Denitrogenative Carbon Skeleton Cleavage and Reorganization of Pyridines by a Trinuclear Titanium Polyhydride Complex

Selective skeletal transformations of aromatic N-heterocycles are of fundamental interest and practical importance but remain a formidable challenge due to their pronounced aromatic stability. Herein we report an unprecedented denitrogenative carbon skeleton cleavage and reorganization of pyridines mediated by the trinuclear titanium polyhydride complex [(Cp'Ti)₃(μ₃-H)(μ-H)₆] (Cp' = C₅Me₄SiMe₃). The reactions of 2-R-, 3-R-, and 4-R-substituted pyridines (R = Me, Et, ⁱPr, ^tBu, Ph) with this titanium hydride complex at 160 °C uniformly yield the denitrogenated 3-R-substituted pentadienyl complexes [(Cp'Ti)₃{μ₃-η¹:η²:η²:η¹-CHCHC(R)CHCH}(μ-H)(μ₃-N)]. Isolation and characterization of key intermediates reveal that the pyridine skeleton can be fragmented into combinations of [N]^3-, [CHC(R)CHCH]^4-, and [CH₂]^2- units or [NC(R)CHCH]^4- and [CHCH]^2- groups depending on the sterics and positions of the R substituents. Upon heating to 160 °C, recombination of the hydrocarbon fragments leads to the thermodynamically favored [CHCHC(R)CHCH]^5- framework. These transformations proceed via multiple steps involving C-H, C-C, and C-N bond cleavages as well as C-H and C-C bond re-formations. This work underscores the unique capability of multinuclear titanium hydride clusters to mediate skeletal cleavage and reorganization of aromatic N-heterocycles, offering a new strategy for heterocycle-to-hydrocarbon molecular editing.