Synthesis and reactivity of new rhenium(I) complexes containing iminophosphorane-phosphine ligands: application to the catalytic isomerization of propargylic alcohols in ionic liquids.

[ReBr(CO)5] reacts with the iminophosphorane-phosphine ligands Ph2PCH2P(═NR)Ph2 (R = P(═O)(OEt)2 (1a), P(═O)(OPh)2 (1b), P(═S)(OEt)2 (1c), P(═S)(OPh)2 (1d), 4-C6F4CHO (1e), 4-C6F4CN (1f), 4-C5F4N (1g)) affording the neutral complexes [ReBr(κ(2)-P,X-Ph2PCH2P{═NP(═X)(OR)2}Ph2)(CO)3] (X = O, R = Et (2a), Ph (2b); X = S, R = Et (2c), Ph (2d)) and [ReBr{κ(2)-P,N-Ph2PCH2P(═NR)Ph2}(CO)3] (R = P(═O)(OEt)2 (3a), P(═O)(OPh)2 (3b), 4-C6F4CHO (3e), 4-C6F4CN (3f), 4-C5F4N (3g)). The reactivity of the cationic complex [Re(κ(3)-P,N,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (4d) has been explored allowing the synthesis of the cationic [Re(L)(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (L = acetone (5a), CH3C≡N (5b), pyridine (5c), PPh3 (5d)) and the neutral [ReY(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3] (Y = Cl (6a), I (6b), N3 (6c)) complexes. The catalytic activity of complex 4d in the regioselective isomerization of terminal propargylic alcohols HC≡CCR(1)R(2)(OH) into α,β-unsaturated aldehydes R(1)R(2)C═CHCHO or ketones R(3)R(4)C═CR(1)COMe (if R(2) = CHR(3)R(4)) under neutral conditions in ionic liquids has being studied. Isolation and X-ray characterization of the key intermediate rhenium(I) oxocyclocarbene complex [Re{═C(CH2)3O}(κ(2)-P,S-Ph2PCH2P{═NP(═S)(OPh)2}Ph2)(CO)3][SbF6] (5e) seems to indicate that the catalytic reaction proceeds through tautomerization of the terminal alkynols to yield vinilydene-type species.