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Following our previous surveys on group 14 divalents, we report new series of N‐heterocyclic germylenes (NHGe) and their analogs that are regarded as cyclic (1C–10C) and linear (1L–10L) forms. Their thermodynamic and structural parameters are compared and contrasted, at the B3LYP/6‐311++G** level of theory. The complexation of these NHGe with Cu metal is investigated. Various analyses such as the atoms in molecules (AIM), natural bond orbital (NBO), non‐covalent interaction (NCI), and ultraviolet‐visible (UV‐Vis) are performed to determine the strength of our germylenes to act as ligands. The results indicate that there are strong interactions between the metal‐ligand bonds with a high contribution of π‐back donation. Every linear germylene demonstrates a higher ability of σ‐donation and π‐acceptation. Our scrutinized germylenes turn out as remarkable ligands to the Cu that can be applied in several types of catalysis. [ABSTRACT FROM AUTHOR]

A series of N6-substituted adenine–ferrocene conjugates was prepared and the reaction mechanism underlying the synthesis was explored. The SN2-like reaction between ferrocenoyl chloride and adenine anions is a regioselective process in which the product ratio (N7/N9-ferrocenoyl isomers) is governed by the steric property of the substituent at the N6-position. Steric effects were evaluated by using Charton (empirical) and Sterimol (computational) parameters. The bulky substituents may shield the proximal N7 region of space, which prevents the approach of an electrophile towards the N7 atom. As a consequence, the formation of N7-isomer is a kinetically less feasible process, i.e., the corresponding transition state structure increases in relative energy (compared to the formation of the N9-isomer). In cases where the steric hindrance is negligible, the electronic effect of the N6-substituent is prevailing. That was supported by calculations of Fukui functions and molecular orbital coefficients. Both descriptors indicated that the N7 atom was more nucleophilic than its N9-counterpart in all adenine anion derivatives. We demonstrated that selected substituents may shift the acylation of purines from a regioselective to a regiospecific mode.

To reach new triplet ground state (T) silylenes, we compare and contrast acyclic silylenes with group 14 substituents (:Si(XH3)2 (X = C, Si, Ge, Sn, and Pb; 1C, 2Si, 3Ge, 4Sn, and 5Pb, respectively), at the B3LYP/6-311++G** level of theory. The results show that in going from 1C to 5Pb, the singlet-triplet energy gap (ΔES-T) and HOMO-LUMO energy gap (ΔEH-L) decrease while the nucleophilicity (N) increases. Structure 5Pb demonstrates the equal possibility of singlet and triplet ground states. Replacing one and two hydrogens with alkaline and alkaline earth metals leads to generate a new series of T silylenes with high stabilities. [ABSTRACT FROM AUTHOR]

DFT calculations in combination with appropriate isodesmic reactions are employed to assess topological effects of nitrogens on thermodynamic parameters of novel mono-, di-, tri-, tetra-, and pentaaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylenes (1–20). Despite the enormous steric strain involved in their cubic structures, all our scrutinized singlet and triplet silylenes (1s-20s vs. 1t-20t, respectively) appear as minima on their energy surfaces, for showing singlet ground states. The highest stability (ΔEs−t) is achieved by 1,3,5-triaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylene (11), where all the three nitrogens are bonded to the central boron atom. All of our silylenes show the same trend for their calculated ΔΕs−t and band gap (ΔΕHOMO−LUMO). Isodesmic reactions are employed to compare and contrast nucleophilicity (N), electrophilicity (ω), and heat of hydrogenation (ΔEH) for our 40 silylenes (1s-20s vs. 1t-20t). In fact, we introduce a novel generation of tridimensional silylenes which have the intrinsic potential of expanding the existing boundaries of semiconductors, cumulated multi-dentate ligands, etc.. [ABSTRACT FROM AUTHOR]

We aim to develop novel four‐membered cyclosilylenes that contain one (1 and 2), two (3), three (4), and four (5) numbers of Si atoms at the M06/6–311 + G*, B3LYP/aug‐cc‐PVTZ, and MP2/3–21G levels of theory. These structures show high stability and turn out as minima on their energy surfaces for showing no imaginary frequency. Structural and thermodynamic parameters, including bond length, divalent bond angle, singlet‐triplet energy gap (ΔES‐T), highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap (ΔEH‐L), proton affinity (PA), complexation energy (ΔECom) with CO molecule, nucleophilicity (N), chemical potential (μ), and natural charges, are assessed. The final order of singlet stability appears in the order 1 > 2 > 3 > 4 > 5 at three levels of theory. [ABSTRACT FROM AUTHOR]

