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Highly reactive dicoordinate (i.e., mono-base-stabilized) borylenes of the form [LBR] (L = Lewis base) have recently shown intriguing reactivity with inert small molecules, including N2. However, t...

The reactions of the rhenium(III)-phosphine complex ReCl3(PMePh2)3 with organonitriles (NCR) were studied and found to give novel addition as well as simple substitution products. Refluxing ReCl3(P...

[(η6-p-cymene)OsI2]2 was found to be a good catalyst for the cyclopropanation reaction of isobutyl vinyl ether with 3-tert-butyldiazoindene. In contrast, the complexes [(η6-p-cymene)OsX2]2 (X = Cl,...

Reactions of OsCl2(PPh3)3 with o-ethynylphenyl-carbonyl compounds o-HC≡CC6H4C(O)R (2, R = H (a) and Et (b)) produced the η3-o-ethynylphenyl-carbonyl complexes OsCl2(PPh3)2{η3-(o-HC≡CC6H4C(O)R)} (3)...

DFT calculations have been carried out to study the mechanisms and origin of regioselectivity in Rh- and Ir-catalyzed hydroalkynylation of enamides with terminal alkynes. The two reactions, despite...

The reactions of [RhCl(COD)]2 with a series of diazoalkanes with different substitutents were investigated. The outcomes of the reactions were found to be substituent-dependent via four different pathways. (1) The reactions with diazoindenes produced η5-cyclopentadienyl complexes. (2) The reaction with diazofluorene produced a mixture of olefin and azine compounds. (3) The reactions with monosubstituted diazoalkanes RCHN2 (R = Ph, MeO2C) produced olefins RCH═CHR. (4) The reaction with the disubstituted diazoalkane Ph2CN2 produced the azine Ph2C═N–N═CPh2 only. Computational studies have been carried out to understand the interesting substituent effect by comparing the kinetics and thermodynamics of the reaction pathways. It was found that the reactions with diazocyclopentadiene, diazoindene, and Ph2CN2 are kinetically controlled, while the reactions with RCHN2 and diazofluorene are both thermodynamically and kinetically controlled.

DFT calculations have been carried out to study the reaction mechanism of copper-catalyzed three-component boracarboxylation of alkene with CO2 and diboron. The competing reaction pathways involving two components have also been investigated for comparison. Through this theoretical study deep mechanistic insight on this multicomponent reaction is provided.

A series of new d2 Re (V) alkylidyne complexes were synthesized, including Re(≡CCH2Ph)Cl2(PR3)3 (PR3 = PMe3, and PMePh2), Re(≡CCH2Ph)I2(PMePh2)3, Re(≡CPh)(S2CNEt2)2(PMePh2), [CpRe(≡CPh)(PMePh2)2]Cl, and Re(≡CCH2Ph)(mnt)(PMePh2)2. The complexes Re(≡CCH2Ar)Cl2(PR3)3 (PR3 = PMe3, PMe2Ph, and PMePh2) as well as Re(≡CCH2Ph)I2(PMePh2)3 were found to undergo alkyne metathesis reactions with PhC≡CPh, while the other complexes are inactive. The activity of Re(≡CCH2Ar)Cl2(PR3)3 toward alkyne metathesis reactions with PhC≡CPh is in the order of PMe3 < PMe2Ph < PMePh2. The complex Re(≡CCH2Ph)I2(PMePh2)3 is slightly less reactive than its chloride analog. The difference in the reactivity of the alkylidyne complexes has been studied computationally.

The luminescent studies of cyclometalated Ir(III) complexes have attracted considerable interests in recent years. To fulfill the needs of emission wavelengths in various areas, the strategic emission color tuning of iridium(III) complexes is vital for their applications as phosphorescent materials. However, a feasible color-tuning method for iridacycles with fused carbon-rings (C∧C) has not been reported yet. Herein, a convenient color-tuning strategy for C∧C-based Iridacycles is accomplished with the aid of DFT calculations. The developed synthetic protocol allowed facile modifications on C∧C units and N∧N units via a one-pot synthesis starting from iridium vinyl complexes, accessing the novel phosphorescent iridapolycycles [(N∧N)Ir(C∧C)ClPPh3]+.

