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

Abstract

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 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 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 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 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 2−6 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 4−6. The mixed phosphine complexes [RuH2{(η2-HSiMe2)2X}(PCy3)(PR3)] 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 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.

σ‐Silane Ruthenium Complexes: The Crucial Role of Secondary Interactions

“…In fact, no matter the nature of the disilane [HMe 2 Si(X)SiMe 2 H with X = C 6 H 4 , (CH 2 ) 2 , OSiMe 2 O] or the phosphane (PCy 3 , PPh 3 ) coordinated, the same overall geometry was obtained (Table 2). [18] We noted that the distances between the classical hydrides and the silicon atoms were close to 2.2 Å, much shorter than the sum of the van der Waals radii (3.4 Å for hydrogen and silicon). Detailed DFT studies by means of two hybrid functionals B3LYP and B3PW91 gave important information on the coordination mode of the disilane ligand to the ruthenium.…”

“…The series of general formula [RuH 2 {(η 2 -HSiMe 2 ) 2 -X}(PCy 3 ) 2 ] [the spacer X between the two Si atoms contains two or three atoms, X = C 6 H 4 , (CH 2 ) n , OSiMe 2 O] was isolated and fully characterized (Scheme 1). [18] The most relevant data from multinuclear NMR experiments (see Table 1, compounds 2-5) were the following: (i) one triplet near -8 ppm for the σ-Si-H protons and an AAЈXXЈ resonance near -12 ppm for the two classical hydrides. Coalescence of the two signals was observed at high temperature and an exchange barrier of roughly 65 kJ·mol -1 was determined.…”

The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers

“…[49] The presence of the secondary interactions is confirmed by DFT calculations. The same features are found for several complexes with different phosphines and different disilanes.…”

Structure and coordinate bonding nature of the manganese–σ–borane complexes

“…Since the report of the first nonclassical dihydrogen complex [2] in 1984, numerous examples of agostic bond of dihydrogen [3][4][5][6][7][8][9][10][11] and silane [12][13][14][15][16][17][18][19][20] complexes have been reported. In contrast to the large number of dihydrogen complexes and r-silane complexes, reports on stable r-complexes of three coordinated boranes are scarce [21][22][23][24][25][26][27][28][29].…”

“…Theoretical calculations have also been carried out to substantiate the presence of g 2 -dihydrogen [9,[31][32][33][34][35][36][37] and g 2 -silane [15,[18][19][20][38][39][40][41] coordination to many different transition metal centers, but less attention has been paid to r-borane complexes. Ab initio calculations have been performed for r-borane complexes [(g 5 -C 5 H 5 )Ti{H-B(OH) 2 } 2 ] and [(g 5 -C 5 H 5 )Ti{HB(H) 2 r-borate complexes [(g 5 -C 5 H 5 ) 2 Nb{H 2 B(OH) 2 }] [42], [(g 5 -C 5 H 5 )Nb{H 2 B(C 8 H 14 )] and [(g 5 -C 5 H 5 )Nb{H 2 B(H) 2 }] [43].…”