Dialkylallenylidenekomplexe mit Pentacarbonylfragmenten der VIb Metalle/Dialkylallenylidene Complexes with Pentacarbonyl Fragments of VI b Metals

Abstract

<jats:title>Abstract</jats:title><jats:p> In the context of the synthesis of allenylidene compounds, the reaction of methylpropiolate with a (OC)<jats:sub>5</jats:sub>CrO(C<jats:sub>2</jats:sub>H<jats:sub>5</jats:sub>)<jats:sub>2</jats:sub> complex was investigated. The species pentacarbonyl- (methylpropiolate)chromium(0) (1), 2,4-bis(methoxycarbonyl)-cyclobut-2-en-1-yliden-1- pentacarbonylchromium(0) (2) and cis-2,4-dimethoxycarbonyl-1,3-butadien-1 -yliden-1 - pentacarbonylchromium (3) were isolated. Attempts to synthesize allenylidene complexes from 1 were unsuccessful. Di-iso-propyl or di-tert-butylallenylidene complexes with chromium or tungsten centers (4a, 4b, 5a, 5b) were finally obtained by the photochemical reaction of pentacarbonylpropargylates, (OC)<jats:sub>5</jats:sub>MC(O)C ≡ CCR<jats:sub>2</jats:sub>O<jats:sup>2-</jats:sup>, M = Cr, W, and subsequent desoxygenation. The complexes 4 a, b were characterized as triphenylphosphane adducts, di-iso-propylallenylidenetriphenylphosphorane complexes (6a und 6b). The structure of 6 a was determined by X-ray methods.</jats:p>

Synthesis and Nonlinear Optical Properties of New Heptapentaenylidene Complexes: Study on the Second Harmonic Generation Efficiencies of Amino-Substituted Group 6 Cumulenylidenes

“…The IR spectra of 5a , b are similar to that of complex 4b . For all of these compounds the E and A 1 (trans) ν(CO) absorptions are at very low energy in comparison to nonheteroatom-substituted pentacarbonyl metallacumulenes, indicating a considerable transfer of electron density from the cumulenylidene ligand to the metal center. Analogously to the pentatetraenylidene complexes 3a , b ,11a the new compounds 5a , b show two IR absorptions for the cumulene system (ν(CCCCC) = 2000 w and 2149 w br cm -1 ( 5a ), 2001 w and 2148 w br cm -1 ( 5b )).…”

Addition of diazoalkanes to alkyne(pentacarbonyl)–chromium and –tungsten—formation of 3H-pyrazole complexes

“…When HC Å/ CPh was employed the displacement of the alkyne by nucleophiles already competed with 3H-pyrazole formation. Therefore, from the slow reaction of [(CO) 5 Cr(HC Å/C Á/Ph)] with Et 2 C Á/N 2 three compounds were isolated (Scheme 4); the pyrazole complex 7, small Scheme 3. amounts of an azine complex (8), and the hydrazone complex (9).…”

“…2 -pentacarbonyl(phenylethyne)-chromium with 3-diazopentane: pentacarbonyl(3,3-diethyl-5-phenyl-3H -pyrazole-N2)chromium(0) (7), pentacarbonyl(tetraethyl azine)chromium(0) (8), and pentacarbonyl(diethyl ketonehydrazone)chromium(0) (9) At (/30 8C, two equivalents of 3-diazopentane (relative to [Cr(CO) 6 ]) was added to the concentrated solutions of [(CO) 5 Cr(HC Å/C Á/Ph)]. The progress of the reaction was monitored by IR spectroscopy.…”

“…The polymerization of acetylene, HC Å/ CH, requires irradiation of the solutions to only initiate the reaction whereas for terminal alkynes continued irradiation is necessary [7]. The reaction of [(CO) 5 Cr(Et 2 O)] with a stoichiometric amount of HC Å/ C Á/COOMe, however, afforded in addition to the alkyne complex [(CO) 5 Cr(HC Å/C Á/COOMe)] two products derived from addition of the alkyne to the vinylidene complex tautomer, a cyclobutenylidene complex and a vinylvinylidene complex [8].…”

A unusual bridging mode of vinylidene ligands in nonacarbonyl(vinylidene)dichromium complexes

“…At room temperature these complexes quickly decompose. Therefore, until now only few pentacarbonyl(vinylidene)chromium complexes have been isolated in a pure form, among them two complexes carrying p-acceptor substituents at the vinylidene C b atom [2,3]. Although labile, alkyl-and aryl-substituted vinylidene complexes could be generated at low temperature and used as starting material for a series of transformations of the vinylidene ligand.…”