Synthesis and Structure of [η5-1,2,4-(Me3Si)3C5H2]2Th(bipy) and Its Reactivity toward Small Molecules.

Halide exchange of (Cp3tms)2ThCl2 (1; Cp3tms = η5-1,2,4-(Me3Si)3C5H2) with Me3SiI furnishes (Cp3tms)2ThI2 (2), which is then reduced with potassium graphite (KC8) in the presence of 2,2'-bipyridine to give the thorium bipyridyl metallocene (Cp3tms)2Th(bipy) (3) in good yield. Complex 3 was fully characterized and readily reacted with various small molecules. For example, 3 may serve as a synthetic equivalent for the (Cp3tms)2Th(II) fragment when exposed to CuI, Ph2S2, organic azides, and CS2. Moreover, upon the addition of thiobenzophenone Ph2CS, p-methylbenzaldehyde (p-MeC6H4)CHO, benzophenone Ph2CO, amidate PhCONH(p-tolyl), seleno-ketone (p,p'-dimethoxy), selenobenzophenone (p-MeOPh)2CSe, di(p-tolyl)methanimine (p-tolyl)2C═NH, 1,2-di(benzylidene)hydrazine (PhCH═N)2, and nitriles PhCN, PhCH2CN, and Ph2CHCN C-C coupling results to give (Cp3tms)2Th[(bipy)(Ph2CS)] (8), (Cp3tms)2Th[(bipy)(p-MePhCHO)] (9), (Cp3tms)2Th[(bipy)(Ph2CO)] (10), (Cp3tms)2Th[(bipy){(p-tolylNH)(Ph)CO}] (11), (Cp3tms)2Th[(bipy){(p-MeOPh)2CSe}] (12), (Cp3tms)2Th[(bipy){(p-tolyl)2CNH}] (13), (Cp3tms)2Th[(bipy)(PhCHNN═CHPh)] (14), (Cp3tms)2Th[(bipy)(PhCN)] (16), (Cp3tms)2Th[(bipy)(PhCH2CN)] (17), and (Cp3tms)2Th[(bipy)(Ph2CHCN)] (18), respectively. However, when thiazole is added to 3, the dimeric sulfido complex [(Cp3tms)2Th]2[µ-(bipy)CH2NCHCHS]2 (15) can be isolated. Moreover, the addition of isonitriles such as Me3CNC and PhCH2NC to 3 results in C-N bond cleavage and C-C coupling processes to form the thorium isocyanido amido complexes (Cp3tms)2Th[4-(Me3C)bipy](NC) (19) and (Cp3tms)2Th[4-(PhCH2)bipy](NC) (20), respectively. Nevertheless, upon exposure of 3 to (trimethylsilyl)diazomethane Me3SiCHN2, the bis-amido complex (Cp3tms)2Th[5,6-(Me3SiCH)bipy] (21), concomitant with N2 release, is isolated.

A Comprehensive Study Concerning the Synthesis, Structure, and Reactivity of Terminal Uranium Oxido, Sulfido, and Selenido Metallocenes.

Terminal uranium oxido, sulfido, and selenido metallocenes were synthesized, and their reactivity was comprehensively studied. Heating of an equimolar mixture of [η5-1,2,4-(Me3Si)3C5H2]2UMe2 (2) and [η5-1,2,4-(Me3Si)3C5H2]2U(NH-p-tolyl)2 (3) in the presence of 4-dimethylaminopyridine (dmap) in refluxing toluene forms [η5-1,2,4-(Me3Si)3C5H2]2U═N(p-tolyl)(dmap) (4), which is a useful precursor for the preparation of the terminal uranium oxido, sulfido, and selenido metallocenes [η5-1,2,4-(Me3Si)3C5H2]2U═E(dmap) (E = O (5), S (6), Se (7)) employing a cycloaddition-elimination methodology with Ph2C═E (E = O, S) or (p-MeOPh)2CSe, respectively. Metallocenes 5-7 are inert toward alkynes, but they act as nucleophiles in the presence of alkylsilyl halides. The oxido and sulfido metallocenes 5 and 6 undergo [2 + 2] cycloadditions with isothiocyanate PhNCS or CS2, while the selenido derivative 7 does not. The experimental studies are complemented by density functional theory (DFT) computations.

Uranium versus Thorium: A Case Study on a Base-Free Terminal Uranium Imido Metallocene.

