Synthesis of 1,2-Dihydroquinazolinium-4-yl Palladium Complexes through a Cyclization Reaction

The reaction of trans-[PdI{C(NXy)C6H4NH2-2}(CNXy)2] (1, Xy = C6H3Me2-2,6) with HO3SCF3 (HOTf) and RC(O)R′ affords 1,2-dihydro-3-xylylquinazolinium-4-yl complexes trans-[PdI{CN(Xy)C(R)(R′)NHC6H4-2}(CNXy)2]OTf (R = Me, R′ = Me (2a), Ph (2b), CH2C(O)Me (2c), H (2d), R = H, R′ = H (2e), CHCH2 (2f), Ph (2g), C6H4Me-4 (To) (2h), {Fe(C5H4)(C5H5)} (Fc) (2i)). In the absence of a carbonyl compound, the reaction of 1 with HOTf yields complex SP-4-4-[PdI{C,N-C(NHXy)C6H4NH2-2}CNXy]OTf (3), which reacts with PPh3 to give SP-4-3-[PdI{C(NHXy)C6H4NH2-2}(CNXy)(PPh3)]OTf (4). In turn, 4 reacts with RC(O)R′ to give complexes SP-4-3-[PdI{CN(Xy)C(R)(R′)NHC6H4-2}(CNXy)(PPh3)]OTf (R = R′ = Me (2′a), R = H, R′ = CH(Me)(Ph) (2′b), To (2′c)). A possible intermediate in the cyclization process, trans-[PdI{C(NXy)C6H4NCHTo-2}(CNXy)2] (6), has been prepared by reacting IC6H4NCHTo-2, [Pd2(dba)3]·dba (“Pd(dba)2”) (dba = dibenzylideneacetone) with N ̂N (to give [PdI(C6H4NCHTo-2)(N ̂N)] (N ̂N̂ = 2,2′-bipyridine (bpy, 5a), 4,4′-di-tert-butyl-2,2′-bipyridine (tbbp, 5b)) and XyNC. The crystal structures of complexes 2i, 2′a, 3, and 6 have been determined, and the electrochemical behavior of 2i has been studied.