Percent buried volume for phosphine and N-heterocyclic carbene ligands: steric properties in organometallic chemistry

Abstract

Electronic and steric ligand effects both play major roles in organometallic chemistry and consequently in metal-mediated catalysis. Quantifying such parameters is of interest to better understand not only the parameters governing catalyst performance but also reaction mechanisms. Nowadays, ligand molecular architectures are becoming significantly more elaborate and existing models describing ligand sterics prove lacking. This review presents the development of a more general method to determine the steric parameter of organometallic ligands. Two case studies are presented: the tertiary phosphines and the N-heterocyclic carbenes.

Late Transition Metal Compounds with 1,1′‐Bis(phosphino)ferrocene Ligands

“…As for the calculated values for the [Pd(PP)Cl 2 ] compounds, the %V bur for 3 in [(AuCl) 2 (PP)] is larger than those of 1 (33.5) and 2 (38.8). [22] The Au-Au distance in [Au 2 (μ-Cl)(3)] + is within the typical range for aurophilic interactions. [30] The formal shortness ratio (FSR AB ) has been defined as the observed interatomic distance divided by the sum of the metallic radius of the metal atoms.…”

“…[22] The %V bur defines the percentage of the volume of a sphere surrounding a metal atom that is occupied by a ligand and is calculated with the recently updated SambVca 2 suite. [23] τ [e] 55.67 (7) 48.51 (14) [f ] [27] The structures of [Zn(2O 2 )Cl 2 ] and [Zn(3O 2 )Cl 2 ] were determined (Figure 3), and selected structural parameters are presented in Table 2.…”

Synthesis and characterisation of Au(I)-(ITent) complexes

“…[6] Recently, our group investigated the steric effect of IPent by preparing [AuCl(IPent)] (1). [4b] We also disclosed a new methodology for preparing gold(I)-NHC complexes that avoids the isolation of the free carbene or the use of copper or silver congeners as transmetallating reagents.…”

Catalytic Electrophilic C−H Borylation Using NHC⋅Boranes and Iodine Forms C2‐, not C3‐, Borylated Indoles

“…The in-situ NMR spectra for borylation using 9 revealed no doubly borylated product analogous to 4 and significantly fewer minor products in the 11 B NMR spectrum, and again there was no evidence for indoline formation (by 1 H NMR spectroscopy). The much lower yield using 10 is notable as based on percentage buried volume (%Vbur) 18 values derived from transition metal NHC complexes the four NHCs used herein appear to have comparable steric demand. To determine the NHC steric impact in NHCBH3 complexes the previously reported solid structures of 1, 8, 9 and 10 were used to calculate modified %Vbur values, termed %Vbur(B-C) values using a B-C distance of 1.59 Å.…”