Synthesis of a phosphapyracene via metal-mediated cyclization: Structural and reactivity effects of acenaphthene precursors

Abstract

Metal-mediated synthesis of a new heterocycle, 1-phenyl-phosphapyracene (Ph-4, Ph-PyraPhos), by tandem phosphination/cyclization of peri-substituted 5-bromo-6-chloromethylacenaphthene (3) was investigated for comparison to Pt-catalyzed formation of 1-phosphaacenaphthenes (2, AcePhos) from the analogous naphthalene precursor (1). Reaction of PH 2 Ph with 3, NaOSiMe 3 and a Cu catalyst gave Ph-4; a Pt catalyst yielded PHPh(CH 2 Ar) (Ph-11, Ar = 5-Br-acenaphthyl). Deprotonation of a complex of this secondary phosphine, [Pt((R,R)-Me-DuPhos)(Ph)(PHPh(CH 2 Ar))][PF 6 ] (17), generated the phosphido intermediate Pt((R,R)-Me-DuPhos)(Ph)(PPhCH 2 Ar) (Ph-8), which cyclized to give [Pt((R,R)-Me-DuPhos)(Ph)(Ph-PyraPhos)][PF 6 ] (18). Treatment of Ph-8 with silver triflate gave 18 and the cyclometalated phosphine complex [Pt((R,R)-Me-DuPhos)(κ 2 -(P,C)-5-Ph 2 PCH 2 -6-C 12 H 8)][PF 6 ] (21), which might form via Pt(iv) intermediates. The effects of the added "ace" bridge on structure and reactivity are discussed.