Hydrosilylation of alkynes by Ni(CO)3-stabilized silicon(II) hydride

Not copy and paste: Although β-diketiminato ligands have been employed for the stabilization of Ge(II) and Sn(II) hydrides, the corresponding Si(II) hydride is not accessible. However, coordination of silicon(II) to a {Ni(CO)(3)} fragment allowed the isolation of the first Si(II) hydride metal complex 1. This complex was used for the first silicon(II)-based and Ni(0)-mediated, stereoselective hydrosilylation of alkynes. R = phenyl, tolyl.     

Bis[N,N'-diisopropylbenzamidinato(-)]silicon(II): a silicon(II) compound with both a bidentate and a monodentate amidinato ligand

Well looked-after: reductive HCl elimination of the λ(6)-silicon(IV) complex 1 leads to the λ(3)-silicon(II) species 2, a novel type of donor-stabilized silylene. Reaction of 2 with [W(CO)(6)] and with I(2) yields the λ(5)-silicon(II) complex 3 and the λ(6)-silicon(IV) complex 4, respectively.     

Careful investigation of the hydrosilylation of olefins at poly(ethylene glycol) chain ends and development of a new silyl hydride to avoid side reactions

Hydrosilylation of olefin groups at poly(ethylene glycol) chain ends catalyzed by Karstedt catalyst often results in undesired side reactions such as olefin isomerization, hydrogenation, and dehydrosilylation. Since unwanted polymers obtained by side reactions deteriorate the quality of end‐functional polymers, maximizing the hydrosilylation efficiency at polymer chain ends becomes crucial. After careful investigation of the factors that govern side reactions under various conditions, it was related that the short lifetime of the unstable Pt catalyst intermediate led to the formation of more side products under the inherently dilute conditions for polymers. Based on these results, two new chelating hydrosilylation reagents, tris(2‐methoxyethoxy)silane (5) and 2,10‐dimethyl‐3,6,9‐trioxa‐2,10‐disilaundecane (6), have been developed. It was demonstrated that the hydrosilylation efficiency at polymer chain ends was significantly increased by employing the internally coordinating hydrosilane 5. In addition, employment of the internally coordinating disilane species 6 in an addition polymerization with 1,5‐hexadiene by hydrosilylation reaction yielded a polymer with high molecular weight (M_n = 9300 g/mol), which was significantly higher than that (M_n = 2600 g/mol) of the corresponding polymer obtained with non‐chelating dihydrosilane, 1,1,3,3‐tetramethyldisiloxane. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 527–536     

Synthesis of di(2-bromoalkyi) disulfides by electrophilic addition of dithiobisamines to olefins

A new method for the synthesis of di(2-haloalkyl) disulfides and ,'-dibromothiacyclanes was proposed based on reactions of dithiobisamines with olefins in the presence of PBr₃, PBr₅, or POBr₃. Reactions with alkenes lead to di(2-bromoalkyl) disulfides. Analogous products and heterocyclic dibromosulfides,i.e., the products of addition of one dithiobisamine molecule to both double bonds of a diene, are obtained in reactions with alkadienes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2511–2525, October, 1996.     

Cobalt bis(2‐ethylhexanoate) and terpyridine derivatives as catalysts for the hydrosilylation of olefins

A simple method for the hydrosilylation of olefins by using air‐stable cobalt catalysts is developed. The catalyst system is composed of simple, cheap, and readily available cobalt(II) salts and well‐defined terpyridine derivatives as cocatalysts or ligands, and the hydrosilylation processes can be processed smoothly under mild conditions without either Grignard reagents or NaHBEt₃ as activator.     

Unusual Structure,Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3]

The reactions of bis(borohydride) complexes [(RN?)Mo(BH₄)₂(PMe₃)₂] ( 4 : R=2,6‐Me₂C₆H₃; 5 : R=2,6‐iPr₂C₆H₃) with hydrosilanes afford new silyl hydride derivatives [(RN?)Mo(H)(SiR′₃)(PMe₃)₃] ( 3 : R=Ar, R′₃=H₂Ph; 8 : R=Ar′, R′₃=H₂Ph; 9 : R=Ar, R′₃=(OEt)₃; 10 : R=Ar, R′₃=HMePh). These compounds can also be conveniently prepared by reacting [(RN?)Mo(H)(Cl)(PMe₃)₃] with one equivalent of LiBH₄ in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe₃ group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non‐Bailar‐twist pathway. The silyl/silane exchange proceeds through an unusual Mo^VI intermediate, [(ArN?)Mo(H)₂(SiH₂Ph)₂(PMe₃)₂] ( 19 ). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans‐(ArN)Mo(OiPr)(SiH₂Ph)(PMe₃)₂] ( 18 ). This latter species does not undergo the elimination of a Si? O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β‐CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN?)Mo(η²‐PhC(O)H)₂(PMe₃)], which reacts further with hydrosilane through a η¹‐silane complex, as studied by DFT calculations.     

