Understanding the Formation of N−H Tautomers from α-Substituted Pyridines: Tautomerization of 2-Ethylpyridine Promoted by Osmium

Reaction of [OsH(η 2 -H 2 ){η 2 -C,C-κ 1 -N-(CH 2 CH- o -C 5 H 4 N)}(P i Pr 3 ) 2 ]BF 4 with benzophenone affords [OsH 2 {κ 2 -C,O−C 6 H 4 C(O)Ph}{κ-C-(HNC 5 H 3 Et)}(P i Pr 3 ) 2 ]BF 4 as a result of the orthometalation of the ketone, the hydrogenation of the vinyl substituent of the pyridine, and its subsequent tautomerization. In acetonitrile, the ketone is released and complex [OsH{κ-C-(HNC 5 H 3 Et)}(NCCH 3 )(P i Pr 3 ) 2 ]BF 4 is formed.