Ruthenium complexes containing two Ru-(eta(2)-Si-H) bonds: Synthesis, spectroscopic properties, structural data, theoretical calculations, and reactivity studies

The bis(dihydrogen) complex RuH2(H-2)(2)(PCy3)(2) (1) reacts with the disil anes (R2SiH)(2)X to produce the dihydride complexes [RuH2{(eta(2)-HSiR2)(2) X}(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(sila ne) ligand is coordinated to ruthenium via two sigma-Si-H bonds, as shown b y 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 di stances and the J(Si-H) values are around 1.49 Angstrom and 200 Hz, respect ively, whereas in the new complexes the values are in the range 1.73-1.98 A ngstrom and 22-82 Hz, respectively for the sigma-Si-H bonds. The importance of nonbonding H ... Si interactions, which control the observed cis geomet ry of the two bulky PCy3 ligands, is highlighted by X-ray data and theoreti cal calculations. The series of bis(silane) model complexes, RuH2{(eta(2)-H SiR2)(2)X}(PR3')(2), with X = (CH)(2), C6H4, (CH2)(n), O, and OSiH2O, and w ith 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 = C6 H4 three isomers were studied, the most stable of which has C-2v symmetry a nd whose structure closely resembles the X-ray structure of 3. Calculated b inding energies for the bis(silane) ligand to the RuH2(PH3)(2) fragment var y 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 t hese complexes has been studied by variable temperature H-1 and P-31{H-1} N MR spectroscopy and exchange between the two types of hydrogen is character ized 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, (BuNC)-Bu-t. 3 is by far the most stable complex as no reaction occ urred even in the presence of CO, whereas elimination of the corresponding disilane and formation of RuH2(H-2)(2)(PCy3)(2), RuH2(CO)(2)(PCy3)(2), or R uH2((BuNC)-Bu-t)(2)(PCy3)(2) were observed in the case of 2 and 4-6. The mi xed phosphine complexes [RuH2{(eta(2)-HSiMe2)(2)X}(PCy3)(PR3)] 3R-6R (with R = Ph and R = pyl) have been isolated in good yields (80-85%) and fully ch aracterized by the addition of I equiv of the desired phosphine to 3-6. In the case of 4Ph, an X-ray determination was obtained. In the case of 2, eli mination of the disiloxane was always observed. Addition of 1 equiv of a di silane to Ru(COD)(COT) in the presence of 2 equiv of the desired phosphine under an H-2 atmosphere produces the complexes [RuH2{(eta(2)-HSiMe2)X-2}(PR 3)(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 de termination.