclometalated N-xylyl-N'-methylperimidine-carbene ligand and C(∧)N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et3SiH to give an iridium hydride complex, (L(4))(C(∧)N)Ir(H)(SiEt3) (8d) (L(4) = N-CH3, N-3,5-(CH3)2C6H3 perimidine), via demetalation of a N-3,5-xylyl ring of the carbene ligand of 2d. The formation of 8d was confirmed by isolating the corresponding chloro complex (L(4))(C(∧)N)Ir(Cl)(SiEt3) (8d-Cl) by treatment with CCl4. The N-methyl moiety of the carbene ligand coordinated to 8d was cyclometalated in the presence of norbornene at room temperature to afford ((Me)C(∧)C:)(C(∧)N)Ir(SiEt3) (10d) ((Me)C(∧)C: = a cyclometalated N-xylyl-N'-methylperimidine-carbene), while at high temperature 8d reacted with norbornene and Et3SiH to afford the silylated product, 2-(2-triethylsilyl)phenylpyridine (3a) and norbornane. A deuterium labeling experiment using 2d and Et3SiD (excess) revealed the incorporation of deuterium atoms at two ortho-positions of the N-xylyl group (>90%) and at the 3-position of 2-pyridylphenyl ligand (ca. 40%) within 3 h at room temperature, indicating that the cyclometalation/demetalation of the N-xylylperimidine carbene and 2-phenylpyridine ligands were reversible processes. Isolation of these cyclometalated iridium complexes under controlled conditions and D-labeling experiments thus revealed a dual function of the N-aryl group bound to the perimidine-carbene ligand, which acted as both a neutral carbene ligand and a monoanionic ortho-metalated aryl-carbene ligand through reversible C-H bond activation and Ir-C bond cleavage of the N-aryl group during the catalytic cycle.

Iridium‐Catalyzed, Diastereoselective Dehydrogenative Silylation of Terminal Alkenes with (TMSO)2MeSiH

Entscheidende Liganden: Die Diastereoselektivität der Titelreaktion, die unter milden Bedingungen in Gegenwart geringer Katalysatormengen abläuft, kann über die Wahl des Hilfsliganden gesteuert werden (siehe Schema; coe=Cycloocten). Die Silylierungsprodukte können anschließend weitere Umsetzungen eingehen, etwa Oxidationen oder Kreuzkupplungen.

Iridium‐Catalyzed, Diastereoselective Dehydrogenative Silylation of Terminal Alkenes with (TMSO)2MeSiH

Ligands' choice: The title reaction was achieved under mild conditions with low catalyst loading. The diastereoselectivity of the reaction can be controlled by choosing the appropriate ancillary ligand (see scheme; coe=cyclooctene). The silylation products undergo further transformation such as oxidation or cross-coupling.

Iridium-catalysed isomerising trialkylsilylation of methyl oleate

Monounsaturated fatty acids from vegetable oils are attractive substrates for applications as renewable feedstock in polymer industry. Applying the concept of transition metal-catalysed isomerising functionalisation, their nearly inaccessible internal CC double bond can be transformed into products with a functional group in the terminal position. In this work, methyl oleate is shown to undergo [Ir(OMe)(cod)]2-catalysed dehydrogenative silylation with triethylsilane to give terminal vinylsilanes 4 in 69% yield. Independent preparation of reference substances is helpful in identifying the desired products in gas chromatograms of complex reaction mixtures.

ChemInform Abstract: Rhodium‐Catalyzed Intramolecular Silylation of Unactivated C(sp3)—H Bonds.

The treatment of a variety of hydrosilanes, each incorporating a benzylic C(sp(3))-H bond, with a rhodium catalyst resulted in intramolecular dehydrogenative silylation. This silylation reaction was found to occur at typically unreactive C(sp(3))-H bonds located at terminal positions on alkyl chains. Interestingly, the rhodium catalyst also promoted regioselective silylation at a site internal to an alkyl chain.

ChemInform Abstract: Dehydrogenative Silylation of Terminal Alkynes with Hydrosilanes under Zinc—Pyridine Catalysis.

AbstractFirst time, alkynylsilanes are synthesized in excellent yields by dehydrogenative silylation of terminal alkynes with hydrosilanes.

