We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.

The reactivity of ruthenacyclic compounds towards ammonia-borane's dehydrogenation was investigated by considering both hydrolytic and anhydrous conditions. The study shows that the highly soluble μ-chlorido dicarbonylruthenium(II) dimeric complex derived from 4-tert-butyl,2-(p-tolyl)pyridine promotes, with an activation energy E(a) of 22.8 kcal mol(-1), the complete hydrolytic dehydrogenation of NH(3)BH(3) within minutes at ca. 40 °C. The release of 3 eq. of H(2) entails the formation of boric acid derivatives and the partly reversible protonolysis of the catalyst, which produces free 2-arylpyridine ligand and a series of isomers of "Ru(CO)(2)(H)(Cl)". Under anhydrous conditions, hydrogen gas release was found to be slower and the dehydrogenation of NH(3)BH(3) results in the formation of conventional amino-borane derivatives with concomitant protonolysis of the catalyst and release of isomers of "Ru(CO)(2)(H)(Cl)". The mechanism of the protonolysis of the ruthenacycle was investigated with state-of-the-art DFT-D methods. It was found to proceed by the concerted direct attack of the catalyst by NH(3)BH(3) leading either to the formation of a coordinatively unsaturated "Ru(CO)(2)(H)(Cl)" species. The key role of "Ru(CO)(2)(H)(Cl)" species in the dehydrogenation of ammonia-borane was established by trapping and quenching experiments and inferred from a comparison of the catalytic activity of a series of dicarbonylruthenium(II) complexes.

In contrast to structural parameters extracted from X-ray diffraction experiments, CC coupling constants (J CC) prove to be reliable and sensitive probes of α-C−C agostic character.

A carbon supported Pd catalyst is used in the liquid phase hydrogenation of the aromatic cyanohydrin mandelonitrile (C6H5CH(OH)CH2CN) to afford the primary amine phenethylamine (C6H5CH2CH2NH2).

The methyl cyclopropyl hydrotris(3,5-dimethylpyrazolyl)borate complex TpMe2NbMe(c-C3H5)(MeCCMe) reacts smoothly with different alkylaromatics XH at 308 K to yield methane and TpMe2NbX(c-C3H5)(MeCCMe). NMR data show that for mesitylene and 1,4-dimethylbenzene, selective benzylic CH bond activation is observed, giving the benzyl cyclopropyl complexes TpMe2Nb(CH2Ar′)(c-C3H5)(MeCCMe) (Ar′ = 3,5-Me2C6H3, 4-MeC6H4, respectively). Selective arene CH bond activation is observed with 1,2-dimethylbenzene, yielding TpMe2Nb(3,4-Me2C6H3)(c-C3H5)(MeCCMe). With 1,3-dimethylbenzene, a 3:1 mixture of arene and benzylic CH activated products, TpMe2Nb(3,5-Me2C6H3)(c-C3H5)(MeCCMe) and TpMe2Nb(CH2-3-MeC6H4)(c-C3H5)(MeCCMe), is observed, translating to a 18:1 preference for aromatic versus benzylic CH bond activation on a per CH bond basis. Kinetic studies are consistent with rate-limiting intramolecular β-H abstraction of methane to yield a transient unsaturated η2-cyclopropene intermediate. This intermediate reacts rapidly with the aromatic or benzylic CH bond of the arene via 1,3-addition across a Nb(η2-cyclopropene) bond. DFT calculations suggest that the observed selectivities are a result of the steric influence of the methyl groups on the arene ring, which blocks activation of an ortho C–H bond.

The intermolecular C-H bond activation of benzene occurs under very mild conditions (room temperature) via a rare stereospecific 1,3-H addition on an unsaturated eta2-cyclopropene intermediate generated by a beta-H abstraction of CH4 from TpMe2NbMe(c-C3H5)(MeCCMe) to give TpMe2NbPh(c-C3H5)(MeCCMe).

Tyramine hydrogen sulphate is produced via the heterogeneously catalysed selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor.

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