Reactions of silanes with transition-metal complexes are of interest because their relevance to Si–H bond activation, the structural properties of polyhydrides, and catalytic hydrosilylation reactions. This work presents the results derived from reactions of arylsilanes Ph2SiH2 and PhSiH3 with OsH3Cl(PPh3)3 (1). Reaction of 1 with 1 equiv or excess Ph2SiH2 affords OsH3(SiClPh2)(PPh3)3 (2) or OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3), respectively. These silyl complexes are formed via the oxidative addition of Si–H bonds and H/Cl exchange via silylene intermediates. Similarly, reaction of 1 with excess PhSiH3 produced the analogous bis(silyl) complex OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4). The bis(silyl) complexes are dodecahedral tetrahydride complexes containing weak Si···H interactions. The complex 3 reacts with PPh3 and CH3CN to selectively eliminate Ph2SiH2. Computational studies show that the preference for reductive eliminations from 3 follows the order Ph2SiH2 > H2 > Ph2SiHCl > Ph2HSi-SiClPh2.

Reactions of (cyclopentadienylidenehydrazono)triphenylphosphorane with RuCl2(PPh3)3 or (η6-cymene)RuCl2(PPh3) in toluene produced the chlorocyclopentadienyl complex (η5-C5H4Cl)RuCl(PPh3)2, which was likely formed through the cyclopentadienylidene intermediate RuCl2{═C(C4H4)}(PPh3)2. Treatment of (η6-cymene)RuCl2(PPh3) with (cyclopentadienylidenehydrazono)triphenylphosphorane in methanol gave [(η5-C5H4Cl)Ru(η6-cymene)]+. Computational studies reveal that the thermodynamic stability of the analogous chlororuthenium complexes RuCl2(═CRR′)(PPh3)2 and [RuCl(═CRR′)(PMe3)(η6-C6H6)]+, with respect to the formation of the corresponding η5-chloropentadienyl complexes via a migratory carbene-insertion reaction is in the order of cyclopentadienylidene < indenylidene < fluorenylidene < phenylcarbene.

Density functional theory calculations have been performed to investigate how different nucleophiles and directing groups affect the preference of C–H versus C–O bond functionalization in the ruthenium-catalyzed coupling reactions of aryl ethers with organoboronates. Our results indicate that the preference depends on the relative stability of the transition state structures for the C–O bond activation in the C–O bond functionalization pathway and the transmetalation with boronate to form a Ru–C bond in the C–H bond functionalization pathway. When the transition state structure for the transmetalation with boronate lies lower in energy than that for the C–O bond activation, C–H bond functionalization is preferred, and vice versa. How different nucleophiles and directing groups affect the relative stability of the transition structures has been discussed in detail.

Density functional theory calculations have been performed to study the reaction mechanisms for the Rh(III)-catalyzed C–H functionalization versus deoxygenation of quinoline N-oxide (QNO) with diazo compounds, dimethyl diazomalonate and methyl phenyldiazoacetate. How different diazo compounds affect the reaction pathways has been analyzed and examined in detail. It was found that the stability of the Rh(III)-carbene intermediates derived from an N2 extrusion is crucial in determining the preferred reaction pathway.

The reactions of the trichloro carbyne complexes OsCl3(≡CR)(PPh3)2 (R = CH═CPh2, CH2Ar) with bromine and hydrogen peroxide were studied. Unlike monochloro carbyne complexes OsCl(≡CAr)(CO)(PPh3)2, the trichloro complexes OsCl3(≡CR)(PPh3)2 do not undergo oxidation reactions at the metal center or the metal–carbyne bond. Treatment of OsCl3(≡CCH═CPh2)(PPh3)2 with Br2/H2O and H2O2/HCl produced OsBr3(≡CCH═CPh2)(H2O)(PPh3) and OsCl3(≡CCCl═CPh2)(PPh3)2, respectively. Reactions of OsCl3(≡CCH2-C6H4-p-R)(PPh3)2 (R = H, CMe3) with H2O2/HCl or H2O2 gave OsCl3{≡CC(O)-C6H4-p-R}(PPh3)2. Computational studies suggest that the difference in the reactivity of OsCl(≡CAr)(CO)(PPh3)2 and OsCl3(≡CR)(PPh3)2 is mainly of thermodynamic origin.

