Stable carbene and diazoalkane complexes of the same complex system. Synthesis, structure, and reactivity of PNP-Ru(II) fluorenylidene and diazofluorene complexes

The choice of synthetic methodology leads to either carbene or diazoalkane complexes of the same system. Thus, treatment of RuCl₂(PPh ₃)₃ with 9-diazofluorene followed ^tBu-PNP (^tBu-PNP = 2,6-bis(diiert-butylphosphinomethyl)pyridine) resulted in loss of dinitrogen and formation of the Ru(II) fluorenylidene complex 1. On the other hand, treatment of the ^tBu-PNP Ru(II) dinitrogen complex 4 with 9-diazofluorene resulted in the formation of η¹-dizaofluorene Ru(II) complex 5, in which the diazo unit remains intact. The cationic Ru(II) carbene complex 2 was obtained by the reaction of 1 with 1 equiv of AgBF ₄ or HBF₄. Chloride dissociation to form a 16-e cationic carbene complex 3 took place also upon refluxing of 1 in toluene. The five-coordinated, unsaturated, charge-neutral diiodide Ru(II) complex 6 was obtained by reaction of 4 with NaI. Complex 6 is stabilized by a C-H agostic interaction, as observed by X-ray crystallography. Reaction of 4 with NaBEt3H followed by 9-dizaofluorene resulted in a novel η¹- diazenofluorene Ru(II) complex 7, accompanied by the migration of one hydrogen atom from the metal center to the coordinated nitrogen atom of the diazenofluorene unit. Heating complex 7 at 65°C resulted in sp² C-H activation followed by elimination of dihydrogen to form the chelated, β-carbon coordinated diazenofluorene ruthenium complex 8. Complexes 1, 2, 5, 6, and 8 were structurally characterized by X-ray crystallography.