Indenylmethyl-molybdenum and -tungsten compounds containing isocyanide ligands. Formation and study of isomeric η2-iminoacyls and η3-1-azaallyls

Group 6 metal complexes with a hemilabile tridentate xantsil ligand and facile insertion of tBuCN into a W–Si bond [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)]

“…The C(1)-N(1) bond length of 1.257(9) A ˚is comparable to those of previously reported tungsten g 2 -iminoacyl complexes. 7 The puckered angle between the leastsquares planes of two aromatic rings of the xantsil moiety [30.9 (3)u] is substantially smaller than that of oxygen-coordinated 2a [44.0 (3)u].…”

η3-Allyl carbonyl complexes of group 6 metals: Structural aspects, isomerism, dynamic behaviour and reactivity

“…Further diversity is introduced by the incorporation of heteroatoms into the allyl ligand. While such compounds remain beyond the scope of the present article, the interested reader will find notable examples of such species in the following references: η 3 -azaallyl [58][59][60][61][62][63][64], η 3 -silaallyl [343][344][345], and silabenzyl [346][347][348][349] complexes, while the related η 3 -bound benzyl species are detailed in [350][351][352][353][354][355][356][357]. The benzyl and related complexes offer an alternative route to coordinative unsaturation, via a relatively facile η 3 → η 1 haptotropic shift.…”

“…Similarly, isolating the contributions to the paramagnetic term (Equation 1) is difficult; although, several computational studies have been used to distinguish the contributions, [52][53][54] However, the aforementioned correspondence observed between the exo/endo ratios and chemical shifts highlights the utility of NMR in establishing empirical correlations between chemical shifts of NMR-active transition metal nuclei, and the dynamic behaviour, chemical reactivity and even catalytic activity of their organometallic complexes. As a particularly interesting example, catalytic efficacy of complexes [(η 5 -R-Cp)Co(COD)] (COD = 1,6-cyclooctadiene, R-Cp = monosubstituted cyclopentadienyl) with regards to the cyclotrimerisation of acetylenes and nitriles has been shown to correlate with their respective 59 Co chemical shifts. [51,55] 95 Mo (and 183 W) NMR studies are promising for the characterisation of catalytic applications.…”

“…Computational studies, however, have challenged this conjecture. [58] The difference in orbital energies concerning 13 and 20 (similarly 15 and 21) are presumably also influenced by a) the endo conformation exclusively adopted by η 3 -azaallyl complexes of this type, [58][59][60][61][62][63][64] as opposed to the exo form of 13 and 15, b) the tert-butyl substituent on the azaallyl ligand, and c) the modified metal-ligand bonding properties as a consequence of the heteroatom incorporated within the allylic backbone. Thus direct comparison of the orbital for the η 3allyl and η 3 -azallyl complexes is here not appropriate.…”

Experimental and DFT Computational Study of β-Me and β-H Elimination Coupled with Proton Transfer: From Amides to Enamides in Cp*2MX (M = La, Ce)

“…The θ angle is less than that expected if it were classified as an aza allylic group in which the θ angle is near 90°, since the bonding occurs between the carbon and nitrogen π-orbitals and the metallocene fragment. 42,43 In the enamide, the NR 1 unit is a σ-donor and the olefinic unit is a π-donor. The orientation of the four substituents on C β −C γ is not coplanar, as the NC β C γ H β torsion angle (ω1) is between 29 and 40°while the C(Me)C β C γ H α torsion angle (ω2) is between 2 and 8°.…”