Issue 6, 2002

Geminal dehydrogenation of ether and amine C(sp3)H2 groups by electron-rich Ru(ii) and Os

Abstract

Reaction of [RuHCl(PiPr3)2]2 with THF or dioxolane doubly dehydrogenates the carbon α to the oxygen to yield RuHCl(H2)(PiPr3)2, together with the coordinated cyclic carbene, RuHCl[[double bond, length half m-dash]CO(CH2)2E](PiPr3)2, where E = CH2 or O. In the presence of CH2[double bond, length half m-dash]CHtBu as hydrogen acceptor, all Ru is converted to its carbene complex. The cyclic amines RN(CH2)4 (R = H, Me) react analogously, to produce N-substituted carbene complexes by geminal dehydrogenation; a crystal structure is presented for the carbene complex with R = H, which reveals intermolecular NH⋯Cl hydrogen bonding. Similar chemistry is established for Os(H)3Cl(PiPr3)2, at 25 °C, in the presence of H2C[double bond, length half m-dash]CHtBu, to give OsHCl[[double bond, length half m-dash]CO(CH2)3](PiPr3)2. Pyrrolidine reacts rapidly at 25 °C to give first a 1∶1 amine adduct, then slowly the trihydride carbene Os(H)3Cl[[double bond, length half m-dash]C(NH)(CH2)3](PiPr3)2, together with H2. Os(H)2Cl2(PiPr3)2 is first dehydrochlorinated by one mole of pyrrolidine, then a second mole of pyrrolidine is geminally dehydrogenated to form Os(H)3Cl[[double bond, length half m-dash]C(NH)(CH2)3](PiPr3)2. The five-coordinated carbene OsHCl[[double bond, length half m-dash]CO(CH2)3](PiPr3)2 will add H2, and the resulting product exists as two isomers, a trihydride with Cl cis to the carbene and a species with Cl trans to carbene and H and “2H” mutually trans. Isomer preferences, strength of H2 binding, and carbene plane orientation are discussed, together with DFT calculations on the thermodynamics of ether dehydrogenation by ruthenium. The latter reveal that coordination of removed H2 to Ru is essential to achieving favorable thermodynamics.

Supplementary files

Article information

Article type
Paper
Submitted
26 Dec 2001
Accepted
03 Jan 2002
First published
07 Jun 2002

New J. Chem., 2002,26, 687-700

Geminal dehydrogenation of ether and amine C(sp3)H2 groups by electron-rich Ru(II) and Os

G. Ferrando-Miguel, J. N. Coalter III, H. Gérard, J. C. Huffman, O. Eisenstein and K. G. Caulton, New J. Chem., 2002, 26, 687 DOI: 10.1039/B200168N

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