A palladium-mediated one-pot synthesis of amidines from aromatic carboxylic acids and carbodiimides (RNCNR) is reported as an isoelectronic adaption of CO 2 ExIn (ExIn = Extrusion−Insertion) reactions developed for the synthesis of thioamides from carboxylic acids and isothiocyanates (RNCS). Multistage mass spectrometry (MS n ) experiments for model systems established "proof of concept", demonstrating decarboxylation of [(L)Pd(O 2 CAr)] + (L = 1,10-phenanthroline or py), to give [(L)PdAr] + , followed by reaction with a carbodiimide, RNCNR, to yield [(L)Pd(NRC(NR)Ar)] + (R = isopropyl). DFT calculations predicted these reactions as highly exothermic and occurring via carbodiimide insertion into the Pd−Ph bond. 2,6-Dimethoxy and 2,4,6-trimethoxy substitution for the Pd−Ar moiety results in slower reactions with minor changes in mechanism. The individual reaction steps associated with the conversion of 2,6-dimethoxybenzoic acid and 2,4,6trimethoxybenzoic acid into amidines in solution was probed by 1 H NMR spectroscopy as was the use of stoichiometric amounts of PdX 2 salts (X = O 2 CCH 3 and O 2 CCF 3 ) and three different carbodiimides, RNCNR (R = i Pr, c Hex, and Ph). Use of palladium trifluoroacetate gives less of the undesired protodecarboxylation product formed by protonation of the Pd−Ar bond to release ArH. DFT studies for solution phase one-pot reactions provide support for the mechanism and explain competitive factors contributing to the desired insertion step or the alternative protonation step to release ArH. An understanding of mechanism obtained from the model studies encouraged development of a solution-phase one-pot synthesis of N,N′diisopropyl-2,6-dimethoxybenzamidine using stoichiometric amounts of palladium carboxylates. Reaction conditions, product isolation and characterization, yields, and the scope of the one-pot synthesis of N,N′-R 2 -2,6-dimethoxybenzamidine were established, in which borohydride is added in workup as a hydrogen source. Attempts to make the chemistry catalytic in palladium are described.

Mechanistic studies of a stoichiometric palladium-mediated ExIn (ExIn = extrusion–insertion) decarboxylative amidation of aromatic carboxylic acids are presented, providing gas-phase and condensed-phase spectroscopic data, as well as theoretical computational evidence for intermediates in a proposed stepwise process. The understanding gained from these mechanistic studies directed the development of a palladium-catalyzed procedure in which benzamides are obtained in good to high yields in a one-pot 30 min microwave irradiation assisted protocol. A combination of experimental data and DFT calculations reveals that certain ligand additives favor the selective formation of benzamides rather than the undesired protodecarboxylation side product.

The use of silver as a catalyst in cross-coupling reactions remains underdeveloped. We show by means of electrospray-ionization mass spectrometry that the diorganylargentates LiAgR′ 2 •Li(CN) (R′ = Me, Bu) formed in situ react with a wide scope of alkyl and aryl halides RX to afford the tetraorganylargentate(III) complexes R′ 3 AgR − . Upon fragmentation in the gas phase, these high-valent species readily undergo reductive elimination. The trimethylorganylargentates Me 3 AgR − furnish the synthetically desired crosscoupling products MeR with high selectivity, whereas the tributylorganylargentates Bu 3 AgR − yield more of the homocoupling product Bu 2 . Quantum chemical calculations reproduce the experimentally observed trends in reactivity and moreover provide insight into the structures and energetics of the species involved. Our findings indicate that the facile formation of tetraorganylargentate complexes and their high tendency toward reductive elimination can be exploited for the development of silver-mediated cross-coupling reactions as a viable alternative to established synthetic methods.

A new decarbonylation reaction is observed for [(K-acetate)Pd(K-diphosphine)] complexes. Gas-phase IR experiments identify the product as [CHPd(OP(Ph)CHPPh)]. DFT calculations uncovered a plausible mechanism involving O atom abstraction by the diphosphine ligand within the coordination sphere to yield the acetyl complex, [CHCOPd(OP(Ph)CHPPh)], which then undergoes decarbonylation.