A Highly Reactive Seven-Coordinate Osmium(V) Oxo Complex: [OsV(O)(qpy)(pic)Cl]2

• Published in: Angewandte Chemie International Edition 2016-01, Vol.55 (1), p.288-291
• Main Authors: Liu, Yingying, Ng, Siu-Mui, Lam, William W. Y., Yiu, Shek-Man, Lau, Tai-Chu
• Format: Article
• Language: English
• Subjects: Beryllium; Catalysis; Catalysts; Chemical bonds; Crystal structure; CH activation; Energy of dissociation; Free energy; Heat of formation; Intermediates; Metals; Osmium; Oxidants; Oxidation; Oxidizing agents; Ruthenium; Species; structure elucidation; Substrates; X-ray diffraction
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201507933

Seven‐coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven‐coordinate group 8 metal‐oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2′′:6′′,2′′′‐quaterpyridine, pic=4‐picoline). The X‐ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an OsO distance of 1.7375 Å. This oxo species undergoes facile O‐atom and H‐atom‐transfer reactions with various organic substrates. Notably it can H atoms from alkylaromatics with CH bond dissociation energy as high as 90 kcal mol−1. This work suggests that highly active oxidants may be designed based on group 8 seven‐coordinate metal oxo species. The magnificent seven: Oxidation of [OsII(qpy)(pic)Cl]+ with cerium(IV) generates the first seven‐coordinate Group 8 oxo species, [OsV(O)(qpy)(pic)Cl]2+, which can an H atom from alkylarenes with CH bond dissociation energies as high as 90 kcal mol−1. The structure elucidation is also discussed. pic=4‐picoline, qpy=2,2′:6′,2′′:6′′,2′′′‐quaterpyridine.