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

The reaction of trans -[PdI{C(═NXy)C 6 H 4 NH 2 -2}(CNXy) 2 ] ( 1, Xy = C 6 H 3 Me 2 -2,6) with HO 3 SCF 3 (HOTf) and RC(O)R′ affords 1,2-dihydro-3-xylylquinazolinium-4-yl complexes trans- [PdI{C═N(Xy)C(R)(R′)NHC 6 H 4 -2}(CNXy) 2 ]OTf (R = Me, R′ = Me ( 2a ), Ph ( 2b ), CH 2 C(O)Me ( 2c ), H ( 2d ), R = H, R′ = H ( 2e ), CH═CH 2 ( 2f ), Ph ( 2g ), C 6 H 4 Me-4 (To) ( 2h ), {Fe(C 5 H 4 )(C 5 H 5 )} (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)C 6 H 4 NH 2 -2}CNXy]OTf ( 3 ), which reacts with PPh 3 to give SP-4-3- [PdI{C(═NHXy)C 6 H 4 NH 2 -2}(CNXy)(PPh 3 )]OTf ( 4 ). In turn, 4 reacts with RC(O)R′ to give complexes SP-4-3- [PdI{C═N(Xy)C(R)(R′)NHC 6 H 4 -2}(CNXy)(PPh 3 )]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)C 6 H 4 N═CHTo-2}(CNXy) 2 ] ( 6 ), has been prepared by reacting IC 6 H 4 N═CHTo-2, [Pd 2 (dba) 3 ]·dba (“Pd(dba) 2 ”) (dba = dibenzylideneacetone) with N ̂N (to give [PdI(C 6 H 4 N═CHTo-2)(N ̂N)] (N ̂N ̂ = 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.