The structure of and bonding in two base-free terminal actinide imido metallocenes, [η5-1,2,4-(Me3C)3C5H2]2An═N(p-tolyl) (An = U (1), Th (1')) are compared and connected to their individual reactivity. While structurally rather similar, the U(IV) derivative 1 is slightly more sterically crowded. Furthermore, density functional theory (DFT) studies imply that the 5f orbital contribution to the bonding within the individual actinide imido An═N(p-tolyl) moieties is significantly larger for 1 than for 1', which makes the bonds between the [η5-1,2,4-(Me3C)3C5H2]2U2+ and [(p-tolyl)N]2- fragments more covalent. Therefore, steric and electronic factors impact the reactivity of these imido complexes. For example, complex 1 is inert toward internal alkynes, but it readily forms Lewis base adducts [η5-1,2,4-(Me3C)3C5H2]2U═N(p-tolyl)(L) (L = OPMe3 (6), dmap (9), PhCN (14), and 2,6-Me2PhNC (17)) with Me3PO, 4-dimethylaminopyridine (dmap), nitrile, PhCN, or isonitrile 2,6-Me2PhNC. It may also react as a nucleophile or undergo a [2 + 2] cycloaddition with CS2, isothiocyanates, thio-ketones, ketones, lactides, and acyl nitriles, forming the four- or five-membered metallaheteroacycles, terminal sulfido, or oxido complexes, and cyanide amidate complexes, respectively. In contrast, after the addition of aldehyde p-tolylCHO, the tetranuclear complex [η5-1,2,4-(Me3C)3C5H2]4[OCH(p-tolyl)CH(p-tolyl)O]2U4O4 (10) is isolated. However, while 1 is unreactive toward dicyclohexylcarbodiimide (DCC), an equilibrium exists in benzene solution between N,N'-diisopropylcarbodiimide (DIC), 1, and the four-membered metallaheterocycle [η5-1,2,4-(Me3C)3C5H2]2U[N(p-tolyl)C(═NiPr)N(iPr)] (12). Furthermore, 1 may also engage in single- and two-electron transfer processes. It is singly oxidized by Ph3CN3, CuI, Ph2S2, and Ph2Se2, yielding the uranium(V) imido complexes [η5-1,2,4-(Me3C)3C5H2]2U═N(p-tolyl)(X) (X = N3 (20), I (22), PhS (23), and PhSe (24)), or is doubly oxidized by organic azides (RN3) and 9-diazofluorene, forming the uranium(VI) bis-imido metallocenes [η5-1,2,4-(Me3C)3C5H2]2U═N(p-tolyl)(=NR) (R = p-tolyl (18), mesityl (19)) and [η5-1,2,4-(Me3C)3C5H2]2U=N(p-tolyl)[=NN=(9-C13H8)] (21), respectively.

Stepwise versus Concerted: Theoretical Insights into the Stereoselectivity in Aryl Imine Formation Assisted by Acid and Water.

The wide applications of the aryl Schiff base require extensive understanding of the mechanism of its formation, which remains unclear. In this work, the detailed formation mechanisms between benzaldehyde and aniline or 4-(9-anthryl) ethynyl aniline were investigated at the CCSD(T)//B3LYP level, and the influence of water molecules and acid catalysis and the stereoselectivity were addressed. The results show that the participation of explicit water molecules greatly accelerates the reactions by alleviating the ring tension of the transition states, and acid catalysis strongly favors the imine formation and provides driving force for the forward reaction. In acidic conditions, both N-protonated carbinolamine formations and imine formations are achieved under mild conditions with the assistance of water molecules, and the proton transfer is more advanced than the C-N and C═N bond formation, which is in good agreement with the experimental observations. In contrast, under neutral conditions, even with the assistance of two water molecules, the reaction is hard to take place at room temperature owing to the high Gibbs free energy barriers with the proton transfer and the C-N or C═N bond formation concerted. The analysis of stereoselectivity shows that the formation of trans imine is both kinetically and thermodynamically more favorable than the cis one under the acidic condition with the assistance of water molecules, and the presence of conjugated substituent 4-(9-anthryl) ethynyl of aniline marginally raises the energy barriers. This work provides a systematic view of the mechanism for the formation of aryl imine and is expected to offer insights for the control of the dynamic covalent chemistry and the synthesis of covalent organic frameworks.

Experimental and Computational Studies on Uranium Diazomethanediide Complexes.

Uranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 U=N(p-tolyl)(dmap) (1) or [η5 -1,3-(Me3 C)2 C5 H3 ]2 U=N(p-tolyl)(dmap) (4) with Me3 SiCHN2 cleanly yields the first isocyanoimido metal complexes [η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 U(=NNC)(µ-CNN=)U(dmap)[η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 (2) and {[η5 -1,3-(Me3 C)2 C5 H3 ]2 U[µ-(=NNC)]}6 (5), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized. According to density functional theory (DFT) studies the bonding between the Cp2 U2+ and [NNC]2- moieties is strongly polarized with a significant 5 f orbital contribution, which is also reflected in the reactivity of these complexes. For example, complex 5 acts as a nucleophile toward alkylsilyl halides and engages in a [2+2] cycloaddition with CS2 , but no reaction occurs in the presence of internal alkynes.

Experimental and Theoretical Study on the Regioselective Radical Cyclization Reactions of 1-(o-Alkenylaryl)-2-amido-1-ketones for the Construction of Indeno[2,1-d][1,3]oxazin-9-ones.

A simple and efficient two-step method for the construction of novel 2,4,9a-trisubstituted-4a,9a-dihydroindeno[2,1-d][1,3]oxazin-9-ones has been developed. The NHC-catalyzed aza-benzoin reaction of o-alkenyl benzaldehydes with N-acylarylimines afforded 1-(o-alkenylaryl)-2-amido-2-aryl-1-ethanones, which underwent regioselective 5-exo-trig radical cyclization to furnish the three-ring-fused heterocyclic products, generally in good yields. The synthetic method displayed good tolerance toward the nature of substituents, substitution pattern, and steric hindrance of o-alkenyl benzaldehydes. Based on this method, the synthesis of unprecedented dihydrobenzo[6,7]indeno[2,1-d][1,3]oxazin-7-ones and dihydropyrido[2',3':3,4]cyclopenta[1,2-d][1,3]oxazin-9-ones has been achieved by employing o-alkenylnaphthaldehyde and o-alkenylnicotinaldehyde as substrates. The regioselectivity between 5-exo-trig and 6-endo-trig radical cyclization reactions of different 1-(o-alkenylaryl)-2-amido-2-aryl-1-ethanones were elucidated with DFT calculations.

Uranium versus Thorium: Synthesis and Reactivity of [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U[η2 -C2 Ph2 ].

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U=P-2,4,6-tBu3 C6 H2 (1) yields the stable uranium metallacyclopropene, [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U[η2 -C2 Ph2 ] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η2 -C=C) moiety increases significantly compared to the related ThIV compound [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 Th[η2 -C2 Ph2 ], which also results in more covalent bonds between the [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 U2+ and [η2 -C2 Ph2 ]2- fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low-valent uranium(II) metallocene [η5 -1,2,4-(Me3 C)3 C5 H2 ]2 UII when reacted with Ph2 E2 (E=S, Se), alkynes and a variety of hetero-unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five-membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones.

Experimental and Computational Studies on a Base-Free Terminal Uranium Phosphinidene Metallocene.

The first stable base-free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp'''2 U(I)Me (2, Cp'''=η5 -1,2,4-(Me3 C)3 C5 H2 ) with Mes*PHK (Mes*=2,4,6-(Me3 C)3 C6 H2 ) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp'''2 U=PMes* (3). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp'''2 U]2+ and [Mes*P]2- fragments than that for the related thorium derivative. This difference in bonding besides steric reasons causes different reactivity patterns for both molecules. Therefore, the uranium derivative 3 may act as a Cp'''2 U(II) synthon releasing the phosphinidene moiety (Mes*P:) when treated with alkynes or a variety of hetero-unsaturated molecules such as imines, thiazoles, ketazines, bipy, organic azides, diazene derivatives, ketones, and carbodiimides.

Evaluation of Influencing Factors in Tetravalent Uranium Complex-Mediated CO2 Functionalization by Density Functional Theory.

