LOW-VALENT RHENIUM-OXO COMPLEXES .13. RHENIUM(I) TRIS(ACETYLENE) COMPLEXES - RE(OR')RCCR)3 AND (RE(L(RCCR)3)OTF

The syntheses of a number of rhenium(I) tris(acetylene) compounds are presented, including an improved synthesis of ReI(RC=CR)3 (1a, R = Me; lb, R = Et). Reaction of the low-valent oxo anions NaRe(O)(RC=CR)2 with Me3SiCl in the presence of RC=CR yields Re(OSiMe3)-(RC=CR)3 (2). Colorless 2a crystallizes in the tetragonal space group I4(1)/a, with a = 27.631(3) A, c = 9.699(1) A, and Z = 16. The structure is similar to those of isoelectronic tungsten(0) tris(acetylene) complexes such as W(CO)(PhC=CPh)3. Compounds 2 react readily with acids and acidic alcohols to form Re(OR)(RC=CR)3 (HOR = acetic acid, p-toluenesulfonic acid, phenol, (CF3)2CHOH); reaction with HCI (g) yields ReCl(RC=CR)3. In addition, the Lewis acids Me3SiCl and Me3SiOTf and 2 form ReCl(RC=CR)3 and Re(OTf)(RC=CR)3 (3), along with (Me3Si)20 (OTf = CF3SO3, triflate). Compounds 3 can also be synthesized from 1 and AgOTf or by addition of 2 equiv of Me3SiOTf to NaRe(O)(RC=CR)2. The triflate ligand appears to be covalently coordinated from IR and F-19 NMR spectroscopy, but it is readily displaced by better ligands (L = PMe3, OPMe3, CH3CN, pyridine, pyridine N-oxide) to give [Re(L)(R=CR)3]OFt complexes. Weakly coordinating ligands form equilibrium mixtures (e.g., 3 + H2O reversible [Re(H2O)(RC=CR)3]OTf (4)). Reactions of 3 with NaOMe in MeOH/C6H6 yield methoxide complexes, Re(OMe)(RC=CR)3(5). Re(OMe)(EtC=CEt)3(5b) reacts with 2-butyne by acetylene exchange. The reaction occurs within 2 days at 25-degrees-C and appears to be first order in 5b and zero order in 2-butyne, consistent with a dissociative pathway. The rates of acetylene exchange for Re(OR')(RC=CR)3 Vary widely in the order OMe almost-equal-to OSiMe3 > OPh >> OAc, OTf, paralleling the basicity of the anionic ligands. Unlike the related hydroxide compound,10 the methoxide, phenoxide, and acetate complexes do not rearrange to the stable oxo-alkyl or oxo-acyl compounds Re(O)R'(RC=CR)2 (R' = Me, Ph, C(O)Me), either thermally or photochemically.