Photochemical Reaction of Mo(CO)₆ with Et₂SiH₂:  Spectroscopic Characterization and Crystal Structure of the Bis{(μ-η²-hydridodiethylsilyl)tetracarbonylmolybdenum(I)} Complex [{Mo(μ-η²-H−SiEt₂)(CO)₄}₂]

Abstract

Photolysis of Mo(CO) 6 in n-heptane solution creates a coordinatiVely unsaturated d 6 species, which interacts with the Si-H bond of Et 2 SiH 2 and leads to the formation of Mo-H and Mo-Si bonds. The formation of a Mo-H bond was corroborated by 1 H NMR spectroscopy due to the detection of a high-field resonance at δ ) -8.33 flanked by 29 Si satellites. The formation of Mo-Si bonds was confirmed by the detection of two sets of 29 Si satellites on the hydride signal, which proVided J Si-H ) 57 and 33 Hz, and by the 29 Si{ 1 H} NMR spectrum, which reVealed a resonance at δ ) 207.7. The latter signal in the 29 Si NMR spectrum was obserVed as a doublet of quintets with 1 J Si-H ) 58 Hz and 2 J Si-H ) 41 Hz. The 95 Mo NMR spectrum showed at high field a resonance at δ ) -3785, characteristic for seVen-coordinate molybdenum compounds. The molecular structure of a noVel bis{(µ-η 2 -hydridodiethylsilyl)tetracarbonylmolybdenum(I)} complex, [{Mo(µ-η 2 -H-SiEt 2 )(CO) 4 } 2 ], was established by single-crystal X-ray diffraction studies. The molybdenum hydride obserVed in the 1 H NMR spectrum was located in the structure at a chemically reasonable position between the Mo and Si atoms of the Mo-Si bonds of the bridging silyl ligand with a Si-H bond length of 1.615(3) Å and that of the Mo-H bond amounting to 1.786(5) Å.

Activation of the Si–H bond of Et2SiH2 in photochemical reaction with W(CO)6: Spectroscopic characterization of intermediate W–Si compounds and the revisited crystal structure of the bis{(μ-η2-hydridodiethylsilyl)tetracarbonyltungsten(I)} complex [{W(μ-η2-H–SiEt2)(CO)4}2]

“…4, establishes the unique l-g 2 geometry of the bridging H-SiEt 2 ligand. The general structural features of 1 are identical as those found by Bennett and Simpson in 1971 [15], and are similar to those observed for the analogous molybdenum complex, [{Mo(l-g 2 -H-SiEt 2 )(CO) 4 } 2 ] [16]. A remarkable feature of the current X-ray crystal structure of 1 is that it shows that the hydrogen atom is located between the tungsten atom (H-W = 1.78 Å ) and the silicon atom (H-Si = 1.54 (2) Å ), to bridge one of the W-Si bonds of the bridging silyl ligands.…”

“…The large downfield chemical shift of silicon resonance compared to that observed for the parent silane (d = À22.6 for Et 2 SiH 2 ) suggests some degree of silylene character of the silicon ligand. The 29 Si NMR chemical shift a little more downfield than here has been observed for a tungsten dimer singly bridged by a silylene SiPh 2 ligand (d = 211) [9], and for the molybdenum analogue of 1, the compound [{Mo(l-g 2 -H-SiEt 2 )(CO) 4 } 2 ] (d = 208 ppm) [16]. The 13 C{ 1 H} NMR spectrum of 1 exhibits three signals in the carbonyl region, at d = 206.66 ( 1 J W-C = 117 Hz), 199.88 ( 1 J W-C = 129 Hz), and 192.71 ( 1 J W-C = 123 Hz), in the intensity ratio 1:1:2, which is in agreement with the presence of two mutually trans carbonyl ligands and two other carbonyl groups cis to the former but having two different ligands in the trans position with a weaker p-accepting ability than the carbonyl ligands, i.e.…”

“…Two sets of 29 Si satellites of the W-H resonance result from the presence of two silicon ligands at the tungsten centre. The 1 J Si-H value of 43 Hz is a typical J Si-H value for g 2 -silane complexes, which usually falls in the range 30-100 Hz [1,[16][17][18][19][20][21][32][33][34], and proves a r (Si-H) interaction with the tungsten centre. The second J Si-H value of 34 Hz establishes the presence of another silicon atom at the tungsten center, coupled with a proton through two bonds.…”

“…Careful analysis of the doublet signal at À8.25 ppm allowed us to detect 29 Si satellites that gave rise to the 1 J Si-H = 37 Hz. This coupling constant suggests a r (Si-H) interaction with the tungsten center [1,2,[10][11][12][13][14][15][16][16][17][18][19][20][21][22][23]. Compound B decays in toluene-d 8 solution in a few days and can be characterized in a freshly prepared sample obtained in a low temperature reaction (À10°C).…”

“…Unfortunately, the hydrogen atoms were not located in the latter compound, and no spectroscopic evidence for W-H or Si-H interaction was offered. An analogous molybdenum complex, [{Mo(l-g 2 -H-SiEt 2 )(CO) 4 } 2 ], has recently been characterized in solution and in the solid state [16].…”