Stopping Hydrogen Migration in its Tracks: The First Successful Synthesis of Group Ten Scorpionate Complexes Based on Azaindole Scaffolds

The first successful synthesis and characterization of group ten complexes featuring flexible scorpionate ligands based on 7-azaindole heterocycles are reported herein. Addition of two equivalents of either K[HB(azaindolyl)3] or Li[HB(Me)(azaindolyl)2] to [M(μ-Cl)(η1,η2-COEOMe)]2 leads to the formation of two equivalents of the complexes [M{κ3-N,N,H-HB(azaindolyl)3}(COEOMe)] and [M{κ3-N,N,H-HB(Me)(azaindolyl)2}(COEOMe)] (where M = Pt, Pd; COEOMe = 8-methoxycyclooct-4-en-1-ide), respectively. In these reactions, the borohydride group is directed towards the metal center forming square based pyramidal complexes. In contrast to analogous complexes featuring other flexible scorpionate ligands, no hydrogen migration from boron is observed in these complexes. The fortuitous linewidths observed in some of the 11B NMR spectra allow for a closer inspection of the B–H•••metal unit in scorpionate complexes than has previously been possible in previous examples.