Metal complexes of phosphorus–nitrogen ligands. Part 1. Synthesis and reactivity of some phosphinoaminopyridine complexes of Group 6 metal carbonyls and of bromopentacarbonylmanganese(I)

Abstract

The interaction of 2-(diphenylphosphinoamino)pyridine (dpy) and 2-(diphenylphosphinoamino)-6-methyl-pyridine (dmpy) with u.v.-irradiated tetrahydrofuran solutions of the appropriate metal hexacarbonyls yields the complexes [M(CO)₅L](M = Cr or W, L = dpy or dmpy), [M(CO)₄L](M = Cr, Mo, or W, L = dpy or dmpy), and [W₂(CO)₁₀(dpy)]. The related complexes [MnBr(CO)₃L] and [Mn(CO)₂L₂]Br may be prepared by thermal methods. The complexes have been characterized by ir., n.m.r., electronic, and mass spectroscopy and the mode of ligand co-ordination has been determined. The [W(CO)₅L](L = dpy or dmpy) complexes react with acids HX (X^–= Cl^– Br^–, I^–, [BF₄]^–, or [PF₆]^–) affording cationic ligand complexes, formulated as [W(CO)₅(HL)]X. The molar conductivities (which are anion dependent, increasing along the series Cl^– < Br^– < I^– < [PF₆]^– < [BF₄]^–), and the v(NH) data are indicative of hydrogen bonding between the anion and protonated ligand. From spectral evidence it is concluded that the pyridine nitrogen has been protonated. Excess of acid (e.g. HBr) cleaves the P–N bond yielding primarily [W(CO)₅(PBrPh₂)] and the protonated amine. The ligating properties of [W(CO)₅L] and the oxidation of [W(CO)₄L] by halogens are also reported.