Mechanism of formation of the metallacyclic iron carbenes (CO)3Fe[C(NR2)OC(O)NR2] formed by thermal evolution of bis carbamoyl complexes, characterization of η2-carbamoyl intermediates

The reaction of oxalyl chloride with carbamoyl ferrates: {Fe[C(O)NR2](CO)4}− or alkoxy–amine exchanges from Fe(CO2R)2(CO)4 (1) are found to afford the same metallacyclic carbene complexes: (CO)3)NR2] (3) instead of the expected bis carbamoyl: Fe[C(O)NR2]2(CO)4 (2) compounds. Low temperature monitorings and trapping experiments (carried out with phosphines) of the two reactions leading to 3 establish the rapid evolution of 2 into 3 and the easy achievement of η2-carbamoyl bonding modes for these iron complexes. It is also shown that the formation of the metallacycle pattern of 3 is obtained by a carbon–oxygen-coupling process performed between the two carbamoyl ligands of [η1-C(O)NR2][η2-C(O)NR2]Fe(CO)3 intermediates.