Steric and electronic properties in bicyclic phosphines. Crystal and molecular structures of Se = Phoban-Q (Q = C2, C3Ph, Cy and Ph)

Reacting a series of the bicylic Phoban-Q (9-Q-9-phosphabicyclo[3.3.1]nonane and 9-Q-9-phosphabicyclo[4.2.1]nonane) derivatives (Q = alkyl, cyclo alkyl, aryl) with KSeCN results in the formation of the corresponding phosphine selenides. The first order phosphorus–selenium coupling constants, 1JP–Se, ranges from 682 to 689 Hz for the [3.3.1] isomers and from 703 to 717 Hz for the [4.2.1] isomers indicating the former to be significantly more electron rich. The crystal structures of Se = Phoban[3.3.1]-Q (Q = CH2CH3, C3H6Ph, Cy, and Ph) and Se = Phoban[4.2.1]-Q (Q = Cy and Ph) are reported and reveal PSe bond distances ranging from 2.1090(9) to 2.1245(7) Å. For Q = Cy and Ph the two isomers ([3.3.1] and [4.2.1]) co-crystallise in the same crystal enabling the determination of the molecular structures for both from the same data collection. The cone angles for all ligand derivatives were determined according to the Tolman model but by using the actual P–Se bond distances and were found to be virtually identical ranging from 165° to 175°. Changes in the Q substituent have a minor effect on the overall steric and electronic properties of the Phoban family of ligands and can be used to manipulate physical properties without changing the chemical properties significantly.

Graphical abstractThe synthesis of a series of Phoban derivatives and their corresponding selenides are reported. The electronic properties of the ligands were determined by measuring the first order P–Se coupling constants by NMR while cone angle were calculated from the crystal structures as a measure of the steric properties.Figure optionsDownload full-size imageDownload as PowerPoint slide