Computational Chemistry

Stability of Pentaorganylsilicates

I have performed quantum chemical calculations to explain the extraordinary stability of specific pentaorganylsilicates. Bond energy decompositions with ADF pointed out the special role of the bidentate biaryl moieties. These substituents are σ-electron withdrawing and sterically undemanding, which stabilizes silicon hypercoordination. Due to their π-electron richness, the biaryl groups have a strong preference to bridge one axial and one equatorial site. The fifth hydrocarbyl moiety then occupies an equatorial position, where it is bound more strongly than in an axial position.

Electronic Structure and Stability of Pentaorganosilicates

This research was published in the Journal of the American Chemical Society

Principal Stereomutation Mechanisms

I have extended the insights into the fluxionality of pentaorganylsilicates to other pentacoordinate compounds, including transition-metal complexes. I developed a method to unambiguously determine the principal mechanisms of stereomutation from computed reaction pathways, which also gives a straightforward interpretation of any constraints imposed by the substituents. The results resolve a long-standing confusion over which interchange mechanisms are true alternatives. Specifically, the Berry pseudorotation and turnstile rotation mechanisms are shown to be equivalent. We propose to reassign the name "turnstile rotation" to an alternative mechanism involving cyclic permutation of three neighbouring ligands, which does resemble the motion of a three-arm turnstile gate (see below). Animations of the different mechanisms can be viewed here.

Stereomutation of Pentavalent Compounds

This research was published in the Journal of the American Chemical Society

Quantifiers of σ-Donor and π-Acceptor Ability

Together with Yu-Ying Lai, I have studied the ligand−metal bonding in a broad range of organometallic complexes. NOCV analysis separates the overall electronic redistribution into contributions from e.g. σ donation, π backbonding, agostic interactions, fragment repolarizations, etc. I developed an extension that quantifies the corresponding σ-donor and π-acceptor abilities, and these correlate well across the different series. These descriptors appear to be more suitable for ligand knowledge bases than the Tolman Electronic Parameter.

Intuitive Quantifiers of Charge Flows in Coordinate Bonding

>> This research just appeared as ASAP in Organometallics <<