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  • Effects of Phosphine Ligand Chelation on the Reactivity ofMonomeric Parent Amido Ruthenium Complexes: Synthesisand Reactivity of Such a Complex Bearing MonodentateLigands
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  • The parent amido complex cis-(PMe3)4Ru(H)(NH2) (2) has been prepared via the deprotonationof [cis-(PMe3)4Ru(H)(NH3)+][BPh4-]. The amido complex is a somewhat weaker base than the DMPEanalogue trans-(DMPE)2Ru(H)(NH2) but is still basic enough to quantitatively deprotonate fluorene andreversibly 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). Becauseof the ligand lability, 2 also undergoes hydrogenolysis and rapid exchange with labeled NH3. The amidecomplex reacts with alkyl halides to yield E2 and SN2 products, along with ruthenium hydrido halidecomplexes including the ruthenium fluoride cis-(PMe3)4Ru(H)(F). Ruthenium hydrido ammonia halide ionpair 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 thatthey benefit from significant hydrogen bonding between X- and NH3 groups. Cumulenes also react withcomplex 2 to afford the products of insertion into an NH bond. The rates of neither these NH insertionreactions nor the reversible deprotonation reactions show any dependence on the concentration of PMe3present, suggesting that these reactions take place directly at the NH2 group and do not involveprecoordination of substrate to the metal center.
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