Synthesis, Electronic Structure, and Reactivity of a Planar Four‐Coordinate, Cobalt–Imido Complex

• Published in: Angewandte Chemie (International ed.) Vol. 60; no. 26; pp. 14376 - 14380
• Main Authors: Park, Yoonsu, Semproni, Scott P., Zhong, Hongyu, Chirik, Paul J.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 21-06-2021; Wiley Blackwell (John Wiley & Sons)
• Edition: International ed. in English
• Subjects: CASSCF; Cobalt; Cobalt compounds; Electronic structure; imido; Magnetic measurement; Mathematical analysis; nitrene transfer; Nitrogen compounds; Selectivity; Stability analysis; Nitrene transfer; Cobalt; CASSCF; Imido; electronic structure
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202104320

A four‐coordinate cobalt–imido complex, (tBumPNP)Co=NMes (tBumPNP=modified PNP pincer ligand) has been synthesized from addition of 2,4,6‐trimethylphenylazide (Mes–N3) to the corresponding dinitrogen complex. The solid‐state structure determined by X‐ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S=1 ground state with CAS‐SCF calculations supporting radical character on the imide nitrogen. Thermolysis of the cobalt–imido compound induced selective insertion of the imido group into a Co−P bond and yielded a three‐coordinate cobalt complex with a distorted T‐shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.
A four‐coordinate, planar cobalt–imido compound was isolated and characterized. Integrated experimental and computational studies identified radical character on the iminyl nitrogen accounting for a reduction in overall bond order. Upon thermolysis, the complex underwent selective P–N coupling with the desymmetrized pincer. Transition state analysis revealed that thermodynamic control is the origin of the observed selectivity.