title: Reversible Borylene Formation from Ring Opening of Pinacolborane and Other Intermediates Generated from Five-Coordinate Tris-Boryl Complexes: Implications for Catalytic C-H Borylation.
abstract: Catalytic C-H borylation using the five-coordinate tris-boryl complex (dippe)Ir(Bpin)3(5a, dippe = 1,2-bis(diisopropylphosphino)ethane) has been examined using31P{1H} and1H NMR spectroscopy. Compound5awas shown to react rapidly and reversibly with HBpin to generate a six-coordinate borylene complex, (dippe)Ir(H)-(Bpin)2(BOCMe2CMe2OBpin) (6), whose structure was confirmed by X-ray crystallography. Under catalytic conditions, the H2generated from C-H borylation converted compound6to a series of intermediates. The first is tentatively assigned from31P{1H} and1H NMR spectra as (dippe)Ir(H2B3pin3) (7), which is the product of formal H2addition to compound5a. As catalysis progressed, compound7was converted to a new species with the formula (dippe)Ir(H3B2pin2) (8), which arose from H2addition to compound7with loss of HBpin. Compound8was characterized by31P{1H} and1H NMR spectroscopy, and its structure was confirmed by X-ray crystallography, where two molecules with different ligand orientations were found in the unit cell. DFT calculations support the formulation of compound8as an IrIIIagostic borane complex, (dippe)IrH2(Bpin)(η2-HBpin). Compound8was gradually converted to (dippe)Ir(H4Bpin) (9), which was characterized by31P{1H} and1H NMR spectroscopy and X-ray crystallography. DFT calculations favor its formulation as an agostic borane complex of IrIIIwith the formula (dippe)IrH3(η2-HBpin). Compound9reacted further with H2to afford the dimeric structure [(dippe)IrH2(μ2-H)]2(10), which was characterized by1H NMR and X-ray crystallography. Compounds7-10are in equilibrium when H2and HBpin are present.
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Behnaz
authors.initials: B
authors.lastname: Ghaffari
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Britt A
authors.initials: BA
authors.lastname: Vanchura
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Ghayoor A
authors.initials: GA
authors.lastname: Chotana
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Staples
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Holmes
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Maleczka
authors.affiliation: Department of Chemistry, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322 United States.
authors.forename: Milton R
authors.initials: MR
authors.lastname: Smith