A theoretical study on the structure and nature of the Mn-X bond in tetraphenylporphyrin and its manganoporphyrines containing halogen as an axial ligand [Mn(TPP)X] {X=F, Cl and Br} was carried through density functional B3LYP/6-311G and M06/def2TZVP methods. Comparison of length and angle of bonds in the optimized geometry of [Mn(TPP)Cl] to its X-ray single crystal structure revealed that M06/def2TZVP basis set resulted in more realistic outcomes. Furthermore, the Mn–X bond was analyzed using AIM and NBO to obtain its nature and order in the presence of different halogen axial ligands. The results showed that the Mn-X bond has a σ nature with no π-back donation from Mn to X ligand and the bond order decreased from F to Br. In addition, the effect of axial ligands on the global and local chemical reactivity descriptors of manganoporphyrins has been discussed. [ABSTRACT FROM AUTHOR]

Nine boat-shaped cyclonona-3,5,7-trienylidenes are compared and contrasted with respect to their multiplicity, nucleophilicity, electrophilicity, band gap (Δ EHOMO − LUMO), Natural bond orbital (NBO) atomic charge, force constant, as well as the aptitude for , and through proper isodesmic reactions at B3LYP/AUG-cc-pVTZ and B3LYP/6-311++G**//B3LYP/6-31+G* levels of theory. The nine cyclic carbenes include unsubstituted (1CH2) plus eight α-cyclopropylcyclonona-3,5,7-trienylidenes, which are substituted with ά-SiMe2, ά-NMe, ά-PMe, ά-O, ά-S, ά-CH2, ά-cyclopropyl, and ά-CMe2 (2SiMe2, 2NMe, 2PMe, 2O, 2S, 2CH2, 2cyclopropyl, and 2CMe2, respectively). The latter eight species enjoy the stabilizing interaction of the occupied Walsh orbital of cyclopropyl with the vacant pπ orbital of the carbene center ( Walshcyclopropyl → pπ carbene). Among them, the singlet closed shell 2NMe appears the most promising for exhibiting the highest relative singlet-triplet energy gap (Δ Es − t = 27.1 kcal mol−1). In contrast, the least stable derivative is triplet 2SiMe2, which exhibits the lowest relative Δ Es − t of −5.5 kcal mol−1. The overall trend of Δ Es-t is 2NMe > 2PMe > 2S > 2O > 2cyclopropyl > 2CMe2 > 2CH2 > 1CH2 > 2SiMe2. With one negative force constant, the unsubstituted 1CH2 turns out to be a transition state, whereas the rest emerge as minima. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

