Rhodium Containing Magnetic Nanoparticles: Effective Catalysts for Hydrogenation and the 1,4-Addition of Boronic Acids Urszula Laska Æ Christopher G. Frost Æ Pawel K. Plucinski Æ Gareth J. Price Received: 13 July 2007 / Accepted: 2 November 2007 / Published online: 1 December 2007 Ó Springer Science+Business Media, LLC 2007 Abstract New efficient rhodium catalysts supported on superparamagnetic iron oxide nanoparticles (NPs) have been prepared using a novel method involving sulfonated triphenylphosphine ligands. They successfully promote the hydrogenation of olefins as well as the addition of aryl- boronic acids to dimethyl itaconate (ItMe 2 ) in water for up to 10 recycles. The catalysts were stable towards leaching of the metal complexes and were readily recovered by applying an external magnetic field. Keywords Magnetic nanoparticles  Rhodium catalyst  Catalyst separation 1 Introduction There has been considerable recent interest in employing dispersed nanoparticles, NPs, as catalysts and supports [1, 2]. Homogeneous catalysts are highly efficient but their separation and recovery from the products can be prob- lematic. Conversely, heterogeneous systems can suffer from lower catalytic activities, generally due to limited mass transport of reactants to the solid surface of the catalyst [3]. Approaches designed to overcome these drawbacks include using biphasic systems [1] and sup- porting the active species on membranes [3], polymers [4] or dendrimers [5]. Nanoparticulate supports form a ‘‘semi- homogeneous’’ system and can serve as an intermediate between these types. One of the most promising nanoparticulate supports for the development of high-performance catalyst supports is superparamagnetic iron oxide. The NPs are attracted to a magnetic field and so may be recovered, but they retain no residual magnetism when the field is removed [6]. Using these NPs offers advantages in ‘‘clean’’ chemistry since, in addition to being readily recovered; they are non-toxic and widely accessible. The NP surface can be functionalized to allow the attachment of catalytically active groups. For example, rhodium species on magnetic NPs (as [Rh(cod)(g 6 -benzoic acid)]BF 4 ) have been used in the hydroformylation of olefins by Lee et al. [7]. The groups of Gao et al. [8–10] and He [11, 12] recently reported the use of iron oxide–Pd systems as efficient catalysts for certain cross-coupling reactions. Magnetic NPs have also been used as a support for chiral ruthenium complexes that have been applied to the catalytic, asymmetric hydrogenation of aromatic ketones [13]. In this paper, we report a novel method for the prepa- ration of magnetically separable rhodium–phosphine complexes by anchoring to Fe 3 O 4 NPs as well as a pre- liminary assessment of their application as recyclable catalysts for the hydrogenation of alkenes and the 1,4- addition of boronic acids. As far as we are aware, this is the first report of Rh-functionalised magnetic NP catalyst that can be used in water and recycled. An attractive feature of this method is the simplicity of immobilisation procedure since no modification of either the NP support or the organometallic species is required. U. Laska (&)  P. K. Plucinski Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK e-mail: U.Laska@bath.ac.uk U. Laska  C. G. Frost  G. J. Price Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK 123 Catal Lett (2008) 122:68–75 DOI 10.1007/s10562-007-9339-7