Usual oxygen bases decompose M/NHC complexes to give “NHC-free” metal species and azolones.

The behavior of ubiquitously used nickel, palladium, and platinum complexes containing N-heterocyclic carbene ligands was studied in solution in the presence of aliphatic amines. Transformation of M(NHC)X 2 L complexes readily occurred according to the following reactions: (i) release of the NHC ligand in the form of azolium salt and formation of metal clusters or nanoparticles and (ii) isomerization of mono-NHC complexes M(NHC)X 2 L to bis-NHC derivatives M(NHC) 2 X 2 . Facile cleavage of the M−NHC bond was observed and provided the possibility for fast release of catalytically active NHC-free metal species. Bis-NHC metal complexes M(NHC) 2 X 2 were found to be significantly more stable and represented a molecular reservoir of catalytically active species. Slow decomposition of the bis-NHC complexes by removal of the NHC ligands (also in the form of azolium salts) occurred, generating metal clusters or nanoparticles. The observed combination of dual fast-and slow-release channels is an intrinsic latent opportunity of M/NHC complexes, which balances the activity and durability of a catalytic system. The fast release of catalytically active species from M(NHC)X 2 L complexes can rapidly initiate catalytic transformation, while the slow release of catalytically active species from M(NHC) 2 X 2 complexes can compensate for degradation of catalytically active species and help to maintain a reliable amount of catalyst. The study clearly shows an outstanding potential of dynamic catalytic systems, where the key roles are played by the lability of the M−NHC framework rather than its stability.

Heating Pd/NHC complexes with aliphatic amines induces Pd–NHC bond cleavage, while treating the complexes with primary or secondary aliphatic amines in the presence of strong bases promotes the activation of molecular Pd/NHC catalysis.

Imidazolium salts have ubiquitous applications in energy research, catalysis, materials and medicinal sciences. Here, we report a new strategy for the synthesis of diverse heteroatom-functionalized imidazolium and imidazolinium salts from easily available 1,4-diaza-1,3-butadienes in one step. The strategy relies on a discovered family of unprecedented nucleophilic addition/cyclization reactions with trialkyl orthoformates and heteroatomic nucleophiles. To probe general areas of application, synthesized N-heterocyclic carbene (NHC) precursors were feasible for direct metallation to give functionalized M/carbene complexes (M = Pd, Ni, Cu, Ag, Au), which were isolated in individual form. The utility of the chloromethyl function for the postmodification of the synthesized salts and Pd/carbene complexes was demonstrated. The obtained complexes and imidazolium salts demonstrated good activities in Pd-or Ni-catalyzed model cross-coupling and CÀ H activation reactions.

Complexes of palladium and nickel with Nheterocyclic carbene ligands (M/NHC, M = Pd, Ni) are widely used as effective catalysts for various amination reactions. A previously unaddressed transformation of M/NHC complexes under typical conditions of the Buchwald−Hartwig amination is disclosed. M II /NHC complexes react with primary aromatic and aliphatic amines in the presence of strong bases to give azol-2(5)imines and M(0) species via a reductive elimination of NHC and azanide (N-deprotonated amine) ligands. Depending on the structures of the NHC and azanide, the N−NHC coupling can make a significant contribution to the M/NHC catalyst decomposition in the Buchwald−Hartwig and other amination reactions conducted in the presence of strong bases. The discovery of the N−NHC coupling reaction has been shown to be critically influenced by the steric bulkiness of N-substituents on the NHC ligand. The high steric bulkiness of the NHC is an important factor in suppressing the N−NHC coupling deactivation pathway.

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Pyridazine derivativesPyridazine derivatives R 0500Pyrrolopyrimidines. Part 5. Reaction of 6-Amino-1,3-dimethylpyrrolo[3,4-d]pyrimidine-2,4(1H,3H)-diones with 1,3-Diketones. -The reaction of the previously unknown aminopyrrolopyrimidine (VII) with 1,3-diketones (VIII) results in the formation of the expected cyclization products (IX). Its analogue lacking the 5-phenyl substituent (X) reacts with these diketones regioselectively furnishing predominantly related product (XI) and only small amounts of the other possible regioisomer (XII). -(TSUPAK, E. B.; SHEVCHENKO, M. A.; POZHARSKII, A. F.; TKACHENKO, Y. N.; Chem. Heterocycl. Compd. (N. Y.) 39 (2003) 7, 953-959; Rostov State Univ., Rostov-on-Don 344006, Russia; Eng.) -Staver 18-146

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