Why does the synthesis of N-phenylbenzamide from benzenesulfinate and phenylisocyanate via the palladium-mediated Extrusion–Insertion pathway not work? A mechanistic exploration

Abstract

The gas-phase extrusion-insertion (ExIn) reactions of the palladium complexes [(phen) n Pd (O 2 SC 6 H 5 )] + (phen = 1,10-phenanthroline, n = 1 or 2), were investigated in the gas phase by multistage mass spectrometry (MS n ) experiments consisting of electrospray ionisation and a linear ion trap combined with density functional theory (DFT) calculations. Desulfination of palladium sulfinate cations under collision-induced dissociation (CID) generates the organopalladium intermediates [(phen) n Pd(C 6 H 5 )] + . Of these two organometallic cations, only [(phen)Pd(C 6 H 5 )] + reacts with phenyl isocyanate via insertion to yield [(phen)Pd(NPhC(O)C 6 H 5 )] + . The formation of a coordinated amidate anion is supported by DFT calculations. In exploring this reactivity in the solution phase, we found that heating a mixture of benzenesulfinic acid, phenylisocyanate and palladium trifluoroacetate under a range of different conditions (ligand free versus with ligand, different solvents, addition of acid or base) failed to lead to the formation N-phenyl-benzamide in all cases. Instead, biphenyl was formed and could be isolated in a yield of 46%. DFT calculations using a solvent continuum reveal that the barrier associated with the insertion reaction lies above the competing sequential reactions of desulfination of a second phenyl sulfinate followed by reductive elimination of biphenyl.

Palladium-mediated CO2 extrusion followed by insertion of ketenes: translating mechanistic studies to develop a one-pot method for the synthesis of ketones

“…Our initial report on transformation of the anionic copper acetate complex [(CH 3 )Cu(O 2 CCH 3 )] − to the anionic copper(I) dithioacetate complex [(CH 3 )Cu(S 2 CCH 3 )] − [17] convinced us that guided by mechanistic studies, these extrusion-insertion (ExIn) reactions could potentially be harnessed for one-pot organic synthetic methods for a wide range of new species including thioamides, amidines, amides, alkenes and ketones (Eqn 1, Scheme 1a). [18][19][20][21][22][23][24] In potential competition with the desired products is the protodecarboxylation side reaction (Eqn 2, Scheme 1a and Cycle B, Scheme 1b). [25,26] Fortunately, comprehensive investigations by Kozlowski's group into the scope of the palladium-catalysed protodecarboxylation side reaction identified potential solvent and additives that suppress this reaction, [25] which provided a valuable starting point in our solution-phase investigations.…”