Dedicated to Dr. Doug Stephan in honour of his 70 th birthdayThe reactivity of alkynylphosphines with Lewis acidic boranes has been well established in recent years thanks to the advent of frustrated Lewis pairs (FLPs), often leading to a 1,1carboboration reaction and the formation of an intramolecular phosphinoborane FLP. Our group recently discovered that introduction of an ionizable group in the γ-position of an alkynylphosphine result in an unexpected rearrangement reaction to yield zwitterionic allenic-phosphonium borate products which are produced via a transient 3-coordinate phosphonium allenylidene. Herein, we describe how substituent effects on the γ-carbon impact this reactivity and explore how bis(alkynyl)phosphines behave under similar reaction conditions.

Zinc complexes of neutral bidentate ligands that contain an electron-poor diacylated cyclic guanidine are reported, along with their reactivity in solvent-free polymerization of rac-lactide. The diacyl groups significantly decrease the electron-donating ability of the ligand compared to the corresponding nonacylated derivative. This manifested itself through restricted rotation about the formal C−N exo double bond, with the Gibbs free-energy rotational barrier (ΔG ‡) ranging from 47.4 to 59.6 kJ mol −1 . Restricted rotation was also observed for the isopropyl substituent syn to the N exo aryl ring with ΔG ‡ values of 47.5−51.9 kJ mol −1 . Coordination of the ligands to zinc caused further π-electron delocalization from the endocyclic to the exocyclic nitrogen, thereby decreasing the Wiberg bond index of the C−N exo bond from 1.67−1.70 to 1.48−1.50 and eliminating all restricted rotations at room temperature. All three complexes were active in the solvent-free polymerization of rac-lactide with the second-order polymerization rate constant for the anthranilate-based complex of 7.30 × 10 −3 M −1 s −1 . The resulting polymers had a slight heterotactic bias (P r = 0.60) with molecular weights lower than anticipated, possibly due to transesterification, as suggested by mass spectrometry. The mass spectrum of the polymer did not show evidence of the ligand dissociating from the metal during the initiation step and its incorporation into the polymer structure. The acylation of the cyclic guanidine thus imparts advantages to the ligand, with the second building block offering additional opportunities to further improve the catalytic performance of these zinc complexes.

A series of luminescent, neutral pentacoordinate dithieno[3,2‐b:2’,3’‐d]phosphole compounds was synthesized by [4+1] cycloaddition of o‐quinones with the corresponding trivalent phospholes. The electronic and geometrical modification of the π‐conjugated scaffold implemented here impacts the aggregation behavior of the species in solution. It proved successful in generating species with improved Lewis acidity of the phosphorus center that was then leveraged for small‐molecule activation. Hydride abstraction from an external substrate involving the hypervalent species is followed by an intriguing P‐mediated umpolung from the hydride to a proton and supports the catalytic potential of this class of main‐group Lewis acids for organic chemistry. This study is a comprehensive investigation into various methods, including electronic, chemical, geometric modifications (and sometimes combinations of these approaches) to systematically improve the Lewis acidity of neutral and stable main‐group Lewis acids with practical value for a range of chemical transformations.

P-Arylation of dithieno [3,2-b : 2',3'-d]phosphole toward cationic phenyl phospholium species using diaryliodonium reagents was explored. Multiple conditions were tested to optimize the reaction, including variation of solvent, temperature, stoichiometry, time, and aryliodonium species employed. Initial use of diphenyliodonium chloride led to an unexpected dithienophosphole Cu(I) chloride complex that was characterized crystallographically. Alternatively, the use of diphenyliodonium hexafluorophosphate in ethanol under microwave conditions led to the successful isolation of the P-arylated target. The phenyl dithienophospholium species exhibits blue luminescence with a quantum yield of 100 % in solution that is considerably red-shifted in the solid state. The photophysics and solid-state organization of the new species were compared with those of a related methyl congener, showing distinct differences that are assigned to the nature of the carbon-based substituent at the phosphorus center, which was also confirmed by DFT calculations, and the supramolecular organization in the solid state.