Nontrigonal constraint enhances 1, 2-addition reactivity of phosphazenes. Issue 18 (27th April 2018)

• Record Type: Journal Article
• Authors: Lin, Yi-Chun; Gilhula, James C.; Radosevich, Alexander T.
• Is Part Of: Chemical science. Volume 9:Issue 18(2018)
• Page Start: 4338
• Page End: 4347
• Publication Date: 2018-04-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c8sc00929e
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The syntheses and 1, 2-addition reactivities of nontrigonal phosphazenes supported by trianionic tricoordinating chelates of the type L3 PNdipp (3 : L3 = N[CHC( t Bu)O]2 3− ;4 : L3 = N( o -NMeC6 H4 )2 3− ; dipp = 2, 6-diisopropylphenyl) are reported. Abstract : The syntheses and 1, 2-addition reactivities of nontrigonal phosphazenes supported by trianionic tricoordinating chelates of the type L3 PNdipp (3 : L3 = N[CHC( t Bu)O]2 3− ;4 : L3 = N( o -NMeC6 H4 )2 3− ; dipp = 2, 6-diisopropylphenyl) are reported. These compounds are characterized by multinuclear NMR and single-crystal X-ray diffraction experiments. Distorted phosphazenes3 and4 are shown to add B–H, B–O, and Si–H bonds across the formal PN double bond, and their reactivities are contrasted with acyclic analogues. Derivatives of phosphazene3 bearing sterically unencumbered N -substitutents readily dimerize to form the corresponding cyclodiphosphazanes; compounds with sterically demanding N -substituents are interconvertible between their monomeric and dimeric forms. The enhanced electrophilicity of the phosphorus center in nontrigonal phosphazenes3 and4 is rationalized by DFT calculations. Gas phase fluoride ion affinities are computed to be markedly higher for distorted phosphazenes, while proton affinities are largely unaffected by geometric distortion. These results are interpreted to suggest that distortion from pseudotetrahedral geometry results in stabilization of the P-based LUMO, while HOMO energies are essentially unchanged.