Synthesis, reactivity and catalytic activity in transfer hydrogenation of ketones of ruthenium(ii) and ruthenium(iv) complexes containing the novel N-thiophosphorylated iminophosphorane-phosphine ligands Ph2PCH2P{NP(S)(OR)2}Ph2 (R = Et, Ph)

Abstract

Iminophosphorane-phosphines Ph₂PCH₂P{NP(S)(OR)₂}Ph₂ (R = Et 1a, Ph 1b) have been prepared by treatment of bis(diphenylphosphino)methane with an equimolar amount of thiophosphorylated azides (RO)₂P(S)N₃. Dimers [{Ru(η⁶-p-cymene)(μ-Cl)Cl}₂] and [{Ru(η³:η³-C₁₀H₁₆)(μ-Cl)Cl}₂] react with a two-fold excess of 1a,b yielding the neutral complexes [Ru(η⁶-p-cymene)Cl₂(κ¹-P-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)] (R = Et 2a, Ph 2b) and [Ru(η³:η³-C₁₀H₁₆)Cl₂(κ¹-P-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)] (R = Et 5a, Ph 5b), respectively. Treatment of 2a,b and 5a,b with one equivalent of AgSbF₆ affords the cationic species [Ru(η⁶-p-cymene)Cl(κ²-P,S-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)][SbF₆] (R = Et 3a, Ph 3b) and [Ru(η³:η³-C₁₀H₁₆)Cl(κ²-P,S-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)][SbF₆] (R = Et 6a, Ph 6b), respectively. The structure of the cation of complex 6a has been confirmed by X-ray crystallography. The preference observed for the κ²-P,S- vs. κ²-P,N- coordination of 1a,b seems to be sterically controlled since theoretical calculations on the models [Ru(η⁶-C₆H₆)Cl(κ²-P,N-H₂PCH₂P{NP(S)(OH)₂}H₂)]⁺A and [Ru(η⁶-C₆H₆)Cl(κ²-P,S-H₂PCH₂P{NP(S)(OH)₂}H₂)]⁺B show that isomer A is ca. 5.0 kcal mol⁻¹ more stable than B. Dicationic complexes [Ru(η⁶-p-cymene)(κ³-P,N,S-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)][SbF₆]₂ (R = Et 4a, Ph 4b) and [Ru(η³:η³-C₁₀H₁₆)(κ³-P,N,S-Ph₂PCH₂P{NP(S)(OR)₂}Ph₂)][SbF₆]₂ (R = Et 7a, Ph 7b) have been obtained by treating 2a,b and 5a,b, respectively, with two equivalents of AgSbF₆. The reactivity of [Ru(η⁶-p-cymene)(κ³-P,N,S-Ph₂PCH₂P{NP(S)(OEt)₂}Ph₂)][SbF₆]₂4a towards neutral and anionic ligands has been explored allowing the synthesis of complexes [Ru(η⁶-p-cymene)(L)(κ²-P,S-Ph₂PCH₂P{NP(S)(OEt)₂}Ph₂)][SbF₆]₂ (L = NCMe 8, PMe₃9, PMe₂Ph 10, PMePh₂11) and [Ru(η⁶-p-cymene)X(κ²-P,S-Ph₂PCH₂P{NP(S)(OEt)₂}Ph₂)][SbF₆] (X = Br 12, I 13, N₃14), respectively. The catalytic activity of complexes 2–7a,b in transfer hydrogenation of ketones by propan-2-ol has been also studied.