Comparison of M−S, M−O, and M-(η²−SO) Structures and Bond Dissociation Energies in d⁶ (CO)₅M(SO₂)^nq Complexes Using Density Functional Theory

Abstract

Density functional theory studies of the series of isomeric d(6) (pentacarbonyl)metal complexes (CO)(5)M(eta(1)-SO(2))(nq), (CO)(5)M(eta(1)-OSO)(nq)(), and (CO)(5)M(eta(2)-SO(2))(nq) (M = Ti-Hf, nq = 2-; M = V-Ta, nq = 1-; M = Cr -W, nq = 0; M = Mn-Re, nq = 1+; M = Fe-Os, nq = 2+) provide accurate structural modeling and quantitative prediction of the relative stabilities of the isomers. The eta(1)-S-bound complexes display planar SO(2) moieties that adopt staggered orientations with respect to the carbonyl ligands, in keeping with experimental observations. The OSO chain in the eta(1)-O-bound complexes generally adopts the u-shape with a staggered orientation. The dianions (CO)(5)(Ti-Hf)(eta(1)-OSO)(2-) differ in that the OSO chain adopts the eclipsed z-shape orientation. The eta(2)-SO(2) complexes exhibit a facial interaction and are stable only for anionic and neutral complexes, supporting the view that this motif involves substantial M --> SO(2) pi-back-bonding. The relative stabilities of the isomers generally follow u-shaped trends both across a row and down a family. This fits with qualitative ideas that the bond dissociation energies (BDEs) for the (CO)(5)M(SO(2))(nq) complexes track competition between relative hardness/softness of the metal fragment and its capacity for pi-back-bonding. Quantitatively, examination of BDEs by bond energy decomposition approaches suggests that electrostatic considerations dominate bonding for the eta(1)-SO(2) complexes and covalent effects dominate for the eta(2)-SO(2) species, while both are important for eta(1)-OSO complexes.

Density Functional Theory Study of the d10Series (H3P)3M(η1-SO2) and (MenPh3-nP)3M(η1-SO2) (M = Ni, Pd, Pt;n= 0−3): SO2Pyramidality and M−S Bond Dissociation Energies

“…The predicted M−S bond dissociation energies (BDEs) appear in Table . The BDEs for the nickel complexes are similar to those estimated for “middle-of-the-transition series” d 6 (CO) 5 M(η 1 -SO 2 ) nq complexes (M = V−Ta, nq = 1−; M = Cr−W, nq = 0; M = Mn−Re, nq = 1+) 9a. These, like the Ni complexes, exhibit a planar SO 2 ligand.…”

“…We have begun a program involving computational modeling of transition metal catalysts that can convert SO 2 into less poisonous and/or more commercially useful materials such as sulfur or sulfates. As part of this, we previously investigated the bond dissociation energies (BDEs) of a variety of L 5 M−SO 2 nq complexes (L = CO, NH 3 ) in the hope of correlating bond energy with reactivity . We report here quantum mechanical density functional theory (DFT) and coupled DFT/molecular mechanics (QMMM) studies of the d 10 compounds (H 3 P) 3 M(η 1 -SO 2 ) and (Me n Ph 3 - n P) 3 M(η 1 -SO 2 ) (M = Ni, Pd, Pt; n = 0−3).…”

A kinetic study of the reactions of vanadium, iron, and cobalt with sulfur dioxide

“…In the condensed phase, SO 2 is known to coordinate to large numbers of substrates in many modes. 39,40 A common mode is the Z 1 S co-planar mode where the bonding involves s donation from the S atom to the metal atom in conjunction with p back donation from the metal to the SO 2 . (The HOMO in SO 2 has significant electron density on the S atom, hence the s donation.)…”