Dioxo Complexes Research Articles

A Linear Two-Coordinate Cr(II) Complex: Synthesis, Characterization, and Reactivity.

The synthesis and characterization of a linear two-coordinate Cr(II) amido complex, Cr{N(t Bu)Dipp}2 (Dipp=2,6-diisopropylphenyl), from the reaction of 1 molar equivalent (equiv) of CrCl2 and 2 equiv. of LiN(t Bu)Dipp is reported. Single-crystal X-ray diffractometry (SC-XRD) analysis revealed that it has a short Cr-N bond distance of 1.8878(9) Å, which could be attributed to the relatively less bulky nature of the amido ligand compared with reported systems. Furthermore, the oxidation reaction of the two-coordinate Cr(II) complex was explored. The oxidation reaction of Cr{N(t Bu)Dipp}2 with the one-electron oxidants AgOTf and [FeCp2 ][BArF 4 ] (BArF 4 - =[B{C6 H3 -3,5-(CF3 )2 }4 ]- ) afforded the trigonal planar three- and bent two-coordinate Cr(III) complexes Cr{N(t Bu)Dipp}2 (OTf) and [Cr{N(t Bu)Dipp}2 ][BArF 4 ], respectively. The reaction of Cr{N(t Bu)Dipp}2 with 1 equiv. of the organic azides AdN3 (Ad=1-adamantyl) and PhN3 afforded the three-coordinate Cr(IV) imido complexes Cr{N(t Bu)Dipp}2 (NAd) and Cr{N(t Bu)Dipp}2 (NPh), respectively. The reaction of Cr{N(t Bu)Dipp}2 and two equiv. of Me3 NO afforded the Cr(VI) dioxo complex Cr{N(t Bu)Dipp}2 (O)2 . The reaction of Cr{N(t Bu)Dipp}2 with 1 equiv. of CyN=C=NCy resulted in the insertion of the carbodiimide into the Cr-N bond, with the formation of a three-coordinate Cr(II) complex. Finally, density functional theory (DFT) calculations were used to elucidate the electronic structure of these complexes.

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

Water co-catalysis in aerobic olefin epoxidation mediated by ruthenium oxo complexes.

We report the development of a versatile Ru-porphyrin catalyst system which performs the aerobic epoxidation of aromatic and aliphatic (internal) alkenes under mild conditions, with product yields of up to 95% and turnover numbers (TON) up to 300. Water is shown to play a crucial role in the reaction, significantly increasing catalyst efficiency and substrate scope. Detailed mechanistic investigations employing both computational studies and a range of experimental techniques revealed that water activates the RuVI di-oxo complex for alkene epoxidation via hydrogen bonding, stabilises the RuIV mono-oxo intermediate, and is involved in the regeneration of the RuVI di-oxo complex leading to oxygen atom exchange. Distinct kinetics are obtained in the presence of water, and side reactions involved in catalyst deactivation have been identified.

Structural features of monomeric octahedral <i>d</i><sup>2</sup>-rhenium dioxo complexes with monoand bidentate ligands [reo<sub>2</sub>(l<sub>bi</sub>)(l<sub>mono</sub>)<sub>2</sub>], [reo<sub>2</sub>(l<sub>bi</sub>)<sub>2</sub>] (a review)

Structural features of mononuclear octahedral dioxo complexes d 2-Re5+, [ReO2(Lbi)(Lmono)2], [ReO2(Lbi)2] with mono- and bidentate ligands were considered. The multiply bound Ooxo ligands are located predominantly in trans -positions to each other, with two exceptions, with the cis -orientaion of the ReO2 fragment. Rhenium atoms in most complexes have the trans -octahedral ReOoxo2X4 (X = N, P, As, O) coordination, in two cases they have the cis -octahedral ReOoxo2N4 structure. Re=Ooxo bonds in d 2-Re(V) monomeric octahedral dioxo compounds ( d average 1.772 Å) are much longer than in d 2-Re(V) monooxo complexes ( d average 1.676-1.699 Å).

