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)4Ru(H)(NH2) (2) has been prepared via the deprotonation
of [cis-(PMe3)4Ru(H)(NH3)+][BPh4-]. The amido complex is a somewhat weaker base than the DMPE
analogue trans-(DMPE)2Ru(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 SN2 products, along with ruthenium hydrido halide
complexes including the ruthenium fluoride cis-(PMe3)4Ru(H)(F). Ruthenium hydrido ammonia halide ion
pair intermediates [cis-(PMe3)4Ru(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.