Theoretical Study of CO Migratory Insertion Reactions with Group 10 Metal−Alkyl and −Alkoxide Bonds

Abstract

The results of density functional calculations on the alternative migratory insertion reactions of CO with the M−OMe and M−Me bonds of group 10 M(Me)(OMe)(PH3)2 model systems are reported. For all three metals insertion into the M−OMe bond to form methoxycarbonyl products is thermodynamically favored over insertion into the M−Me bond to give acyls. This preference is small when M = Ni (ΔΔE R = 3 kcal/mol) but increases down the triad and becomes significant for M = Pt (ΔΔE R = 12 kcal/mol). Both associative five-coordinate and phosphine displacement four-coordinate mechanisms for migratory insertion were considered. For Ni associative mechanisms are more accessible and the lowest energy pathway is for reaction with the Ni−Me bond. With Pd and Pt the five- and four-coordinate pathways are close in energy, and for Pd there is a small kinetic preference for insertion into the Pd−OMe bond. For Pt however there is a clear kinetic preference for reaction with the Pt−OMe bond. During migratory insertion into M−OMe bonds the methoxide ligand rotates in the transition state to allow the participation of an oxygen lone pair in C−O bond formation while maintaining some residual M···OMe interaction. This M···OMe interaction is retained to some extent in the three-coordinate methoxycarbonyl species formed along the four-coordinate pathways. For an isostructural series of reactive species the trend in activation energy is always Ni < Pd ≪ Pt for reaction with the M−Me bond and Ni > Pd < Pt (with Pt > Ni) for reaction with the M−OMe bond. Trends in the computed thermodynamic and kinetic data of the alternative migratory insertions can be understood in terms of metal−ligand homolytic bond strengths. All M−C bonds studied show a marked increase down the group 10 triad, whereas much less variation is seen in the M−OMe bonds, which results in reaction with the M−OMe bonds being generally favored. A key additional driving force, however, is the stronger C−O bond formed in the methoxycarbonyl product compared to the C−C bond of the alternative acyl species.

Pd‐Catalysed Mono‐ and Dicarbonylation of Aryl Iodides: Insights into the Mechanism and the Selectivity

“…This result is in agreement with the equilibrium between cis and trans species observed by NMR spectroscopy 8. For phenyl migration we considered a three‐centre mechanism16b and located transition state TS2 a‐3 a with an energy barrier of 11.1 kcal mol −1 and the phenyl group migrating in the plane of the complex (see Figure 1). Both the energy and the geometry closely resemble those recently calculated for trans ‐[PdPh(CO)(OEt)(PMe 3 )] by Lei et al 16a.…”

Nickel and Palladium Complexes with Reactive σ‐Metal‐Oxygen Covalent Bonds

“…Independently of the participation of the oxygen electron pairs, the carbonylation mechanisms of M-OR bonds in squareplanar d 8 metal complexes resembles the situation for similar alkyls, clearly favoring an associative pathway with a 5coordinate carbonyl intermediate for Ni, and 4-coordinate intermediates for Pd and Pt. [80] Further DFT studies on more realistic [Ni(Me)(OR)(HN=CHCH=NH)] and [Pt(Me)(OR) (PH 2 CH 2 CH 2 PH 2 )] models confirmed the main predictions from the above study and showed the influence of the OÀ R group on the thermodynamic balance of the reaction, the carbonylation of the MÀ O bonds becoming thermodynamically disfavored when OR is an aryloxide group. [81] The widespread application of pincer ligands in the 1990's opened new opportunities in the study of the fundamental reactivity of NiÀ OR and PdÀ OR bonds.…”

“…[79] Computational (DFT) analysis of the mechanism of CO insertion in simplified Group 10 models of the type [M(Me)(OMe)(PH 3 ) 2 ] (M=Ni, Pd, Pt) confirmed that CO insertion into the MÀ OMe bonds proceeds through the migratory mechanism. [80] Insertion in the MÀ OMe bond is thermodynamically favored over the MÀ CH 3 , although the balance in favor of the MÀ OMe insertion decreases in the order Pt (12 Kcal · mol À 1 ) > Pd (7 Kcal · mol À 1 ) > Ni (3 Kcal/mol). The energy barriers for CO insertion, either in the MÀ C or MÀ O bonds are significant only for Pt, and much lower for Pd and Ni.…”

Mass spectrometry in the characterization of reactive metal alkoxides

“…This ion arises by nucleophilic attack of the alkoxide ion to the carbon atom of one carbonyl ligand giving rise to a C(O)OR group (Macgregor & Neave, ). This reaction is characterized by rapid kinetics and large equilibrium costant (Gross & Ford, ).…”