The reactivity and catalytic activity of bidentate indenyl-phosphine tethered complexes of rhodium and ruthenium

Abstract

A higher-yielding route to racemIC ligand 2-cyclohexyl-2-(3' H-I '-indenyl)ethyl diphenylphosphine has been adapted from the known route to the chiral phosphine. Protection via formation of the borane adduct allows easy handling of the air-sensitive phosphine and has improved overall yields of known complexes (l{lJl-indenyl-CH(CY) CH2PPh2)Rh(CO) and (lJ5:lJl-indenyl-CH(Cy)-CH2PPh2)RuCI(PPh3). Tetrahydroindenyl and cationic derivatives have been synthesised from the ruthenium complex and all the complexes have been tested for catalytic activity, along with (lJ5:lJl-indenyl-CH(CY) CH2CH2PPh2)RuCI(PPh3) and [(lJ5:lJl-indenyl-CH(Cy)-CH2CH2PPh2)Ru(PPh3)t[PF6r (from P. Wright). Catalytic activity was seen for the transfer hydrogenation of acetophenone, but the resulting alcohol was racemic. It was also seen for the hydrogenation of iminium tetrafluroroborate salts, though the amount of reduction seen was too small to observe a reproducible e.e. The complexes were catalytically inactive for the nucleophilic displacement of allylic acetates, the cyclopropanation of styrene and the Diels-Alder reaction between cyclopentadiene and methacrolein. It has also been shown that displacement of PPh3 from ruthenium complex (lJ5:lJl-indenyl CH(Cy)-CH2PPh2)RuCl(PPh3) with more electron-rich phosphines occurs with retention of stereochemistry at the metal centre. X-ray structures of the tetrahydroindenyl and cationic ruthenium complexes, as well as the complexes formed by phosphine displacement, have been obtained.

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