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

Abstract

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.