Although alkyne metathesis reactions mediated by high-valent d0 carbyne complexes are well established, similar reactions mediated by well-defined low-valent (non-d0) carbyne complexes are rare. This work demonstrates that d2 Re(V) carbyne complexes Re(≡CR)Cl2(PMe2Ph)3 (R = CH2(o-C6H4Br), Ph, CO2Et) can undergo stoichiometric alkyne metathesis reactions. For example, reactions of Re{≡CCH2(o-C6H4Br)}Cl2(PMe2Ph)3 with TMSC≡CR (R = CO2Et, CH2Ph) and PhC≡CPh produced carbyne complexes Re(≡CR)Cl2(PMe2Ph)3 and Re(≡CPh)Cl2(PMe2Ph)3, respectively. Theoretical studies suggest that the metathesis reactions most likely proceed through six-coordinate alkyne-carbyne intermediates Re(≡CR)Cl2(η2-alkyne)(PMe2Ph)2 that undergo reversible cycloaddition reactions.

Treatment of [Re(dppm)3]I (dppm = PPh2CH2PPh2) with HC≡CPh produced the rhenium vinylidene complex ReI(═C═CHPh)(dppm)2. In the presence of HI, [Re(dppm)3]I reacted with HC≡CR (R = Ph, p-tolyl, C6H4-o-CHO, (CH2)5CH3) to give the rhenium carbyne complexes [ReI(≡CCH2R)(dppm)2]I and with HC≡CSiMe3 to give [ReI(≡CMe)(dppm)2]I. One-pot reactions of [Re(dppm)3]I, HC≡CC(OH)RR′ (RR′ = Ph2, Me2, PhMe), and HI produced the vinylcarbyne complexes [ReI(≡CCH═CRR′)(dppm)2]I.

The carbene-stabilized electron-rich iminocarboranyl boron(I) compound [(Dipp)NC(But)C2B10H10]B(NHC) (1) (Dipp = 2,6-diisopropylphenyl, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is an excellent precursor for the preparation of the unprecedented carborane-fused azaborolyl radical cation [{(Dipp)NC(But)C2B10H10}B(NHC)]•+ ([2]•+) and dicarbollyl-fused azaborole 7,8-nido-C2B9H9-7,8-C(But)N(Dipp)B(NHC) (3) via controlled single-electron oxidation and two-electron oxidative deboration, respectively. Single-crystal X-ray analyses and DFT calculations indicate that the unpaired electron in [2]•+ is delocalized over the BNC unit, and the two fused five-membered rings in 3 form a sort of π-conjugated system.

An unsymmetrical diborane(4), pinB-BMes2, reacted with 2,6-dimethylphenyl isocyanide to give a spirocyclic 1,2-oxaboretane or isocyanide-coordinated boraalkene. The former product formed via ring contraction of the pinacolatoboryl group. DFT calculations revealed the ring contraction proceeded via a carbocationic intermediate. This new degradation pathway from the Bpin group would provide important information in Bpin-related chemistry.

Treatment of OsCl2(PPh3)3 with HC≡CAr (Ar = Ph, p-tolyl) produced the η3-allenylcarbene complexes OsCl2(═CAr-η2-CH═C═CHAr)(PPh3)2. Reactions of the η3-allenylcarbene complexes with gold alkynyls Au(C≡CR)(PPh3) (R = Ph, p-tolyl, TMS, nBu, CH(OEt)2) or copper(I) alkynyls Cu(C≡CR) (R = Ph, TMS) in the presence of HNEt3Cl produced the osmabenzynes Os{≡CC(R)═C(CH2Ar)CH═CAr}Cl2(PPh3)2. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt3Cl.

Structures, stabilities, and electron affinities of closo-supercarboranes C2Bn–2Hn (n = 13–20) were studied with the aid of DFT calculations. The results regarding the relative stability of positional isomers for each closo-supercarborane can be well understood with the qualitative rules established on the basis of early studies on 5- to 12-vertex carboranes C2Bn–2Hn (n = 5–12). The calculated cumulative BH addition energies for the most stable CAd (CAd = carbon-atoms-adjacent) and CAp (CAp = carbon-atoms-apart) positional isomers (using the equation 1,2-C2B10H12 + (n – 12) BHinc → C2Bn–2Hn (n = 13–20), where BHinc is set as the energy difference between B6H10 and B5H9) suggest that the thermodynamic stability should not be the reason for nonobservation of 15-vertex CAp closo-carborane and other larger closo-supercarboranes C2Bn–2Hn (n = 16–20), and effort toward their synthesis is worth spending. The calculated HOMO–LUMO energy gaps show the relatively low chemical stability of 15-vertex closo-carboranes...