Rhodium-Catalyzed Intramolecular Silylation of Unactivated C(sp3)–H Bonds

The treatment of a variety of hydrosilanes, each incorporating a benzylic C(sp(3))-H bond, with a rhodium catalyst resulted in intramolecular dehydrogenative silylation. This silylation reaction was found to occur at typically unreactive C(sp(3))-H bonds located at terminal positions on alkyl chains. Interestingly, the rhodium catalyst also promoted regioselective silylation at a site internal to an alkyl chain.

Well-defined NHC-rhodium hydroxide complexes as alkenehydrosilylation and dehydrogenative silylation catalysts

Alkene hydrosilylation and dehydrogenative silylation reactions, mediated by [Rh(cod)(NHC)(OH)] complexes (cod = 1,5-cyclooctadiene; NHC = N-heterocyclic carbene) are described. The study details a comparison of the catalytic activity and steric characteristics of four rhodium complexes bearing different NHC ligands. The novel [Rh(cod)(Ii-PrMe)(OH)] complex (Ii-PrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidine) was designed to improve the reactivity of Rh(I)-hydroxides and proved to be a successful promoter of hydrosilylation and dehydrogenative silylation, displaying good stereo- and regiocontrol.

Dehydrogenative Silylation of Terminal Alkynes with Hydrosilanes under Zinc–Pyridine Catalysis

AbstractA combination of zinc triflate and pyridine in a nitrile medium was found to act as an effective catalytic system for dehydrogenative silylation with flexible pieces of terminal alkynes and hydrosilanes, thereby producing diverse alkynylsilanes in high to excellent yields.

Mechanistic aspects of hydrosilylation catalyzed by (ArN=)Mo(H)(Cl)(PMe3)3.

The reaction of (ArN=)MoCl(2)(PMe(3))(3) (Ar = 2,6-diisopropylphenyl) with L-Selectride gives the hydrido-chloride complex (ArN=)Mo(H)(Cl)(PMe(3))(3) (2). Complex 2 was found to catalyze the hydrosilylation of carbonyls and nitriles as well as the dehydrogenative silylation of alcohols and water. Compound 2 does not show any productive reaction with PhSiH(3); however, a slow H/D exchange and formation of (ArN=)Mo(D)(Cl)(PMe(3))(3) (2(D)) was observed upon addition of PhSiD(3). Reactivity of 2 toward organic substrates was studied. Stoichiometric reactions of 2 with benzaldehyde and cyclohexanone start with dissociation of the trans-to-hydride PMe(3) ligand followed by coordination and insertion of carbonyls into the Mo-H bond to form alkoxy derivatives (ArN=)Mo(Cl)(OR)(PMe(2))L(2) (3: R = OCH(2)Ph, L(2) = 2 PMe(3); 5: R = OCH(2)Ph, L(2) = η(2)-PhC(O)H; 6: R = OCy, L(2) = 2 PMe(3)). The latter species reacts with PhSiH(3) to furnish the corresponding silyl ethers and to recover the hydride 2. An analogous mechanism was suggested for the dehydrogenative ethanolysis with PhSiH(3), with the key intermediate being the ethoxy complex (ArN=)Mo(Cl)(OEt)(PMe(3))(3) (7). In the case of hydrosilylation of acetophenone, a D-labeling experiment, i.e., a reaction of 2 with acetophenone and PhSiD(3) in the 1:1:1 ratio, suggests an alternative mechanism that does not involve the intermediacy of an alkoxy complex. In this particular case, the reaction presumably proceeds via Lewis acid catalysis. Similar to the case of benzaldehyde, treatment of 2 with styrene gives trans-(ArN=)Mo(H)(η(2)-CH(2)═CHPh)(PMe(3))(2) (8). Complex 8 slowly decomposes via the release of ethylbenzene, indicating only a slow insertion of styrene ligand into the Mo-H bond of 8.

Selective Dehydrogenative Silylation–Hydrogenation Reaction of Divinyldisiloxane with Hydrosilane Catalyzed by an Iron Complex

A hydride and a silyl group of hydrosilane is introduced into 1,3-divinyldisiloxane in the presence of a catalytic amount of (η(5)-C(5)H(5))Fe(CO)(2)Me. Instead of the product expected from the well-known hydrosilylation reaction, the product obtained is that characteristic of dehydrogenative silylation at one vinyl group and hydrogenation at the other vinyl group of 1,3-divinyldisiloxane. Based on deuterium labeling experiments, a catalytic cycle for this new reaction has been proposed.