High-level Density Functional Theory calculations, coupled with appropriate isodesmic reaction, are employed to investigate the effects of α-carbon, ammonium, phosphorus, and sulfur ylides, , and unsaturation on the stability, multiplicity, and reactivity of novel singlet (S) and triplet (T) carbenes. Among them the highly π-donating α-ammonium ylide is found to exert the highest stabilizing effect on the carbenic center. α-Ammonium ylides resist and . They show wider singlet-triplet energy gap (Δ ΕS-T), broader band gap (Δ ΕHOMO-LUMO), and higher nucleophilicity compared to the reported stable N-heterocyclic carbenes. Aromatic cyclic unsaturated ammonium, phosphorus, and sulfur ylide carbenes appear more stable than their saturated cyclic analogs which are in turn more viable than their acyclic counterparts. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Replacement of α-methylenes with BH, AlH, CMe2, SiH2, NH, NMe, N tButyl, NPh, PH, O, and S in non-planar cyclonona-3,5,7-trienylidene (CH2) alters its status from an unstable transition state to rather stable minima, at B3LYP/6-311++G**//B3LYP/6-31 + G* levels of theory. All species appear with singlet closed shell (S cs) global minima, except for SiH2 and CH2 which exhibit triplet electronic ground states. The order of stability based on singlet-triplet energy gap (Δ Es-t / kcalmol−1) is: CMe2 (45.8) > NH (35.8) > NMe (32.3) > O (31.5) > N tButyl (27.7) ≥ NPh (27.5) ≥ BH (27.4) > S (21.9) > PH (17.0) > CH2 (−4.4) > SiH2 (−12.5). In contrast to many reports on N-heterocyclic carbenes, here alkyl groups appear to exert a higher stabilizing effect than heteroatoms, making CMe2 the most stable. In addition bulky NMe, N tButyl, and NPh appear more than their synthesized imidazol-2-ylidene congeners. Excluding SiH2, isodesmic reactions reveal that all substituents stabilize singlet state considerably more than the corresponding triplet. Finally, this work is hoped to pave the path for future matrix isolations and IR studies of these rather stable cyclic non-planar carbenes. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Following the quest for stable silylenes, we have found high thermodynamic and kinetic viabilities for a series of novel cyclic alkylaminosilylenes [CAASs: including 1N –4N )] over their corresponding cyclic alkylphosphinosilylenes (CAPSs: 1P –4P , respectively), at ab initio and DFT levels, coupled with appropriate isodesmic reactions. Among silylenes scrutinized, 4N immerged the most promising for its higher singlet–triplet energy difference (ΔE S–T), wider band gap (ΔE HOMO–LUMO), higher heat of hydrogenation (ΔE H), significant resistance to dimerization and resistance to rearrangement to its full valence octet isomer, etc. Unsaturation destabilized 2N , 3N , and 3P through cross conjugation. [Copyright &y& Elsevier]

Abstract: The global and local quantum chemical reactivity descriptors of 34 pyridine ligands are calculated using the DFT/B3LYP/6-311++G** method. These reactivity descriptors are used to describe the HSAB interaction of the studied pyridine ligands as N-nucleophile with the hard H+, the soft Cu+ and the border line Cu2+ Lewis acids as electrophile. The calculations predicted higher electron density on the ring N-atom and higher E HOMO values in case of electron releasing substituents compared to electron attracting groups which indicate harder N-nucleophiles in case of the former compared to the latter. It is found that, the global chemical hardness (η) does not offer acceptable prediction for the ligand hardness. On the other hand, good correlations are obtained between the calculated nucleophilicity index (N) with the Mayr’s experimental nucleophilicity values and the inverse of electrophilicity index (1/ω). The calculated Fukui function values at the N-site are small in case of electron releasing substituents indicating a preferred N-site for hard reaction. In contrast, large values in case of electron attracting groups indicate a preferred N-site for soft reaction. The Cu(I) affinities of the studied ligands decrease with increase their experimental ionization potentials in agreement with the HSAB principle. Similarly, the proton affinities decrease with increase the ligand ionization potentials, a contradiction to the HSAB principle as H+ is a hard acid and Cu+ is a soft acid. These results are explained in terms of electrostatic interaction which is the dominant processes in gas phase ion–molecule reactions. [Copyright &y& Elsevier]

Abstract: Nucleophilicty of 32 nitrogen nucleophiles belonging to the families of amine, amide, carbamate, amidine, and pyridine have been calculated at the DFT/B3LYP/6-31G (d, p) level of theory using the gas-phase ionization potential based nucleophilicity index N. The calculated gas phase nucleophilicities of the pyridine series correlate well with Mayr’s nucleophilicity values calculated on the basis of experimental quantities and the inverse of electrophilicity index. Local nucleophilicity trend and site selectivity have been analyzed using local nucleophilicity index Nk and the philicity index . In most cases both the two local indices reproduced the experimentally observed trend. [Copyright &y& Elsevier]