The catalytic properties of a series of ruthenium complexes for H/D exchange between D2O and alcohols were studied. The catalytic activity of the ruthenium complexes and the regioselectivity of the H/D exchange reactions were found to be dependent on the auxiliary ligands. While ruthenium η6-cymene complexes such as [(η6-cymene)RuCl(NH2CH2CH2NTs)]Cl, (η6-cymene)RuCl2/NH2CH2CH2OH, and (η6-cymene)Ru{(S,S)-NHCHPhCHPhNTs} catalyzed regioselective deuteration of alcohols with D2O at the β-carbon positions only, octahedral ruthenium complexes such as RuCl2(2-NH2CH2Py)(PPh3)2 (2-NH2CH2Py = 2-aminomethylpyridine) and RuCl2(NH2CH2CH2NH2)(PPh3)2 catalyzed regioselective H/D exchange reactions of D2O with alcohols at both the α- and β-carbon positions of alcohols. The H/D exchange reactions proceed through reversible dehydrogenation of alcohols and hydrogenation of carbonyl compounds involving hydride species and H/D exchange among D2O and carbonyl and hydride species. The different regioselectivities of the H/D exc...

Density functional theory calculations were carried out to study the mechanisms of gold-catalyzed intramolecular cyclization reactions of terminal alkyne and phenyl-substituted alkyne tethered pyrroles leading to pyrrolopyridinones and pyrroloazepinones, respectively. The calculation results indicate that the reaction mechanisms mainly involve metal-coordination of a substrate molecule (alkyne tethered pyrrole) through the alkyne moiety, nucleophilic attack of the pyrrole’s α-carbon on the metal-coordinated alkyne, and 1,2-migration of either the carbonyl carbon or an alkenyl carbon (derived from the alkyne moiety) from the pyrrole’s α-carbon to the β-carbon, followed by a series of protodeaurylation to finally give cyclization products. Through the detailed mechanistic study, we have explained the regioselectivity and rationalized the major/minor products observed in the gold-catalyzed intramolecular cyclization reactions of alkyne-tethered pyrroles.

Treatment of the osmabenzyne complex Os{≡C-C(SiMe3)═C(CH3)-C(SiMe3)═CH−}Cl2(PPh3)2 with Mo(CO)6 in refluxing benzene produced the η5-chlorocyclopentadienyl complex Os{η5-C5HCl(CH3)(SiMe3)2}Cl(CO)(PPh3) and Mo(CO)5(PPh3). A computational study suggests that the chlorocyclopentadienyl complex is most likely produced via the carbene intermediate Os{═C(C(SiMe3)═C(CH3)-C(SiMe3)═CH−)}Cl2(CO)(PPh3) formed by a migratory insertion reaction of the osmabenzyne complex Os{≡C-C(SiMe3)═C(CH3)-C(SiMe3)═CH}Cl2(CO)(PPh3). DFT calculations show that the relative thermal stability of metallabenzynes Os(≡C-CH═CHCH═CH)Cl2(L)2 and the corresponding isomeric carbene complexes Os{═C(−CH═CHCH═CH−)}Cl2(L)2 as well as the chlorocyclopentadienyl complexes Os(η5-C5ClH4)Cl(L)2 (L = CO, phosphine, pyridine, amine) is strongly dependent on ligand L.

Treatment of Na[Re(CO)5] with methyl 3-(naphthalen-1-yl)propiolate (NpC≡CCO2Me) followed by acetyl chloride and alcohols ROH (R = Me, nPr) afforded the rhenacyclobutadiene complexes Re{-C(Np)═C(CO2Me)C(OR)═}(CO)4. Reactions of these rhenacyclobutadiene complexes with HC≡COEt produced the rhenabenzene complexes Re{-C(Np)═C(CO2Me)C(OR)═CHC(OEt)═}(CO)4 and new rhenacyclobutadienes with a pendant vinyl substituent Re{-C(Np)═C(C(OR)═CH(CO2Et))C(OMe)═}(CO)4. In the vinyl-substituted rhenacyclobutadiene products, the ethyl of the ester group is from the alkyne HC≡COEt, the alkyl of the ReC(OR) group is from the ester group of the starting rhenacyclobutadienes, and the alkyl group of the OR of the vinyl substituent is from the ReC(OR) group of the starting rhenacyclobutadienes. A plausible mechanism for the formation of the vinyl-substituted rhenacyclobutadienes is discussed.