Rhodium(I) complex catalyst immobilized on terpolymers of N‐vinylpyrrolidinone and 1‐vinylimidazole

AbstractThe hydrosilylation of cyclohexanone and acetone with triethysilane and diphenysilane catalyzed by polymer‐supported Rh(I) complex has been investigated. Two terpolymers of styrene, divinylbenzene, and 1‐vinylimidazole (S/DVB/VI) or N‐vinylpyrrolidinone (S/DVB/NVP) were used as the catalysts supports. Physical characterization of these materials has involved the measurements of the structural parameters in the dry and swollen states by DSC, the nitrogen BET adsorption method and inverse steric exclusion chromatography ISEC. From these results it can be concluded that the original polymer structure has been changed during the complex attachment giving rise to materials of higher porosity. X‐ray photoelectron spectroscopy XPS, IR, and AAS spectroscopy were used to characterization of heterogeneous complexes before and after use. The effect of the morphology of the support on the catalytic properties of the polymer‐supported Rh(I) species was tested in the hydrosilylation of ketones and correlated with the reaction mechanism. It was demonstrated that the high selectivity of homogeneous rhodium complex toward the silyl ethers can be partially reversed to the dehydrogenative silylation products by a proper choice of polymer support with favorable microporous structure. Recycling tests demonstrated high stability of the supported catalysts during prolonged use. The constant selectivity of the supported catalysts demonstrated during recycling experiments showed that they could be useful for practical application. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Borylation and Silylation of C–H Bonds: A Platform for Diverse C–H Bond Functionalizations

Methods that functionalize C-H bonds can lead to new approaches for the synthesis of organic molecules, but to achieve this goal, researchers must develop site-selective reactions that override the inherent reactivity of the substrates. Moreover, reactions are needed that occur with high turnover numbers and with high tolerance for functional groups if the C-H bond functionalization is to be applied to the synthesis of medicines or materials. This Account describes the discovery and development of the C-H bond functionalization of aliphatic and aromatic C-H bonds with borane and silane reagents. The fundamental principles that govern the reactivity of intermediates containing metal-boron bonds are emphasized and how an understanding of the effects of the ligands on this reactivity led us to broaden the scope of main group reagents that react under mild conditions to generate synthetically useful organosilanes is described. Complexes containing a covalent bond between a transition metal and a three-coordinate boron atom (boryl complexes) are unusually reactive toward the cleavage of typically unreactive C-H bonds. Moreover, this C-H bond cleavage leads to the formation of free, functionalized product by rapid coupling of the hydrocarbyl and boryl ligands. The initial observation of the borylation of arenes and alkanes in stoichiometric processes led to catalytic systems for the borylation of arenes and alkanes with diboron compounds (diborane(4) reagents) and boranes. In particular, complexes based on the Cp*Rh (in which Cp is the cyclopentadienyl anion) fragment catalyze the borylation of alkanes, arenes, amines, ethers, ketals, and haloalkanes. Although less reactive toward alkyl C-H bonds than the Cp*Rh systems, catalysts generated from the combination of bipyridines and iridium(I)-olefin complexes have proven to be the most reactive catalysts for the borylation of arenes. The reactions catalyzed by these complexes form arylboronates from arenes with site-selectivity for C-H bond cleavage that depends on the steric accessibility of the C-H bonds. These complexes also catalyze the borylation of heteroarenes, and the selectivity for these substrates is more dependent on electronic effects than the borylation of arenes. The products from the borylation of arenes and heteroarenes are suitable for a wide range of subsequent conversions to phenols, arylamines, aryl ethers, aryl nitriles, aryl halides, arylboronic acids, and aryl trifluoroborates. Studies of the electronic properties of the ancillary ligand on the rate of the reaction show that the flat structure and the strong electron-donating property of the bipyridine ligands, along with the strong electron-donating property of the boryl group and the presence of a p-orbital on the metal-bound atom, lead to the increased reactivity of the iridium catalysts. Based on this hypothesis, we studied catalysts containing substituted phenanthroline ligands for a series of additional transformations, including the silylation of C-H bonds. A sequence involving the silylation of benzylic alcohols, followed by the dehydrogenative silylation of aromatic C-H bonds, leads to an overall directed silylation of the C-H bond ortho to hydroxyl functionality.

