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

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, [Os^V(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 abstract 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.