The effects of phosphorous atom on the stability, multiplicity, and reactivity of six-member cyclic silylenes are investigated at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G* and MP2/6-311++G**//B3LYP/6-31+G* coupled with appropriate isodesmic reactions. From a thermodynamic point of view, 1 H-2-silaphosphinine-2-ylidene ( 1a) and 1 H-4-silaphosphinine-4-ylidene ( 2a) are relatively the most stable with singlet-triplet energy gaps (Δ ES-T) of 37.0 and 28.1 kcal/mol, respectively. The calculated energy barrier for the 1,2- H shift of 1a to the corresponding 2-silapyridine ( 1) is 26.5 kcal/mol, which is lower than the 28.8 kcal/mol required for the 1,4- H shift of 2a to the corresponding 4-silapyridine ( 2). In contrast to the previous reports, isodesmic reactions indicate that π-donor/σ-donor phosphorous destabilizes the singlet while stabilizes the triplet state. Both 1a and 2a silylenes appear invulnerable to the head-to-head as well as the head-to-tail dimerization, inviting experimental explorations. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: 1-(X)-3,3-dimethyl-2-cyclohexanylidenes, where X=amino, oxy, phosphino, and thio, are compared and contrasted to probe the effect of monoheteroatom substitution on the stability, multiplicity and reactivity of six-membered saturated and unsaturated cyclic carbenes. The stabilizing effects of substituents are discussed through geometrical parameters, and AIM analysis. The strong π-donor/σ-acceptor amino group exerts singlet–triplet energy separation (ΔE S–T) of 38.4kcal/mol while more electronegative oxy group induces a ΔE S–T of 23.0kcal/mol. Aminoalkylcarbenes rebuff dimerization while oxyalkylcarbenes show a high dimerizing affinity. The reactivity of species is discussed in terms of nucleophilicity and electrophilicity indices as well as proton affinities. It seems that our six-membered carbenes are more nucleophilic than common five-membered N-heterocyclic carbenes. [ABSTRACT FROM AUTHOR]

Abstract: Conceptual density functional theory based reactivity descriptors are used to study nucleophilic reactivity of silyl enol ethers and ketene silyl acetals having substituents of both electron releasing and electron withdrawing nature at various key positions of the molecules. While intramolecular reactivity towards electrophilic attack is studied on the basis of local softness () and local nucleophilicity index (Nk ), intermolecular reactivity is assessed using group softness () and group nucleophilicity (Ng ). Ionization potential, inner sphere reorganization energy and structural changes associated with single electron-transfer oxidation for the selected trimethylsilyl enolates have been evaluated. Role of β-methyl substituents are found to be crucial for both nucleophilic reactivity and single electron-transfer oxidation of these systems. [Copyright &y& Elsevier]

Abstract: Three novel germanimines, 2-, 3-, and 4-germapyridines (1, 2, and 3, respectively) along with their isomeric germylenes, are compared and contrasted at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G∗ level of theory. From a thermodynamic viewpoint, two germylenes out of a total of eight singlet minima, 1H-2-germapyridine-2-ylidene (1a) and 1H-4-germapyridine-4-ylidene (3a), are found 29.2 and 15.4kcal/mol more stable than their corresponding aromatic germapyridine isomers, respectively. Indeed, 1a is the global minimum on the potential energy surface of cyclic C4NGeH5 with a singlet–triplet energy gap larger than that of Herrmann’s germylene, i.e. 57.4 vs. 49.7kcal/mol. From a kinetic viewpoint, the calculated energy barrier for 1,2-H shift of 1a to 1 is 70.8kcal/mol compared to more prohibitive 92.5kcal/mol for 1,4-H shift of 3a to 3. No Ge bonded minimum structure is found as dimer for 1a. The doubly bonded dimer of 3a is 11.2kcal/mol less stable than its two separate monomers. This study signifies the thermodynamic and kinetic stabilities of divalent 1a and 3a hoping to prompt the experimental attentions toward them. [Copyright &y& Elsevier]

Abstract: Protonation of (PNP)RuN, where PNP is (tBu2PCH2SiMe2)2N, with HCl occurs at the amide nitrogen, with coordination of chloride to RuIV, while triflic acid protonates the same nitrogen, but has triflate anion hydrogen-bonded to the proton on the PNP amide nitrogen, not triflate coordinated to the metal. Methyl triflate however alkylates the nitride nitrogen, to give a C2v symmetric product. DFT calculations show that the thermodyamic preference is for proton on amide nitrogen while alkyl favors nitride alkylation, even without the need for a hydrogen bond to reverse the H vs. alkyl preference. Alkylation at the amide nitrogen leads to nearly complete loss of the PN(R)P Ru/N bond in this unobserved isomer. These preferences among nucleophilic sites on (PNP)RuN are rationalized based on the frontier orbitals of this molecule. [Copyright &y& Elsevier]

