Joseph J. W. McDouall

Influence of the N‐Bridging Ligand on Magnetic Relaxation in an Organometallic Dysprosium Single‐Molecule Magnet

Organometallic single-molecule magnet: Studies of two dimeric organometallic dysprosium compounds reveal one to be the first organometallic single-molecule magnet (see picture). A comparison of the magnetic properties and electronic structures of the two compounds shows that Dy⋅⋅⋅Dy interactions have a profound influence on the dynamic magnetic behaviour, while having little effect on the static magnetic measurements.

A simple MC SCF perturbation theory: Orthogonal valence bond Møller-Plesset 2 (OVB MP2)

Abstract A multi-reference Moller-Plesset perturbation theory - orthogonal valence bond Moller-Plesset 2 (OVB MP2) - is derived using an effective Hamiltonian formalism. The method is characterized by the use of localized CAS SCF orbitals in order to achieve a quasi-degenerate (in terms of the one-electron reference Hamiltonian) reference space. Thus the reference CI expansion corresponds to orthogonal valence bond. The efficiency of the method is illustrated for two molecules (CH 2 3 B 1 1 A 1 :H 2 O r e , 1.5 r e , 2 r e ) and the Be atom, where full CI results are available.

Structure and bonding in three-coordinate N-heterocyclic carbene adducts of iron(II) bis(trimethylsilyl)amide

The molecular structures, chemical bonding and magnetochemistry of the three-coordinate iron(II) NHC complexes [(NHC)Fe{N(SiMe(3))(2)}(2)] (NHC = IPr, 2; NHC = IMes, 3) are reported.

Controlling Axial Conformation in 2-Arylpyridines and 1-Arylisoquinolines: Application to the Asymmetric Synthesis of QUINAP by Dynamic Thermodynamic Resolution

Unlike related biphenyl compounds, 2-arylpyridines and 1-arylisoquinolines can be induced to adopt preferentially one of two axial conformations by the presence of a sulfinyl substituent adjacent to the Ar-Ar bond. In the case of more substituted biaryls, the compounds are atropisomeric, and thermodynamic selectivities of about 4:1 may be attained on heating. In the case of less hindered compounds, conformer ratios of up to 20:1 may be achieved. Preferred conformations are deduced by comparison of experimental CD spectra with those derived from theory. The conformational preferences induced by the sulfoxides may be exploited in the asymmetric synthesis of atropisomers, including the ligand QUINAP, by dynamic resolution under thermodynamic control.

MCSCF gradient calculation of transition structures in organic reactions

The applicability of MCSCF gradient methods to the calculation of transition structures and diradicaloid intermediates is discussed. It is shown how the diabatic surface model provides a useful criterion for the choice of the valence space in the MCSCF method and also provides useful qualitative information about the electronic rearrangement associated with various transition states. These ideas are then applied to the synchronous and asynchronous 1,3-dipolar cycloaddition of fulminic acid to acetylene.

Parametrization of a Heitler–London valence bond Hamiltonian from complete‐active‐space self‐consistent‐field computations: An application to chemical reactivity

A simple practical procedure is proposed for the transformation of a complete‐active‐space self‐consistent‐field (CAS‐SCF) wave function to Heitler–London valence bond space via the construction of an effective (Heisenberg) Hamiltonian. With such a procedure, the computed Heitler–London parameters Q and Kij can be used for a posteriori rationalization of the bonding effects in molecular structures. In particular, the diabatization of the adiabatic potential surface, first proposed by Evans can now be accomplished in a rigorous way. The technique is applied to some previously computed transition structures for cycloaddition reactions.

Analytical gradients for unrestricted Hartree–Fock and second order Mo/ller–Plesset perturbation theory with single spin annihilation

Unrestricted Hartree–Fock (UHF) wave functions and Mo/ller–Plesset perturbation theory (UMPn) based on a single spin‐unrestricted reference determinant can contain significant contamination from unwanted spin states. This contamination may lead to large distortions of the potential energy surface, particularly at the UMPn level. A simple approximation to projected UMPn theory (PMPn) improves the shape of the potential energy surface significantly. Formulas for analytical gradients of the PUHF and approximate projected UMP2 energies with single annihilation have been derived and programmed. This code has been applied to the optimization of transition states for H+C2H4, H+CH2O and H+C2H2 at the PMP2/6‐31G* level.