The functionalization of CO2 mediated by a series of U(IV) mixed-sandwich compounds, (COTTIPS2)Cp*UR (R = -CH3, -CH2Ph, -CH2TMS, -CH(TMS)2, -NHPh, -OPh, -SPh, -SePh; COTTIPS2 = C8H6(SiiPr3-1,4)2; Cp* = C5Me5; TMS = SiMe3), was investigated by the density functional theory method. A two-step mechanism was revealed, in which the insertion of CO2 into the U-C bond was identified as the rate-determining step via a transition state featured by a four-membered ring with a free-energy barrier of 18.8 kcal/mol to the reaction of the (COTTIPS2)Cp*UCH3 system. The whole reaction was strongly exothermic by 45.0 kcal/mol. Substitution effect was discussed, including the bulkiness of the R group and the nature of the ligating atom, and steric hindrance and electrostatic interactions were found to be responsible for the observed variation in reactivity. The reactivity of U(III) and U(IV) complexes in CO2 functionalization was also compared and discussed. The results were consistent with experimental studies and complemented with molecular level of understanding on the mechanisms of CO2 functionalization promoted by tetravalent U complexes.

An Alkali-Metal Halide-Bridged Actinide Phosphinidiide Complex.

The salt metathesis reaction of the thorium methyl chloride complex [η5-1,3-(Me3C)2C5H3]2Th(Cl)Me (3) with 2,4,6-(Me3C)3C6H2PHK in benzene furnishes an alkali-metal halide-bridged phosphinidiide actinide metallocene, {[η5-1,3-(Me3C)2C5H3]2Th(═P-2,4,6- tBu3C6H2)(ClK)}2 (4), whose structure and reactivity was investigated in detail. On the basis of density functional theory (DFT) studies, the 5f orbitals in the model complex [η5-1,3-(Me3C)2C5H3]2Th(═P-2,4,6- tBu3C6H2) (4') contribute significantly to the bonding of the phosphinidene Th═P(2,4,6- tBu3C6H2) moiety. Furthermore, compared to the related thorium imido complex, the bonds between the [η5-1,3-(Me3C)3C5H2]2Th2+ and [P-2,4,6- tBu3C6H2]2- fragments are more covalent. The reactivity of compound 4 toward alkynes and a variety of heterounsaturated molecules such as nitriles, isonitriles, carbodiimides, imines, isothiocyanates, aldehydes, ketones, thiazoles, quinolines, organic azides, pyridines, and imidazoles, forming metallacycles, phospholes, imidos, metallaheterocycles, sulfidos, oxidos, pinacolates, pseudophosphinimidos, and phosphidos, was comprehensively studied. Moreover, complex 4 reacts with elemental selenium and PhSSPh, yielding selenido and sulfido compounds, respectively. DFT computations were performed to complement these experimental investigations and to provide further insights.

A Base-Free Terminal Actinide Phosphinidene Metallocene: Synthesis, Structure, Reactivity, and Computational Studies.

The synthesis, structure, and reactivity of a base-free terminal actinide phosphinidene metallocene have been comprehensively studied. The salt metathesis reaction of the thorium methyl iodide complex Cp‴2Th(I)Me (2; Cp‴ = η5-1,2,4-(Me3C)3C5H2) with Mes*PHK (Mes* = 2,4,6-(Me3C)3C6H2) in THF furnishes the first stable base-free terminal phosphinidene actinide metallocene, Cp‴2Th═PMes* (3). Density functional theory (DFT) shows that the bonds between the Cp‴2Th2+ and [PMes*]2- fragments are more covalent than those in the related thorium imido complex. While the phosphinidene complex 3 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as CS2, isothiocyanate, nitriles, isonitriles, and organic azides, forming carbodithioates, imido complexes, metallaaziridines, and azido compounds. These experimental observations are complemented by DFT computations.

The pH-dependent activation mechanism of Ser102 in Escherichia coli alkaline phosphatase: a theoretical study.

The accepted catalytic mechanism of alkaline phosphatases was established on the hypothesis that Mg-coordinated water is a readily available hydroxide ion that functions as a general base and accepts a proton from the Ser102 hydroxyl group. The roles of the two distinctive residues Asp153 and Lys328 in Escherichia coli alkaline phosphatase (ECAP), which distinguish it from the mammalian enzymes, are elusive. Based on the crystal structures of ECAP in the absence and presence of inorganic phosphate, we have investigated the activation of Ser102 for nucleophilic attack and the subsequent formation of a covalent phosphoseryl intermediate using hybrid density functional theory (DFT) with the B3LYP functional. Our calculations confirmed a proton transfer path from the hydroxyl group of Ser102 to the carboxyl group of Asp153 via water-mediated interactions through which Ser102 can be activated for nucleophilic attack. Our calculations further suggest that the activation mechanism of Ser102 is pH dependent, which explains why ECAP achieves its maximum activity at an alkaline pH for enzyme-catalysed reactions. This activation mechanism can also be extended to all APs with similar active-site structures. Our study, for the first time, provides the definite activation mechanism of Ser102 in ECAP, which is universal for all APs and explains the alkaline phosphatase activity of these enzymes. This work also sheds new light on the relationship between enzyme-catalytic mechanisms and enzyme-catalytic properties.

