Synthesis and reactivity of four-membered azapalladacycles derived from N,N-dialkyl-2-iodoanilines:: Insertion reactions of carbenes into the carbon-palladium bond

Three new four-membered azapalladacycles derived from N,N-dialkyl-2-iodoanilines have been synthesized: [Pd(kappa(2)-C6H4NMe2-2)I(PPh3)] (4a), [Pd{kappa(2)-C6H4N(Me)CH2Ph-2}I(PPh3)] (4b), and [Pd{kappa(2)-C6H4N(Me)Pr-(2)}I(PPh3)] (4c). On heating in solution azapalladacycles 4a and 4c undergo aryl-aryl interchange between the palladium atom and the phosphine ligand to give the phosphanyl-amine palladium complexes [PdPhI(PNMe2)] (7a) and [PdPhI{PN(Me)Pr}] (7c), respectively. Azapalladacycles 4a-c react with dichlorocarbene to give acyl palladium complexes [Pd{kappa(2)-C(O)C6H4NMe2-2}I(PPh3)] (8a), [Pd{kappa(2)-C(O)C6H4N(Me)CH2Ph-2}I(PPh3)] (8b), and [Pd{kappa(2)-C(O)C6H4N(Me)Pr-(2)}I(PPh3)] (8c), respectively. Smooth insertion of N2CHCO2Et into the carbon-palladium bond of azapalladacycles 4a-c results in the formation of the single-insertion products [Pd{kappa(2)-CH(CO2Et)C6H4NMe2-2}I(PPh3)] (9a), [Pd-{kappa(2)-CH(CO2Et)C6H4N(Me)CH2Ph-2}I(PPh3)] (9b), and [Pd{kappa(2)-CH(CO2Et)C6H4N(Me)Pr-2}I(PPh3)] (9c), respectively. On the other hand, complexes 4a and 4c react with N2CHTMS to give mainly the single-insertion products [Pd{kappa(2)-CH(SiMe3)C6H4NMe2-2}I(PPh3)] (10a) and [Pd{kappa(2)-CH(SiMe3)C6H4N(Me)Pr-2}I(PPh3)] (10c), respectively, while under similar reaction conditions 4b affords N-benzyl-N-methyl-2-[(Z)-2-(trimethylsilyl)vinyl]aniline (11b) as a consequence of a double-insertion process. Solid state structures of palladium complexes 4b, 8b(.)EtOAc, 9a, 9b, and 9e(.)Et(2)O have been determined by X-ray analysis.