Scorpionate Ligands Based on 2-Mercaptopyridine: A Ligand with a Greater Propensity To Sting?

The synthesis and characterization of the first platinum
group
metal complexes of the recently reported ligand [H2B­(mp)2]− (where mp = 2-mercaptopyridyl) are presented
herein. Addition of 2 equiv of Na­[H2B­(mp)2]
to [MCl­(COD)]2 (where M = Rh, Ir; COD = 1,5-cyclooctadiene)
leads to the hydride migration products [Rh­{κ3-SSB-BH­(mp)2}­(η3-C8H13)] and [Ir­(H)­{κ3-SSB-BH­(mp)2}­(η4-C8H12)], respectively. Structural characterization of the rhodium complex
reveals a notably short rhodium–boron distance of 2.054(2)
Å. The reactivity observed for the rhodium complex is different
from that of all known scorpionate ligands, suggesting a higher propensity
for hydride migration within the 2-mercaptopyridine-based ligands.
The complex [Ir­(Cl)­{κ3-SSB-BH­(mp)2}­(η4-C8H12)], which
is formed via hydride/halide exchange in chloroform, is also structurally
characterized. The new complexes provide rare examples of metallaboratrane
complexes where one hydrogen substituent remains at the boron center.