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 = CH 3, Ph) with ( p -tolyl)(R 1 ) NR 2 (R 1 = H, t Bu; R 2 = alkyl, H) results in the generation of the cyclometalated imine complexes (CO) 4 Mn[η 2 -4-CH 3 -2-(C(R 1 ) NR 2 )-C 6 H 3 ] in 50−84% isolated yield. However, when the reaction of ( p -tolyl)(H)C NCH 3 with (CO) 5 MnCH 3 is performed in the presence of AlCl 3, the product of sequential carbon monoxide and imine insertion is generated in 35% yield: (CO) 4 Mn[η 2 -C(H)( p -tolyl)N(CH 3 )COCH 3 ]. The addition of PPh 3 to the latter complex results in replacement of a carbonyl ligand and formation of the isolable fac -(CO) 3 (PPh 3 )Mn[η 2 -C(H)( p -tolyl)N(CH 3 )COCH 3 ]. In an alternative route to metal-bound amides, the oxidative addition of the N-acyl iminium salt ( p -tolyl(H)C N(CH 3 )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[η 2 -COC(H)( p -tolyl)N(CH 3 )COPh]. The latter represents the first example of a acyl-bound transition-metal-chelated α-amino acid complex and has been characterized by X-ray crystallography. Preliminary reactivity studies demonstrate that (CO) 4 Mn[η 2 -COC(H)( p -tolyl)N(CH 3 )COPh] reacts with PPh 3 to generate the unchelated ci s -(CO) 4 (PPh 3 )Mn[COC(H)( p -tolyl)N(CH 3 )COPh], while reaction with NaBH 4 leads to the liberation of the amide ( p -tolyl)CH 2 N(CH 3 )COPh, rather than the amino acid residue.