Synthesis and properties of a new nine-membered triphospha-macrocyclic complex via a manganese(I) tricarbonyl template

Abstract

Reaction of the primary diphosphine H2P(CH2)2PH2 with [MnBr(CO)5], followed by removal of the bromide by treatment with AgOTf (OTf = CF3SO3) and addition of PAr3 (Ar = o-C6H4F), gives the acyclic precursor complex, fac-[Mn(CO)3{H2P(CH2)2PH2}(PAr3)][OTf], thus positioning the primary phosphine functions adjacent to the o-fluorophenyl substituents. The identity of this species was confirmed by multinuclear NMR (1H, 19F{1H}, 31P{1H} and 55Mn) and IR spectroscopic analysis, as well as from a single crystal X-ray analysis. Subsequent treatment of this complex with KOtBu (potassium tertiary butoxide) causes a double P-C coupling reaction, with defluorination of two aryl groups, and leads to formation of a nine-membered triphosphine macrocyclic complex. Methylation (KOtBu/MeI) of the two remaining secondary phosphine function yields the complex [Mn(CO)3(1)][OTf], which has been characterised similarly by multinuclear NMR and IR spectroscopy, and by electrospray mass spectrometry. A single crystal X-ray structure determination confirms the distorted octahedral coordination at Mn(I), with the triphosphine macrocycle occupying three mutually facial coordination sites. As expected, this complex is extremely thermodynamically stable and kinetically inert, being unaffected by prolonged refluxing with either Me3NO or thiophenolate in MeCN.