Syntheses, Structures, and Reactivity of Barium Carbene Complexes with Chelating Bis-iminophosphorano Arms

Abstract

Reaction of (Me 3 SiN PPh 2 ) 2 CH 2 with Ba[N(SiMe 3 ) 2 ] 2 in 1:1 ratio gave only monodeprotonation and the homoleptic product [(Me 3 SiN PPh 2 ) 2 CH] 2 Ba ( 3-Ba ) was formed. Reaction with the strong base dibenzylbarium gave fast and clean 2-fold deprotonation and the dimeric complex [(Me 3 SiN PPh 2 ) 2 CBa·THF] 2 ( 1-Ba ) was isolated. Also the bulkier ligand (2,6- i Pr 2 C 6 H 3 −N PPh 2 ) 2 CH 2 was doubly deprotonated by this reagent, which gave clean formation of the monomeric complex (2,6- i Pr 2 C 6 H 3 −N PPh 2 ) 2 CBa·(THF) 3 ( 2-Ba ). Although organobarium compounds generally show high reactivity, the monomeric barium carbene complex 2-Ba reacted sluggishly with benzophenone or adamantyl cyanide and reaction products could not be identified. Reaction of 2-Ba with cyclohexyl isocyanate, however, cleanly gave the [2+2]-cycloaddition product, which crystallized as a dimer ( 4 ). Crystal structures of monomers 2-Ba and 3-Ba and dimers 1-Ba and 4 show in all cases tridentate ( C, N, N ‘)-coordination of the bis-iminophosphorano ligand. In some cases the large coordination sphere of Ba 2+ was saturated by agostic i Pr···Ba 2+ and π-Ph···Ba contacts.