DFT calculations have been carried out to study the detailed mechanism of Rh(III)-catalyzed C–H activation/cyclization of 2-acetyl-1-arylhydrazines with alkynes leading to the formation of indoles, in which the hydrazine moiety is used as the internal oxidant. The energy profiles associated with the catalytic cycle, involving N–H deprotonation, C–H activation (a concerted metalation–deprotonation (CMD) process), alkyne insertion, ring rearrangement/isomerization, and finally N–N bond cleavage/reductive elimination to regenerate the active species, are presented and analyzed. Through analysis of the calculation results, we found that the combined processes of the CMD and alkyne insertion contribute to the overall rate-determining step. The N–N bond cleavage step was examined in detail to understand how the internal oxidant interacts with the metal center to facilitate the catalytic reactions. The factor influencing regioselectivity was also investigated. How different types of substrates (alkynes versus al...

DFT calculations have been carried out to study the detailed mechanisms for the nickel-catalyzed reductive carboxylation of ester-substituted styrenes H2C═CHAr using CO2 to form α-carboxylated products. Two possible mechanisms, the oxidative coupling mechanism and the nickel hydride mechanism, were calculated and compared. Our calculations show that, for the oxidative coupling mechanism, a metallacycle thermodynamic sink is generated from oxidative coupling between CO2 and a styrene substrate molecule on the nickel(0) metal center, which should be avoided in order for smooth reductive carboxylation of styrenes. For the nickel hydride mechanism, a nickel hydride species is the active species, from which styrene insertion into the Ni–H bond followed by reductive elimination produces the α-carboxylated product. Calculations show that either of these two steps (insertion and reductive elimination) can be the rate-determining step, and both transition states are only slightly more stable than the oxidative cou...

A density functional theory (DFT) study was carried out to elucidate the mechanism of [2 + 2 + 1] cyclotrimerization of o-carboryne with CH2═CHnBu and TMS–≡–Ar mediated by a nickel complex. The calculated results reveal that the commonly proposed mechanism via a nickel vinylidene intermediate is kinetically and thermodynamically disfavored. An unprecedented reaction mechanism involving alkyne insertion, η1-alkenyl to η2-alkenyl rearrangement, and TMS migrations is found to be responsible for the favorable [2 + 2 + 1] cycloaddition. The new mechanism rationalizes well the substituent effect on the stereoselectivity of E/Z [2 + 2 + 1] products 3E/3Z and the chemoselectivity of [2 + 2 + 1] over [2 + 2 + 2] cyclotrimerization.

The detailed reaction mechanisms of the C═O hydrosilylation of isocyanate and the C═S bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex Cp*(CO)(H)Ru═Si(H){C(SiMe3)3} have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between isocyanate and isothiocyanate toward the ruthenium silylene hydride complex has been examined and discussed. The different bond strengths and π-accepting abilities of C═O and C═S and the different degrees of affinity of O and S toward the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally.

In this paper, DFT calculations have been carried out to study the reaction mechanism of copper-catalyzed hydrocarboxylation of alkynes using CO2 and hydrosilanes. In addition to hydrocarboxylation of alkynes, possible competitive reactions such as hydrosilylation of alkynes, hydrosilylation of CO2, and silacarboxylation of alkynes have also been investigated and compared. Through these DFT calculations, we are able to understand the reason only hydrocarboxylation of alkynes has been observed experimentally.

With the aid of DFT calculations, we have examined the mechanism of the Ni-catalyzed cycloaddition of 3-azetidinone with alkynes. Our DFT results did not support the originally proposed mechanism, which involves a ring expansion through β-carbon elimination. Instead, our calculations supported a mechanism which involves oxidative addition of 1-Boc-3-azetidinone to a Ni(0) center to form an intermediate having both Ni–C(O) and Ni–C(sp3) bonds, then alkyne insertion into either the Ni–C(O) or Ni–C(sp3) bond depending on the alkyne substrates being studied, and finally reductive elimination to give the cycloaddition products. The nature of insertion of alkynes into a Ni–C bond was also discussed. When an alkyne substrate inserts into the Ni–C(O) bond, we found that the alkyne acts as a nucleophile to attack the electron-deficient, metal-bonded C═O carbon center. When an alkyne substrate inserts into the Ni–C(sp3) bond, the alkyne acts as an electrophile to interact with the Ni–C(sp3) bond.

