Comparison of H−H versus Si−H σ-Bond Coordination and Activation on 16e Metal Fragments. Organosilane, N₂, and Ethylene Addition to the Agostic Complex W(CO)₃(PR₃)₂and Dynamic NMR Behavior of the Latter

Abstract

Variable-temperature (31)P{(1)H} NMR spectroscopy of the agostic complexes M(CO)(3)(PCy(3))(2) (M = Mo, W) indicates dynamic behavior as evidenced by collapse below -20 degrees C of a singlet to an AB signal plus a shifted singlet. The inequivalency of the phosphines is possibly due to the presence of conformational isomers resulting from hindered rotation of the M-P bond or, less likely, a geometric isomer with pseudo-cis PCy(3) ligands. Further studies on the coordination chemistry of W(CO)(3)(PR(3))(2) (R = iPr, Cy) were performed. The bridging dinitrogen complex [W(CO)(3)(PiPr(3))(2)](2)(&mgr;-N(2)) (1) was cleanly formed in the reaction of W(CO)(3)(PiPr(3))(2) with N(2). Complex 1 was structurally characterized and compared with other bridging dinitrogen compounds of tungsten. The ethylene complex W(CO)(3)(PCy(3))(2)(eta(2)-C(2)H(4)) (2) was synthesized and characterized by X-ray crystallography in order to compare the binding mode of ethylene with that of H(2). Phenylsilane reacted with W(CO)(3)(PR(3))(2) (R = iPr, Cy) to form the thermally unstable oxidative addition (OA) products WH(SiH(2)Ph)(CO)(3)(PR(3))(2) (3, R = Cy; 4, R = iPr). Diphenylsilane reacted with W(CO)(3)(PiPr(3))(2) at 60 degrees C to form the bridging silyl species [W(CO)(3)(PiPr(3))(&mgr;-SiHPh(2))](2) (5), which was confirmed by spectroscopic techniques and X-ray crystallography to have two 3-center 2-electron W.H.Si interactions. Detailed comparisons of the binding and activation of silanes versus H(2) on various 16e metal centers suggest a high degree of similarity, but relative ease of OA depends on the electrophilicity of the metal-ligand fragment and other factors such as bond energetics. Increasing the electrophilicity of the metal center (e.g., adding positive charge) may aid in stabilizing alkane coordination.

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]

“…The 29 Si satellites on the latter hydride signal provided the 1 J Si-H value of 93 Hz, which is in a similar range as has recently been observed for similar g 2 -silane compounds ( 1 J Si-H = 98 Hz for [W(CO) 5 (g 2 -H-SiHPh 2 )]) [11], proving the correct assignment of this signal to the g 2 -H-SiHEt 2 moiety of the g 2 -silane complex. The 183 W satellites on the hydride signal allowed us to calculate the 1 J W-H = 38 Hz, which is very close to those observed for other a-agostic hydrides [10,11,20,21,38]. Based on these data, the signal can be assigned without a doubt to the intermediate compound [W(CO) 5 (g 2 -H-SiHEt 2 )] (A) (Scheme 1).…”

“…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).…”

DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

“…In 1997, Butts et al [12] reported the synthesis and structure of W(CO) 3 (PCy 3 ) 2 (g 2 -C 2 H 4 ) which agrees with structure 1. An interesting structural feature in this complex is the coplanar orientation of the ethylene and phosphine ligands.…”

The UV‐Light Initiated Reaction of Organosilanes with Tungsten Hexacarbonyl: Formation of an Organosilylene Complex and Organosilylium Salts

“…Associated with this is the desire to get more insight into the mechanism of Si-H bond activation by transition metal compounds [20][21][22][23][24][25][26][27][28][29] which in turn is relevant even for the topic of C-H bond activation [30] as well as for the understanding of transition metal-catalyzed oligo-and polysilane formation [31].…”