Syntheses, characterisation and some ligand substitution chemistry of Ru(ii)–diphosphine triflate complexes

Abstract

The complexes cis-[Ru(OTf)2(L–L)2] {L–L = Ph2PCH2PPh2, dppm (1a); (Ph2P)2CCH2, dppen (1b)} react with halide ions, with retention of stereochemistry, to give cis-[RuX2(L–L)2] {L–L = dppm, dppen; X = Br (2), I (3)}. With MeCN, 1a, b yield cis-[Ru(L–L)2(MeCN)2](OTf)2 (4a, b), but cis-[Ru(OTf)2(dppe)2] (1c; dppe = Ph2PCH2CH2PPh2) reacts to give trans-[Ru(dppe)2(MeCN)2](OTf)2 (4c). Whereas 1a reacts readily with 1,2-diaminoethane (en) to give [Ru(dppm)2(en)](OTf)2 (5a) cleanly, 1a, b only react under forcing conditions with 2,2′-bipyridine (bipy) to provide [Ru(L–L)2(bipy)](OTf)2 (6a, b); in addition to 6a (L–L = dppm), some [Ru(dppm)(bipy)2](OTf)2 is also formed via diphosphine displacement. Attempts to obtain [Ru(dppe)2(bipy)](OTf)2 (6c) by this route were unsuccessful. The outcome of reactions of 1a, b with phosphorus donors is governed by steric considerations. For example, while reaction of 1a, b with PMe3 failed to provide [Ru(L–L)2(PMe3)2](OTf)2 complexes, P(OMe)3 reacted readily to yield [Ru(L–L)2{P(OMe)3}2](OTf)2 (7a, b). The reaction of 1a with one equivalent of Me2PCH2CH2PMe2 (dmpe) gave [Ru(dppm)2(dmpe)](OTf)2 (8a) and [Ru(dppm)(dmpe)2](OTf)2 (9a) in a 5 ∶ 1 ratio, although [Ru(dppen)2(dmpe)](OTf)2 (8b) was the only product from an analogous reaction with 1b. However, with one equivalent of Me2PCH2PMe2 (dmpm), 1a reacted to form exclusively [Ru(dppm)(dmpm)2](OTf)2 (10a). The complexes have been characterised by 31P{1H} and 1H NMR spectroscopy, FAB mass spectrometry, and X-ray crystallography in the case of 4a and 7b.