Density functional theory calculations have been performed to investigate the mechanisms of the Pd-catalyzed dearomatization reaction between chloromethylnaphthalene and the cyclic amine morpholine. The calculation results indicate that the reductive elimination leading to the formation of the dearomatic product takes place via an intramolecular C–N bond coupling between the para carbon of an η3-exo-(naphthyl)methyl ligand and the nitrogen atom of the amide ligand. The free energy barrier is calculated to be only 13.1 kcal/mol, significantly lower than that (37.8 kcal/mol) through the η3-endo-(naphthyl)methyl intermediate originally thought. For comparison, various C–N coupling reaction pathways leading to the formation of dearomatic and aromatic products have also been examined.

Reactions of both terminal and internal alkynols with ReOCl2(OEt)(PPh3)2 (1) are described. Treatment of ReOCl2(OEt)(PPh3)2 (1) with HC≡CC6H4-2-CH2OH and HC≡CCH2CH2CH2OH produced the six-membered ylide complexes ReOCl2(C(═CH(PPh3))-C6H4-CH2O)(PPh3) (2) and ReOCl2(C(═CH(PPh3))CH2CH2CH2O)(PPh3) (3), respectvely, derived from addition of PPh3 to the terminal alkyne carbon. Similarly, phosphine addition to the terminal alkyne carbon occurred in the reactions of ReOCl2(OEt)(PPh3)2 (1) with HC≡CCH2CH(OH)Me and HC≡CCH2CH(OH)CH(OH)CH2C≡CH to give the five-membered ylide complexes ReOCl2(C(═CH(PPh3))CH2CH2CHMeO)(PPh3) (5) and {ReOCl2(C(═CH(PPh3)CH2CHO)(PPh3)}2 (6), respectively. Interestingly, related reactions of ReOCl2(OEt)(PPh3)2 with RC≡CCH2CH2OH (R = Me, Et, Ph) produced the six-membered ylide complexes ReOCl2(CR═C(PPh3)CH2CH2O)(PPh3) (7, R = Me; 8, R = Et; 9, R = Ph), derived from addition of PPh3 to the alkyne carbon closer to the OH group.

Cu(I)/TF-BiphamPhos catalyzed reactions of alkylidene bisphosphates and alkylidene malonates with azomethine ylides have been investigated with the aid of density functional theory calculations at the B3LYP level. Michael addition and 1,3-dipolar cycloaddition were calculated. For reactions of alkylidene bisphosphates, the Michael addition pathway is both kinetically and thermodynamically more favorable than 1,3-dipolar cycloaddition. However, for reactions of alkylidene malonates, the 1,3-dipolar cycloaddition pathway is kinetically and thermodynamically more favorable than Michael addition. In the reactions of alkylidene bisphosphates, the significant repulsion between the two bulky phosphonate groups of the alkylidene bisphosphates and the phenyl substituent of the azomethine ylides suppresses 1,3-dipolar cycloaddition and favors Michael addition. In the reactions of alkylidene malonates the less bulky ester groups in the alkylidene malonates allow 1,3-dipolar cycloaddition to occur.

The reaction mechanisms for the MTO-catalyzed deoxygenation of epoxides and diols were investigated with the aid of density functional theory (DFT) calculations. The DFT results indicate that the reaction starts with a [2σ+2π] addition of epoxide to MTO to give a five-membered-ring rhena-2,5-dioxolane intermediate, followed by H2 addition, proton transfer, and extrusion of olefin to regenerate the catalyst. The experimental observation for formation and subsequent disappearance of diol appearing in the catalytic reaction is explained as follows. Diol was produced by the hydrolysis of epoxide with the coproduct water through the five-membered-ring rhena-2,5-dioxolane intermediate. Then the diol produced undergoes catalytic conversion to olefin by reacting with H2 under the catalytic conditions.

The catalytic activity of a series of ruthenium complexes lacking cyclopentadienyl ligands has been evaluated for the cycloaddition of terminal alkynes and azides to give selectively 1,4-disubstitu...

Gold-catalyzed cycloisomerization of 1,5-enynes has been investigated with the aid of density functional theory calculations at the B3LYP level of theory. We have examined how substituents influence the reaction paths in the cycloisomerization of 1,5-enynes catalyzed by both AuCl and [AuL]+ (L = phosphine).

