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Ruthenium Complexes Containing Two Ru−(η2-Si−H) Bonds:  Synthesis, Spectroscopic Properties, Structural Data, Theoretical Calculations, and Reactivity Studies

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journal contribution
posted on 30.06.1999, 00:00 by Fabien Delpech, Sylviane Sabo-Etienne, Jean-Claude Daran, Bruno Chaudret, Khansaa Hussein, Colin J. Marsden, Jean-Claude Barthelat
The bis(dihydrogen) complex RuH2(H2)2(PCy3)2 (1) reacts with the disilanes (R2SiH)2X to produce the dihydride complexes [RuH2{(η2-HSiR2)2X}(PCy3)2] (with R = Me and X = O (2a), C6H4 (3), (CH2)2 (4), (CH2)3 (5), OSiMe2O (6)) and R = Ph, X = O (2b)). In these complexes, the bis(silane) ligand is coordinated to ruthenium via two σ-Si−H bonds, as shown by NMR, IR, and X-ray data and by theoretical calculations. 3, 4, and 6 were characterized by X-ray diffraction. In the free disilanes the Si−H bond distances and the JSi-H values are around 1.49 Å and 200 Hz, respectively, whereas in the new complexes the values are in the range 1.73−1.98 Å and 22−82 Hz, respectively for the σ-Si−H bonds. The importance of nonbonding H···Si interactions, which control the observed cis geometry of the two bulky PCy3 ligands, is highlighted by X-ray data and theoretical calculations. The series of bis(silane) model complexes, RuH2{(η2-HSiR2)2X}(PR‘3)2, with X = (CH)2, C6H4, (CH2)n, O, and OSiH2O, and with R and R‘ = H or Me, was investigated by density functional theory (DFT) by means of two hybrid functionals B3LYP and B3PW91. In the case of X = C6H4 three isomers were studied, the most stable of which has C2v symmetry and whose structure closely resembles the X-ray structure of 3. Calculated binding energies for the bis(silane) ligand to the RuH2(PH3)2 fragment vary from 130 to 192 kJ/mol, showing that in the more stable complexes, the Si−H bonds are bound more strongly than dihydrogen. The dynamic behavior of these complexes has been studied by variable temperature 1H and 31P{1H} NMR spectroscopy and exchange between the two types of hydrogen is characterized by barriers of 47.5 to 68.4 kJ/mol. The effect of the bridging group X between the 2 silicons is illustrated by reactions of compounds 26 with H2, CO, tBuNC. 3 is by far the most stable complex as no reaction occurred even in the presence of CO, whereas elimination of the corresponding disilane and formation of RuH2(H2)2(PCy3)2, RuH2(CO)2(PCy3)2, or RuH2(tBuNC)2(PCy3)2 were observed in the case of 2 and 46. The mixed phosphine complexes [RuH2{(η2-HSiMe2)2X}(PCy3)(PR3)] 3R6R (with R = Ph and R = pyl) have been isolated in good yields (80−85%) and fully characterized by the addition of 1 equiv of the desired phosphine to 36. In the case of 4Ph, an X-ray determination was obtained. In the case of 2, elimination of the disiloxane was always observed. Addition of 1 equiv of a disilane to Ru(COD)(COT) in the presence of 2 equiv of the desired phosphine under an H2 atmosphere produces the complexes [RuH2{(η2-HSiMe2)2X}(PR3)2] (X = C6H4, R = Ph (3Ph2) and R = pyl (3pyl2); X = (CH2)2, R = Ph, 4Ph2; R = pyl, 4pyl2). 4Ph2 was also characterized by an X-ray structure determination.