The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW 11 O 39 Ru VI N] 4− has been extended to the N-heterocyclic carbene {CH 2 (Mes)N} 2 C and the coupling product {CH 2 (Mes)N} 2 CNH 2 + characterized by 1 H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW 11 O 39 Ru III {NC{N(Mes)CH 2 } 2 }] 5− has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.