Cu-catalyzed arylation of aromatic C–H bonds with phenyl iodide has been investigated with the aid of density functional theory calculations at the B3LYP level. Both the neutral and anionic catalytic cycles have been examined by considering the neutral (phen)Cu–OMe and anionic [MeO–Cu–OMe]− complexes, respectively, as the active species. Various heterocycle and polyfluorobenzene substrates were studied. The relationship between the overall reaction barrier and the acidity of the cleaved C–H bond was studied in both the neutral and anionic catalytic cycles. Comparing the overall reaction barriers based on the neutral and anionic catalytic cycles, we were able to understand that some substrates prefer the anionic mechanism while others prefer the neutral mechanism. We also examined how different ligands influence the overall barriers in the neutral catalytic cycles by employing N,N′-dimethylethylenediamine (DMEDA) and N-methylpyrrolidine-2-carboxamide as the ligands.

We have investigated the reduction of CO2 to CO mediated by the anionic niobium nitride complex [NNb(NtBuMe)3]−, a model complex of [NNb(NtBuAr)3]−, using density functional theory. We mainly calculated the energetics for the interesting reaction sequence, reported recently by Cummins and his co-workers, involving reactions of the anionic niobium nitride complex [NNb(NtBuAr)3]− with CO2 to first give a carbamate complex. The carbamate complex then reacts with MeC(O)Cl to give an isocyanate–acetate, which can be reduced by SmI2 to give the isocyanate complex (OCN)Nb(NtBuAr)3. Further reduction of the isocyanate complex by Na/Hg extrudes CO and regenerates [NNb(NtBuAr)3]−. In addition, we compare the reaction pathways for the reduction reaction of the isocyanate complexes (OCN)M(NtBuMe)3 (M = Nb, V), model complexes of (OCN)M(NtBuAr)3, with sodium and explain why these two reduction reactions give remarkably different products.

Reactions of the lithium boryl LiB(R′NCH═CHNR′) (R′ = 2,6-iPr2C6H3), 1, with organohalides (RX) giving RB(R′NCH═CHNR′) and/or XB(R′NCH═CHNR′) were studied computationally using density functional theory calculations at the B3LYP level. Our calculations indicate that the boryl anion in the lithium boryl can undergo nucleophilic attack at an organohalide on the halide-bonded carbon atom and/or the halogen atom to form RB(MeNCH═CHNMe) (an expected SN2 substitution product) and/or XB(MeNCH═CHNMe) (a halogen-abstraction product), respectively. Our energetic calculation results show that an organohalide having a halogen with lower electronegativity and higher ability to engage in hypervalent bonding promotes the halogen-abstraction pathway. Benzyl halides were also found to promote the halogen-abstraction pathway due to conjugation effects that stabilize a benzyl anion in the transition state during the halogen-abstraction process.

The detailed reaction mechanism for the Stille cross-coupling reaction of vinylstannane with vinyl iodide mediated by copper(I) thiophene-2-carboxylate (CuTC) was studied with the aid of density functional theory (DFT) calculations. The results of the DFT calculations show that the reaction mechanism involves two major steps: (1) the transmetalation between (NMP)CuTC (NMP = N-methylpyrrolidone, a solvent molecule) and CH2═CHSnMe3 to give the organocopper intermediate (NMP)Cu-CH═CH2 and (2) a one-step process involving both oxidative addition of CH2═CHI to (NMP)Cu-CH═CH2 and reductive elimination of the coupling product CH2═CH−CH═CH2. We found that the overall barrier involves the effect of both steps. In this paper, we also examined the role of the thiophene-2-carboxylate ligand in the reaction and discussed the possibility of a catalytic version of the reaction.

Treatment of the rhenium polyhydride complex ReH5(PMe2Ph)3 with HC≡CR (R = Ph, SiMe3, (CH2)4Me) in the presence of 2.2 equiv of HCl produces a mixture of the carbyne complexes Re(≡CCH2R)Cl2(PMe2Ph)3 and the η2-vinyl complexes Re(η2-CH2CR)Cl2(PMe2Ph)3. When HC≡CC(OH)Ph2 was used, the reaction gave the carbyne complexes Re(≡CCH═CPh2)Cl2(PMe2Ph)3 and Re(≡CCH2C(OH)Ph2)Cl2(PMe2Ph)3 along with the η2-vinyl complex Re(η2-CH2CC(OH)Ph2)Cl2(PMe2Ph)3.

