Hypercoordinate Ketone Adducts of Electrophilic η3-H2SiRR′ Ligands on Ruthenium as Key Intermediates for Efficient and Robust Catalytic Hydrosilation

Combined Computational and Experimental Study Reveals Complex Mechanistic Landscape of Brønsted Acid-Catalyzed Silane-Dependent P═O Reduction

The reaction mechanism of Brønsted acid-catalyzed silane-dependent P═O reduction has been elucidated through combined computational and experimental methods. Due to its remarkable chemo- and stereoselective nature, the Brønsted acid/silane reduction system has been widely employed in organophosphine-catalyzed transformations involving P(V)/P(III) redox cycle. However, the full mechanistic profile of this type of P═O reduction has yet to be clearly established to date. Supported by both DFT and experimental studies, our research reveals that the reaction likely proceeds through mechanisms other than the widely accepted "dual activation mode by silyl ester" or "acid-mediated direct P═O activation" mechanism. We propose that although the reduction mechanisms may vary with the substitution patterns of silane species, Brønsted acid generally activates the silane rather than the P═O group in transition structures. The proposed activation mode differs significantly from that associated with traditional Brønsted acid-catalyzed C═O reduction. The uniqueness of P═O reduction originates from the dominant Si/O═P orbital interactions in transition structures rather than the P/H-Si interactions. The comprehensive mechanistic landscape provided by us will serve as a guidance for the rational design and development of more efficient P═O reduction systems as well as novel organophosphine-catalyzed reactions involving P(V)/P(III) redox cycle.

Trivalent Rare-Earth Metal Amide Complexes as Catalysts for the Hydrosilylation of Benzophenone Derivatives with HN(SiHMe2 )2 by Amine-Exchange Reaction

The rare-earth metal complexes Ln(L1 )[N(SiHMe2 )2 ](thf) (Ln=La, Ce, Y; L1 =N,N''-bis(pentafluorophenyl)diethylenetriamine dianion) were synthesized by treating Ln[N(SiHMe2 )2 ]3 (thf)2 with L1 H2 . The lanthanum and cerium derivatives are active catalysts for the hydrosilylation of benzophenone derivatives with HN(SiHMe2 )2 . An amine-exchange reaction was revealed as a key step of the catalytic cycle, in which Ln-Si-H β-agostic interactions are proposed to promote insertion of the carbonyl moiety into the Si-H bond.

Efficient and selective alkene hydrosilation promoted by weak, double Si-H activation at an iron center

Cationic iron complexes [Cp*(ⁱPr₂MeP)FeH₂SiHR]⁺, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature.

Cationic iron complexes [Cp*(ⁱPr₂MeP)FeH₂SiHR]⁺, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature. These reactions yield only the corresponding secondary silane product, even with SiH₄ as the substrate. Mechanistic experiments and DFT calculations indicate that the high rate of hydrosilation is associated with an inherently low barrier for dissociative silane exchange (product release).

An H-Substituted Rhodium Silylene

Divergent reactivity of organometallic rhodium(I) complexes, which led to the isolation of neutral rhodium silylenes, is described. Addition of PhRSiH₂ (R=H, Ph) to the rhodium cyclooctene complex (^iPr NNN)Rh(COE) (1-COE; ^iPr NNN=2,5-[iPr₂ P=N(4-iPrC₆ H₄ )]₂ N(C₆ H₂ )^- , COE=cyclooctene) resulted in the oxidative addition of an Si-H bond, providing rhodium(III) silyl hydride complexes (^iPr NNN)Rh(H)SiHRPh (R=H, 2-SiH₂ Ph; Ph, 2-SiHPh₂ ). When the carbonyl complex (^iPr NNN)Rh(CO) (1-CO) was treated with hydrosilanes, base-stabilized rhodium(I) silylenes κ² -N,N-(^iPr NNN)(CO)Rh=SiRPh (R=H, 3-SiHPh; Ph, 3-SiPh₂ ) were isolated and characterized using multinuclear NMR spectroscopy and X-ray crystallography. Both silylene species feature short Rh-Si bonds [2.262(1) Å, 3-SiHPh; 2.2702(7) Å, 3-SiPh₂ ] that agree well with the DFT-computed structures. The overall reaction led to a change in the ^iPr NNN ligand bonding mode (κ³ →κ² ) and loss of H₂ from PhSiRH₂ , as corroborated by deuterium labelling experiments.

