Compounds with Alternating Single and Double Bonds of Antimony and Silicon; Isoelectronic to Ethane-1,2-diimine.

We present an approach for preparing chain-type unsaturated molecules with low oxidation state Si(I) and Sb(I) supported by amidinato ligands that exploit to generate heavy analogues of ethane 1,2-diimine. The reduction of antimony dihalide (R-SbCl) with KC in the presence of silylene chloride afforded L─(Cl)Si═Sb─Tip () and L()Si═Sb─Ph (), respectively. Compounds and further undergo reduction with KC to produce Tip─Sb═LSi─LSi═Sb─Tip () and Ph─Sb═LSi─LSi═Sb─Ph (). The solid-state structures and DFT studies show that all compounds have σ-type lone pairs at each Sb atom. It forms a strong pseudo-π-bond with Si. The pseudo-π-bond is formed by the hyperconjugative donation of the π-type lone pair at Sb to the Si-N σ* MO. The quantum mechanical studies indicate that compounds and has delocalized pseudo-π-MOs arising from hyperconjugative interactions. Hence, and can be considered as isoelectronic to imine, while and are isoelectronic to ethane-1,2-diimine. The proton affinity studies indicate that the pseudo-π-bond resulting from the hyperconjugative interaction is more reactive than the σ-type lone pair.