Azobenzenyl Calcium Complex: Synthesis and Reactivity Studies of a Ca(I) Synthon.

Attempted preparation of a low-valent Ca(I) complex by reduction of Ca iodide precursor [LCaI(THF)]2 ( 1 ) (L = [CH3 C(NAr)CHC(CH3 )NCH2 CH2 N(CH3 )2 ]- , Ar = 2,6- i Pr2 C6 H3 ), with KC8 led to isolation of a dinuclear calcium azaallyl complex {[H2 CC(NAr)CHC(CH3 )(NCH2 CH2 N(CH3 )2 )]Ca(THF)}2 ( 2 ). Alternatively, reaction of 1 with KC8 in the presence of azobenzene gives an azobenzenyl calcium complex LCa(PhNNPh)(THF) ( 3 ). The electron paramagnetic resonance and UV-vis spectra of complex 3 suggest that the (PhNNPh) moiety should be regarded as a radical anion. Complex 3 can react with Me3 SiN3 , Me3 SiCHN2 , CS2 , W(CO)6 , elemental sulfur, and AgBr, resulting in the formation of the azido complex [LCaN3 (THF)]2 ( 5 ), isonitril complex {LCa[CNN(Si(CH3 )3 )]}2 ( 6 ), dimeric bis(thiolate) complex {[S2 CC(CMe(NAr))C(Me)NCH2 CH2 NMe2 ]Ca(DME)}2 ( 7 ), metallocyclic carbene complex {[OC(W(CO)5 )N(C6 H5 )]Ca(THF)3 }2 ( 8 ), bis(thiolate) complex {[S2 C(CMe(NAr))C(Me)NCH2 CH2 NMe2 ]Ca(THF)}2 ( 9 ), and bromide complex [LCaBr(THF)]2 ( 10 ). Additional insights on the reaction process resulting in the formation of complex 7 are provided by density-functional theory studies. These results demonstrate that the (PhNNPh)•- radical anion can serve as a very potent one-electron donor, and 3 acts as a low-valent calcium(I) synthon.