Structural Features of Monomeric Octahedral d2-Rhenium Dioxo Complexes [ReO2(Lbi)(Lmono)2] and [ReO2(Lbi)2] with Mono- and Bidentate Ligands (A Review)

Structural Features of Monomeric Octahedral d2-Rhenium Dioxo Complexes [ReO2(Lbi)(Lmono)2] and [ReO2(Lbi)2] with Mono- and Bidentate Ligands (A Review)

The Role of Anionic Ligands on Photoreactivity in Mo(VI) Dioxo Complexes of the Form MoO2 X2 (NN).

The photoreactivity of d0 metal dioxo complexes in activating C-H bonds has been recently studied.[1-3] We have previously reported that MoO2 Cl2 (bpy-t Bu) is an effective platform for light initiated C-H activation with unique product selectivity for the overall functionalization.[1] Herein we expand on these studies and report the synthesis and photoreactivity of several new Mo(VI) dioxo complexes with the general formula MoO2 (X)2 (NN); where X=F- , Cl- , Br- , CH3 - , PhO- , t BuO- and NN=2,2'-bipyridine (bpy) or 4,4'-tert-butyl-2,2'bipyridine (bpy-t Bu). Among these compounds, MoO2 Cl2 (bpy-t Bu) and MoO2 Br2 (bpy-t Bu) are able to participate in bimolecular photoreactivity with several substrates containing C-H bonds of various types such as allyls, benzyls, aldehydes (RCHO) and alkanes. MoO2 (CH3 )2 bpy and MoO2 (PhO)2 bpy do not participate in bimolecular photoreactions and instead they undergo photodecompositions. Computational studies indicate that the nature of the HOMO and LUMO is critical in supporting photoreactivity, with access to an LMCT (bpy→Mo) being necessary for tractable hydrocarbon functionalization.

Mechanistic Studies of the Deoxydehydration of Polyols Catalyzed by a Mo(VI) Dioxo(pyridine-2,6-dicarboxylato) Complex

The need for renewable resources to displace petrochemical feedstocks is of great interest. Deoxydehydration (DODH) reduces biomass-derived polyols and diols to alkenes and dienes, possibly moving alkene production closer to carbon-neutral sources. We report the DODH of numerous aromatic, aliphatic, and biomass model diols by a dioxo-Mo(VI) catalyst, MoO2(pyridine-2,6-dicarboxylato)(HMPA). Optimal reaction conditions were found using PPh3 and 1-phenyl-1,2-ethanediol yielding up to 93% styrene. Mechanistic studies using in situ infrared spectroscopy support a biexponential kinetic regime where the rate constant of the rate-determining step is ∼5 × 10–5 s–1. DFT calculations support the kinetic studies and suggest that the largest kinetic barrier is a proton transfer from the substrate to a metal–oxo bond during diolate formation.

Biodiesel and adipic acid production using molybdenum(VI) complex of a bis(phenol) diamine ligand supported on Fe3O4 magnetic nanoparticles

• Mo(VI)-dioxo complex of bis(phenol) diamine supported on Fe 3 O 4 was synthesized. • Efficient trans esterification reaction of cooking oil to biodiesel was performed. • The reaction was investigated at room temperature and low mole ratio of MeoH:oil. • The catalyst performed conversion of cyclohexene to adipic acid under mild condition. • The catalyst showed stability, recovery and reusability after some cycles. A homogeneous Mo(VI)-dioxo complex including tetradentate bis(phenol) diamine ligand covalently grafted onto amine-functionalized heterogeneous magnetic nanoparticles has been synthesized. We further characterized this new catalyst using the TEM, SEM, FTIR, TGA, VSM, XPS, XRD, EDX, NH 3 -TDP, BET, and elemental analysis techniques. The resulting solid material’s ability was inspected in the transesterification reaction of cooking oil to biodiesel. The study demonstrates a novel and green biodiesel production by means of cooperation of Lewis acidic core of molybdenum-based homogenized heterogeneous catalyst and trace amounts of alkaline KOH for methanol activation. Applying the advantages of both homogeneous and heterogeneous catalytic properties leads to the 99% conversion of produced biodiesel under pretty mild reaction conditions comprising 2.3 mol% of catalyst, 0.05 mmol of KOH, methanol/oil molar ratio 3:1, time of 45 min at room temperature. The generated biodiesel was identified using 1 H NMR, FTIR, and GC–MS. In addition, the industrially indispensable oxidative conversion of cyclohexene to adipic acid over heterogeneous molybdenum(VI)-dioxo-involved catalyst was investigated under optimized conditions (1 mmol cyclohexene, 60 mg catalyst, 5 eq H 2 O 2 , time 13 h at 80 °C) and 68% of pure adipic acid was yielded. Furthermore, our studies show the structural and morphological stability of the catalyst and its nice reusability after 5 and 11 cycles for oxygen atom transfer and transesterification reactions, respectively.

