Comparison of B–B π-bonding in singly reduced and neutral diborane (4) derivatives: isolation and structure of [{Li(Et2O)2}{MeO(mes)BB(mes)OMe}]

Abstract

A single-crystal X-ray diffraction study of [{Li(Et₂O)₂}-{MeO(mes)BB(mes)OMe}]1(mes = C₆H₂Me₃-2,4,6) allows the first structural comparison between singly reduced and neutral diborane(4) species; compound 1 features a shortened B–B bond distance of 1.636(7)Å which may be compared to the 1.724(9)Å observed in the neutral precursor MeO(mes)BB(mes)OMe 2 and a distance of 1.62–1.64 Å observed in related doubly reduced [R₂BBR₂]^2– species; the B–B bond in 1, which has a formal π-bond order of 0.5, is thus similar in length to that found in the doubly reduced diborane(4) dianions that possess a formal B–B π-bond order of unity.