Effects of phosphine ligand chelation on the reactivity of monomeric parent amido ruthenium complexes: Synthesis and reactivity of such a complex bearing monodentate ligands

The parent amido complex cis-(PMe3)(4)Ru(H)(NH2) (2) has been prepared via the deprotonation of [cis-(PMe3)(4)Ru(H)(NH3)(+)][BPh4-]. The amido complex is a somewhat weaker base than the DMPE analogue trans-(DMPE)(2)Ru(H)(NH2) but is still basic enough to quantitatively deprotonate fluorene and reversibly deprotonate 1,3-cyclohexadiene and toluene. Complex 2 exhibits very labile phosphine ligands, two of which can be replaced by DMPE to yield the mixed complex cis-(PMe3)(2)(DMPE)Ru(H)(NH2). Because of the ligand lability, 2 also undergoes hydrogenolysis and rapid exchange with labeled NH3. The amide complex reacts with alkyl halides to yield E2 and S(N)2 products, along with ruthenium hydrido halide complexes including the ruthenium fluoride cis-(PMe3)(4)Ru(H)(F). Ruthenium hydrido ammonia halide ion pair intermediates [cis-(PMe3)(4)Ru(H)(NH3)(+)][X-] are observed in some deprotonation and E2 reactions, and measurement of the equilibrium constants for NH3 displacement from these complexes suggests that they benefit from significant hydrogen bonding between X- and NH3 groups. Cumulenes also react with complex 2 to afford the products of insertion into an NH bond. The rates of neither these NH insertion reactions nor the reversible deprotonation reactions show any dependence on the concentration of PMe3 present, suggesting that these reactions take place directly at the NH2 group and do not involve precoordination of substrate to the metal center.