Unmasking the Iron-Oxo Bond of the [(Ligand)Fe-OIAr]2+/+ Complexes.

ArIO (ArI = 2-(tBuSO2)C6H4I) is an oxidant used to oxidize FeII species to their FeIV-oxo state, enabling hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions at low energy barriers. ArIO, as a ligand, generates masked Fen=O species of the type Fe(n-2)-OIAr. Herein, we used gas-phase ion–molecule reactions and DFT calculations to explore the properties of masked iron–oxo species and to understand their unmasking mechanisms. The theory shows that the I–O bond cleavage in [(TPA)FeIVO(ArIO)]2+ (12+, TPA = tris(2-pyridylmethyl)amine)) is highly endothermic; therefore, it can be achieved only in collision-induced dissociation of 12+ leading to the unmasked iron(VI) dioxo complex. The reduction of 12+ by HAT leads to [(TPA)FeIIIOH(ArIO)]2+ with a reduced energy demand for the I–O bond cleavage but is, however, still endothermic. The exothermic unmasking of the Fe=O bond is predicted after one-electron reduction of 12+ or after OAT reactivity. The latter leads to the 4e– oxidation of unsaturated hydrocarbons: The initial OAT from [(TPA)FeIVO(ArIO)]2+ leads to the epoxidation of an alkene and triggers the unmasking of the second Fe=O bond still within one collisional complex. The second oxidation step starts with HAT from a C–H bond and follows with the rebound of the C-radical and the OH group. The process starting with the one-electron reduction could be studied with [(TQA)FeIVO(ArIO)]2+ (22+, TQA = tris(2-quinolylmethyl)amine)) because it has a sufficient electron affinity for electron transfer with alkenes. Accordingly, the reaction of 22+ with 2-carene leads to [(TQA)FeIIIO(ArIO)]2+ that exothermically eliminates ArI and unmasks the reactive FeV–dioxo species.

Synthesis and anti-microbial activity of a new series of bis(diphosphine) rhenium(V) dioxo complexes.

Rhenium-based metallodrugs have recently been highlighted as promising candidates for new antibiotics to combat multi-drug resistant (MDR) pathogens. A new class of rhenium(V) dioxo complexes were prepared from readily accessible diphosphine ligands, and have been shown to possess potent activity against Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans) alongside low human cell toxicity.

Ammonia Synthesis through Hydrolysis of a Trianionic Pincer Ligand‐Supported Molybdenum–Nitride Complex

Reported is the hydrolysis of a homogeneous Mo-nitride complex bearing a trianionic pincer-type ligand to produce ammonia. Treating the anionic [(ONO)]Mo≡N(OtBu)]Ph3 PCH3 with two equivalents of water produces ammonia and the dioxo complex [(ONO)]MoO2 ]Ph3 PCH3 . X-Ray crystal structures of the starting nitrido complex and product dioxo complex are presented. Evidence for ammonia release comes from GC-MS and deuterium-labelling studies. The reaction is presented in the context of a two-stage solar thermochemical dinitrogen fixation process as the solid-state nitride hydrolysis step.

Unexpected Molecular Structure of a Putative Rhenium-Dioxo-Benzocarbaporphyrin Complex. Implications for the Highest Transition Metal Valence in a Porphyrin-Type Ligand Environment.

A combination of quantum chemical calculations and synthetic studies was used to address the possibility of very high (>6) valence states of transition metals in porphyrin‐type complexes. With corrole as a supporting ligand, DFT calculations ruled out Re(VII) and Ir(VII) dioxo complexes as stable species. Attempted rhenium insertion into benzocarbaporphyrin (BCP) ligands on the other hand led to two products with different stoichiometries – Re[BCP]O and Re[BCP]O2. To our surprise, single‐crystal structure determination of one of the complexes of the latter type indicated an ReVO center with a second oxygen bridging the Re−C bond. In other words, although the monooxo complexes Re[BCP]O are oxophilic, the BCP ligand cannot sustain a trans‐ReVII(O)2 center. The search for metal valence states >6 in porphyrin‐type ligand environments must therefore continue.

