Mechanism of formation of [(PMe3)(3)Rh(-C equivalent to C-R)(2)(H)] via C-H oxidative addition: Isomerization, alkyne exchange, and hydride replacement

Rourke, J.P. ORCID: https://orcid.org/0000-0002-8961-1021, Stringer, G., Chow, P., Deeth, R.J., Yufit, D.S., Howard, J.A.K. and Marder, T.B. 2002. Mechanism of formation of [(PMe3)(3)Rh(-C equivalent to C-R)(2)(H)] via C-H oxidative addition: Isomerization, alkyne exchange, and hydride replacement. Organometallics 21 (2) , pp. 429-437. 10.1021/om010685r

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Abstract

The mechanism of formation of mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] from [(PMe3)4Rh(Me)] and terminal alkyne has been studied. The initial step of the reaction is the elimination of methane and the formation of the trigonal bipyramidal complex [(PMe3)4Rh(−C⋮C−R)], a reaction that is complete in time of mixing at −78 °C. This intermediate undergoes an oxidative addition reaction with a second equivalent of alkyne to give fac-[(PMe3)3Rh(−C⋮C−R)2H] as the kinetic product. This fac isomer is not stable above −20 °C and isomerizes to the thermodynamic product mer,trans-[(PMe3)3Rh(−C⋮C−R)2H]. fac-[(PMe3)3Rh(−C⋮C−R)2H] will exchange alkynyl groups with free alkyne, a reaction that has a lower energetic barrier than the isomerization to mer,trans-[(PMe3)3Rh(−C⋮C−R)2H]. Density functional theory studies on all stages of the formation of mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] have been carried out and give ground state energies in line with those experimentally observed. Once formed, mer,trans-[(PMe3)3Rh(−C⋮C−R)2H] is configurationally stable and not prone to scrambling, although it will react with chloroform, whereupon the hydride is replaced by chloride. The initial product of this reaction is mer,trans-[(PMe3)3Rh(−C⋮C−R)2Cl], and this compound has been studied by single-crystal X-ray diffraction. In solution mer,trans-[(PMe3)3Rh(−C⋮C−R)2Cl] isomerizes slowly to mer,cis-[(PMe3)3Rh(−C⋮C−R)2Cl].

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry
Publisher:	American Chemical Society
ISSN:	0276-7333
Last Modified:	05 Apr 2023 14:45
URI:	https://orca.cardiff.ac.uk/id/eprint/155208

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