title: P-N Cooperative Borane Activation and Catalytic Hydroboration by a Distorted Phosphorous Triamide Platform.
abstract: Studies of the stoichiometric and catalytic reactivity of a geometrically constrained phosphorous triamide 1 with pinacolborane (HBpin) are reported. The addition of HBpin to phosphorous triamide 1 results in cleavage of the B-H bond of pinacolborane through addition across the electrophilic phosphorus and nucleophilic N-methylanilide sites in a cooperative fashion. The kinetics of this process of were investigated by NMR spectroscopy, with the determined overall second-order empirical rate law given by ν = -k[1][HBpin], where k = 4.76 × 10-5M-1s-1at 25 °C. The B-H bond activation process produces P-hydrido-1,3,2-diazaphospholene intermediate 2, which exhibits hydridic reactivity capable of reacting with imines to give phosphorous triamide intermediates, as confirmed by independent synthesis. These phosphorous triamide intermediates are typically short lived, evolving with elimination of the N-borylamine product of imine hydroboration with regeneration of the deformed phosphorous triamide 1. The kinetics of this latter process are shown to be first-order, indicative of a unimolecular mechanism. Consequently, catalytic hydroboration of a variety of imine substrates can be realized with 1 as the catalyst and HBpin as the terminal reagent. A mechanistic proposal implicating a P-N cooperative mechanism for catalysis that incorporates the various independently verified stoichiometric steps is presented, and a comparison to related phosphorus-based systems is offered.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Lin
authors.affiliation: Department of Food Science and Technology, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Hatzakis
authors.forename: Sean M
authors.initials: SM
authors.lastname: McCarthy
authors.forename: Kyle D
authors.initials: KD
authors.lastname: Reichl
authors.forename: Ting-Yi
authors.initials: TY
authors.lastname: Lai
authors.forename: Hemant P
authors.initials: HP
authors.lastname: Yennawar
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Alexander T
authors.identifier: 0000-0002-5373-7343
authors.initials: AT
authors.lastname: Radosevich
mesh_terms: D000577:Amides / Q000737:chemistry*; D001880:Boranes / Q000138:chemical synthesis* / Q000737:chemistry*; D002384:Catalysis; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000577:Amides; D001880:Boranes; D010758:Phosphorus; D009584:Nitrogen