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DFT calculations have been performed to study the relative preference of different unsaturated organic molecules (CO2, PhCHO and styrene) for insertion into different Cu--X (X = B, C, O) bonds, which are competing processes in copper-catalyzed three-component boracarboxylation reactions involving CO2 and B2pin2. In this work, the variations in the insertion barriers and in the relative stability of the insertion products have been systematically analyzed and discussed in-depth. Our DFT calculations also allow us to make a prediction that when both aldehyde and styrene are present with CO2 and B2pin2, styrene will undergo the three-component boracarboxylation reaction rather than the aldehyde. [ABSTRACT FROM AUTHOR]

Clusters of group 14 elements show plenty of similarities with borane clusters. As such, chemists often try to understand their structure and bonding on the basis of Wade’s rules to predict and classify various clusters. Such practice, albeit very common, often faces challenges and difficulties due to significant differences in the bonding abilities between group 13 and 14 atoms, as well as the changes in the ionization energies and radial characteristics of atomic orbitals as the groups are descended. In this chapter, we have extensively discussed the structure and bonding of a wide variety of group 14 clusters, including bare clusters, substituent-decorated clusters, endohedral clusters, transition metal doped clusters, and their combinations. By thoroughly analyzing their electronic structures within the framework of molecular orbital theory, we have summarized their bonding patterns and explored the factors that affect the applicability of Wade’s rules in various group 14 clusters. [ABSTRACT FROM AUTHOR]

Modular bonding picture is a central part of chemical understanding as exemplified by the wide usage of Lewis structure as a chemical language to describe molecular electronic structures. A chemically intuitive bonding picture requires the descriptors to be localized and transferable. Molecular orbitals directly derived from quantum calculations are too delocalized to interpret in this regard, hence many efforts have been devoted to the development of bonding analysis methods. After a brief overview of various bonding analysis methods, this review outlines the framework of principal interacting orbital (PIO) analysis and presents its role in recovering intuitive chemical concepts and producing modular bonding pictures. The PIO analysis identifies the most important fragment orbitals that are involved in fragment interactions and characterizes a one-to-one orbital interaction pattern that underlies a unique set of bonding and anti-bonding orbitals derived from pairwise orbital interactions between two fragments. By making use of the principal component analysis (PCA), PIO analysis can effectively combine complex delocalized interaction patterns involved in numerous molecular orbitals into a handful of localized PIOs to provide easily interpretable results with intimate connection to localized chemical concepts, while maintaining necessary delocalized features when dealing with systems that involve mutlicentered interactions such as cluster compounds and various reactions. Such adaptability guarantees the robustness of PIO analysis with respect to change of substituents and the transferability of obtained PIOs across different systems. [ABSTRACT FROM AUTHOR]

Although chiral allene preparation via formal SN2’ nucleophilic substitutions of enantioenriched propargylic derivatives or metal-catalyzed reactions of racemic propargylic derivatives has attracted considerable attention and found applications in many areas of research, direct use of propargylic alcohols instead of propargylic derivatives for catalytic asymmetric allene synthesis is unknown. Here, we show that a highly enantioselective synthesis of tetrasubstituted allenes from racemic propargylic alcohols has been realized by organocatalysis with good efficiency (up to 96% yield and 97% ee). The intermolecular C–C and C–S bond formation was achieved efficiently with simultaneous stereocontrol over the axial chirality. Furthermore, an adjacent quaternary stereocenter could also be constructed. Mechanistically, the reaction may involve efficient stereocontrol on the propargylic cation by its chiral counter anion or 1,8-conjugate addition of para-quinone methides. In sharp contrast to previous central chirality construction, this process employs quinone methides for axial chirality construction. [ABSTRACT FROM AUTHOR]

Transition metal boryl complexes play an important role as reactive intermediates in many catalytic processes. The reactivities and electronic properties of boryl ligands, in particular their nucleophilic and electrophilic behaviors, are discussed and reviewed in this article. [ABSTRACT FROM AUTHOR]

DFT calculations have been carried out to study the detailed mechanism of Pd-catalyzed intermolecular coupling reactions of 2-silylaryl bromides with alkynes via selective cleavage of C(sp³)-Si bonds. Through our calculations, we found that, starting from the alkenylpalladium intermediate derived from oxidative addition of the substrate C-Br bond followed by alkyne insertion, there are two possible pathways leading to the formation of the benzosilole product. Furthermore, these two pathways were found to be competitive. In this paper, we will present the detailed mechanistic study and analyze the results we have obtained. [ABSTRACT FROM AUTHOR]

