View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by RERO DOC Digital Library Published in Chemistry - A European Journal, 10, issue 1, 208-217, 2003 1 which should be used for any reference to this work Framework Fluxionality of Organometallic Oxides: Synthesis, Crystal 6 Structure, EXAFS, and DFT Studies on [{Ru(h -arene)}4Mo4O16] Complexes Danielle Laurencin,[a] Eva Garcia Fidalgo,[b] Richard Villanneau,[a] FranÁoise Villain,[a, c] Patrick Herson,[a] Jessica Pacifico,[b] Helen Stoeckli-Evans,[b] Marc Bÿnard,[d] Marie-Madeleine Rohmer,[d] Georg S¸ss-Fink,[b] and Anna Proust*[a] Dedicated to Professor Pierre Gouzerh on the occasion of his 60th birthday Abstract: Reactions of the molybdates This triple-cubane isomer was also electrostatic interactions and steric Na2MoO4¥2H2O and (nBu4N)2[Mo2O7] used as a spectroscopic model to ac- bulk induced by substituted arenes with [{Ru(arene)Cl2}2] (arene= count for isomerization of the p- were found to modulate but not to re- 6 C6H5CH3, 1,3,5-C6H3(CH3)3, 1,2,4,5- cymene windmill [{Ru(h -1,4- verse the energy difference between C6H2(CH3)4) in water or organic sol- CH3C6H4CH(CH3)2)}4Mo4O16] in solu- the isomers. The stability of the triple- vents led to formation of the triple- tion. Using both Raman and XAS cubane isomers should therefore be ac- cubane organometallic oxides [{Ru(h6- techniques, we were then able to deter- counted for by effects of the surround- arene)}4Mo4O16], whose crystal and mine the ratio between the windmill ings that induce a shift in the energy molecular structures were determined. and triple-cubane isomers in dichloro- balance between both forms. Refluxing triple cubane [{Ru(h6- methane and in chloroform. Density 6 C6H5CH3)}4Mo4O16] in methanol functional calculations on [{Ru(h -are- caused partial isomerization to the ne)}4Mo4O16] (arene =C6H6,C6H5CH3, windmill form. The two isomers of 1,3,5-C6H3(CH3)3, 1,4-CH3C6H4CH- 6 [{Ru(h -C6H5CH3)}4Mo4O16] were char- (CH3)2,C6(CH3)6) suggest that the Keywords: density functional acterized by Raman and Mo K-edge windmill form is intrinsically more calculations ¥ EXAFS spectroscopy X-ray absorption spectroscopy (XAS), stable, provided the complexes are as- fluxionality ¥ organo-metallic oxides both in the solid-state and in solution. sumed to be isolated. Intramolecular polyoxometalates Introduction Stoichiometric or catalytic transformations of organic sub- strates by ruthenium complexes, and especially by {Ru(ar- [a] D. Laurencin, Dr. R. Villanneau, Dr. F. Villain, P. Herson, ene)}2+-containing species, are now well documented. Com- Prof. A. Proust pounds of this type are active catalysts in a growing number Laboratoire de Chimie Inorganique et Matÿriaux Molÿculaires [1] [2] UMR CNRS 7071, Universitÿ Pierre et Marie Curie of reactions, which include hydrogenation, oxidation, CÀC case courrier 42, 4 Place Jussieu, 75252 Paris Cedex 05 (France) coupling (including olefin metathesis),[3] and nucleophilic Fax : (+33)1-4427-3841 addition to multiple bonds.[4] In fact, the impact of rutheni- E-mail: [email protected] um in organic synthesis has now attained that of palladi- [b] Dr. E. Garcia Fidalgo, Dr. J. Pacifico, Prof. H. Stoeckli-Evans, um.[5] This extensive reactivity is associated with the excep- Prof. G. S¸ss-Fink Institut de Chimie, Universitÿ de Neuch‚tel tional properties of ruthenium: 1) it has the widest scope of case postale 2, CH-2000 Neuch‚tel (Switzerland) oxidation states of all elements (from Àii to +viii), 2) a [c] Dr. F. Villain large number of coordination geometries are known for Laboratoire d’Utilisation du Rayonnement Electromagnÿtique ruthenium complexes, and 3) it can be surrounded by hard Batiment 209d, Centre Universitaire Paris-Sud VIII (s+p) donor ligands (e.g., oxo ligands as in [Ru O4]) or BP 34, 91898 Orsay Cedex (France) by soft s-donor/p-acceptor ligands (e.g., carbonyl ligands as [d] Dr. M. Bÿnard, Dr. M.-M. Rohmer in [RuÀII(CO) ]2À). Hence, ruthenium is particularly suited Laboratoire de Chimie Quantique, UMR CNRS 7551 4 Universitÿ Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg for the design of organometallic oxo complexes, at the inter- (France) face of classical coordination chemistry and organometallic 2 2+ 6 chemistry. Although {Ru(arene)} derivatives of polyoxo- plex [{Ru(h -C6H6)}2Mo2O6(OMe)4], the structure of which [6] 2À [10] metalates have been known for almost fifteen years, this is derived from that of [Mo4O10(OMe)6] . field has experienced growing interest after the report of the The triple-cubane complexes 1a, 2a and 3a were obtained 6 windmill-like structure of the p-cymene complex [{Ru(h - in water from the reaction of Na2MoO4¥2H2O with [7] 6 6 1,4-CH3C6H4CH(CH3)2)}4Mo4O16]. Since then, more than a [{Ru(h -C6H5CH3)Cl2}2], [{Ru(h -1,3,5-C6H3(CH3)3)Cl2}2] and 6 dozen arene Ru oxo complexes with various nuclearities [{Ru(h -1,2,4,5-C6H2(CH3)4)Cl2}2], respectively, in a 1/1 Mo/ and structures have been reported.