Eco-Friendly New Ligands for Catalysts Design: Chemistry of O-Functionalized Cp Ligands and Rh-Coordination

New Catalysis Methodologies aimed to reduce toxicity for human health and environment constitute a recognized target for Sustainable Chemistry. Our studies concern new ligands design and development by using non-injurious solvents, moderate conditions and no waste products. Currently our group is working on projects involving the synthesis and characterization of new water soluble polydentate Cyclopentadienyl ligands, tethering 1-3 alcoholic pendants of the type CpO,O,O = [C5H5-nRn] (n=1,2,3 R = CH(CH2)3CHOH), obtained by one-pot reaction between NaCp and oxirane excess [CH(CH2)3CH]O (Scheme1). The reaction discriminates position and chirality sequence of the cycloalkyl substituents stereocentres {for example (S,R,S) for (1,2,4)-C5H2[C*H(CH2)3CHOH]3}. Coordination to transition metals stereospecifically selects less congested enantioface (pR), affording one unique stereoisomer. Coordinative pi-abilities give raise to Mn, Fe and Rh complexes. The nature of complexes has determined by different spectroscopic means (ESI-Ms, UV, ORD, CD, IR, bidimensional and n.O.e. NMR techniques). X-ray diffraction studies on examples of the class (LL)Rh{C5H2[CH(CH2)3CHOH]3} (LL = NBD,CO)(1) species confirm the suggested structure. The [NBDRhCpO,O,O] complexes show a peculiar solubility and high stability in ethanol or water. Currently, we are exploring further coordination abilities of alcoholic pendants towards Titanium centre, to obtain bimetallic complexes. Extension of the described synthetic protocol to test general applicability on further polyfunctionalized pi-ligands as Indenyl, Fluorenyl and Thienyl is also under investigation. These experiments are of support to investigate on discrete model the cooperativity exerted by metal of different nature (Rh, Ti) or acidic sites (Ti, OH) inside heterogeneous catalytic structures (zeolites, perowskites or mixed oxides) and to test grafting ability or alterations in the stereo-electronic requisites of immobilized Rh sites. We plan to get insight into hydrophilic Rhodium complexes as promising transfer hydrogenation mediator or polymerization of oxygenated olefins in biphasic catalysis