Computational Comparative Mechanistic Study of C-E (E=C,N,O,S) Coupling Reactions through CO2 Activation Mediated by Uranium(III) Complexes.

A DFT mechanistic study is undertaken on the functionalization of CO2 to form C-C, C-N, C-S, and C-O bonds promoted by trivalent uranium complexes (Tp*)2 UR [Tp*=hydrotris(3,5-dimethylpyrazolyl)-borate ligand, R= -C≡CPh (Cpda-CC), -C≡CSiMe3 (Cpda-CSi), -NHPh (Cpda-N), -SPh (Cpda-S), and -OPh (Cpda-O)]. These model systems are similar in view of their two-step reaction mechanisms, that is, the insertion of CO2 into the U-E (E=C, N, O, S) bond to form a [U-κ1 -O2 C] intermediate, followed by the reorientation of the carboxylate group to coordinate with the U atom in the κ2 manner (Cpdb-X, X=CC, CSi, N, S, O). However, the free energy barriers to the rate-determining steps are substantially different, increasing in the order Cpda-S

Influence of the 5f Orbitals on the Bonding and Reactivity in Organoactinides: Experimental and Computational Studies on a Uranium Metallacyclopropene.

The synthesis, structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Reduction of (η(5)-C5Me5)2UCl2 (1) with potassium graphite (KC8) in the presence of bis(trimethylsilyl)acetylene (Me3SiC≡CSiMe3) allows the first stable uranium metallacyclopropene (η(5)-C5Me5)2U[η(2)-C2(SiMe3)2] (2) to be isolated. Magnetic susceptibility data confirm that 2 is a U(IV) complex, and density functional theory (DFT) studies indicate substantial 5f orbital contributions to the bonding of the metallacyclopropene U-(η(2)-C═C) moiety, leading to more covalent bonds between the (η(5)-C5Me5)2U(2+) and [η(2)-C2(SiMe3)2](2-) fragments than those in the related Th(IV) compound. Consequently, very different reactivity patterns emerge, e.g., 2 can act as a source for the (η(5)-C5Me5)2U(II) fragment when reacted with alkynes and a variety of heterounsaturated molecules such as imines, bipy, carbodiimide, organic azides, hydrazine, and azo derivatives.

Experimental and Computational Studies on the Formation of Thorium-Copper Heterobimetallics.

The formation of actinide-transition metal heterobimetallics mediated by a terminal actinide imido complex was comprehensively studied. The reaction of the thorium imido complex [(η5 -C5 Me5 )2 Th=N(mesityl)(DMAP)] (3), prepared from [(η5 -C5 Me5 )2 ThMe2 ] (1) and mesitylNH2 or [(η5 -C5 Me5 )2 Th(NHmesityl)2 ] (2) in the presence of 4-(dimethylamino)pyridine (DMAP), with copper(I) halides gave the first thorium-copper heterobimetallic compounds [(η5 -C5 Me5 )2 Th(X){N(mesityl)Cu(DMAP)}] (X=Cl (4), Br (5), I (6)). Complexes 4-6 feature an unusual geometry with a short Th-Cu distance, which DFT studies attribute to a weak donor-acceptor bond from the Cu+ atom to the electropositive Th4+ atom. They are reactive species, as was shown by their reaction with the dimethyl complex [(η5 -C5 Me5 )2 ThMe2 ] (1). Furthermore, a comparison between Th and early transition metals confirmed that Th4+ exhibits distinctively different reactivity from d-transition metals.

Highly enantioselective Rh-catalyzed asymmetric reductive dearomatization of multi-nitrogen polycyclic pyrazolo[1,5-a]pyrimidines.

A highly enantioselective rhodium-catalyzed reductive dearomatization of 7-substituted pyrazolo[1,5-a]pyrimidines has been realized for the first time by two strategies to afford chiral 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidines with excellent enantioselectivities of up to 98% ee. This method also provides an efficient approach for the synthesis of the powerful BTK inhibitor, zanubrutinib.

