Diego M. Andrada

Energy decomposition analysis

The energy decomposition analysis (EDA) is a powerful method for a quantitative interpretation of chemical bonds in terms of three major expressions. The instantaneous interaction energy ΔEint between two fragments A and B in a molecule A–B is partitioned in three terms, namely, (1) the quasiclassical electrostatic interaction ΔEelstat between the fragments, (2) the repulsive exchange (Pauli) interaction ΔEPauli between electrons of the two fragments having the same spin, and (3) the orbital (covalent) interaction ΔEorb, which comes from the orbital relaxation and the orbital mixing between the fragments. The latter term can be decomposed into contributions of orbitals with different symmetry, which makes it possible to distinguish between σ, π, and δ bonding. After a short introduction into the theoretical background of the EDA, we present illustrative examples of main group and transition metal chemistry. The results show that the EDA terms can be interpreted in a chemically meaningful way, thus providing a bridge between quantum chemical calculations and heuristic bonding models of traditional chemistry.

Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl(amino) carbene (cAAC:)-stabilized acyclic germylones (Me2-cAAC:)2Ge (1) and (Cy2-cAAC:)2Ge (2) were prepared utilizing a one-pot synthesis of GeCl2(dioxane), cAAC:, and KC8 in a 1:2:2.1 molar ratio. Dark green crystals of compounds 1 and 2 were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of 1 and 2 feature the C-Ge-C bent backbone, which possesses a three-center two-electron π-bond system. Compounds 1 and 2 are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds 1 and 2 confirmed the singlet spin ground state. DFT calculations on 1/2 revealed that the singlet ground state is more stable by ~16 to 18 kcal mol(-1) than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (1)/267.1 (2) and 180.4 (1)/183.8 (2) kcal mol(-1), respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of 1 and 2. The TD-DFT calculations exhibit an absorption band at ~655 nm in n-hexane solution that originates from the diradicaloid character of germylones 1 and 2.

Carbon Monoxide Bonding With BeO and BeCO3: Surprisingly High CO Stretching Frequency of OCBeCO3

The complexes OCBeCO3 and COBeCO3 have been isolated in a low-temperature neon matrix. The more stable isomer OCBeCO3 has a very high CO stretching mode of 2263 cm(-1) , which is blue-shifted by 122 cm(-1) with respect to free CO and 79 cm(-1) higher than in OCBeO. Bonding analysis of the complexes shows that OCBeO has a stronger OCBeY bond than OCBeCO3 because it encounters stronger π backdonation. The isomers COBeCO3 and COBeO exhibit red-shifted CO stretching modes with respect to free CO. The inverse change of CO stretching frequency in OCBeY and COBeY is explained with the reversed polarization of the σ and π bonds in CO.

Experimental and Theoretical Studies of the Infrared Spectra and Bonding Properties of NgBeCO3 and a Comparison with NgBeO (Ng = He, Ne, Ar, Kr, Xe)

The novel neon complex NeBeCO3 has been prepared in a low-temperature neon matrix via codeposition of laser-evaporated beryllium atoms with O2 + CO/Ne. Doping by the heavier noble gas atoms argon, krypton and xenon yielded the associated adducts NgBeCO3 (Ng = Ar, Kr, Xe). The noble gas complexes have been identified via infrared spectroscopy. Quantum chemical calculations of NgBeCO3 and NgBeO (Ng = He, Ne, Ar, Kr, Xe) using ab initio methods and density functional theory show that the Ng-BeCO3 bonds are slightly longer and weaker than the Ng-BeO bonds. The energy decomposition analysis of the Ng-Be bonds suggests that the attractive interactions come mainly from the Ng → BeCO3 and Ng → BeO σ donation.

Formation and Characterization of the Boron Dicarbonyl Complex [B(CO)2]−

We report the synthesis and spectroscopic characterization of the boron dicarbonyl complex [B(CO)2 ](-) . The bonding situation is analyzed and compared with the aluminum homologue [Al(CO)2 ](-) using state-of-the-art quantum chemical methods.

