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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‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (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‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]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‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (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. [ABSTRACT FROM AUTHOR]

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‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (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‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]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‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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*)2UR [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‐O2C] 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

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. [ABSTRACT FROM AUTHOR]

We reported a density functional theory study on the complexation of six hydrated actinyl cations, AnO2(H2O)52+/+ (aq) (An = U/Np/Pu), with three expanded porphyrins, amethyrin (H4L1), oxasapphyrin (H2L2), and grandephyrin (H3L3). The geometries have been fully optimized and analyzed, and the electronic structures, the binding free energies, and the NMR properties were calculated. Natural population analysis and Quantum Theory of Atoms in Molecules (QTAIM) topology analysis techniques were applied to understand the interaction modes between two entities of each complex. The calculations show that for the same ligand, PuO22+ and NpO22+ display stronger binding affinity than UO22+, UO2+, NpO2+, and PuO2+, and among the three ligands tested, L22− fits better with the actinyl cations than L33− and H2L12−. The redox process was observed in the complexation of PuO22+ and NpO22+ with specific ligands, which agrees with the experimental results. In the characterization of the nature of the coordination bonding interactions, QTAIM gives a consistent description with the natural population analysis method and shows that the interaction between An and the electron donor atoms in the first coordination shell has a strong ionic feature, while the interaction between An and Oyl atoms of the actinyls in the complexes remains covalent. This work complements the earlier experimental studies by providing a molecular level of understanding on the interaction between actinyls and expanded porphyrins, and is expected to contribute to the communities of the chemistry of actinides and expanded porphyrins. [ABSTRACT FROM AUTHOR]

Themechanisms of CO2insertion into the U–Nbond of a silylamido NHC (N-heterocyclic carbene) U(III) complex wereinvestigated theoretically. An earlier reported mechanism involvinga reversible NHC carboxylation was found to be energetically too demanding,and a novel four-step mechanism featuring a direct CO2insertioninto the U–N bond is proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The thorium bipyridyl metallocene (Cp 3 t Bu ) 2 Th(bipy) ( 1 ; Cp 3 t Bu = η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ) shows a rich reactivity toward a series of small molecules. For example, complex 1 may act as a synthon for the (Cp 3 t Bu ) 2 Th(II) fragment as illustrated by its reactivity toward to CuI, hydrazine derivative (PhNH) 2 , Ph 2 E 2 ( E = S, Se), elemental sulfur (S 8 ) and selenium (Se), organic azides, CS 2 , and isothiocyanates. Moreover, in the presence of polar multiple bonds, such as those in ketones Ph 2 CO and (CH 2 ) 5 CO, aldehydes p -MePhCHO and p -ClPhCHO, seleno-ketone ( p -MeOPh) 2 CSe, nitriles PhCN, Ph 2 CHCN, C 6 H 11 CN, and p -(NC) 2 Ph, and benzoyl cyanide PhCOCN, C-C coupling occurs to furnish (Cp 3 t Bu ) 2 Th[(bipy)(Ph 2 CO)] ( 10 ), (Cp 3 t Bu ) 2 Th[(bipy)((CH 2 ) 5 CO)] ( 11 ), (Cp 3 t Bu ) 2 Th[(bipy)( p -MePhCHO)] ( 12 ), (Cp 3 t Bu ) 2 Th[(bipy)( p -ClPhCHO)] ( 13 ), (Cp 3 t Bu ) 2 Th[(bipy){( p -MeOPh) 2 CSe}] ( 14 ), (Cp 3 t Bu ) 2 Th[(bipy)(PhCN)] ( 16 ), (Cp 3 t Bu ) 2 Th[(bipy)(Ph 2 CHCN)] ( 17 ), (Cp 3 t Bu ) 2 Th[(bipy)(C 6 H 11 CN)] ( 18 ), [(Cp 3 t Bu ) 2 Th] 2 {μ-(bipy)[ p -Ph(CN) 2 ](bipy)} ( 20 ), and (Cp 3 t Bu ) 2 Th{(bipy)[PhC(CN)O]} ( 21 ), respectively. Nevertheless, ketazine (PhCH═N) 2 or benzyl nitrile PhCH 2 CN forms the dimeric complexes [(Cp 3 t Bu )Th] 2 [μ-NC(Ph)(bipy)] 2 ( 15 ) and (Cp 3 t Bu ) 2 Th[(bipy){C(═CHPh)NH}] ( 19 ), respectively. In contrast, C-N bond cleavage and C-C coupling processes occur upon addition of isonitriles Me 3 CNC and C 6 H 11 NC to 1 to yield the thorium isocyanido amido complexes (Cp 3 t Bu ) 2 Th[4-(Me 3 C)bipy](NC) ( 22 ) and (Cp 3 t Bu ) 2 Th[4-(C 6 H 11 )bipy](NC) ( 23 ), respectively. Furthermore, a single-electron transfer (SET) process ensues when 1 equiv of CuI is added to 1 to yield the Th(VI) bipyridyl iodide complex (Cp 3 t Bu ) 2 Th(I)(bipy) ( 3 ).

