Insertion of imines and carbon monoxide into manganese-alkyl bonds:: Synthesis and structure of a manganese-α-amino acid derivative

Two new routes have been developed to generate manganese-chelated amides from imine and carbon monoxide building blocks. The reaction of (CO)(5)MnR (R = CH3, Ph) with (p-tolyl)(R-1)= NR2 (R-1) = NR2 (R-1 = H,tBu; R-2 = alkyl, H) results in the generation of the cyclometalated imine complexes (CO)(4)Mn[eta (2)-4-CH3-2-(C(R-1)=NR2)-C6H3] in 50-84% isolated yield. However, when the reaction of (p-tolyl)(H)C=NCH3 with (CO)(5)MnCH3 is performed in the presence of AlCl3, the product of sequential carbon monoxide and imine insertion is generated in 35% yield: (CO)(4)Mn[eta (2)-C(H)(p-tolyl)N(CH3)COCH3], The addition of PPh3 to the latter complex results in replacement of a carbonyl ligand and formation of the isolable fac-(CO)(3)(PPh3)Mn[eta (2)-C(H)(p-tolyl)N(CH3)COCH3], In an alternative route to metal-bound amides, the oxidative addition of the N-acyl iminium salt (p-tolyl(H)C=N(CH3)COPh+Cl- to (CO)(5)Mn-Na+ has been found to lead to the generation of the product of subsequent CO insertion, (CO)(4)Mn[eta (2)-COC(H)(p-tolyl)N(CH3)COPh]. The latter represents the first example of a acyl-bound transition-metal-chelated a-amino acid complex and has been characterized by X-ray crystallography. Preliminary reactivity studies demonstrate that (CO)(4)Mn[eta (2)-COC(H)(p-toyl)N(CH3)COPh] reacts with PPh3 to generate the unchelated cis-(CO)(4)(PPh3)Mn[COC-(H)(p-tolyl)N(CH3)COPh], while reaction with NaBH4 leads to the liberation of the amide (p-tolyl)CH2N(CH3)COPh, rather than the amino acid residue.