A -Phosphinoamidinato NHC-Diborene Catalyst for Hydroboration.

The use of the -phosphinoamidinato NHC-diborene catalyst for hydroboration is described. The -phosphinoamidine BuPN(H)C(Ph)═N(2,6-PrCH) was reacted with BuLi in EtO to afford the lithium derivative, which was then treated with BBr(SMe) in toluene to form the -phosphinoamidinate-bridged diborane . It was reacted with the N-heterocyclic carbene IMe (:C{N(CH)C(CH)}) and excess potassium graphite at room temperature in toluene to give the -phosphinoamidinato NHC-diborene compound . It can stoichiometrically activate ammonia-borane and carbon dioxide. It also showed catalytic capability. A 2 mol % portion of catalyzed the hydroboration of carbon dioxide (CO) with pinacolborane (HBpin) in deuterated benzene (CD) at 110 °C (conversion >99%), which afforded the methoxyborane [pinBOMe] (yield 97.8%, TOF 33.3 h) and the bis(boryl) oxide [(pinB)O]. In addition, 5 mol % of catalyzed the N-formylation of secondary and primary amines by carbon dioxide and pinacolborane to yield the N-formamides (average yield 91.6%, TOF 25.9 h). Moreover, showed chemoselectivity toward catalytic hydroboration of carbonyl compounds. In mechanistic studies, the B═B double bond in compound activated the substrates, the intermediates of which then underwent hydroboration with pinacolborane to yield the products and regenerate catalyst .