Coupling of iminoacyl groups to diazabutadienes on manganese carbonyl complexes

Article abstract of DOI:10.1021/om00108a025

RC(O)Mn(CO)₄(CNC₆H₄-p-Me) (R = p-ClC₆H₄CH₂, C₆H₅CH₂, p-MeOC₆H₄CH₂) couple in refluxing THF giving diazabutadiene (DAB) complexes [p-MeC₆H₄N=C(R)C(R)=NC₆H ₄-p-Me]Mn₂(CO)₆. The DAB ligand acts as an eight-electron donor. This behavior contrasts with that of acyl complexes of aliphatic isocyanides that undergo simple thermal decarbonylation in refluxing THF. Trapping studies with isocyanide, triphenylphosphine, and galvinoxyl suggest that decarbonylation is followed by rapid preferential isocyanide insertion and that the coupling involves a free radical process. The DAB dimers are resistant to thermal displacement of DAB by CO and of CO by triphenylphosphine and substituted acetylenes. [PhN=C-(Ph)C(Ph)=NPh]Mn₂(CO)₆ (5e) was prepared in low yield from the thermal reaction of PhN=C(Ph)Cl with Mn₂(CO)₁₀. The crystal structures of the compounds [p-MeC₆H₄N=C(CH₂C₆H ₄-p-Cl)C(CH₂C₆H₄-P-Cl)=NC ₆H₄-p-Me]Mn₂(CO)₆ (5a) and 5e were determined. For 5a, data are as follows: monoclinic, P2₁2₁2₁; a = 10.540 (2) ?, b = 12.775 (2) ?, c = 25.510 (2) ?; Z = 4. For 5e, crystal data are as follows: monoclinic; P2₁/c; a = 12.457 (2) ?, b = 11.204 (2) ?, c = 22.454 (4) ?; β = 108.46 (1)°; Z = 4. Both structures display an almost planar manganacyclic ring folded slightly at the N's and a Mn-Mn distance shorter than that in Mn₂(CO)₁₀.