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

Abstract

After displacement of the η 2 -H 2 ligand from [(triphos)Re(CO) 2 (η 2 -H 2 )]BF 4 (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-C 6 H 13 , SiMe 3 ). 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 (CdCH 2 )]BF 4 (7-BF 4 ) can also be obtained by reaction of the (trimethylsilyl)vinylidene complex [(triphos)Re(CO) 2 {CdC(H)SiMe 3 }]BF 4 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-BF 4 into the secondary hydroxycarbene complex [(triphos)Re(CO) 2 {C(OH)-CH 3 }]BF 4 (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 ]BF 4 and methane. Deprotonation of 11 by mild bases gives the acetyl derivative (triphos)Re-(CO) 2 (COCH 3 ), which regenerates the hydroxycarbene precursor by protonation with strong acids. The ethoxycarbene complexes [(triphos)Re(CO) 2 {C(OEt)CH 2 R}]BPh 4 (R ) H, COOEt) are prepared by nucleophilic addition of ethanol across the CdC 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-C 6 H 13 , 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 {CdC(Me)Ph}](OSO 2 CF 3 ). The structural identities in the solid state of the phenylvinylidene complex [(triphos)Re(CO) 2 {CdC(H)Ph}]BF 4 and of the ethoxycarbene complex [(triphos)Re(CO) 2 {C(OEt)CH 3 }]BPh 4 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.

2-Oxacyclopentylidene, 2-Oxacyclohexylidene, and 2-Oxacycloheptylidene Rhenium Complexes by Reaction of ω-Alkynols with the [{MeC(CH2PPh2)3}Re(CO)2]+ Auxiliary

“…[20] The magnetic equivalence Results and Discussion of the two phosphorus atoms lying trans to the two carThe preparations and principal reactions reported in this bonyl ligands is consistent with a rapid rotation of the oxarticle are summarized in Scheme 2. Selected spectroscopic acyclopentylidene group about the ReϭC bond.…”

“…vided in the Experimental Section. The total and unam-A very low-energy barrier to rotation is typical of carbene biguous assignment of all the hydrogen and carbon reso-and vinylidene groups bonded to the [(triphos)Re(CO) 2 ] ϩ nances for all rhenium complexes was obtained by a combi-fragment, [19] [20] and it is also commonly encountered in carnation of 1D-and 2D-NMR spectroscopy including bene complexes with other transition metals.…”

“…[4] A cyclic oxacarbene ligand in 3 is finally supported by the IR spectrum displaying a medium intensity ν(COC) band at 1194 cm Ϫ1 and two strong ν(CO) absorptions at wavenumbers (1962 and 1912 cm Ϫ1 ) that are typical of [(triphos)Re(CO) 2 {ϭCRRЈ}]Y carbene compounds. [20] Replacing 3-butyn-1-ol with (±)-4-pentyn-2-ol in the reaction with 2 affords the substituted 2-oxa-3-methyl-cyclopentylidene complex [(triphos)Re(CO) 2 {ϭCCH 2 CH 2 CH-(Me)O}]BF 4 (4) as air-stable orange crystals. As expected, the presence of a stereogenic carbon atom in the oxacarbene ring differentiates the spectroscopic characteristics of 4 from those of 3.…”

“…[20] Noticeably, the present ReϪC carbene distance is also shorter than that found in (CO) 5 [23] The oxacyclopentylidene ring adopts The solid-state structure of the 2-oxa-3-methyl-cyclopentylidene complex (4) has been determined by a single-crys-an "envelope" conformation with small deviations from the mean plane defined by the rhenium atom, and by the O3 tal X-ray analysis. A view of the complex cation is shown in Figure 2, while selected bond lengths and angles are and C8 to C12 atoms.…”

“…[20] A careful and complete analysis of the 13 C{ 1 H}-NMR The presence of oxacyclohexylidene rings in 5 and 6 is shown by the 13 C{ 1 H}-NMR spectra which exhibit four dif-spectrum was carried out for the unambiguous identification of 8. Key features are a doublet of triplets at δ ϭ ferent methylene resonances (singlets at δ ϭ 16.7, 21.6, 55.6, and 75.0), while the carbene carbon atoms resonate at δ ϭ 310.8, assigned to the carbene carbon atom, and five methylene resonances assigned to the five CH 2 groups of the 2-303.0 (5: dt, J CPtrans ϭ 36.8 Hz, J CPcis ϭ 9.5 Hz) and at δ ϭ 305.3 (6: dt, J CPtrans ϭ 36.9 Hz, J CPcis ϭ 8.6 Hz).…”