Electron paramagnetic resonance and structural studies of small-ring metallacycles. Bonding in a metallacyclopropene formed by the oxidative addition of an acetylene to vanadocene

Quantifying the Electron Donor and Acceptor Abilities of the Ketimide Ligands in M(N═CtBu2)4 (M = V, Nb, Ta)

“…As shown in Figure 6, in hexanes at 125 K, complex 1 displays average g and A values in good agreement with the room temperature isotropic (i.e., rotationally averaged) values (see Table 2), but with significant uniaxial anisotropy, defined here as the z-direction ( A x = A y = A ⊥ = 65 MHz, A z = A ‖ = 245 MHz). Similar EPR anisotropy has been observed in the pseudo four-coordinate V(IV) complex [Cp 2 V(dbm)][ClO 4 ] (dbm = dibenzoylmethanate) 52 and in V(Mes) 4 . 42 Indeed, the ratio of A ‖ / A ⊥ in V(Mes) 4 equals 3.72, and in 1 this ratio is 3.77.…”

Reactivity Studies of a Masked Three‐Coordinate Vanadium(II) Complex

“…Solution susceptibility measurement (300 K, Evans method, μ eff =1.92 μ B ) is consistent with oxidation to V IV ( S =1/2) as result of two‐electron reduction of the alkyne moiety. The presence of a V IV ion is further corroborated by the room temperature X‐band EPR spectrum in toluene solution ( g iso =1.97), which reveals an eight line pattern arising from hyperfine coupling to 51 V ( I =7/2; 99.6 %) of A iso =166 MHz,10 and in the range reported for [V(Cp) 2 ] 2+ complexes ( A iso =120–210 MHz) 1e. Furthermore, XRD studies unambiguously reveal formation of a metallacyclopropene (VC44, 2.0009(19) Å; VC51, 2.0063(18) Å; C51VC44, 38.10(8)°) moiety derived from two‐electron reduction of the alkyne (Figure 1).…”

“…Formation of V IV in 4 is again confirmed by room temperature susceptibility (Evans method, μ eff =1.84 μ B ) as well as X‐band EPR ( g iso =1.97 and A iso ( 51 V)=74 MHz) 10. This hyperfine coupling value is low compared to that of [V(Cp) 2 ] 2+ complexes1e and may reflect greater delocalization of the unpaired electron onto the imido ligand. XRD studies reveal formation of a terminal imido (VN, 1.654(2) Å, VNC, 177.4(2)°).…”

“…Furthermore, XRD studies unambiguously reveal formation of a metallacyclopropene (VC44, 2.0009(19) Å; VC51, 2.0063(18) Å; C51VC44, 38.10(8)°) moiety derived from two‐electron reduction of the alkyne (Figure 1). This reaction of 2 with an alkyne is reminiscent of the reaction of vanadocene and diphenylacetylene 1e…”

Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 30. Synthesis of the vanadium–tungsten complexes [VW(µ-CR)(CO)2(η-C5H5)3](R = C6H4Me-4 or Me) and the crystal structure of the tolylmethylidyne compound

“…measurements. The equilibrium point is reached for complex (1) 8 These values are appreciably lower than those obtained from the spectra of vanadocene d' complexes, such as [VMe2(q-C5H5)2] (64 G), and it has been concluded 698 that in the former complexes the unpaired electron is delocalised on to the alkyne ligand. Similar reasoning would imply that in complexes ( 1) and (2) the unpaired electron is appreciably associated with the alkylidyne tungsten group.…”