Exploring the coordination chemistry and reactivity of dialkylamino- and bis(dialkylamino)-phosphines in the coordination sphere of metals

Abstract

The coordination chemistry of a range of dialkylamino- and bis(dialkylamino)-phosphines, R_xP(NR′₂)_{3 − x} (x = 1 or 2; R = Cl, Me, Ph, C₆F₅; R′ = Et, Prⁱ), 1–7, has been studied and the resulting Group 6 tetracarbonyl and platinum dichloride bis(phosphine) complexes fully characterised. Subsequently, the reactivity of the P–N bonds of the metal-bound phosphines was probed. Treatment of R″OH (R″ = Me, Et, allyl) solutions of the bis(dialkylaminodiphenylphosphine) complexes with anhydrous HCl gas led to substitution of NR′₂ by OR″; the resulting P-alkoxy complexes were isolated in excellent yields. Acidification of ethylene glycol solutions of the aminophosphine complexes afforded the corresponding bis(chlorodiphenylphosphine) derivatives. Following reaction of trans-[W(CO)₄(P{NEt₂}Ph₂)₂] with either aqueous HCl or H₂SO₄, trans-[W(CO)₄(P{OH}Ph₂)₂] could be isolated as its dichloromethane solvate in excellent yield (81%). Reactions of the bis(bis{dialkylamino}phenylphosphine) complexes under identical conditions yielded a range of unidentified products. Reactions of ligands 1–7 with [{RhCl(CO)₂}₂] and elemental selenium have been undertaken and the products used to assess the phosphines' donor capabilities. Depending on the substituents at phosphorus, either trans-diphosphine or cis-dicarbonyl complexes result from reaction with [{RhCl(CO)₂}₂]. The sterically demanding phosphine P(NPrⁱ₂)₂Ph (5) proved unreactive towards complexation with metals, although its selenide could be prepared and isolated. In order to probe the observed lack of oxidation or complexation the molecular structure P(NPrⁱ₂)₂(C₆F₅) has been determined by X-ray crystallography.