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

Abstract

Attempted preparation of a low-valent Ca(I) complex by reduction of Ca iodide precursor [LCaI(THF)]2 (1) (L = [CH3C(NAr)CHC(CH3)NCH2CH2N(CH3)2]-, Ar = 2,6-iPr2C6H3), with KC8 led to isolation of a dinuclear calcium azaallyl complex {[H2CC(NAr)CHC(CH3)(NCH2CH2N(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 Me3SiN3, Me3SiCHN2, 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 {[S2CC(CMe(NAr))C(Me)NCH2CH2NMe2]Ca(DME)}2 (7), metallocyclic carbene complex {[OC(W(CO)5)N(C6H5)]Ca(THF)3}2 (8), bis(thiolate) complex {[S2C(CMe(NAr))C(Me)NCH2CH2NMe2]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.