Vanadium(I) Chloride and Lithium Vanadium(I) Dihydride as Epimetallating Reagents for Unsaturated Organic Substrates: Constitution and Mode of Reaction

Abstract

Keywords: Epimetallation / EPR spectroscopy of VH 2 -/ Vanadium(I) chloride / Lithium vanadium(I) dihydride / Organic radical intermediates Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH 2 , lithium vanadium(I) dihydride, can be conveniently prepared in THF solution, starting at -78°C, by treating either VCl 3 or VCl 4 with an appropriate number of equivalents of nBuLi. As judged by the stability of solutions or solid samples of LiVH 2 , the preparation of LiVH 2 from VCl 4 is the preferred method. Individual physical characterization of solid samples of VCl or of LiVH 2 , admixed with their LiCl by-product, was carried out after removal of all volatiles in vacuo and by the following measurements: 1) gasometric protolysis with glacial acetic acid and measurement of the H 2 evolved in the oxidation of V I to V II ; 2) infrared spectroscopic search for V-H bands; and 3) examination for unpaired electrons by EPR activity. Such measurements applied to VCl lend strong support for a V I oxidation state but only probable evidence for paramagnetism and for the association of VCl units. Similar measurements applied to

Vanadium(I) Chloride and Lithium Vanadium(I) Dihydride as Selective Epimetallating Reagents for π‐ and σ‐Bonded Organic Substrates

“…In the preceding publication in this series [1] we have described the preparation and structural characterization of these vanadium reagents. The significance of these transition metal complexes lies in their being the first chromium or vanadium reductants shown to exist in a univalent oxidation state.…”

“…[1] Likewise, all apparatus and instrumentation required for the gasometric, IR spectral and EPR analyses are described or specified in the same reference.…”

“…Part 43: Ref. [1] [a] State University of New York at Binghamton, Department of Chemistry, P.O. Box 6000, Binghamton, NY 13902-6000, U.S.A Fax: +1-607-777-4865 E-mail: jjeisch@binghamton.edu smooth McMurry carbonyl coupling to their reductive dimers; 2) deoxygenation of epoxides; 3) selective aromatic C-X reduction; 4) high yields of epimetallated carbonyls or imines as intermediates to α-hydroxy and α-amino acids; 5) 1,4-reductions of 1,3-alkadienes; 6) reductive dimerization of nitriles to ketones; 7) 1,4 or 1,n-epimetallations leading to acyloins or indoles; and 8) reductive dimerizations of azines to produce unusual imidazole derivatives.…”

“…[6] Illustrated in Equation (1) for TiCl 2 (3), [7] it appears to be generally applicable to early transition metal salts, such as Ti(i-OPr) 2 , [8] ZrCl 2 , [9] Zr(OEt) 2 , [10] HfCl 2 [9] and CrCl. [11] The reaction occurs by the partial alkylation of TiCl 4 (1) in THF at -78°C by n-butyllithium and the subsequent loss of butyl radicals from 2 above 0°C. (1) In an important modification, the interaction of the initial CrCl 3 (4) or TiCl 4 (1) salt with four or five equivalents of n-butyllithium, respectively, appears to form a lithium alkylmetallate (5) in Equation (2), whose reductive dealkylation leads to the lithium metal hydride, LiCrH 2 (6).…”

“…[11] The reaction occurs by the partial alkylation of TiCl 4 (1) in THF at -78°C by n-butyllithium and the subsequent loss of butyl radicals from 2 above 0°C. (1) In an important modification, the interaction of the initial CrCl 3 (4) or TiCl 4 (1) salt with four or five equivalents of n-butyllithium, respectively, appears to form a lithium alkylmetallate (5) in Equation (2), whose reductive dealkylation leads to the lithium metal hydride, LiCrH 2 (6). [12] The corresponding reactions starting with TiCl 4 would produce LiTiH 3 , but this hydride has been found to be stable only below 0°C.…”