DOI: 10.1002/cctc.201200448 Chemoselective Hydrogenation and Transfer Hydrogenation of Olefins and Carbonyls with the Cluster- Derived Ruthenium Nanocatalyst in Water Arindam Indra, Prasenjit Maity, Sumit Bhaduri,* and Goutam Kumar Lahiri* [a] Introduction Among many of the require- ments of environmentally benign and economically viable chemical processes, the use of water rather than organic sol- vents is an important theme of current research. [1, 2] Water is cheap and nonhazardous, and a number of gases such as hy- drogen have good solubility in water. Although catalytic hydrogenation reactions are widely performed in chemical industry, [3] hydrogen gas under high pressure is hazardous. Therefore, for selected reactions, transfer hydrogenation with a suitable hydrogen donor should be ex- plored as an alternative. [4] For both hydrogenation and transfer hydrogenation reactions, homogeneous catalysts are generally far more selective than heterogeneous ones but separation from the product and recycling of the catalysts are often difficult. The need for efficient separation of the product and the cat- alyst while maintaining the selectivity advantage of a soluble catalyst has led to the concept of liquid–liquid biphasic cataly- sis. [5] Here the catalyst is dissolved/dispersed in one liquid phase and the reactants and product(s) in the second liquid phase. Recovery and recycling of the catalyst are achieved through simple phase separation. With water-soluble/dispersi- ble catalysts, another point of considerable interest is that many organic reactions if performed in water show improve- ments in rates and selectivities. [1, 6] Nanoparticle catalysis in green solvents such as water has shown tremendous potential, and systematic guidelines for the further development of metal cores, stabilizers, and solvents have been presented. [7] Given the above-mentioned back- ground and our own involvement with nanocatalysis over the years, we wanted to evaluate the potential of the water-solu- ble ruthenium precatalyst 2 (see Scheme 1) in a broad range of hydrogenation and transfer hydrogenation reactions. [8–18] We also wanted to determine whether the literature reported “on water” effect, that is, improved rate in water, could be ob- served in these reactions. Thus, the main motivations for the work reported here are as follows: 1) to evaluate the feasibility of water as a reaction medium for hydrogenation and transfer hydrogenation reactions with 2 as the precatalyst, 2) to investi- Ion pairing of [H 3 Ru 4 (CO) 12 ]  with the quaternary ammonium groups of water-soluble poly(diallyldimethylammonium chlo- ride) gives the precursor of a nanocatalyst for hydrogenation and transfer hydrogenation reactions in water. In hydrogena- tion reactions, “on water” effect is seen for substrates such as cyclohexanones, methyl pyruvate, acetophenone, and safflow- er oil. With these substrates, higher turnover numbers are ob- tained in water than in methanol. The cluster-derived catalyst shows unique chemoselectivity, which is not seen either in a catalyst prepared through ion pairing of [RuCl 4 ]  with the quaternary ammonium groups of the same polymer or in com- mercial (5 %) Ru/Al 2 O 3 . In contrast to Ru/Al 2 O 3 , the [RuCl 4 ]  -de- rived catalyst, or many other ruthenium-based catalytic sys- tems, the cluster-derived catalyst is totally inert toward the hy- drogenation of NO 2 , CN, and aromatic ring functionalities. In water, typical ketones and aldehydes could be reduced by using the cluster-derived catalyst and formate as the hydrogen donor. Industrially important cyano- and nitrobenzyl alcohols could thus be made from the corresponding aldehydes. High- resolution TEM data suggest that unique chemoselectivity is a result of highly crystalline ruthenium nanoparticles that con- sist mainly of Ru(111) crystal planes. Scheme 1. Synthetic routes for the preparation of the water-soluble poly(diallyldimethylammonium chloride) (PDADMAC]-supported catalysts (2–4). [a] Dr. A. Indra, Dr. P. Maity, Prof. Dr. S. Bhaduri, Prof. Dr. G.K. Lahiri Department of Chemistry Indian Institute of Technology Bombay Powai, Mumbai 400 076 (India) Fax: (+ 91) 22-25723480 E-mail : lahiri@chem.iitb.ac.in sbhaduri@chem.iitb.ac.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200448.  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 2013, 5, 322 – 330 322 CHEMCATCHEM FULL PAPERS