Calcium silicate hydrate (C-S-H) is a main product of Portland cement hydration. Although C-S-H is treated as an amorphous phase in macro scale, the atomic-scale structure of C-S-H is considered to be nanocrystalline and shortordered. Various studies have been carried out and many models have been proposed in the past few decades to describe the structure of C-S-H at nano scale. Tobermorite and jennite are considered as two naturally existing crystalline solids sharing similar structures with C-S-H, especially tobermorite. As a result, tobermorite-based models are predominant in the literature. Besides, combination models with both tobermorite and jennite as well as exceptive models have also been developed in the same period. In this paper, the C-S-H models developed in the past decades are reviewed systematically. The reliability of the models is discussed based on the fundamental requirements of the C-S-H structure from consideration of experimental observations and structural chemistry, including charge balance, Ca/Si (C/S) ratio and Qn distribution. Finally, some considerations on the understanding of C-S-H are put forward for possible development of C-S-H structure in the future. [ABSTRACT FROM AUTHOR]

Silver- and copper-catalyzed decarboxylation reactions of aryl carboxylic acids were investigated with the aid of density functional theory calculations. The reaction mechanism starts with a carboxylate complex of silver or copper. Decarboxylation occurs viaejecting CO2from the carboxylate complex followed by protodemetallation with an aryl carboxylic acid molecule to regenerate the starting complex. Our results indicated that the primary factor to affect the overall reaction barriers is the orthosteric destabilization effect on the starting carboxylate complexes for most cases. Certain orthosubstituents that are capable of coordinating with the catalyst metal center without causing significant ring strain stabilize the decarboxylation transition states and reduce the overall reaction barriers. However, the coordination effect is found to be the secondary factor when compared with the orthoeffect. [ABSTRACT FROM AUTHOR]

The electronic structure of so-called ‘xenophilic’ clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn2(thf)4(Fe(CO)4)2is best described as an exchange-coupled MnII2dimer, the closed-shell organometallic [Fe(CO)4]2−fragments acting simply as bridging ligands. The high-spin configuration of the MnIIions leads to single occupation of the Mn–Fe σ* orbitals and therefore substantially weaker metal–metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (Jcalc= −44 cm−1), leading to the measured effective magnetic moment of ∼5 μBat 300 K, considerably lower than the limiting value of 8.37 μBfor two uncoupled S= 5/2 MnIIcentres. [ABSTRACT FROM AUTHOR]

The use of diethynylsilane, diethynyldisilane and diethynyldisiloxane in the synthesis of some linked metal carbonyl clusters is demonstrated. New dimeric η-diyne complexes of cobalt [{Co(CO)}(η-diyne)], ruthenium [{(μ-H)Ru(CO)}(μ-η,η-diyne)] and osmium [{(μ-CO)Os(CO)}(μ-η-diyne)] {diyne=HC≡CSi(CH)C≡CH, HC≡CSi(CH)–Si(CH)C≡CH, HC≡CSi(CH)–O–Si(CH)C≡CH or HC≡CSi(Ph)C≡CH} have been prepared in good yields from the reaction of [Co(CO)], [Ru(CO)] and [Os(CO)(NCMe)] with half an equivalent of the appropriate diyne ligand, respectively. All the twelve compounds have been characterized by IR and H NMR spectroscopies and mass spectrometry. The molecular structures of eight of them have been determined by X-ray crystallography. Structurally, each of the tetracobalt species displays two CoC cores adopting the pseudo-tetrahedral geometry with the alkyne bond lying essentially perpendicular to the Co–Co vector. For the group 8 ruthenium and osmium analogues, the hexanuclear carbonyl clusters consist of two trinuclear metal cores with the μ-η,η bonding mode for the acetylene groups in the former case and μ-(η-||) bonding mode in the latter one. Density functional theory was employed to study the electronic structures of these molecules in terms of the nature of the silyl or disilyl unit and its substituents. [ABSTRACT FROM AUTHOR]

In this feature article, we discuss selected recent aspects of metal boryl (M-BR2) chemistry pertaining, in particular, to the role of late and post-transition metal boryl complexes in various catalytic processes. The exceptionally strong σ-donor properties of boryl ligands and their related nucleophilic behaviour are highlighted. [ABSTRACT FROM AUTHOR]

By fusing an electron-deficient ring system with the phenyl ring of a 2-phenylpyridine (ppy)-type ligand, a new and synthetically versatile strategy for the phosphorescence color tuning of cyclometalated iridium(III) and platinum(II) metallophosphors has been established. Two robust red electrophosphors with enhanced electron-injection/electron-transporting features were prepared by using an electron-trapping fluoren-9-one chromophore in the ligand design. The thermal, photophysical, redox and electrophosphorescent properties of these complexes are reported. These exciting results can be attributed to a switch of the metal-to-ligand charge-transfer (MLCT) character of the transition from the pyridyl groups in the traditional IrIIIor PtIIppy-type complexes to the electron-deficient ring core, and the spectral assignments corroborate well with the electrochemical data as well as the time-dependent density functional theory (TD-DFT) calculations. The electron-withdrawing character of the fused ring results in much more stable MLCT states, inducing a substantial red-shift of the triplet emission energy from yellow to red for the IrIIIcomplex and even green to red for the PtIIcounterpart. Electrophosphorescent organic light-emitting devices (OLEDs) doped with these red emitters fabricated by using vacuum evaporation technique have been realized with reasonable performance. [ABSTRACT FROM AUTHOR]

