Contracted CI calculations of models for catalytic reactions involving transition metals

Abstract

Theoretical models for reductive elimination from transition metal containing molecules have been studied using large scale contracted CI calculations. Four different models were treated, namely, NiH2, PdH2, Ni(CH3)2, and Pd(H20)zHz. in order to study the effects of adding ligands, exchanging hydrogens with methyl groups, and comparing nickel and palladium. The most interesting result already appeared for the simplest system NiH2. A closed-shell-type ' A 1 state with a small bond angle of only 57O is bound compared to Ni and H2 with only a very small barrier for formation. The bond distance is short, shorter than in NiH, and the d orbitals are strongly involved in the binding. The hydrogen atoms bind both to nickel and to each other. With methyl groups rather than hydrogens, this double sided bonding situation is destroyed and Ni(CH3)Z has a negative binding energy with the carbon bonds pointing towards nickel. For PdH2 only a weakly bound complex between an essentially unchanged H Z and Pd was found. ThePond distance is very long. Adding H 2 0 ligands to Pd shortens the bond distance and significantly opens up the bond angle. The methods used in the investigation and the chemical implications of the results are discussed.

Mechanisms for the reactions between methane and the neutral transition metal atoms from yttrium to palladium

“…The results for these metals are presented in Figure 2. The shapes of these potential curves are to a large extent determined by the large loss of exchange energy upon both bond formation and low-spin coupling of atomic d-electrons.31 The product complexes, dominated by the low-lying 4d"+15s1 configuration (ground state for molybdenum and only 9 kcal/mol (exp) excited for technetium), are therefore fairly strong unbound, by [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] kcal/mol, relative to the high-spin ground states of the atoms. Relative to the low-spin coupled (i.e., the same spin as the product complexes) excited states, however, these metals have rather strongly bound insertion products, particularly for molybdenum, with a bond strength of 19 kcal/mol.…”

Theoretical study of the interaction of carbon monoxide with palladium clusters: relations between surface and organometallic chemistry

“…The presence of a ligand like Ff20 slightly changes the ground state configuration of Pdatom and makes it more similar to Ni and therefore more reactive. 47 The role of the phosphine ligands in organometallic Pd clusters may be to perturb the electronic configuration of the metal atoms and to make them more suitable for the formation of metal-metal bonds.…”

Magneto-infrared spectra of matrix-isolated NiH and NiH2 molecules and theoretical calculations of the lowest electronic states of NiH2

“…Apparently, theoretical studies carried out on the NiH 2 molecule to date 19,[23][24][25][26] all predict a linear 3 ⌬ g ground state.…”