DFT calculations have been carried out to study the carboxylation reactions of arylboronate esters with CO2 catalyzed by (NHC)Cu(I) complexes (NHC = N-heterocyclic carbene). The results affirm the basic mechanistic proposal that (1) the transmetalation of the aryl group of the boronic ester to the Cu(I) metal center occurs first; (2) CO2 then inserts into the resulting Cu−Ar bond to give a carboxylate complex; and (3) displacement of the carboxylate by the base adduct of the arylboronic ester substrate completes the catalytic cycle and affords the product ArCOOK. Transmetalation was shown to proceed via a B−O−Cu-bridged intermediate that is formed from the KOR adduct of the arylboronic acid, rather than by the CuOR complex, although both pathways leading to the bridged intermediate are extremely facile. Insertion of CO2 into the Cu−Ar bond is the rate-determining step, in which nucleophilic attack of the aryl ligand on the electron-deficient carbon atom of CO2 leads to the formation of the new C−C bond. S...

The catalytic activity of a series of ruthenium complexes for C−H amination reactions of organic azides was investigated. The most active catalyst was found to be RuCl3, which promotes C−H amination reactions of ortho-aryl phenylazides, 1-azido-2-arylvinylazides, and 1-azido-1,3-butadienes to give carbazoles, indoles, and pyrroles, respectively. Both computational and experimental results support that a two-step process involving formal electrocyclization is involved in the catalytic reaction.

Reactions between 6-substitued fulvenes and the hydride complex RuHCl(PPh3)3 are described. Treatment of RuHCl(PPh3)3 with fulvenes without sp3-CH protons at the carbon α to the exocyclic carbon of fulvene produces cleanly monosubstituted cyclopentadienyl ruthenium complexes (η5-C5H4R)RuCl(PPh3)2 via hydride transfer to the electrophilic exocyclic carbon of fulvenes. When fulvenes containing sp3-CH protons at the carbon α to the exocyclic carbon were used, the reactions produce the expected (η5-C5H4R)RuCl(PPh3)2 complexes along with minor amounts of vinylcyclopentadienyl ruthenium complexes due to dehydrogenation.

DFT calculations have been carried out to study the mechanisms for reactions of O2 with a series of metal complexes, including d6 CpRuL2, d6 ML5, and d8 ML4 complexes. The calculation results indicate that the reaction is initiated by an end-on coordination of O2 to the metal center, which gives an (η1-O2)[M] intermediate. The uncoordinated oxygen atom of the η1-O2 ligand then approaches the metal center to give a new η1-O2 intermediate in which the η1-O2 ligand is oriented approximately the same as the one defined in the product. An intersystem conversion from the triplet to singlet energy surface (MECP) then occurs to enable the metal peroxide product to be formed.

Density functional theory calculations have been carried out to study the reaction mechanism for the reduction of CO2 to CO by a (NHC)Ni0 complex (where NHC = N-heterocyclic carbene). A plausible r...

DFT calculations have been carried out to study the detailed mechanisms of the O-abstraction reaction of N2O with Cp2Ti(II). The reaction is initiated by coordination of N2O to Cp2Ti via the N-end to form a linear N2O-coordinated species Cp2Ti(N2O), from which the metal center transfers one of its metal d electrons to one π* orbital of the N2O ligand and gives a bent N2O-coordinated intermediate Cp2Ti←N═N−O. The intermediate then reacts barrierlessly with another molecule of Cp2Ti to form an N2O-bridged intermediate Cp2Ti←N═N−O−TiCp2, from which the singly oxo-bridged product (Cp2Ti)2O is formed with a release of N2. Reactions of N2O with other middle transition metal complexes have also been calculated and discussed. General mechanisms for O-abstraction reactions of N2O with early and middle transition metal complexes have been provided.

The cationic complexes Tp*Zr(CH2Ph)2+ (I, B(C6F5)4− salt; Tp* = HB(3,5-Me2-pyrazolyl)3) and {(PhCH2)(H)B(μ-Me2pz)2}Zr(η2-Me2pz)(CH2Ph)+ (II; Me2pz = 3,5-Me2-pyrazolyl) polymerize ethylene at −78 to...