Comparison of Structure and Reactivity of Phosphine-Amido and Hemilabile Phosphine-Amine Chelates of Rhodium

A series of mono- and binuclear rhodium(I) complexes bearing ortho-phosphinoanilido and ortho-phosphinoaniline ligands has been synthesized. Reactions of the protic monophosphinoanilines, Ph(2)PAr or PhPAr(2) (Ar = o-C(6)H(4)NHMe), with 0.5 equiv of [Rh(μ-OMe)(COD)](2) result in the formation of the neutral amido complexes, [Rh(COD)(P,N-Ph(2)PAr(-))] or [Rh(COD)(P,N-PhP(Ar(-))Ar)] (Ar(-) = o-C(6)H(4)NMe(-)), respectively, through stoichiometrically controlled deprotonation of an amine by the internal methoxide ion. Similarly, the binuclear complex, [Rh(2)(COD)(2)(μ-P,N,P',N'-mapm(2-))] (mapm(2-) = Ar(Ar(-))PCH(2)P(Ar(-))Ar), can be prepared by reaction of the protic diphosphinoaniline, mapm (Ar(2)PCH(2)PAr(2)), with 1 equiv of [Rh(μ-OMe)(COD)](2). An analogous series of hemilabile phosphine-amine compounds can be generated by reactions of monophosphinoanilines, Ph(2)PAr' or PhPAr'(2) (Ar' = o-C(6)H(4)NMe(2)), with 1 equiv of [Rh(NBD)(2)][BF(4)] to generate [Rh(NBD)(P,N-Ph(2)PAr')][BF(4)] or [Rh(NBD)(P,N-PhPAr'(2))][BF(4)], respectively, or by reactions of diphosphinoanilines, mapm or dmapm (Ar'(2)PCH(2)PAr'(2)), with 2 equiv of the rhodium precursor to generate [Rh(2)(NBD)(2)(μ-P,N,P',N'-mapm)][BF(4)](2) or [Rh(2)(NBD)(2)(μ-P,N,P',N'-dmapm)][BF(4)](2), respectively. Displacement of the diolefin from [Rh(COD)(P,N-Ph(2)PAr(-))] by 1,2-bis(diphenylphosphino)ethane (dppe) yields [Rh(P,P'-dppe)(P,N-Ph(2)PAr(-))] which, while unreactive to H(2), reacts readily and irreversibly with oxygen to form the peroxo complex, [RhO(2)(P,P'-dppe)(P,N-Ph(2)PAr(-))], and with iodomethane to yield [RhI(CH(3))(P,P'-dppe)(P,N-Ph(2)PAr(-))]. Hemilabile phosphine-amine compounds can also be prepared by reactions of [Rh(P,P'-dppe)(P,N-Ph(2)PAr(-))] with Me(3)OBF(4) or HBF(4)·Et(2)O, resulting in (thermodynamic) additions at nitrogen to form [Rh(P,P'-dppe)(P,N-Ph(2)PAr')][BF(4)] or [Rh(P,P'-dppe)(P,N-Ph(2)PAr)][BF(4)], respectively. The nonlabile phosphine-amido and hemilabile phosphine-amine complexes were tested as catalysts for the silylation of styrene. The amido species do not require the use of solvents in reaction media, can be easily removed from product mixtures by protonation, and appear to be more active than their hemilabile, cationic congeners. Reactions catalyzed by either amido or amine complexes favor dehydrogenative silylation in the presence of excess olefin, showing modest selectivities for a single vinylsilane product. The binuclear complexes, which were prepared in an effort to explore possible catalytic enhancements of reactivity due to metal-metal cooperativity, are in fact somewhat less active than mononuclear species, discounting this possibility.

