Non-Innocence of Lutidine-Based PNP Ligands in Nitridorhenium(V) Complexes

The nitridorhenium pincer complexes (tBu2,6-Py)(N)ReCl2 and [(tBu2,6-Py)(N)ReCl][OTf] where tBu2,6-Py = 2,6-bis(ditert-butylphosphinomethyl)pyridine,
in the presence of organometallic reagents and inorganic bases, lead
to three disparate reactions: (1) Base-induced deprotonation of the
methylene side arm leads to dearomatization and formation of complexes
with the ligand tBu2-PyNHO, (where tBu2-PyNHO
= (Z)-6-((ditert-butylphosphaneyl)methyl)-2-((ditert-butylphosphaneyl)methylene)-1,2-dihydropyridine), (2)
nucleophilic addition to the pyridyl ring followed by migration of
protons from the methylene side arm, leading to complexes incorporating
ligands derived from tBu2,6-Pip, (tBu2,6-Pip
= 2,6-bis((di-tert-butylphosphaneyl)methyl)piperidine)
and, (3) transmetalation at rhenium leads to complexes with the tBu2,6-Py ligand. Complexes with all three ligands were alkylated
or arylated with Grignard reagents or alkyl or aryl lithium reagents.
The results presented illustrate the diversity of reactions possible
with lutidine-based PNP ligands.