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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 using 31P{1H} and 1H NMR spectroscopy. Compound 5a was 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 H2 generated from C-H borylation converted compound 6 to a series of intermediates. The first is tentatively assigned from 31P{1H} and 1H NMR spectra as (dippe)Ir(H2B3pin3) (7), which is the product of formal H2 addition to compound 5a. As catalysis progressed, compound 7 was converted to a new species with the formula (dippe)Ir(H3B2pin2) (8), which arose from H2 addition to compound 7 with loss of HBpin. Compound 8 was characterized by 31P{1H} and 1H 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 compound 8 as an IrIII agostic borane complex, (dippe)IrH2(Bpin)(?2-HBpin). Compound 8 was gradually converted to (dippe)Ir(H4Bpin) (9), which was characterized by 31P{1H} and 1H NMR spectroscopy and X-ray crystallography. DFT calculations favor its formulation as an agostic borane complex of IrIII with the formula (dippe)IrH3(?2-HBpin). Compound 9 reacted further with H2 to afford the dimeric structure [(dippe)IrH2(?2-H)]2 (10), which was characterized by 1H NMR and X-ray crystallography. Compounds 7-10 are in equilibrium when H2 and HBpin are present.

SUBMITTER: Ghaffari B 

PROVIDER: S-EPMC5297890 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Reversible Borylene Formation from Ring Opening of Pinacolborane and Other Intermediates Generated from Five-Coordinate Tris-Boryl Complexes: Implications for Catalytic C-H Borylation.

Ghaffari Behnaz B   Vanchura Britt A BA   Chotana Ghayoor A GA   Staples Richard J RJ   Holmes Daniel D   Maleczka Robert E RE   Smith Milton R MR  

Organometallics 20150811 19


Catalytic C-H borylation using the five-coordinate tris-boryl complex (dippe)Ir(Bpin)<sub>3</sub> (<b>5a</b>, dippe = 1,2-bis(diisopropylphosphino)ethane) has been examined using <sup>31</sup>P{<sup>1</sup>H} and <sup>1</sup>H NMR spectroscopy. Compound <b>5a</b> was shown to react rapidly and reversibly with HBpin to generate a six-coordinate borylene complex, (dippe)Ir(H)-(Bpin)<sub>2</sub>(BOCMe<sub>2</sub>CMe<sub>2</sub>OBpin) (<b>6</b>), whose structure was confirmed by X-ray crystallograph  ...[more]

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