Gallium phosphaketenes derived from bis(imino)acenaphthenes (bian): synthesis and reactivity towards a trityl radical and bian-gallylene

Abstract

Phosphaketenes are important versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel mono- and bis-phosphaketenes based on redox-active acenaphthene-1,2-diimine ligands (bian) and their reactions with bian-gallylene and a trityl radical. The interaction of diiodide gallium(III) [(Ar^BIG-bian)GaI₂] (Ar^BIG-bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) with two equivalents of sodium phosphaethynolate [Na(PCO)(diox)_0.5] gives the first paramagnetic phosphaketene [(Ar^BIG-bian)Ga(PCO)₂] (1). Reaction of 1 with gallylene [(Ar^BIG-bian)Ga] leads to phosphaketene [(Ar^BIG-bian)Ga(PCO)] (2). Gallium phosphaketene [(Ar^BIG-bian)Ga(Py)(PCO)] (3) is formed as a result of the interaction between diimine Ar^BIG-bian and excess gallium metal in the presence of gallium chloride in pyridine and a subsequent metathesis reaction with sodium phosphaethynolate. The addition of a trityl radical to 3 produces a sterically hindered alkyl complex [(Ar^BIG-bian)Ga(CPh₃)] (4). New compounds 1–4 have been characterized by ESR (1) and NMR (2–4) spectroscopy; their molecular structures have been established by single-crystal X-ray analysis. The electronic structures of 1–4 and reaction thermodynamics were studied by DFT calculations.