Abstract: This work extends recent developments relating simple models of electrophilicity index to the experimental Mayr’s electrophilicity parameter [E. Chamorro, M. Duque-Noreña, P. Pérez, J. Mol. Struct. (THEOCHEM), in press]. We further explore here the usefulness of reactivity models based on density functional theory (DFT) to the study of nucleophilicity for organic compounds. The results for a series of primary and secondary amine and diaryl carbenium ions selected as donor and acceptor species, respectively, indicates that the simplified models are linearly related, within good agreements, to the experimental Mayr’s nucleophilicity parameters, within the validity of the Mayr–Patz free energy equation, log k = s(N + E). These results contribute to further validate theoretical models for both electrophilicity and nucleophilicity in the establishment of general and independent scales of reactivity. [Copyright &y& Elsevier]

Abstract: Four different theoretical models of electrophilicity and nucleophilicity has been discussed in the light of experimental available evidence for a series of 20 benzhydrylium ions taken as reference electrophilic systems and 16 primary and secondary amines as nucleophilic systems. It is shown that the theoretical scales are linearly related to the well-known experimental ones based on the electrophilicity (E) and nucleophilicity (N and ) parameters derived by Mayr from the rate constants k 20 °C associated to general electrophile–nucleophile combinations, log k 20 °C = s(N + E). [Copyright &y& Elsevier]

• Every Hammick singlet carbene exhibits more thermodynamic stability, and lower Δ Ε HOMO-LUMO than its corresponding triplet state. We investigated the structure, stability and chemical properties of novel singlet (s) and triplet (t) Hammick carbenes with different fused aromatic rings, at (U)B3LYP/6‐311+G*, (U)M06-2X/6‐311+G*, (U)B3LYP/AUG-cc-pVTZ and (U)M06-2X/AUG-cc-pVTZ levels of theory. It is observed that: (1) All singlet and triplet structures appear as minima on their energy surfaces and each singlet carbene displays more thermodynamic stability than its corresponding triplet state; (2) Regarding to the relationship among carbenic center and substituted heteroatom, the order of thermodynamic stability based on singlet-triplet energy differences (Δ Ε s-t) for fused rings is ortho -pyrrole > furan > thiophene > phosphole in a "W" arrangement; (3) The highest kinetic stability based on band gap (Δ Ε HOMO-LUMO) is demonstrated by substituted ortho -pyrrole carbene in a "W" arrangement; (4) Regardless of how orchestrated, the order of stabilization for fused rings is pyrrole > furan > thiophene > phosphole; (5) The ortho -phosphole ring in a "W" arrangement destabilizes carbene more than benzene ring. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Assuming aromaticity (cyclic continuous conjugation, planarity, and obeying the Hückel 4n + 2 rule), nucleophilic (N), and electrophilic (ω) characters are anticipated to alternate for σ2 and π2 singlet 3‐, 5‐, 7, and 9‐membered silylenes, 1sσ2 (N?), 2sπ2 (ω?), 3sσ2 (N?), and 4sπ2 (ω?), respectively. Our calculations show silacyclopropenylidene (1sσ2) and silacyclopenta‐2,4‐dienylidene (2sπ2) as N and ω, respectively, for exhibiting all the above criteria, at B3LYP/6‐311++G**, B3LYP/6‐311++G(2df,2p), and M06/6‐311++G** levels of theory. Silacyclohepta‐2,4,6‐trienylidene (3sσ2) meets our prediction of being N, despite deviating from planarity. Contrary to our expectation, silacyclonona‐2,4,6,8‐tetraenylidene (4sπ2) not only does not turn out to be ω but also because of its intrinsic angle strain and boat‐like structure, turns out as the most N among singlet silylenes. In all cases, singlet silylenes appear as ground states, exhibiting more stability than their corresponding triplet states. In contrast to our previous report on the 3‐, 5‐, 7‐, and 9‐membered carbenes (Kassaee, et al, Tetrahedron, 1985), all the above singlet and triplet silylenes appear as minima on their energy surfaces. Besides, no allenic isomer is found as a minimum in the silylene series, and finally, 2sπ2 appears planar while its carbenic analog is nonplanar. Nucleophilicity for singlets increases as a function of the ring size 4s > 3s > 2s > 1s, and it decreases as the aromaticity increases. Our triplet silylenes show higher N than their corresponding singlet structures. [ABSTRACT FROM AUTHOR]