Dioxo-, Oxo-imido-, and Bis-imido-Molybdenum(VI) Complexes with a Bis-phenolate-NHC Ligand

We report the facile synthesis of five rare high-valent Mo(VI)-NHC complexes with a dianionic OCO-pincer benzimidazolylidene ligand (L1) with the general formula L1MoO2 (1), L1Mo(O)(NtBu)(THF) (2), L1Mo(NtBu)(NHtBu)Cl (3), L1Mo(NtBu)2 (4), and L1 Mo(NMes)2 (5). These complexes represent a complete series of high-valent molybdenum(VI) complexes, obtained by consecutive exchange of the oxo for imido ligands from the dioxo complex (1) to the bis-imido complexes (4 and 5). The complexes can be synthesized in high yields following a simple deprotonation protocol, using either triethylamine or lithium diisopropylamide (LDA) as a base. All complexes have been characterized by various techniques, including 1H, 13C{1H}, and 15N NMR spectroscopy, IR spectroscopy, and X-ray diffraction analysis. Except for the dioxo complex 1, all complexes adopt monomeric structures in the solid state. Compounds 1, 4, and 5 are rare examples of five-coordinated molybdenum(VI) complexes in the solid state, while 2 is six-coordinated...

New insight into the DNA binding studies, In-Vitro anti-cancer activity and molecular modelling of dioxo complexes of Molybdenum(VI) and Tungsten(VI) hydroxamic acids

The present study embodies the detail of interaction of Complex 1, Bis(N-phenyl-o-methoxybenzohydroxamato)Molybdenum(VI): [N-PMBHA-Mo(VI)] and Complex 2, Bis(N-phenylbenzohydroxamato)Tungsten(VI): [N-PBHA-W(VI)] with ct-DNA (Calf thymus-DNA) and its consequences by UV–Visible absorption spectroscopy, fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, viscosity measurements and molecular docking. The intrinsic binding constant, Kb of complexes were determined which follows the order as complex 1 > complex 2 along with variation in shift and intensity for the complexes. Fluorescence spectroscopy applied for the determination of Stern–Volmer quenching constant, binding constant and the number of binding sites which reveals groove mode of binding. Non-radiative energy transfer between donor and acceptor molecule exposed by Förster energy transference theory (FRET) studies. The increase in the relative viscosity of ct-DNA with increasing the concentration of the complex 1 and complex 2 is also revealed. FTIR analysis also revealed that both the complexes interacted positively with bases and phosphates of ct-DNA. The docking studies complemented the experimental results revealing minor groove mode of binding for both the complexes. Finally, the in-vitro cytotoxicity studies indicate that the complexes have excellent anticancer activity against the breast cancer cell line, MCF-7, which could be a constructive guideline to produce new generations of anticancer agents.

DFT study on mechanism of carbonyl hydrosilylation catalyzed by high-valent molybdenum (IV) hydrides

Density functional theory (DFT) calculations have been employed to investigate hydrosilylation of carbonyl compounds catalyzed by three high-valent molybdenum (VI) hydrides: Mo(NAr)H(Cp)(PMe3) (1A), Mo(NAr)H(PMe3)3 (1B), and Mo(NAr)H (Tp)(PMe3) (Tp = tris(pyrazolyl) borate) (1C). Three independent mechanisms have been explored. The first mechanism is “carbonyl insertion pathway”, in which the carbonyls insert into Mo−H bond to give a metal alkoxide complex. The second mechanism is the “ionic hydrosilylation pathway”, in which the carbonyls nucleophilically attacks η1-silane molybdenum adduct. The third mechanism is [2 + 2] addition mechanism which was proposed to be favorable for the high-valent di-oxo molybdenum complex MoO2Cl2 catalyzing the hydrosilylation. Our studies have identified the “carbonyl insertion pathway” to be the preferable pathway for three molybdenum hydrides catalyzing hydrosilylation of carbonyls. For Mo(NAr)H (Tp)(PMe3) (Tp = tris(pyrazolyl) borate), the proposed nonhydride mechanism experimentally is calculated to be more than 32.6 kcal/mol higher than the “carbonyl insertion pathway”. Our calculation results have derived meaningful mechanistic insights for the high-valent transition metal complexes catalyzing the reduction reaction.

