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Reacting various N\u2010substituted imidazoles with 2\u2010bromo\u20104(<jats:italic>S<\/jats:italic>)\u2010<jats:italic>tert<\/jats:italic>\u2010butyl\u2010 and 2\u2010bromo\u20104(<jats:italic>S<\/jats:italic>)\u2010isopropyloxazoline gave the imidazolium precursors of the stereodirecting ancillary ligands. A library of ten different ligand precursors was obtained by using this simple procedure (65\u201397\u2009% yield). These protioligands were metalated in a subsequent step by reaction with [{Rh(\u03bc\u2010O<jats:italic>t<\/jats:italic>Bu)(nbd)}<jats:sub>2<\/jats:sub>] (nbd=norbornadiene), generated in situ from KO<jats:italic>t<\/jats:italic>Bu and [{RhCl(nbd)}<jats:sub>2<\/jats:sub>] giving the corresponding N\u2010heterocyclic carbene complexes [RhBr(nbd)(oxazolinyl\u2010carbene)] <jats:bold>4\u2009a<\/jats:bold>\u2013<jats:bold>j<\/jats:bold> in good yields. X\u2010ray diffraction studies of two of the rhodium complexes, <jats:bold>4\u2009d<\/jats:bold> and <jats:bold>4\u2009j<\/jats:bold>, established a distorted square\u2010pyramidal coordination geometry with the bromo ligand occupying the apical position. The rhodium\u2013carbene bond length was found to be 2.070(4) \u00c5 (<jats:bold>4\u2009d<\/jats:bold>) and 2.012(3) \u00c5 (<jats:bold>4\u2009j<\/jats:bold>). Complexes <jats:bold>4\u2009a<\/jats:bold>\u2013<jats:bold>j<\/jats:bold> were treated with AgBF<jats:sub>4<\/jats:sub> in dichloromethane, giving the active cationic square\u2010planar catalysts for the hydrosilylation of ketones. As a reference reaction for the catalyst optimisation, the hydrosilylation of acetophenone with diphenylsilane was studied and the system optimised with respect to the counterion (BF<jats:sub>4<\/jats:sub><jats:sup>\u2212<\/jats:sup>), solvent (THF) and the silane reducing agent (diphenylsilane). The reaction product (1\u2010phenylethanol) was obtained with the highest enantiomeric excess (<jats:italic>ee<\/jats:italic>) by carrying out the reaction at \u221260\u2009\u00b0C, whilst the enantioselectivity drops upon going both to lower and higher temperatures. The observation that the temperature dependence of the <jats:italic>ee<\/jats:italic> values goes through a maximum indicated a change in the rate\u2010determining step as the temperature is varied. The determination of the initial reaction rate in the hydrosilylation of acetophenone upon varying the catalyst (<jats:bold>4\u2009d<\/jats:bold>) and substrate concentrations at \u221255\u2009\u00b0C established a rate law for the initial conversion which is first\u2010order in both substrates as well as the catalyst (<jats:italic>V<\/jats:italic><jats:sub>i<\/jats:sub>=<jats:italic>k<\/jats:italic>[<jats:bold>4<\/jats:bold>][PhCOMe][Ph<jats:sub>2<\/jats:sub>SiH<jats:sub>2<\/jats:sub>]). The catalytic system derived from complex <jats:bold>4\u2009d<\/jats:bold> was found to afford high yields and good enantioselectivities in the reduction of various aryl alkyl ketones (acetophenone: 92\u2009% isolated yield and 90\u2009% <jats:italic>ee<\/jats:italic>, 2\u2010naphtyl methyl ketone: 99\u2009% yield, 91\u2009% <jats:italic>ee<\/jats:italic>). The selectivity for the reduction of prochiral dialkyl ketones is comparable or even superior to the best previously reported for prochiral nonaromatic ketones; whereas cyclopropyl methyl ketone is hydrosilylated with an enantioselectivity of 81\u2009% <jats:italic>ee<\/jats:italic>, the increase of the steric demand of one of the alkyl groups leads to improved <jats:italic>ee<\/jats:italic>'s, reaching 95\u2009% <jats:italic>ee<\/jats:italic> in the case of <jats:italic>tert<\/jats:italic>\u2010butyl methyl ketone. Linear chain <jats:italic>n<\/jats:italic>\u2010alkyl methyl ketones, which are particularly challenging substrates, are reduced in good asymmetric induction, such as 2\u2010octanone (79\u2009% <jats:italic>ee<\/jats:italic>) and even 2\u2010butanone (65\u2009% <jats:italic>ee<\/jats:italic>).<\/jats:p>","DOI":"10.1002\/chem.200500132","type":"journal-article","created":{"date-parts":[[2005,3,3]],"date-time":"2005-03-03T07:17:10Z","timestamp":1109834230000},"page":"2862-2873","source":"Crossref","is-referenced-by-count":122,"title":["Designing the \u201cSearch Pathway\u201d in the Development of a New Class of Highly Efficient Stereoselective Hydrosilylation Catalysts"],"prefix":"10.1002","volume":"11","author":[{"given":"Vincent","family":"C\u00e9sar","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"St\u00e9phane","family":"Bellemin\u2010Laponnaz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hubert","family":"Wadepohl","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lutz H.","family":"Gade","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2005,4,15]]},"reference":[{"key":"e_1_2_6_1_2","doi-asserted-by":"publisher","DOI":"10.1039\/b401123f"},{"key":"e_1_2_6_2_2","unstructured":"Reviews:"},{"key":"e_1_2_6_3_2","doi-asserted-by":"publisher","DOI":"10.1002\/1521-3757(20020415)114:8<1342::AID-ANGE1342>3.0.CO;2-A"},{"key":"e_1_2_6_3_3","doi-asserted-by":"publisher","DOI":"10.1002\/1521-3773(20020415)41:8<1290::AID-ANIE1290>3.0.CO;2-Y"},{"key":"e_1_2_6_4_2","doi-asserted-by":"publisher","DOI":"10.1021\/cr940472u"},{"key":"e_1_2_6_5_2","first-page":"2257","volume":"109","author":"Herrmann W. 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