[8,9] With respect to their Ru ratio for 1a and 2a and a 5/1 Mo/Ru ratio for 3a catalytic potential, particular attention was paid to the (method 1). Increasing the Mo/Ru ratio in the synthesis of 1 framework fluxionality of these complexes in solution. a and 2a did not improve the yield, which never exceeded 6 Indeed, [{Ru(h -1,4-CH3C6H4-CH(CH3)2)}4Mo4O16] was pro- 50%. These preparations were adapted from that of the p- posed to isomerize into its triple-cubane isomer (Scheme 1) cymene complex 4b, which has a windmill-like structure in the solid state but is proposed to isomerize into its triple- cubane isomer 4a in solution.[7] The windmill complex 6 5b was similarly obtained from [{Ru(h -C6Me6)Cl2}2] 6 6 but together with [{Ru(h -C6Me6)}2Mo5O18{Ru(h -C6Me6)- [9b] (H2O)}]. Both 1a and 2a could also be obtained in aceto- nitrile solution by reaction of (nBu4N)2[Mo2O7] and the cor- responding [{Ru(arene)Cl2}2] complex (method 2). Further- more, 2a was also obtained from the reaction of (nBu4N)2- 6 [Mo2O7] with [Ru(h -C6H3(CH3)3)Cl2]2 in methanol at a Mo/ Scheme 1. Ru ratio of 2/1 (method 3). Refluxing a suspension of 1a in methanol for 2 h led to formation of the windmill isomer 1 b. However, the isomerization of 1a to 1b was incomplete, on dissolution in chlorinated solvents, as suggested by multi- even when heating was prolonged to almost 12 h, and led to nuclear NMR techniques.[9a] By varying the arene ligands a mixture of the isomers in the solid state, as far as can be (hexamethylbenzene instead of p-cymene) and/or the metal judged from the IR and Mo K-edge EXAFS spectra. (tungsten instead of molybdenum), it was possible to favour the windmill-like isomers, which have been characterized Triple-cubane isomers: both in solution and in the solid state.[9a,b] In the present 6 work, the influence of less bulky arenes such as toluene, me- ½fRuðh -C6H5CH3Þg4Mo4O16 1a 6 sitylene and durene on the formation of [{Ru(h -arene)}4- 6 ½fRuðh -C6H3ðCH3Þ3Þg4Mo4O16 2a Mo4O16] complexes and their isomerization is addressed. Here we report on the synthesis and structural characteriza- 6 6 6 ½fRuðh -C6H2ðCH3Þ4Þg4Mo4O16 3a tion of [{Ru(h -C6H5CH3)}4Mo4O16], [{Ru(h -1,3,5- 6 C6H3(CH3)3}4Mo4O16] and [{Ru(h -1,2,4,5- 6 ½fRuðh -1; 4-CH3C6H4CHðCH3Þ2Þg4Mo4O16 4a C6H2(CH3)4}4Mo4O16], and on studies on the framework iso- merization of [{Ru(h6-C H CH )} Mo O ] and [{Ru(h6-1,4- 6 5 3 4 4 16 Windmill isomers: CH3C6H4CH(CH3)2)}4Mo4O16] in solution by Raman and X- 6 ray absorption techniques. Density functional geometry opti- ½fRuðh -p-CH3C6H4CHðCH3Þ2Þg4Mo4O16 4b 6 mizations were carried out on the two isomers of [{Ru(h - 6 ½fRuðh -C6Me6Þg4Mo4O16 5b arene)}4Mo4O16] for a variety of arene ligands, including 6 benzene, to clarify the influence of steric crowding and elec- ½fRuðh -C6H5CH3Þg4Mo4O16 1b trostatic interactions of the ligand framework on the relative stabilities of the two isomers. Spectroscopic characterization: The IR spectra of the triple- cubane complexes 1a, 2a and 3a display the same absorp- Results and Discussion tion pattern, with two strong bands characteristic of cis- MoO2 units (nas and ns modes) in the range of 900± Syntheses: We previously reported the reactions of the mo- 930 cmÀ1.[11] The Raman spectrum of solid 1a (Figure 1) in lybdates Na2MoO4¥2H2O and (nBu4N)2[Mo2O7] with this region also displays cis-MoO2 nas and ns modes, at 905 À1 [{Ru(arene)Cl2}2] (arene =p-cymene, hexamethylben- (w) and 940 cm (s). It is noteworthy that the classical re- zene).[8,9] In an attempt to rationalize the effect of various versal of relative band intensities is observed on changing arene ligands on the formation of {Ru(arene)}2+-containing from IR to Raman spectroscopy.[11a] By contrast, the IR and organometallic oxides, we studied the reactivity of the less Raman spectra of the solid windmill-like complex 4b exhibit bulky toluene, mesitylene and durene analogues. This study a single broad band at about 920 cmÀ1, characteristic of the 6 also included the parent benzene complex [{Ru(h - n(Mo=Ot)mode;n(M-Ob-M) bands are observed in the À1 C6H6)Cl2}2]; however, due to their insolubility, none of the range of 700±850 cm . In this region, the triple-cubane com- products formed in this case could be properly character- plexes exhibit only one band in the IR (ca.