Organometallic nitrosyl chemistry. 42. Unambiguous example of a .eta.2-benzyl group functioning as a formal three-electron ligand: solid-state molecular structure of Cp*Mo(NO)(CH2SiMe3)(.eta.2-CH2C6H5)

Silylene Complexes of Late 3d Transition Metals Supported by tris-Phosphinoborate Ligands

“…Evidently, the strong binding of DMAP inhibits the coordination of an unsaturated substrate, a step that precedes Si−H insertion in related complexes. 12 The lack of electrophilic character at silicon is also consistent with the 29 Si chemical shift of 6 (53.4 ppm), which is substantially upfield from the region commonly observed for silylene complexes (∼150−400 ppm), 1 and is similar to those commonly observed for metal-silyl complexes (−100 to 100 ppm). 10 Previous reports of base-stabilized silylene complexes have indicated substantial sp 3 (i.e., silyl) character at silicon and M−Si single-bond character; 1 the aforementioned properties of 6 are consistent with this characterization.…”

“…The 1 H NMR spectrum of 5 contains a multiplet corresponding to the bridging hydride ligand at −7.17 ppm and another resonance belonging to the cyclohexyl methine proton at 2.03 ppm. A cross-peak between both resonances and a 29 Si nucleus is observed at 220.9 ppm in the 29 Si− 1 H HMBC NMR spectrum. The moderate coupling constant ( 1 J (Ni)H−Si = 52 Hz) for the bridging hydride indicates a diminished H−Si interaction relative to 1, possibly indicating that 5 has progressed further along the reaction coordinate for the α-H migration.…”

“…As with 1 , the 31 P­{ 1 H} NMR spectrum of 4 at room temperature contains only a sharp singlet corresponding to the three phosphorus nuclei of the [BP 3 Ph ] ligand, indicative of approximate C 3 v symmetry in solution. The η 2 -coordination of the benzyl ligand in 4 , with net donation of three electrons, has been documented in the literature, and in this case likely results from steric crowing about the metal center resulting from the Ph-substituents of the [BP 3 Ph ] ligand which precludes η 3 -coordination. Consistent with this, the solid-state structure of 4 (Figure ) shows Ni–CH 2 and Ni–C ipso distances of 1.982(2) and 2.226(3) Å, while the nonbonding Ni–C ortho distances are 2.644(3) and 3.149(3) Å.…”

“…The purity of 3 following purification via recrystallization was verified by 1 H NMR spectroscopy, which indicated the exclusive formation of one species (3) whose spectroscopic features are identical to those reported previously. 27 The NMR spectra were recorded on Bruker Avance 400, 500, and 600 MHz spectrometers, and spectra were referenced to solvent residual signals ( 1 H, 13 C), 35 or to external references ( 31 P, 11 B, 29 Si). The IR spectra were collected on a Bruker Vertex spectrometer, with samples prepared as Nujol mulls sandwiched between NaCl plates; absorption bands in spectra that are masked by peaks for Nujol are not reported.…”

“…H} NMR (150 MHz, benzene-d 6 ): δ 26.9 (Cy-C), 28.2 (Cy-C),29.0 (Cy-C), 29.4 (Cy-C), 31.1 (Cy-C), 38.6 (Cy-C), 125.6, 126.9, 127.5 (m), 127.6, 128.5 (d, J = 10.2), 128.9 (d, J = 13.2), 129.3, 131.9 (m), 132.9 (m), 133.1 (m), 133.2, 134.9 (m). Note: a resonance for the carbon nucleus in each PCH 2 B unit was not found by direct or indirect detection methods 31.…”