Radical Hydrophosphination Initiated by Triamidoamine-Supported Titanium Despite Insertion into the Ti–P Bond

Abstract

Titanium compounds supported by the triamidoamine ligand (N3N, N(CH2CH2NSiMe33–)3) have been investigated for hydrophos-phination catalysis. The simple titanium alkyl compound (N3N)TiMe (2) demonstrate modest activity as a precatalyst for the pho-tocatalytic hydrophosphination of styrene, but the terminal phosphido compound, (N3N)TiPHPh (4), is inactive. Analysis of these reactions by EPR spectroscopy indicates that (N3N)TiMe undergoes homolytic Ti–C bond cleavage to achieve radical hydrophos-phination. This pathway was further supported in a radical trapping experiment. The phosphido derivative 4 does not produce rad-icals under similar conditions, despite undergoing facile migratory insertion reactions with polar substrates featuring C–N and C–O multiple bonds. Both nitrile and isonitrile substrates insert with ultimate formation of phosphaalkene products, a change in reactivi-ty as comparted to the zirconium congener. Molecular structures of (N3N)TiPHPh (4), (N3N)TiNBnC=PPh (5), and (N3N)TiN(H)C(Ph)=PPh (6) are reported.