Double Reduction of Ph 3 B to a Dianionic Borane With a Powerful Sr I Intermediate

Abstract

ABSTRACT Reduction of [(BDI)SrI] 2 with KC 8 generated in situ a (BDI)Sr I species which enabled the reduction of Ph 3 B to the Ph 3 B 2− dianion (BDI = HC[(Me)C═N‐DIPeP] 2 , DIPeP = 2,6‐(Et 2 CH) 2 ‐phenyl). The product (BDI)Sr(BPh 3 )Sr(BDI) features a Ph 3 B 2− dianion that is bridging two Sr 2+ cations by interaction with one of the Ph rings. This polarizes a large part of the electron density in the bridging Ph ring (NPA charge: −1.53) whereas the B is slightly positive (+0.44). The HOMO of the complex mainly consists of the π*‐orbital in the bridging Ph ring overlapping with Sr d ‐orbitals. However, there is also 18% contribution of the B p ‐orbital. In solution, there is coalescence of 1 H NMR signals of all three Ph rings. Complex (BDI)Sr(BPh 3 )Sr(BDI) can react as a 2 e transfer reagent or as a B‐nucleophile. It reacts with I 2 to Ph 3 B and [(BDI)SrI] 2 . Reaction with Ph 3 B led to formation of a Gomberg‐type dimer. The reaction with PhI is smooth and selectively gave (BDI)Sr(Ph 4 B) and [(BDI)SrI] 2 , likely through direct nucleophilic attack of an electron rich B atom at PhI. Isolation of a complex with the elusive Ph 3 B 2− dianion demonstrates the very high reducing power of in situ generated (BDI)Sr I species.