Triphenylsilanolate ligands were found to impart excellent reactivity and outstanding functional group tolerance on molybdenum alkylidyne complexes, which catalyze alkyne metathesis reactions of all sorts. The active species either can be obtained in high yield by adaptation of the established synthesis routes leading to Schrock alkylidynes or can be generated in situ from the molybdenum nitride complex 11, which itself is readily accessible in large quantity from inexpensive sodium molybdate. Complexation of the active silanolate complexes 12 and 24 with 1,10-phenanthroline affords complexes 15 and 25, respectively, which are stable in air for extended periods of time. Although these phenathroline adducts are per se unreactive vis-a-vis alkynes, catalytic activity is conveniently restored upon exposure to MnCl(2). Therefore, the practitioner has the choice of different alkyne metathesis (pre)catalysts, which are easy to handle yet broadly applicable and exceedingly tolerant. A host of representative inter- as well as intramolecular alkyne metathesis reactions, including applications to a considerable number of bioactive and, in part, labile natural products, shows the remarkable scope of these new tools. Moreover, it was found that the addition of molecular sieves (5 A >or= 4 A >> 3 A) to the reaction mixture significantly improves the chemical yields while simultaneously increasing the reaction rates. This benefit is ascribed to effective binding of 2-butyne, which is released as the common byproduct in reactions of alkynes bearing a methyl end-cap. Thus, alkyne metatheses can now be performed at ambient temperature with neither the need to apply vacuum to drive the conversion nor recourse to tailor-made substrates. The structures of representative examples of this new generation of alkyne metathesis catalysts in the solid state were determined by X-ray analysis.

Nitride- and alkylidyne complexes of molybdenum endowed with triarylsilanolate ligands are excellent (pre)catalysts for alkyne-metathesis reactions of all sorts, since they combine high activity with an outstanding tolerance toward polar and/or sensitive functional groups. Structural and reactivity data suggest that this promising application profile results from a favorable match between the characteristics of the high-valent molybdenum center and the electronic and steric features of the chosen Ar(3)SiO groups. This interplay ensures a well-balanced level of Lewis acidity at the central atom, which is critical for high activity. Moreover, the bulky silanolates, while disfavoring bimolecular decomposition of the operative alkylidyne unit, do not obstruct substrate binding. In addition, Ar(3)SiO groups have the advantage that they are more stable within the coordination sphere of a high-valent molybdenum center than tert-alkoxides, which commonly served as ancillary ligands in previous generations of alkyne metathesis catalysts. From a practical point of view it is important to note that complexes of the general type [(Ar(3)SiO)(3)Mo≡X] (X = N, CR; R = aryl, alkyl, Ar = aryl) can be rendered air-stable with the aid of 1,10-phenanthroline, 2,2'-bipyridine or derivatives thereof. Although the resulting adducts are themselves catalytically inert, treatment with Lewis acidic additives such as ZnCl(2) or MnCl(2) removes the stabilizing N-donor ligand and gently releases the catalytically active template into the solution. This procedure gives excellent results in alkyne metathesis starting from air-stable and hence user-friendly precursor complexes. The thermal and hydrolytic stability of representative molybdenum alkylidyne and -nitride complexes of this series was investigated and the structure of several decomposition products elucidated.

A matter of convenience: Schrock molybdenum alkylidenes are amongst the most powerful olefin metathesis catalysts known to date, but their sensitivity to air and moisture mandates their handling in a glove-box or by Schlenk techniques. This inconvenience is circumvented by using the corresponding phenanthroline- or bipyridine adducts, which are bench-stable and hence very user-friendly. The active species can be liberated from these precatalysts in uncompromised form on treatment with ZnCl₂ in toluene

A wide variety of metabolic products of polyunsaturated fatty acids is of paramount importance for improving our medical knowledge in the field of oxidized lipids. Two novel metabolites of n-3 polyunsaturated fatty acids, 8-F3t-IsoP and 10-F4t-NeuroP as well as a deuterated derivative thereof were synthesized based on an acetylenic intermediate. An original approach achieved lateral chain insertion of 8-F3t-IsoP by a ring-closing alkyne metathesis/semi-reduction strategy together with a temporary tether.

Using TMPZnCl·LiCl as a kinetically highly active base, nitriles and esters undergo a Pd-catalyzed α-arylation under mild conditions. Remarkably, in the case of α,β- or β,γ-unsaturated nitriles, a regioselective γ-arylation or a γ-alkenylation is observed.