Aromatic C-C Bond Cleavage in a Curved π-System of Aminocorannulene.

We report a metal- and oxidant-free aromatic C-C bond cleavage in the curved corannulene skeleton. Reaction of 1-aminocorannulene with hydrazonyl chloride generates an amidrazone intermediate that undergoes facile intramolecular proton migrations and ring annulation to give a 1,2,4-triazole derivative of planar benzo[ghi]fluoranthene, in which the release of strain associated with the curved π-surface and the formation of an aromatic triazole moiety are the driving forces. This report provides new insights into the aromatic C-C bond cleavage.

The His23 and Lys79 pair determines the high catalytic efficiency of the inorganic pyrophosphatase of the haloacid dehalogenase superfamily.

Haloacid dehalogenase (HAD) superfamily members are mainly phosphomonoesterases, while BT2127 from Bacteroides thetaiotaomicron of the HAD superfamily is identified as an inorganic pyrophosphatase. In this study, to explore the roles of the Lys79 and His23 pair in the hydrolysis reaction of inorganic pyrophosphate (PPi) catalyzed by BT2127, a series of models were designed. Calculations were performed by using the density functional theory (DFT) method with the dispersion energy D3-B3LYP. The His23 and Lys79 pair plays a key role in the high catalytic efficiency of BT2127 with PPi. First, the His23 and Lys79 pair prompts Asp13 to easily provide a proton to the leaving group, which remarkably reduces the energy barrier of the phospho-transfer step; then, Lys79 provides a proton to the first leaving phosphate group via His23, produces a more electrically stabilized phosphate (H3PO4), makes this step exothermal, and further promotes the subsequent phospho-enzyme intermediate hydrolysis. The results suggest that the Lys79-His23 pair helps BT2127 reach high catalytic efficiency by strengthening the acid catalysis. Our study provides detailed chemical insights into the evolution of the inorganic pyrophosphatase function of BT2127 from the phosphomonoesterase of the HAD superfamily and the biomimetic enzyme design.

Theoretical investigation of the first-shell mechanism of acetylene hydration catalyzed by a biomimetic tungsten complex.

The reaction mechanism of the hydration of acetylene to acetaldehyde catalyzed by [W(IV)O(mnt)(2)](2-) (where mnt(2-) is 1,2-dicyanoethylenedithiolate) is studied using density functional theory. Both the uncatalyzed and the catalyzed reaction are considered to find out the origin of the catalysis. Three different models are investigated, in which an aquo, a hydroxo, or an oxo coordinates to the tungsten center. A first-shell mechanism is suggested, similarly to recent calculations on tungsten-dependent acetylene hydratase. The acetylene substrate first coordinates to the tungsten center in an η(2) fashion. Then, the tungsten-bound hydroxide activates a water molecule to perform a nucleophilic attack on the acetylene, resulting in the formation of a vinyl anion and a tungsten-bound water molecule. This is followed by proton transfer from the tungsten-bound water molecule to the newly formed vinyl anion intermediate. Tungsten is directly involved in the reaction by binding and activating acetylene and providing electrostatic stabilization to the transition states and intermediates. Three other mechanisms are also considered, but the associated energetic barriers were found to be very high, ruling out those possibilities.

Experimental and computational studies on a three-membered diphosphido thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2].

A three-membered thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2] (4) is readily prepared besides H2 from [η5-1,3-(Me3C)2C5H3]2Th(PH-2,4,6-iPr3C6H2)2 (3) upon heating in toluene solution. Density functional theory (DFT) studies were performed to elucidate the 5f orbital contribution to the bonding within Th-(η2-P-P) revealing more covalent bonds between the [η5-1,3-(Me3C)2C5H3]2Th2+ and [η2-P2(2,4,6-iPr3C6H2)2]2- fragments than those in the related thorium metallacyclopropene. Consequently, distinctively different reactivity patterns emerge, e.g., while 4 reacts with pyridine derivatives such as 4-dimethyaminopyridnie (DMAP) and forms the DMAP adduct [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2](DMAP) (5), it may also act as a [η5-1,3-(Me3C)2C5H3]2Th(ii) synthon when reacted with bipy, Ph2S2 or Ph2Se2. Nevertheless, no reaction of complex 4 with alkynes is observed, but it reacts as a nucleophile towards nitriles and aldehydes resulting in five- or seven-membered metallaheterocycles, respectively. DFT computations provide some additional insights into the experimental observations.