Stabilization of Heterodiatomic SiC Through Ligand Donation: Theoretical Investigation of SiC(L)2 (L=NHCMe, CAACMe, PMe3)

Quantum chemical calculations have been carried out at the BP86/TZ2P+ level for the compounds SiC(L)2 with L=NHC(Me) , CAAC(Me) , PMe3 (NHC=N-heterocyclic carbene, CAAC=cyclic (alkyl)aminocarbene). The optimized geometries exhibit a trans arrangement of the ligands L at SiC with a planar coordination when L=NHC(Me) and PMe3 , while a twisted conformation is calculated when L=CAAC(Me) . The bending angle L-Si-C is significantly more acute than the angle L-C-Si. Both angles become wider with the trend PMe3 <NHC(Me) <CAAC(Me) . The latter trend is also found for the bond dissociation energies of the reaction SiC(L)2 →SiC+2 L, which have absolute values between De =98-163 kcal mol(-1) . Calculations suggest that the compounds SiC(L)2 have a very large first and second proton affinity, which takes place at the central carbon and silicon atoms, respectively. Energy decomposition analyses indicate that the best description of the bonding situation in SiC(L)2 features a cumulenic carbon-carbon bond and a dative carbon-silicon bond LCSi←L at the center.

Carbene-Dichlorosilylene Stabilized Phosphinidenes Exhibiting Strong Intramolecular Charge Transfer Transition

The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)SiCl2 can form a coordinate bond with metal-carbonyls. Herein we report that (carbene)SiCl2 can stabilize a phosphinidene (Ar-P, a carbone analogue) with the general formula carbene→SiCl2→P-Ar (carbene = cyclic alkyl(amino) carbene (cAAC; 2) and N-heterocyclic carbene (NHC; 3)). Compounds 2 and 3 are stable, isolable, and storable at 0 °C (2) to room temperature (3) under an inert atmosphere. The crystals of 2 and 3 are dark blue and red, respectively. The intense blue color of 2 arises due to the strong intramolecular charge transfer (ICT) transition from πSi═P→π*cAAC. The electronic structure and bonding of 2, 3 were studied by theoretical calculations. The HOMO of the molecule is located on the πSi═P bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (3, NHC) to blue (2, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC.

The [B3(NN)3]+ and [B3(CO)3]+ Complexes Featuring the Smallest π-Aromatic Species B3+

We report the spectroscopic identification of the [B3 (NN)3](+) and [B3 (CO)3](+) complexes, which feature the smallest π-aromatic system B3 (+). A quantum chemical bonding analysis shows that the adducts are mainly stabilized by L→[B3 L2 ](+) σ-donation.

A Triatomic Silicon(0) Cluster Stabilized by a Cyclic Alkyl(amino) Carbene.

Reduction of the neutral carbene tetrachlorosilane adduct (cAAC)SiCl4 (cAAC=cyclic alkyl(amino) carbene :C(CMe2)2 (CH2)N(2,6-iPr2C6H3) with potassium graphite produces stable (cAAC)3Si3, a carbene-stabilized triatomic silicon(0) molecule. The Si-Si bond lengths in (cAAC)3Si3 are 2.399(8), 2.369(8) and 2.398(8) Å, which are in the range of Si-Si single bonds. Each trigonal pyramidal silicon atom of the triangular molecule (cAAC)3Si3 possesses a lone pair of electrons. Its bonding, stability, and electron density distributions were studied by quantum chemical calculations.

Isolation of Bridging and Terminal Coinage Metal–Nitrene Complexes

Transition metal complexes featuring a metal-nitrogen multiple bond have been widely studied due to their implication in dinitrogen fixation and catalytic nitrogen-carbon bond formation. Terminal copper- and silver-nitrene complexes have long been proposed to be the key intermediates in aziridination and amination reactions using azides as the nitrogen source. However, due to their high reactivity, these species have eluded isolation and spectroscopic characterization even at low temperatures. In this paper we report that a stable phosphinonitrene reacts with coinage metal trifluoromethanesulfonates, affording bridging and terminal copper- and silver-nitrene complexes, which are characterized by NMR spectroscopy and single crystal X-ray diffraction analysis.