A hypervalent and cubically coordinated molecular phase of IF8 predicted at high pressure

Up to now, the maximum coordination number of iodine is seven in neutral iodine heptafluoride (IF7) and eight in anionic octafluoride (IF8 -). Here, we explore pressure as a method for realizing new hypercoordinated iodine compounds. First-principles swarm structure calculations have been used to predict the high-pressure and T → 0 K phase diagram of binary iodine fluorides. The investigated compounds are predicted to undergo complex structural phase transitions under high pressure, accompanied by various semiconductor to metal transitions. The pressure induced formation of a neutral octafluoride compound, IF8, consisting of eight-coordinated iodine is one of several unprecedented predicted structures. In sharp contrast to the square antiprismatic structure in IF8 -, IF8, which is dynamically unstable under atmospheric conditions, is stable and adopts a quasi-cube molecular configuration with R3[combining macron] symmetry at 300 GPa. The metallicity of IF8 originates from a hole in the fluorine 2p-bands that dominate the Fermi surface. The highly unusual coordination sphere in IF8 at 300 GPa is a consequence of the 5d levels of iodine coming down and becoming part of the valence, where they mix with iodine's 5s and 5p levels and engage in chemical bonding. The valence expansion of iodine under pressure effectively makes IF8 not only hypercoordinated, but also hypervalent.

A two-coordinate Ni(i) silyl complex: CO2 insertion and oxidatively-induced silyl migrations

Synthesis of the first open-shell two-coordinate silyl complex and its oxidatively-induced silyl rearrangements.

Entrapment of THF-Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination

The reaction of H₃ SiR (R=Ph, nBu) with cationic η₅ -C₅ Me₅ - (Cp*) and benzo[h]quinolinyl-based iridacycle [1 b]⁺ gives rise to new [(IrH)→SiRH₂ ]⁺ adducts. In the presence of THF these adducts readily undergo elimination of H₂ gas at subambient temperature to form THF-stabilized metallacyclic Ir^III silylene complexes, which were characterized in situ by NMR spectroscopy, trapped in minute amounts by reactive crystallization, and structurally characterized by XRD. Theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) support the promoting role of THF in the H₂ elimination step and the consolidation of the Ir-to-Si interaction in the spontaneous (ΔG<0) formation of Ir silylenes in the presence of THF. Mechanistic insights indicate that the Ir silylene species arising from the [1 b]⁺ /phenylsilane system are relevant catalytic species in the hydrodefluorination of fluoroalkanes.

Remarkably high catalyst efficiency of a disilaruthenacyclic complex for hydrosilane reduction of carbonyl compounds

A disilaruthenacyclic complex (1) showed extremely high catalytic activity for hydrosilane reduction of aldehydes and ketones to silyl ethers and secondary and tertiary amides to the corresponding amines. An σ-CAM mechanism was proposed to explain the activity.

Mechanistic insights into the catalytic carbonyl hydrosilylation by cationic [CpM(CO)2(IMes)]+ (M = Mo, W) complexes: the intermediacy of η1-H(Si) metal complexes

The ionic S_N2-type mechanistic pathway initiated by silane end-on coordination on the metal centers, forming η¹-H(Si) Mo/W complexes, is the preferred reaction pathway for the two cationic cyclopentadienyl molybdenum/tungsten complexes, [CpM(CO)₂(IMes)]⁺ (M = Mo, W) in catalyzing carbonyl hydrosilylation.

