N-Heterocyclic Carbene Stabilized 1-Bora-1,3-butadienes.

Deprotonation of [(NHC)(Fmes)B-allyl] borenium cations (NHC, IMes () or IMe (); Fmes, 2,4,6-(CF)CH) provides an easy entry to the NHC-stabilized 1-bora-1,3-butadienes. They feature a planar s-trans-conformation just like 1,3-butadiene. The 1-borabutadiene undergoes hydroboration reactions; the HB(CF) hydroboration product is trapped with CO or an isonitrile to give the respective cyclic zwitterionic borenium-borate enolate or enamide products. 1-Borabutadiene undergoes 1,4-chalcogenation with elemental sulfur or selenium, and it gives the six-membered heterocyclic 1,4-addition product with the S═O bond of sulfur dioxide. Compound served as a precursor for the formation of a borylated η-allyl ligand at Ru. formed a Rh complex by reaction with [Rh(ethylene)Cl]. It subsequently underwent an intramolecular C-H activation reaction to a mixture of η-methyl-boraallyl Rh complex isomers.