A Silica-Supported Monoalkylated Tungsten Dioxo Complex Catalyst for Olefin Metathesis

A well-defined silica-supported monoalkylated tungsten dioxo complex [(≡Si–O−)W(═O)2(CH2–tBu)] was prepared by treatment of highly dehydroxylated silica (SiO2-700: silica treated at 700 °C under high vacuum) with an ionic precursor complex [NEt4][W(═O)3(CH2–tBu)]. The identity of the resulting neutral monoalkylated tungsten dioxo surface complex was established by means of elemental microanalysis and spectroscopic studies (IR, solid-state NMR, Raman, and X-ray absorption spectroscopies). The supported tungsten complex was found to act as a precatalyst for the self-metathesis of 1-octene in a batch reactor. The mechanistic implications of this reaction are discussed with the support of DFT calculations highlighting the potential occurrence of thus-far unexplored mechanistic pathways.

Deprotonation of a formato ligand by a cis-coordinated carbyne ligand within a bis(phenolate) tungsten complex.

Deprotonation of a formato ligand by a cis-coordinated propylidyne ligand in a tungsten(vi) complex [(OSSO)W([triple bond, length as m-dash]CEt)(OCHO)] (3) that contains a tetradentate bis(phenolato) ligand (OSSO = {1,4-dithiabutanediyl-2,2'-bis(4,6-di-tert-butyl-phenolato)}) gave the dioxo complex [(OSSO)WO2] (4) along with CO, ethylene and propylene as major products of decomposition.

Synthesis, characterization and oxygen atom transfer reactivity of a pair of Mo(iv)O- and Mo(vi)O2-enedithiolate complexes – a look at both ends of the catalytic transformation

Two new molybdenum complexes (Bu4N)2[MoIVO(ntdt)2] (1) and (Ph4P)2[MoVIO2(ntdt)2] (2) (ntdt = 2-naphthyl-1,4-dithiolate) were synthesized using asymmetric dithiolene precursors and were characterized as structural models for the active site of arsenite oxidase, a molybdopterin bearing enzyme. The ligand was obtained readily by a two-step synthesis starting from 2-bromo-2'-acetonapthone. Complexes 1 and 2 were obtained by reaction of the resulting 4-naphthyl-1,3-dithiol-2-one with metal precursors trans-[MoO2(CN)4]4- and cis-[MoO2(NCS)4]2- respectively. Notably and to the best of our knowledge, this work constitutes the first utilization of the latter in dithiolene chemistry. 1 and 2 were characterized by NMR and IR spectroscopy, by cyclic voltammetry, mass spectrometry, elemental analysis and in case of 1 by single-crystal X-ray diffraction. The molecular structure of compound 1 exhibits the less common cis isomeric form (i.e. the naphthyl groups of the 2-naphthyl-1,4-dithiolate ligands are located on the same side of the MoS4 square base). Structural, spectroscopic and electrochemical data are discussed in context. The catalytic oxo-transfer properties of 1 and 2 were investigated by oxo-transfer reactions from DMSO to PPh3 with varied catalyst : PPh3 ratios. Interestingly, the oxygen atom transfer reaction from DMSO to PPh3 starting from compound 2 was found to be more efficient under the given conditions than when the reduced catalyst 1 was employed as initial species. The two catalytic systems are discussed and compared in terms of their reactivity.

A quantum chemical study of the mechanisms of olefin addition to group 9 transition metal dioxo compounds.