A simple scaling for combining multiconfigurational wavefunctions with density functionals

Abstract A simple scaling procedure is presented for combining multiconfigurational wavefunctions with density functional estimates of the dynamic electron correlation. It is based on the idea of assigning an average correlation energy to each electron in the system. The procedure is illustrated by application to the potential energy curves of Li 2 and F 2 using different choices of the number of electrons which are correlated in the reference wavefunction. The method is also applied to calculating the excitation energies of the first-row transition metals (Sc–Cu). Results are presented for four widely used correlation density functionals.

Nickel(II) and Palladium(II) Complexes of Azobenzene-Containing Ligands as Dichroic Dyes

A large series of complexes has been synthesized with two chelating, Schiff base azobenzene derivatives connected linearly by coordination to a central nickel(II) or palladium(II) ion. These compounds have the general formulas M(II)(OC(6)H(3)-2-CHNR-4-N═NC(6)H(4)-4-CO(2)Et)(2) [M = Ni; R = n-Bu (3c), n-C(6)H(13) (3d), n-C(8)H(17) (3e), n-C(12)H(25) (3f), Ph (3g), OH (3h), C(6)H(4)-4-CO(2)Et (3i). M = Pd; R = i-Pr (4a), t-Bu (4b), n-Bu (4c), n-C(6)H(13) (4d), n-C(8)H(17) (4e), n-C(12)H(25) (4f), Ph (4g)], M(II)[OC(6)H(3)-2-CHN(n-C(8)H(17))-4-N═NC(6)H(4)-4-CO(2)(n-C(8)H(17))](2) [M = Ni (9), Pd (10)], M(II)[OC(6)H(3)-2-CHN(n-C(8)H(17))-4-N═NC(6)H(4)-4-C(6)H(4)-4-O(n-C(7)H(15))](2) [M = Ni (14), Pd (15)], and M(II)[OC(6)H(3)-2-CHN(CMe(2))-4-N═NC(6)H(4)-4-CO(2)Et](2) [M = Ni (17), Pd (18); the CMe(2) groups are connected]. These compounds have been characterized by using various physical techniques including (1)H NMR spectroscopy and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Single-crystal X-ray structures have been obtained for two pro-ligands and five complexes (3e, 4e, 14, 15, and 17). The latter always show a strictly square planar arrangement about the metal center, except for the Ni(II) complex of a salen-like ligand (17). In solution, broadened (1)H NMR signals indicate distortions from square planar geometry for the bis-chelate Ni(II) complexes. Electronic absorption spectroscopy and ZINDO_S (Zerners intermediate neglect of differential overlap) and TD-DFT (time-dependent density functional theory) calculations show that the lowest energy transition has metal-to-ligand charge-transfer character. The λ(max) of this band lies in the range of 409-434 nm in dichloromethane, and replacing Ni(II) with Pd(II) causes small blue-shifts. Dichroic ratios measured in various liquid crystal hosts show complexation-induced increases with Ni(II), but using Pd(II) has a detrimental effect.

Copper-Catalyzed Borylative Cross-Coupling of Allenes and Imines: Selective Three-Component Assembly of Branched Homoallyl Amines

Abstract A copper‐catalyzed three‐component coupling of allenes, bis(pinacolato)diboron, and imines allows regio‐, chemo‐, and diastereoselective assembly of branched α,β‐substituted‐γ‐boryl homoallylic amines, that is, products bearing versatile amino, alkenyl, and borane functionality. Alternatively, convenient oxidative workup allows access to α‐substituted‐β‐amino ketones. A computational study has been used to probe the stereochemical course of the cross‐coupling.