Combining Low‐Valent Al^I and Sn^II Metal Centers for Small Molecule Activation

The recently discovered class of potassium aluminyl complexes (R 2 Al − K + ) enables facile access to heterobimetallic Al‐metal bonds by salt metathesis. Reaction of Al I complex ( DIPP BDI‐H)Al − K + with the low‐valent Sn II complex ( DIPP BDI)SnCl gave ( DIPP BDI‐H)AlSn( DIPP BDI) ( 1 ); DIPP BDI = HC[C(Me)N(DIPP)] 2 , DIPP = 2,6‐diisopropylphenyl and DIPP BDI‐H = H 2 CC(N‐DIPP)‐C(H)C(Me)‐N‐DIPP. The crystal structure shows an asymmetric complex with a planar but strongly distorted trigonal coordination geometry at Al and trigonal pyramidal coordination at Sn. This geometry supports a donor–acceptor bonding model in which ( DIPP BDI‐H)Al − donates an sp 2 electron pair in an empty p ‐orbital of ( DIPP BDI)Sn + . Extensive computational analyses support polar covalent AlSn bonding which based on energy decomposition analysis is best described as the interaction of two neutral open shell Al II /Sn I fragments: ( DIPP BDI‐H)Al • /( DIPP BDI)Sn • . Effective‐oxidation state analysis assigns the oxidation states Al I /Sn II supporting the description of the bond as a ( DIPP BDI‐H)Al − → ( DIPP BDI)Sn + donor–acceptor interaction. Reacting the electron‐rich, polarized Al δ+ Sn δ− bond with alkynes gave cis ‐insertion, indicating a concerted reaction with a four‐membered ring transition state. Reaction with CO 2 selectively gave AlO 2 CSn insertion, supporting the nucleophilic character of the electron‐rich Sn center. The dianionic ( DIPP BDI‐H) 2 − ligand is in these reactions not inert and reacts as C‐centered nucleophile with alkyne or CO 2 resulting in dianionic tridentate ligands.