Complex 1 and related tetracoordinate molybdenum alkylidenes developed by Schrock and co-workers range amongst the most powerful alkene metathesis catalysts known to date. [1,2] They are distinguished by exceptional reactivity, good functional group tolerance and a remarkable scope, encompassing olefins that are considered difficult substrates on steric and/or electronic grounds. [3,4] The modularity of the established synthesis route allowed the operative motif of 1 to be systematically edited and hence gave rise to several generations of descendant catalysts with tailored properties. Most notable among them are Schrock alkylidenes with chiral alkoxide or diolate ligands and/or alkylidenes that are chiral at metal for all sorts of asymmetric metathesis reactions, [3,5] as well as catalysts that impose high Z-selectivity on certain metathesis reactions. [6] As complex 1 and relatives, however, are very sensitive to air and moisture, their handling is clearly more demanding than that of the competing ruthenium carbenes introduced by Grubbs. [7] To overcome this disadvantage, we now present a simple way of rendering prototype Schrock alkylidenes largely air-stable, which facilitates their handling and may hence encourage more widespread use of these able catalysts in preparative laboratories.Based on recent observations made in the alkyne metathesis arena, [8,9] solutions of 1 in toluene were reacted at room temperature with equimolar amounts of 1,10-phenanthroline or 2,2'-bipyridine. The resulting crystalline adducts 2 and 3 turned out to be surprisingly robust in the solid state as well as in solution. [10] Their integrity can be easily checked by NMR spectroscopy due to the characteristic downfield shift of the alkylidene proton from d H (CD 2 Cl 2 ) = 12.19 ppm in the parent complex 1 to d H (CD 2 Cl 2 ) = 13.88 and 13.74 ppm in 2 and 3, respectively. According to this distinctive signature, a sample of the bipyridine adduct 3 stored at the bench in an open flask was fully intact after eight weeks, whereas the corresponding phenanthroline adduct 2 was found to be somewhat less stable (only ca. 50 % intact after four weeks). Other prototype molybdenum alkylidenes such as the triphenylsilanolate complex 4 [11] and the chiral variant 6 [12] also form adducts that remain intact when stored without any precautions for extended periods (Scheme 1).The structure of the particularly robust complex 3 in the solid state is depicted in Figure 1. The coordination geometry about the Mo VI center can be described as distorted octahedral, with the imido ligand and one of the two inequivalent hexafluoro-tert-butanolates residing trans to each other, even though the corresponding N3-Mo1-O2 angle (167.04(4)8) strongly deviates from linearity. Likewise, the angle between the alkylidene C19 carbon and the trans-positioned N2 atom of the bipyridine is reduced to 167.02(4)8. The distortion of the ligand sphere also manifests in very uneven bond distances between the Mo center and the N atoms of the chelating bipyridine unit. The fact...

1,4-Bis[1-(2-hydroxyethyl)-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12a), 1,4-bis[1-isopropoxycarbonylmethyl-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (12b), and 1,4-bis[1-carboxymethyl-1H-tetrazol-5-yl]-1,4-dimethyl-2-tetrazene (13) have been synthesized as new nitrogen-rich compounds. The tetrazenes were obtained by oxidation of the corresponding tetrazolylhydrazines using bromine. Moreover, a new method to prepare tetrazolylhydrazines in high yield using 5-bromotetrazoles has been developed. 12a, 12b, and 13 were characterized using vibrational spectroscopy (IR, Raman), mass spectrometry, and multinuclear NMR spectroscopy. The crystal structures of 12a, 12b, and 13 were determined using single crystal X-ray diffraction. Furthermore, the energetic properties of 12a, 12b, and 13 have been investigated using DSC and bomb calorimetric measurements. The sensitivity data toward impact and friction has been determined using BAM methods.

Deprotonating substituted cyclohexanecarbonitriles with TMPZnCl·LiCl affords zincated nitriles that diastereoselectively couple with aryl bromides in the presence of catalytic Pd(OAc)(2) and S-Phos. Steric and electronic effects influence the diastereoselectivity; 4-t-butyl-, 4-TBSO-, and 2-Me-cyclohexanecarbonitriles exert virtually complete diastereocontrol whereas modest diastereoselectivity is observed with 4-i-Pr-, 4-Me-, and 3-Me-cyclohexanecarbonitriles. The unusual diastereoselectivity trends should prove useful for synthesizing substituted cyclohexanecarbonitrile-containing pharmaceuticals.