Formation of and equilibria between some five- and six-co-ordinate chloro-oxomolybdenum(V) complexes in dichloromethane

Abstract

The equilibria [MoOCl₃L₂]⇌[MoOCl₃L]+ L in CH₂Cl₂ solution at 25 °C have been studied by e.s.r. Spectroscopy. When L = Ph₃PO, (Me₂N)₃PO, or thf, no [MoOCl₃L] species have been detected, where as when L = Ph₃PS, (Me₂N)₂CS, or Me₂S, [MoOCl₃L] predominates. The new complexes [MoOCl₃L][L = Ph₃PS, (Me₂N)₂CS, Ph₃PSe, orPh₃PO] and [MoOCl₃{SC(Nme₂)₂}₂] have been isolated. Similarly the equilibria [MoOCl₄]^–+ L^n–⇌[MoOCl₄L]^(n+1)– have been studied [L = Ph₃PO, (Me₂N)PO, py, Et₃N, thf, H₂O, Ph₃PS, and (Me₂N)₂CS, n= 0; L = Cl^–, n= 1]. When L =(Me₂N)₃PO only [MoOC₄L]^– has been detected. With the other neutral donors the order of ability to form [MoOCl₄L]^– is py > Ph₃PO ≈ H₂O thf Et₃N, whereas no six-co-ordinate species have been detected for L = Ph₃PS or (Me₂N)₂CS. With L = Cl^– the degree of formation of [MoOCl₅]^2–is low and dependent on both the nature of the cation and total molybdenum concentration. By comparison of the results in CH₂Cl₂, it is concluded that the molybdenum(V) species formed on dissolving [Et₃N]₂[MoOCl₅] or MoOCl₅ in concentrated aqueous HCl is [MoOCl₄(OH₂)]^– and not [MoOCl₅]^2– as is generally supposed.