The mechanistic aspects of ethylene addition to MO2(CH2)(CH3) (M=Co, Rh, Ir) have been investigated with a Hartree–Fock/DFT hybrid functional at the MO6/LACVP* and B3LYP/LACVP* levels of theory to elucidate the reaction pathways on the singlet, doublet and triplet potential energy surfaces (PES). In the reaction of the IrO2CH2CH3 complex with ethylene, [3 + 2]C,O addition is the most plausible pathway on the singlet PES, the [3 + 2]O,O addition is the most favoured pathway on the doublet surface whiles the stepwise [1 + 1] addition involving the oxygen atom of the complex in the first step and the carbon atom of the complex in the second step is the most plausible pathway on the triplet PES. For the reaction of the RhO2(CH2)(CH3) complex, the [2 + 2]Rh,O addition pathway is the most favoured on the singlet surface, the [2 + 2]Rh,C is the most plausible pathway on the triplet PES and [3 + 2]C,O is the most plausible on the doublet surface. For the reactions of the CoO2(CH2)(CH3) complex, the [1 + 2]O addition is the most plausible on the singlet PES, [3 + 2]C=Co=O cycloaddition to form the five–membered intermediate is the most preferred pathway on the doublet PES, whiles on the triplet PES the preferred pathway is the [3 + 2] addition across the O=Co=O bond of the metal complex. The reactions of olefins with the Co dioxo complex have lower activation barriers for the preferred [3 + 2] and [2 + 2] addition pathways as well as fewer side reactions than those of the rhodium and iridium systems. This could imply that the cobalt dioxo complexes can efficiently and selectively catalyze specific reactions in oxidation of olefins than Rh and Ir oxo complexes will do and therefore Co oxo complexes may be better catalysts for specific oxidation reactions of olefins than Rh and Ir complexes are. The activation barriers for the formation of the four—or five-membered metallacycle intermediates through [2 + 2] or [3 + 2] cyclo-addition are lower on the triplet PES than on the singlet PES for the formation of similar analogues. There are fewer competitive reaction pathways on the triplet surface than on the singlet PES. Also, cycloadditions that seem impossible on the singlet PES seem possible on the doublet and or triplet PESs, this is the case typically for the Rh and Co complexes, illustrating the importance of multiple spin states in organometallic reactions.Graphical Table of Contents Synopsis: A study of the mechanism of ethylene addition to MO2(CH2)(CH3)(M=Co,Rh,Ir) shows the reactions of the Co complex have lower activation barriers for the preferred [3+2] and [2+2] addition pathways and fewer side reactions than those of Rh and Ir. Reactions are more feasible and selective on the triplet PES than on the singlet PES. These illustrate the importance of multiple spin states in organometallic reactions and shows catalyst activity and selectivity decreases down the group.

New Insights into Mechanism of Molybdenum(VI)-Dioxo Complex Catalyzed Hydrosilylation of Carbonyls: An Alternative Model for Activating Si-H Bond.

Recently, a series of oxo/nitrido-Re(V)/Mo(VI)/Ru(VI)/Mn(V) complexes were demonstrated to be efficient catalysts in activating silanes and catalyzing hydrosilylations of unsaturated organic substrates. In the present study, the high-valent molybdenum(VI)-dioxo complex MoO2Cl2 catalyzed hydrosilylations of carbonyls was reinvestigated using density functional theory method. Previous experimental and theoretical investigations suggested a [2 + 2] addition pathway for MoO2Cl2 catalyzed hydrosilylations of ketones. In the present study, we propose an ionic outer-sphere mechanistic pathway to be the most favorable pathway. The key step in the ionic outer-sphere pathway is oxygen atom of C═O bonds nucleophilically attacking the silicon atom in an η(1)-silane molybdenum adduct. The Si-H bond is then cleaved heterolytically. This process features a novel SN2@Si transition state, which then generates a loosely bound ion pair: anionic molybdenum hydride paired with silylcarbenium ion ([MoO2Cl2H](-) [SiR3(OCR'R″)](+)) in solvent. The last step is silylcarbenium ion abstracting the hydride on molybdenum hydride to yield silyl ether. The calculated activation free energy barrier of the rate-determing step was 24.1 kcal/mol for diphenylketone (PhC═OPh) and silane of PhMe2SiH. Furthermore, the ionic outer-sphere pathway is calculated to be ∼10.0 kcal/mol lower than the previously proposed [2 + 2] addition pathway for a variety of silanes and aldehyde/ketone substrates. This preference arises from stronger electrophilicity of the high-valent molybdenum(VI) metal center toward a hydride. Here, we emphasize MoO2Cl2 behaves similar to Lewis acidic trispentafluorophenyl borane B(C6F5)3 in activating Si-H bond.