Catalysis of hydrosilylation part XVIII. Pt(PPh3)2(CH2CH2) – a versatile catalyst for hydrosilylation of olefins

Pt(PPh₃)₂(CH₂?CH₂) appeared to be a versatile catalyst in hydrosilylation of alkenes (with 5–22 C atoms) as well as of functionalized alkenes such as allyl chloride, allylamine, allyl methacrylate and vinylsilanes. In comparison with a well-known Speier catalyst or with Pt(PPh₃)₄, this complex is characterized by a very high effectiveness (activity and selectivity) and relative resistance to oxygenation and it may be applied in recycling runs with a minor induction period. The catalytic processes examined are of great industrial importance since they lead to a synthesis of alkylsilanes, disilylethanes and silane coupling agents.     

Novel Transition‐Metal (M=Cr,Mo, W,Fe) Carbonyl Complexes with Bis(guanidinato)silicon(II) Ligands

The donor‐stabilized silylene 2 (the first bis(guanidinato)silicon(II ) complex) reacts with the transition‐metal carbonyl complexes [M(CO)₆] (M=Cr, Mo, W) to form the respective silylene complexes 7 – 10 . In the reactions with [M(CO)₆] (M=Cr, Mo, W), the bis(guanidinato)silicon(II ) complex 2 behaves totally different compared with the analogous bis(amidinato)silicon(II ) complex 1 , which reacts with [M(CO)₆] as a nucleophile to replace only one of the six carbonyl groups. In contrast, the reaction of 2 leads to the novel spirocyclic compounds 7 – 9 that contain a four‐membered SiN₂C ring and a five‐membered MSiN₂C ring with a M?Si and M?N bond (nucleophilic substitution of two carbonyl groups). Compounds 7 – 10 were characterized by elemental analyses (C, H, N), crystal structure analyses, and NMR spectroscopic studies in the solid state and in solution.     

Synthesis and characterization of an isolable base-stabilized silacycloprop-1-ylidene

Strained but stable: An isolable silacycloprop-1-ylidene stabilized by intramolecular complexation with an iminophosphorus ylide fragment was successfully synthesized and fully characterized. The formation of this small highly strained cyclic silylene involves an unprecedented Si(IV)→Si(II) rearrangement under very mild conditions.     

主链含有冠醚基团的聚硅氧烷及其铂配合物的催化硅氢化性能

报道了一种合成主链含有冠醚基团的聚硅氧烷的方法.首先,从适当的冠醚出发,合成带有两个烯基侧链的双套索冠醚,再与含氢硅单体进行硅氢加成.合成两端带有烷氧硅基的含冠醚基的硅单体,然后与八甲基环四硅氧烷共聚合,得到标题聚硅氧烷.后者与氯亚铂酸钾反应,得到相应的铂配合物,该配合物对于烯烃与三乙氧基硅烷的硅氢加成反应具有催化活性.     

Synthesis of novel poly(ethylene glycol)‐containing imidazolium‐functionalized phosphine ligands and their application in the hydrosilylation of olefins

A series of polyethylene glycol‐containing imidazolium‐functionalized phosphine ligands (mPEG‐im‐PPh₂) were successfully synthesized and used in the rhodium‐catalyzed hydrosilylation of olefins. The results indicate that the RhCl₃/mPEG‐im‐PPh₂ catalytic system exhibits both excellent activity and selectivity for the β‐adduct. In addition, the catalytic system may be recycled at least six times.     

Synthesis and Reactivity of Bis(silylene)-Coordinated Calcium and Divalent Lanthanide Complexes

Divalent lanthanide complexes of Eu ( 1 ) and Yb ( 2 ) coordinated by a chelating pyridine-based bis(silylene) ligand were isolated and fully characterized. Compared to the Eu^II complex 1 , the Yb^II complex 2 presents a lower thermal stability, resulting in the activation of one Si^II−N bond and formation of an Yb^III complex ( 3 ), which features a unique silylene-pyridyl-amido ligand. The different thermal stability of 1 and 2 points towards reduction-induced cleavage of one Si^II−N bond of the bis(silylene) ligand. Successful isolation of the corresponding redox-inert bis(silylene) Ca^II complex ( 5 ) was achieved at low temperature and thermal decomposition into a Ca^II complex ( 4 ) bearing the same silylene-pyridyl-amido ligand was identified. In this case, the thermolysis reaction proceeds through another, non-redox induced, mechanism. An alternative higher yielding route to 4 was developed through an in situ generated silylene-pyridyl-amine proligand.