Halide exchange of (Cp 3tms ) 2 ThCl 2 ( 1 ; Cp 3tms = η 5 -1,2,4-(Me 3 Si) 3 C 5 H 2 ) with Me 3 SiI furnishes (Cp 3tms ) 2 ThI 2 ( 2 ), which is then reduced with potassium graphite (KC 8 ) in the presence of 2,2'-bipyridine to give the thorium bipyridyl metallocene (Cp 3tms ) 2 Th(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 (Cp 3tms ) 2 Th(II) fragment when exposed to CuI, Ph 2 S 2 , organic azides, and CS 2 . Moreover, upon the addition of thiobenzophenone Ph 2 CS, p -methylbenzaldehyde ( p -MeC 6 H 4 )CHO, benzophenone Ph 2 CO, amidate PhCONH( p -tolyl), seleno-ketone ( p , p '-dimethoxy), selenobenzophenone ( p -MeOPh) 2 CSe, di( p -tolyl)methanimine ( p -tolyl) 2 C═NH, 1,2-di(benzylidene)hydrazine (PhCH═N) 2 , and nitriles PhCN, PhCH 2 CN, and Ph 2 CHCN C-C coupling results to give (Cp 3tms ) 2 Th[(bipy)(Ph 2 CS)] ( 8 ), (Cp 3tms ) 2 Th[(bipy)( p -MePhCHO)] ( 9 ), (Cp 3tms ) 2 Th[(bipy)(Ph 2 CO)] ( 10 ), (Cp 3tms ) 2 Th[(bipy){( p -tolylNH)(Ph)CO}] ( 11 ), (Cp 3tms ) 2 Th[(bipy){( p -MeOPh) 2 CSe}] ( 12 ), (Cp 3tms ) 2 Th[(bipy){( p -tolyl) 2 CNH}] ( 13 ), (Cp 3tms ) 2 Th[(bipy)(PhCHNN═CHPh)] ( 14 ), (Cp 3tms ) 2 Th[(bipy)(PhCN)] ( 16 ), (Cp 3tms ) 2 Th[(bipy)(PhCH 2 CN)] ( 17 ), and (Cp 3tms ) 2 Th[(bipy)(Ph 2 CHCN)] ( 18 ), respectively. However, when thiazole is added to 3 , the dimeric sulfido complex [(Cp 3tms ) 2 Th] 2 [μ-(bipy)CH 2 NCHCHS] 2 ( 15 ) can be isolated. Moreover, the addition of isonitriles such as Me 3 CNC and PhCH 2 NC to 3 results in C-N bond cleavage and C-C coupling processes to form the thorium isocyanido amido complexes (Cp 3tms ) 2 Th[4-(Me 3 C)bipy](NC) ( 19 ) and (Cp 3tms ) 2 Th[4-(PhCH 2 )bipy](NC) ( 20 ), respectively. Nevertheless, upon exposure of 3 to (trimethylsilyl)diazomethane Me 3 SiCHN 2 , the bis-amido complex (Cp 3tms ) 2 Th[5,6-(Me 3 SiCH)bipy] ( 21 ), concomitant with N 2 release, is isolated.

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.

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U=P-2,4,6-tBu 3 C 6 H 2 (1) yields the stable uranium metallacyclopropene, [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U[η 2 -C 2 Ph 2 ] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η 2 -C=C) moiety increases significantly compared to the related Th IV compound [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Th[η 2 -C 2 Ph 2 ], which also results in more covalent bonds between the [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U 2+ and [η 2 -C 2 Ph 2 ] 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 [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 U II when reacted with Ph 2 E 2 (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., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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'''=η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ) with Mes*PHK (Mes*=2,4,6-(Me 3 C) 3 C 6 H 2 ) 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., (© 2020 The Authors. Published by Wiley-VCH GmbH.)