Twist of a Silicon-Silicon Double Bond: Selective Anti-Addition of Hydrogen to an Iminodisilene

Hydrogenation of alkenes with C=C bonds is a ubiquitous reaction in organic chemistry. However, this transformation remains unknown for heavier counterparts, disilenes with Si=Si bonds. Here we report the isolation of (Z)-diiminodisilyldisilene 2 featuring a highly trans-bent and twisted structure and the longest silicon-silicon double bond reported to date. In silico studies suggested that the Si=Si bond in 2 is described as very weak double donor-acceptor bond. We utilized the remarkable electronic and structural features of this product to achieve the first demonstration of hydrogen activation by a multiply bonded silicon compound under ambient conditions. Interestingly, NMR and X-ray analysis gave exclusively racemic (RR/SS)-1,2-disilane 3a, indicating a stereospecific trans-hydrogenation of the Si=Si bond. In-depth calculations revealed that in strong contrast to the reactivity of C=C bonds, a concerted anti-addition pathway was favored due to the twisted structure of 2.