Preparation and reactions of alkyl- and arylpentacarbonyltungsten anions

Abstract

Photolysis of (C0)5WCOR-leads to loss of CO and formation of (C0)5WR-. Reaction of RLi with (C0)5WBr-also gives (C0)5WR-species. Reaction of (C0)5WR-with HCI leads to protonation of the carbon-metal bond and formation of RH. Treatment of (C0)5WR-with CO or with P(C&s)3 leads to carbonyl insertion products when R = CH3 or C6H5 but not when R = cH2csI-I~.

Synthesis and Reactivity of New Pyrazolyl‐Functionalized Potassium Silanides

“…This also increases the electron density at the CO trans oxygen atom allowing it to weakly coordinate to the potassium cation. However, the W-Si [2.68 Å], the W-C trans [1.965 Å] [13] and are very similar to the values of the tungsten silyl complexes mentioned above. [11,12] With 4a in hand we investigated its reactivity toward alcohols known to easily replace amino groups at the central silicon by nucleophilic substitution.…”

“…Although extremely oxygen-and moisture-sensitive, 3a is thermally stable and soluble in most organic solvents (benzene, ether, toluene, THF) except hexanes and heptanes. Through 1 H-, 13 C-and 29 Si-NMR spectroscopic studies in C 6 D 6 , the structure in solution has been assigned to be the crown ether complex (Pz tBu Me 2 Si) 3 SiK(18-crown-6) (3a). The 29 Si-NMR spectroscopic data are most instructive as the signal of the central silicon drastically shifted to higher field, from -133.5 in 2a to -197.4 ppm upon replacement of one of the silyl groups by potassium.…”

Interaction of Dihydropyridines and Nucleophiles with Carbene Complexes of Chromium: Diastereo‐ and Enantioselective Synthesis of Polycyclic Butenolides

“…Such insertions were also induced by triphenylphosphane. Scheme 3 That the ligands in these negatively charged alkyl-and acylmetal complexes are even more labile than in carbene complexes [13] has been firmly established by Cooper, [21] since scrambling of the carbonyl groups of the acyl ligand and the additional CO ligands of the metal was observed in the presence of labelled CO. However, the most important and early observation, as far as our investigations are concerned, came from the group of E. O.…”

“…Ϫ (M ϭ Cr, Mo, W) has been achieved by Ruff, [11] Ellis [12] and Casey [13] starting either from [M 2 (CO) 10 ] 2Ϫ and alkyl halides or from [M(CO) 5 Br]…”

“…It is known that benzylic groups are not very prone to migrate to a coordinated carbon monoxide ligand to give an acylmetal derivative. [13,74] However, due to the presence of electron-rich substituents, such as alkoxy groups, the reaction takes place, although the presence of a nitrile, an electron-withdrawing group, inhibits the ''insertion'' of CO completely. Such a behaviour is also known from the literature: methoxycarbonyl substituents on an alkylmetal derivative inhibit the formation of metalacyl complexes.…”