Racemic and Meso Diastereomers of a P-Chirogenic Diboranyldiphosphinoethane

Diphosphine ligands have enjoyed great success as sup-porting moieties for transition elements, where modifica-tion of both primary and secondary coordination sphere has been shown to illicit differences in chemical reactivi-ty. This work describes a new family of such ligands con-structed from the previously reported scaffold, (±)-rac/meso-(t-Bu)ClP-CH2CH2-PCl(t-Bu) that bears bulky tert-butyl substituents. Reaction of this precursor with allyl magnesium chloride and subsequent hydroboration using HBCy2 (Cy = cyclohexyl) provides access to a di-boranyldiphosphinoethane – the first in a class of ligands having two electrophilic boranes in their secondary coor-dination sphere. As a testing ground for coordination, these motifs (and their allyl precursor) have been in-stalled 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 NMR spectroscopic and crystallographic means. Density func-tional theory optimizations and accurate DLPNO-CCSD(T) energy calculations were also performed to sup-port structural assignment.