Microwave-Assisted Synthesis of Functionalized Shvo-Type Complexes Cristiana Cesari, Letizia Sambri, Stefano Zacchini, Valerio Zanotti, and Rita Mazzoni* Dipartimento di Chimica Industriale “Toso Montanari”, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy * S Supporting Information ABSTRACT: A simple and expeditious microwave-assisted procedure for the synthesis of a variety of Shvo-type ruthenium complexes has been developed by reacting Ru 3 (CO) 12 with variously functionalized tetraarylcyclopentadienones under microwave irradiation in MeOH. Ligand precursors have also been prepared under microwave heating by a bis-aldol condensation of 1,3- diphenylacetone with variously functionalized aromatic diketones. All the reactions were very fast and clean, leading to good yields and purities. ■ INTRODUCTION Hydroxycyclopentadienylruthenium hydride dimer complexes, well-known as Shvo-type complexes, 1 are precursors of useful and versatile catalysts, successfully applied in a broad variety of hydrogen-transfer processes such as hydrogenation of carbonyls and imines and oxidation of alcohols and amines. 2 More recently, applications have been extended to a broader number of reactions including synthesis of primary amines by using ammonia, 3 biomimetic aerobic oxidation, 4 chemoenzymatic dynamic kinetic resolution of amines, 5 N-acylation of hetero- cycles with aldehydes, 6 ammonia-borane dehydrogenation, 7 and α,β-deuteration of bioactive amines. 8 Furthermore, the catalyst, supported on silica, has been used in the hydro- formylation and hydrogenation of propene to butanol, 9 and, combined with Rh complexes, it has been exploited in tandem reactions, resulting in the isomerization/hydroformylation/ hydrogenation of internal alkenes to yield n-alcohols. 10 Promising perspectives are also in the field of green chemistry, in the transformation of renewable feedstocks, 11 including upgrading of bio-oil by hydrogenation 11a and selective conversion of levulinic and formic acids into γ-valerolactone. 12 Stimulated by the possibility to decorate the cyclopentadienyl of Shvo’s complexes with various functionalities, we inves- tigated the synthesis of new hydroxypropargyl arylcyclopenta- dienone ligands. These functionalized tetraarylcyclopentadie- nones, besides providing a tool for controlling the properties of the catalyst, are themselves fascinating compounds, with interesting properties as organogels, 13 and useful applications in material science. 14 The considerable potential of the Shvo catalyst, which might be further improved by use of functionalized tetraarylcyclo- pentadienones, is unfortunately affected by the lack of a simple and efficient synthetic method. Indeed, different synthetic approaches have been developed since its first synthesis, 2a-c,15 but all the reported procedures still require high temperatures and long reaction times. Here we report a new rapid, clean, and general method for the synthesis of variously functionalized Shvo-type complexes, which takes advantage of microwave heating. Furthermore, microwave irradiation also provides easier access to the corresponding tetraarylcyclopentadienone ligands. ■ RESULTS AND DISCUSSION Microwave-Assisted Tetraarylcyclopentadienone Li- gand Synthesis. Most common synthetic routes to tetraarylcyclopentadienones involve reaction of diaryl-α-dike- tones 1 with the diphenylacetone 2, in the presence of KOH or NaOH, in refluxing EtOH for variable reaction times (2-16 h) (Scheme 1). 13,16 Received: March 31, 2014 Published: May 27, 2014 Scheme 1. Examples of Conventional Synthesis of Tetraarylcyclopentadienones 3 Article pubs.acs.org/Organometallics © 2014 American Chemical Society 2814 dx.doi.org/10.1021/om500335m | Organometallics 2014, 33, 2814-2819