Racemic and Meso Diastereomers of a P‑Chirogenic Diboranyldiphosphinoethane

Diphosphine ligands have enjoyed great success as supporting moieties for transition elements, where modification of both primary and secondary coordination spheres has been shown to elicit differences in chemical reactivity. This work describes a new family of such ligands constructed from the previously reported scaffold (±)-rac/meso-(t-Bu)ClP-CH2CH2-PCl(t-Bu) that bears bulky tert-butyl substituents. The reaction of this precursor with allyl magnesium chloride and subsequent hydroboration using HBCy2 (Cy = cyclohexyl) provide access to a diboranyldiphosphinoethanethe first in a class of ligands having two electrophilic boranes in their secondary coordination sphere. As a testing ground for coordination, these motifs (and their allyl precursor) have been installed at Ni(0) using [Ni(COD)2] (COD = 1,5-cyclooctadiene) in order to determine methods for clean installation. Product stereochemical outcomes are in some cases complicated and have been determined by nuclear magnetic resonance spectroscopic and crystallographic means. Density functional theory optimizations and accurate DLPNO-CCSD(T) energy calculations were also performed to support structural assignment.