Activation of cyanamide by a molybdenum(0) diphosphinic centre. Formation of cyanoimide and its reactivity with electrophiles

Cyanamide NC–NH2, on reaction with trans-[Mo(N2)2(dppe)2] (dppe = Ph2PCH2CH2PPh2) in thf, undergoes reductive dehydrogenation to cyanoimide NCN2− with formation of trans-[Mo(NCN)2(dppe)2] 1 which is susceptible to protonation, alkylation, acylation, aroylation and silylation, on treatment with electrophiles (E+) such as HBF4, [Et3O][BF4], RC(O)Cl (R = Et, Ph) or Me3SiI, affording the corresponding addition products trans-[Mo(NCN)(NCNH)(dppe)2][BF4] 2, trans-[Mo(NCN)(NCNH2)(dppe)2][BF4]23, trans-[Mo(NCN)(NCNEt)(dppe)2][BF4] 4, trans-[Mo(NCN)(NCNHEt)(dppe)2][BF4]27, trans-[Mo(NCN){NCNC(O)R}(dppe)2]Cl (R = Et 5a, Ph 5b) and trans-[Mo(NCN)(NCNSiMe3)(dppe)2]I 6. The electrophilic addition to the exo-N atom is confirmed by the X-ray crystal structures of 2 and 4 which also show a linear multiple-bond coordination of the cyanoimide and the derived NCNE (E = H or Et) ligands, the latter behaving as weaker π-electron donors than the former.