Multiple Re−C Bonds at the [{MeC(CH₂PPh₂)₃}Re(CO)₂]⁺Auxiliary

Abstract

After displacement of the η2-H2 ligand from [(triphos)Re(CO)2(η2-H2)]BF4 (2), ethyne and various 1-alkynes, HC≡CR, are tautomerized at the Re(I) center to vinylidene ligands (R = H, Ph, p-tolyl, COOEt, n-C6H13, SiMe3). A kinetic π-alkyne adduct is intercepted at low temperature during the reaction between 2 and ethyne. The primary vinylidene complex [(triphos)Re(CO)2(CCH2)]BF4 (7-BF4) can also be obtained by reaction of the (trimethylsilyl)vinylidene complex [(triphos)Re(CO)2{CC(H)SiMe3}]BF4 with stoichiometric water. Unprecedented examples of addition of either water or alcohols to Re−vinylidene moieties to give hydroxycarbene or alkoxycarbene complexes are presented. In particular, an excess of water transforms 7-BF4 into the secondary hydroxycarbene complex [(triphos)Re(CO)2{C(OH)CH3}]BF4 (11), which can be isolated in the solid state. Upon thermolysis in refluxing tetrahydrofuran, 11 selectively converts to the tricarbonyl complex [(triphos)Re(CO)3]BF4 and methane. Deprotonation of 11 by mild bases gives the acetyl derivative (triphos)Re(CO)2(COCH3), which regenerates the hydroxycarbene precursor by protonation with strong acids. The ethoxycarbene complexes [(triphos)Re(CO)2{C(OEt)CH2R}]BPh4 (R = H, COOEt) are prepared by nucleophilic addition of ethanol across the CC double bond of the corresponding vinylidene derivatives. Neutral σ-alkynyl complexes of the general formula (triphos)Re(CO)2(C≡CR) (R = Ph, p-tolyl, COOEt, n-C6H13, H) are obtained by reaction of the vinylidene derivatives with strong bases. The reaction of the σ-alkynyl complexes with various methylating agents affords disubstituted vinylidene derivatives, herein exemplified by [(triphos)Re(CO)2{CC(Me)Ph}](OSO2CF3). The structural identities in the solid state of the phenylvinylidene complex [(triphos)Re(CO)2{CC(H)Ph}]BF4 and of the ethoxycarbene complex [(triphos)Re(CO)2{C(OEt)CH3}]BPh4 have been determined by X-ray diffraction analyses. In both complexes the metal center is octahedrally coordinated by a fac triphos ligand, by two mutually cis terminal carbonyls, and by the organyl ligand.