Synthesis of silyl iron hydride via Si–H activation and its dual catalytic application in the hydrosilylation of carbonyl compounds and dehydration of benzamides

A silyl iron hydride as a dual catalyst was synthesized for the reduction of carbonyl compounds and the dehydration of amides.

Significant Cooperativity Between Ruthenium and Silicon in Catalytic Transformations of an Isocyanide

Complexes [PhBP3]RuH(η(3)-H2SiRR') (RR' = Me,Ph, 1a; RR' = Ph2, 1b; RR' = Et2, 1c) react with XylNC to form carbene complexes [PhBP3]Ru(H)═[C(H)(N(Xyl)(η(2)-H-SiRR'))] (2a-c; previously reported for 2a,b). Reactions of 1a-c with XylNC were further investigated to assess how metal complexes with multiple M-H-Si bonds can mediate transformations of unsaturated substrates. Complex 2a eliminates an N-methylsilacycloindoline product (3a) that results from hydrosilylation, hydrogenation, and benzylic C-H activation of XylNC. Turnover was achieved in a pseudocatalytic manner by careful control of the reaction conditions. Complex 1c mediates a catalytic isocyanide reductive coupling to furnish an alkene product (4) in a transformation that has precedent only in stoichiometric processes. The formations of 3a and 4 were investigated with deuterium labeling experiments, KIE and other kinetic studies, and by examining the reactivity of XylNC with an η(3)-H2SiMeMes complex (1d) to form a C-H activated complex (6). Complex 6 serves as a model for an intermediate in the formation of 3a, and NMR investigations at -30 °C reveal that 6 forms via a carbene complex (1d) that isomerizes to aminomethyl complex 7d. These investigations reveal that the formations of 3a and 4 involve multiple 4-, 5-, and 6-coordinate silicon species with 0, 1, 2, or 3 Ru-H-Si bonds. These mechanisms demonstrate exceptionally intricate roles for silicon in transition-metal-catalyzed reactions with a silane reagent.

NHC carbene supported half-sandwich hydridosilyl complexes of ruthenium: the impact of supporting ligands on Si⋯H interligand interactions

Electron donating NHC carbene ligand IPr exerts stronger RuH⋯Si interactions in complexes Cp(IPr)RuH₂(SiR₃) than in related ⁱPr₃P complexes Cp(ⁱPr₃P)RuH₂(SiR₃).

Peripheral mechanism of a carbonyl hydrosilylation catalysed by an SiNSi iron pincer complex

Combined experimental and theoretical analysis of the carbonyl hydrosilylation catalysed by an iron(0) pincer complex reveals an unprecedented mechanism of action. The iron(0) complex is in fact a precatalyst that is converted into an iron(ii) catalyst through oxidative addition of a hydrosilane. Neither the hydrogen atom nor the silicon atom bound to the iron(ii) centre are subsequently transferred onto the carbonyl acceptor, instead remaining at the sterically inaccessible iron(ii) atom throughout the catalytic cycle. A series of labelling, crossover and competition experiments as well as the use of a silicon-stereogenic hydrosilane as a stereochemical probe suggest that the iron(ii) site is not directly involved in the hydrosilylation. Strikingly, it is the silyl ligand attached to the iron(ii) atom that acts as a Lewis acid for carbonyl activation in this catalysis. The whole catalytic process occurs on the periphery of the transition metal. Computation of the new peripheral as well as plausible alternative inner and outer sphere mechanisms support the experimental findings.

Mild partial deoxygenation of esters catalyzed by an oxazolinylborate-coordinated rhodium silylene

An oxazoline-stabilized rhodium silylene complex catalyzes the deoxygenation of carbonyls using PhSiH₃as the reductant, including esters to ethers, amides to amines, and ketones to hydrocarbons rapidly at room temperature.

Platinum-catalyzed reduction of amides with hydrosilanes bearing dual Si–H groups: a theoretical study of the reaction mechanism

A platinum-catalyzed hydrosilane reduction of amides proceeds via the classical Chalk–Harrod mechanism with dual Si–H groups.