Ruthenium Complexes Containing Two Ru−(η 2 -Si−H) Bonds: Synthesis, Spectroscopic Properties, Structural Data, Theoretical Calculations, and Reactivity Studies

The bis(dihydrogen) complex RuH 2 (H 2 ) 2 (PCy 3 ) 2 ( 1 ) reacts with the disilanes (R 2 SiH) 2 X to produce the dihydride complexes [RuH 2 {(η 2 -HSiR 2 ) 2 X}(PCy 3 ) 2 ] (with R = Me and X = O ( 2a ), C 6 H 4 ( 3 ), (CH 2 ) 2 ( 4 ), (CH 2 ) 3 ( 5 ), OSiMe 2 O ( 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 J Si - 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 PCy 3 ligands, is highlighted by X-ray data and theoretical calculations. The series of bis(silane) model complexes, RuH 2 {(η 2 -HSiR 2 ) 2 X}(PR‘ 3 ) 2, with X = (CH) 2, C 6 H 4, (CH 2 ) n, O, and OSiH 2 O, 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 = C 6 H 4 three isomers were studied, the most stable of which has C 2 v symmetry and whose structure closely resembles the X-ray structure of 3 . Calculated binding energies for the bis(silane) ligand to the RuH 2 (PH 3 ) 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 1 H and 31 P{ 1 H} 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 2 − 6 with H 2, CO, t BuNC. 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 RuH 2 (H 2 ) 2 (PCy 3 ) 2, RuH 2 (CO) 2 (PCy 3 ) 2, or RuH 2 ( t BuNC) 2 (PCy 3 ) 2 were observed in the case of 2 and 4 − 6 . The mixed phosphine complexes [RuH 2 {(η 2 -HSiMe 2 ) 2 X}(PCy 3 )(PR 3 )] 3R − 6R (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 3 − 6 . 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 H 2 atmosphere produces the complexes [RuH 2 {(η 2 -HSiMe 2 ) 2 X}(PR 3 ) 2 ] (X = C 6 H 4, R = Ph ( 3Ph2 ) and R = pyl ( 3pyl2 ); X = (CH 2 ) 2, R = Ph, 4Ph2; R = pyl, 4pyl2 ). 4Ph2 was also characterized by an X-ray structure determination.