Catalytic and Stoichiometric Reactivity of β-Silylamido Agostic Complex of Mo: Intermediacy of a Silanimine Complex and Applications to Multicomponent Coupling

The reaction of complex (ArN═)(2)Mo(PMe(3))(3) (Ar = 2,6-diisopropylphenyl) with PhSiH(3) gives the β-agostic NSi-H···M silyamido complex (ArN═)Mo(SiH(2)Ph)(PMe(3))(η(3)-ArN-SiHPh-H) (3) as the first product. 3 decomposes in the mother liquor to a mixture of hydride compounds, including complex {η(3)-SiH(Ph)-N(Ar)-SiHPh-H···}MoH(3)(PMe(3))(3) characterized by NMR. Compound 3 was obtained on preparative scale by reacting (ArN═)(2)Mo(PMe(3))(3) with 2 equiv of PhSiH(3) under N(2) purging and characterized by multinuclear NMR, IR, and X-ray diffraction. Analogous reaction of (Ar'N═)(2)Mo(PMe(3))(3) (Ar' = 2,6-dimethylphenyl) with PhSiH(3) affords the nonagostic silylamido derivative (Ar'N═)Mo(SiH(2)Ph)(PMe(3))(2)(NAr'{SiH(2)Ph}) (5) as the first product. 5 decomposes in the mother liquor to a mixture of {η(3)-PhHSi-N(Ar')-SiHPh-H···}MoH(3)(PMe(3))(3), (Ar'N═)Mo(H)(2)(PMe(3))(2)(η(2)-Ar'N═SiHPh), and other hydride species. Catalytic and stoichiometric reactivity of 3 was studied. Complex 3 undergoes exchange with its minor diastereomer 3' by an agostic bond-opening/closing mechanism. It also exchanges the classical silyl group with free silane by an associative mechanism which most likely includes dissociation of the Si-H agostic bond followed by the rate-determining silane σ-bond metathesis. However, labeling experiments suggest the possibility of an alternative (minor) pathway in this exchange including a silanimine intermediate. 3 was found to catalyze dehydrogenative coupling of silane, hydrosilylation of carbonyls and nitriles, and dehydrogenative silylation of alcohols and amines. Stoichiometric reactions of 3 with nitriles proceed via intermediate formation of η(2)-adducts (ArN═)Mo(PMe(3))(η(2)-ArN═SiHPh)(η(2)-N≡CR), followed by an unusual Si-N coupling to give (ArN═)Mo(PMe(3))(κ(2)-NAr-SiHPh-C(R)═N-). Reactions of 3 with carbonyls lead to η(2)-carbonyl adducts (ArN═)(2)Mo(O═CRR')(PMe(3)) which were independently prepared by reactions of (ArN═)(2)Mo(PMe(3))(3) with the corresponding carbonyl O═CRR'. In the case of reaction with benzaldehyde, the silanimine adduct (ArN═)Mo(PMe(3))(η(2)-ArN═SiHPh)(η(2)-O═CHPh) was observed by NMR. Reactions of complex 3 with olefins lead to products of Si(ag)-C coupling, (ArN═)Mo(Et)(PMe(3))(η(3)-NAr-SiHPh-CH═CH(2)) (17) and (ArN═)Mo(H)(PMe(3))(η(3)-NAr-SiHPh-CH═CHPh), for ethylene and styrene, respectively. The hydride complex (ArN═)Mo(H)(PMe(3))(η(3)-NAr-SiHPh-CH═CH(2)) was obtained from 17 by hydrogenation and reaction with PhSiH(3). Mechanistic studies of the latter process revealed an unusual dependence of the rate constant on phosphine concentration, which was explained by competition of two reaction pathways. Reaction of 17 with PhSiH(3) in the presence of BPh(3) leads to agostic complex (ArN═)Mo(SiH(2)Ph)(η(3)-NAr-Si(Et)Ph-H)(η(2)-CH(2)═CH(2)) (24) having the Et substituent at the agostic silicon. Mechanistic studies show that the Et group stems from hydrogenation of the vinyl substituent by silane. Reaction of 24 with PMe(3) gives the agostic complex (ArN═)Mo(SiH(2)Ph)(PMe(3))(η(3)-NAr-Si(Et)Ph-H), which slowly reacts with PhSiH(3) to furnish silylamide 3 and the hydrosilylation product PhEtSiH(2). A mechanism involving silane attack on the imido ligand was proposed to explain this transformation.

Mechanism of the Dehydrogenative Silylation of Alcohols Catalyzed by Cationic Gold Complexes: An Experimental and Theoretical Study

The catalytic activity both of cationic [(XDPP)Au][X] (XDPP = bis-2,5-diphenylphosphole xantphos X = BF(4)) and of the isolated gold hydride complex [(XDPP)(2)Au(2)H][OTf] in the dehydrogenative silylation process is presented. A parallel theoretical study using density functional theory revealed a mechanism involving the counter anion as a co-catalyst, which was experimentally confirmed by testing various counterions (X = OTf, NTf(2), PF(6)). Finally, a "Au(2)H(+)" species was determined as the intermediate during the catalytic cycle, which correlates well with the experimental findings on the first example of catalytic activity of an isolated "Au-H" complex.

Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes

The reduction of the mononitrosyl Re(II) salt [NMe(4)](2)[ReCl(5)(NO)] (1) with zinc in acetonitrile afforded the Re(i) dichloride complex [ReCl(2)(NO)(CH(3)CN)(3)] (2). Subsequent ligand substitution reactions with PCy(3), PiPr(3) and P(p-tolyl)(3) afforded the bisphosphine Re(i) complexes [ReCl(2)(NO)(PR(3))(2)(CH(3)CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H(2) (1 bar) to afford the dihydrogen Re(I) complexes [ReCl(2)(NO)(PR(3))(2)(η(2)-H(2))] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me(2)NH·BH(3), dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me(2)NH·BH(3), the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy(3) ligands exhibit high catalytic activities. Monochloro Re(I) hydrides [Re(Cl)(H)(NO)(PR(3))(2)(CH(3)CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.

A Ruthenium-Catalyzed Hydrosilane-Induced Polymerization of 3-Alkyl-3-hydroxymethyloxetane Derivatives: Facile Access to Functionalized Polyoxetanes by Virtue of Organosilyl Groups

Abstract Ring-opening polymerization of 3-alkyl-3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes is catalyzed by a triruthenium cluster, [Ru3{μ3-(η2,η3,η5-C12H8)}(CO)7], in the presence of trialkylsilanes, providing a novel accessible method for functionalized polyoxetanes of Mn = 103–105. Oxetanes having alkoxy-, fluoroalkoxy-, triethyleneglycoloxy-, and trialkylsiloxy functions undergo polymerization and copolymerization. Consumption rates of two monomers in the copolymerization of 3-benzyloxymethyl- and 3-trimethylsiloxymethyl-3-alkyloxetanes are almost the same, indicating formation of random copolymers. The organosilyl group in the polymer and copolymers with siloxymethyl side chains is converted to CH2OH or CH2OCOR groups by hydrolysis or silyl/acyl exchange. These protocols give the way to access polymers or copolymers bearing OH and OCOR side chains. A ruthenium-catalyzed reaction of 3-ethyl-3-hydroxymethyloxetane with trialkylsilanes results in dehydrogenative silylation to give 3-ethyl-3-siloxymethyloxetane, which is followed by ring-opening polymerization. Combination of tandem dehydrogenative silylation/ring-opening polymerization/the silyl/acyl exchange realizes one-pot synthesis of polymers with CH2OCOR side chains from 3-ethyl-3-hydroxymethyloxetane. DSC analyses of the formed polymers provided Tg and Tm data, which are a good example showing that the polymer properties are controlled by appropriate selection of functional groups at the side chain.

ChemInform Abstract: Platinum Complex Catalyzed Dehydrogenative Double Silylation of Olefins and Dienes with o-Bis(dimethylsilyl)benzene.

Abstract Olefins underwent dehydrogenative 1,2- and/or 1,1-double silylation with o-bis(dimethylsilyl)benzene (1) in the presence of a catalytic amount of Pt(CH2CH2)PPh3)2 to afford benzo-1,4-disilacyclohexene (3) and/or benzo-1,3-disilacyclopentene (4) derivatives, respectively. In reactions of aliphatic olefins, single hydrosilylation with one of the SiH bonds took place as a side reaction to give HMe2Si(o-C6H4)SiMe2R compounds. Depending on the conditions of the latter reactions, HMeRSi(o-C6H4)SiMe3 compounds arising from 1,4-rearrangement of a methyl group were also formed. The cyclic bis(silyl)platinum complex Me2 Si(o-C 6 H 4 )SiMe 2 P t(PPh3)2 (11) formed upon treatment of 1 with the platinum-ethylene complex readily reacted with olefins in the presence of 1 to afford 3 and/or 4. Compound 4 coming from the catalytic reaction of styrene with o-bis(deuteriodimethylsilyl)benzene did not have the deuterium label incorporated. Based on these results, the dehydrogenative double silylation is proposed to take place via 11 as a key intermediate.