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.