The relative stability of the trans and cis isomers in the square planar palladium(II) complexes Pd(I)(PPh3)(η3-XCHC(Ph)CHR) (X = H, Me, CMe3, CO2Me, P(O)(OMe)2, and SO2H; R = H, Me) was investigated with the aid of the B3LYP density functional theory calculations. We examined how the substituents X, with different electronic properties, of the η3-allyl ligands affect the relative stability of the trans and cis isomers. Through the investigation, we were able to explain the trans/cis relative stability derived from the experimentally measured trans/cis isomer ratios in the palladium(II) complexes. [ABSTRACT FROM AUTHOR]

We present herein a high yield, highly selective catalytic synthesis of vinylboronate esters (VBEs), including 1,1-disubstituted VBEs, from alkenes without significant hydrogenation or hydroboration, using the simple catalyst precursor, trans-[RhCl(CO)(PPh3)2] (1), and the diboron reagents B2pin2 (2a, pin = pinacolato = OCMe2CMe2O) or B2neop2 (2b, neop = neopentylglycolato = OCH2CMe2CH2O), or the monoboron reagent HBpin, all of which are commercially available. The reactions were conducted at 80 °C using conventional heating, or in a microwave reactor at 150 °C. [ABSTRACT FROM AUTHOR]

Extended Hckel Theory (EHT) and Density Functional Theory (DFT) calculations on hexacapped cubic aluminum clusters of the type [(AlH)8(μ4-CH)6−n (μ4-H) n ]+/−q (n ≤ 6) indicate that their favored number of skeletal electron pairs (SEP), 12 SEPs for n ≥ 3, 14 SEPs for n = 2, 16 SEPs for n = 1 and 18 SEPs for n = 0, depends on the relative number of the two types of capping ligands: one-orbital ligands such as H and conical three-orbital CH units. Although only 16- and 18-SEP species have been isolated so far, DFT calculations indicate that 14-SEP clusters of the type [(AlR′)8(μ4-CR)4(μ4-X)2]2+ (X = one-orbital ligand) should be synthesized. Computed 12-SEP models were not found to be energy minima, but this should not preclude the possibility for stabilizing such species, for example with bulky substituents. Changing the CR capping ligands into AlR units in the above series is expected to limit their electron counts to 12 SEPs. The incorporation of a main-group atom in the middle of the cube does not change the favored cluster electron count. However, calculations indicate that only 12-SEP species are likely to be synthesized. [ABSTRACT FROM AUTHOR]

Abstract Thermal reaction of [Ru2(CO)6(µ-PFu2)(µ-?1,?2-Fu)] (Fu=2-furyl) with (9-anthracenyl)diphenylphosphine (AnPPh2) produces a novel diruthenium complex [Ru2(CO)5(µ-PFu2)(µ-?1,?1,?2-C14H8PPh2)] (1) in good yield whereas the corresponding reaction between [(µ-H)4Ru4(CO)12] and AnPPh2 gives [HRu(CO)3(PPh2C14H8)][(µ-H)4Ru4(CO)11(AnPPh2)] (2). Both compounds 1 and 2 were fully characterized by spectroscopic methods and their X-ray crystal structures were determined. For 1, initial coordination of the PPh2 functionality at the Ru atom is accompanied by cyclometalation of the anthracenyl ring to form a Ru–C s bond together with concomitant formation of a p bond to the adjacent Ru center and loss of the furyl ligand. The formation of 2 involves the cleavage of two Ru–Ru bonds, and the making of a Ru–P bond, followed by orthometalation of the anthracenyl ring. The optical absorption and emission spectra of 1 were recorded and the results were correlated to the DFT calculations. [ABSTRACT FROM AUTHOR]

The group theoretical consequences of the Tensor Surface Harmonic Theory have been developed for [ML], [ML] and [ML] clusters where either the xz and yz or x− y and xy components to L and L do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the interconversion of conformers of these clusters are described. [ABSTRACT FROM AUTHOR]

High-precision phase detection is critical to the timing and synchronization system for particle accelerators. A live calibration signal is introduced to femtosecond-level phase detection in order to measure the relative phase jitter between a reference wave and a radio frequency (RF) signal, and compensate for the cable electrical length drift due to the thermal variation effect. Non-IQ sampling and 2-stage cascaded integrator-comb filters are integrated into the field-programmable gate array-based digital signal processing to reduce spectrum aliasing and suppress noise. Fine adjustment of hardware components has been made to ensure the isolation between different signals and the linearity over the full-range power level. We have achieved a 6.3 fs root mean square timing jitter for a 2856 MHz RF signal in a single channel, compared to the theoretical limit of 5.1 fs for the current hardware component. [ABSTRACT FROM AUTHOR]