Experimental and theoretical studies on the course of CO insertion into Pt–C and Pd–C bonds in neutral and cationic complexes, [MR(Cl){P(CH3)3}2] and [MR{P(CH3)3}2(s)]+BF4– (M=Pt, Pd, R=CH3, C6H5, s=coordinated solvent)

Experimental and Theoretical Evidence for Relativistic Catalytic Activity in C-H Activation of N-Phenylbenzamide Using a Cationic Iridium Complex

This study elucidates that relativistic effect plays a key role in catalytic C-H activation using a cationic Ir complex. Experiments show that the cationic Ir(I)-diphosphine catalyst can be used for the deuterium substitution of N-phenylbenzamide, whereas a cationic Rh(I)-diphosphine catalyst is scarcely effective. Density functional theory calculations, including the relativistic effect, demonstrate a large difference in the reaction energy diagrams for the C-H activation of N-phenylbenzamide between the cationic Ir and Rh catalysts. In particular, the relatively low reaction barrier and considerably stabilized product obtained for the Ir catalysts are rationalized by strong Ir-C and Ir-H interactions, which originate from the relativistic self-consistent d-orbital expansion of Ir.

RECENT ADVANCES IN ELECTRONIC STRUCTURE THEORY

Accurate quantum computational chemistry has evolved dramatically. The size of molecular systems, which can be studied accurately using molecular theory is increasing very rapidly. Theoretical chemistry has opened up a world of new possibilities. It can treat real systems with predictable accuracy. Computational chemistry is becoming an integral part of chemistry research. Theory can now make very significant contribution to chemistry.

This review will focus on our recent developments in the theoretical and computational methodology for the study of molecular structure and molecular interactions. We are aiming at developing accurate molecular theory on systems containing hundreds of atoms. We continue our research in the following three directions: (i) development of new ab initio theory, particularly multireference-based perturbation theory, (ii) development of exchange and correlation functionals in density functional theory, and (iii) development of molecular theory including relativistic effects.

We have enjoyed good progress in each of the above areas. We are very excited about our discoveries of new theory and new algorithms and would like to share this enthusiasm with readers.

Aryl-Fluoride Reductive Elimination from Pd(II): Feasibility Assessment from Theory and Experiment

DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar-F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F(-). Three-coordinate T-shaped geometry of Pd(II)Ar(F)L (L = NHC, PR(3)) was shown to offer kinetics and thermodynamics of Ar-F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect. Synthesis and characterization of the novel [Pd(C(6)H(4)-4-NO(2))ArL(mu-F)](2) (L = P(o-Tolyl)(3), 17; P(t-Bu)(3), 18) revealed stability of the fluoride-bridged dimer forms of the requisite Pd(II)Ar(F)L as the key remaining obstacle to Ar-F reductive elimination in practice. Interligand steric repulsion with P(t-Bu)(3) served to destabilize dimer 18 by 20 kcal/mol, estimated with DFT relative to PMe(3) analog, yet was insufficient to enable formation of greater than trace quantities of Ar-F; C-H activation of P(t-Bu)(3) followed by isobutylene elimination was the major degradation pathway of 18 while Ar/F- scrambling and Ar-Ar reductive elimination dominated thermal decomposition of 17. However, use of Buchwald's L = P(C(6)H(4)-2-Trip)(t-Bu)(2) provided the additional steric pressure on the [PdArL(mu-F)](2) core needed to enable formation of aryl-fluoride net reductive elimination product in quantifiable yields (10%) in reactions with both 17 and 18 at 60 degrees over 22 h.

Relativistic electronic structure theory

The theoretical and technical foundations are presented for the efficient relativistic electronic structure theories to treat heavy-atomic molecular systems. This review contains two surveys of four-component and two-component quasi-relativistic approaches. First, we review our highly efficient computational scheme for four-component relativistic ab initio molecular orbital (MO) methods over generally contracted spherical harmonic Gaussian-type spinors (GTSs). Illustrative calculations, which are performed with a new four-component relativistic ab initio molecular orbital program package REL4D, clearly show the efficiency of our computational scheme by the Dirac-Hartree-Fock (DHF) and Dirac-Hartree-Fock (DKS) methods. Next, in the two-component quasi-relativistic framework, two relativistic Hamiltonians, RESC and higher order Douglas-Kroll (DK) Hamiltonians, are introduced, and several illustrative calculations are shown. Numerical results for several systems show that good accuracy can be obtained with our third-order DK (DK3) Hamiltonian.