We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a coordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wave function (such as from a Hartree–Fock or Kohn–Sham calculations) based on projectors to targeted atomic valence orbitals. We discuss the premises, theory, and implementation of the idea, and several of its variations are tested. To investigate the performance and accuracy, we calculate the excitation energies for various transition-metal complexes in typical application scenarios. Additionally, we follow the homoly...

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Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals

Vinyl cyclopropanes are amongst the most useful building blocks in organic synthesis. Their easy opening and capacity to generate dipoles have been exploited for the synthesis of cyclopentanes with good yields and sometimes excellent stereoselectivities. In this review we give an overview of their applications, focusing on the present century.

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Synthetic applications of vinyl cyclopropane opening.

The nucleophilic iron complex Bu4N[Fe(CO)3(NO)] (TBA[Fe]) catalyzes the direct intramolecular C-H amination of α-azidobiaryls and (azidoaryl)alkenes into the corresponding carbazoles and indoles, respectively, under mild conditions and with low catalyst loadings. These features and the broad functional-group tolerance render this method a particularly attractive alternative to established noble-metal-based procedures.

Iron‐Catalyzed Intramolecular C(sp2)−H Amination

The nucleophilic iron complex Bu4 N[Fe(CO)3 (NO)] (TBA[Fe]) catalyzes the direct intramolecular amination of unactivated C(sp3 )-H bonds in alkylaryl azides, which results in the formation of substituted indoline and tetrahydroquinoline derivatives.

Iron-Catalyzed Intramolecular Aminations of C(sp3)−H Bonds in Alkylaryl Azides

Racemic cyclopropyl ketones undergo enantioselective rearrangement to deliver the corresponding dihydrofurans in the presence of a chiral phosphoric acid as the catalyst. The reaction involves activation of the donor-acceptor cyclopropane substrate by the chiral Bronsted acid catalyst to promote the ring-opening event, thus generating a carbocationic intermediate that subsequently undergoes cyclization. Computational studies and control experiments support this mechanistic pathway.

Catalytic Enantioselective Cloke-Wilson Rearrangement.

The base metal complex Bu4N[Fe(CO)3(NO)] (TBA[Fe]) catalyzes the rearrangement of vinyl and arylcyclopropanes both under thermal or photochemical conditions to give the corresponding vinyl or aryldihydrofurans in good to excellent yields. Under photochemical conditions the reaction is performed at room temperature. Spectroscopic investigations show that the metal carbonyl catalyst is not decarbonylated. The best performance was observed at a wavelength of 415 nm. icMRCI+Q analysis of the excited singlet and triplet states of the [Fe(CO)3(NO)] anion was performed and used to calculate the vertical excitation energies which are in good agreement with the experimental data. CASSCF analysis indicates that the Fe center in all excited states of the ferrate becomes more electrophilic while adopting a distorted tetrahedral configuration. Both aspects have a positive synergistic effect on the formation of the initial π-complex with the incoming organic substrate.

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Non-decarbonylative photochemical versus thermal activation of Bu4N[Fe(CO)3(NO)] – the Fe-catalyzed Cloke–Wilson rearrangement of vinyl and arylcyclopropanes

The Fe-catalyzed Cloke—Wilson rearrangement of vinylcyclopropanes (I), (IV), and (VI) under photochemical conditions proceeds in a shorter time and with similar or higher yields compared to the reaction under thermal conditions.

Non-decarbonylative Photochemical versus Thermal Activation of Bu4N[Fe(CO)3(NO)] — The Fe-Catalyzed Cloke—Wilson Rearrangement of Vinyl and Arylcyclopropanes.

Jennifer A. Allen

Papers

Non-decarbonylative photochemical versus thermal activation of Bu4N[Fe(CO)3(NO)] – the Fe-catalyzed Cloke–Wilson rearrangement of vinyl and arylcyclopropanes

Non-decarbonylative Photochemical versus Thermal Activation of Bu4N[Fe(CO)3(NO)] — The Fe-Catalyzed Cloke—Wilson Rearrangement of Vinyl and Arylcyclopropanes.