ansa-Metallocene derivatives

Abstract

In the reduction of tetramethylethylene-bridged (CH3)4C2(CsH4hTiCI2 under argon, studied by cyclic voltammetry, a first reduction to the Ti III stage occurs at a potential of-0.92 V vs. SCE, close to that of (CsHshTiCI2, and a second reduction to the Ti II stage at a potential of-2.53 V, about 0.3 V more negative than in the corresponding reduction of the unbridged analogue. Decay of the tetramethylethylene-bridged Ti II product is considerably faster than that of its unbridged analogue. Changes induced by the presence of an N2 or H2 atmosphere indicate the occurrence of secondary reactions. In the presence of CO, reduction to (CH3)4C2(CsH4hTi(COh occurs at-2.0 V. This tetramethylethylene-bridged titanocene dicarbonyl complex, which is also formed by reduction of (CH3)4C2(CsH4hTiCI2 with Mg metal under CO, undergoes irreversible reduction and oxidation at-2.78 and-0.08 V, respectively. When the latter process is conducted in the presence of Cl-, the dichloride (CH3)4C2(CsH4hTiCI2 is regenerated.

Syntheses of [ethylene-1,2-bis(.eta.5-4,5,6,7-tetrahydro-1-indenyl)]zirconium and -hafnium hydride complexes. Improved syntheses of the corresponding dichlorides

“…NMR (300 MHz, CgD6): & 6.6-7.3 (m, 5 H, NPh), 6.42 (d, J = 3.0 Hz, 1 H, EBTHI), 6.30 (s, 1 H, EBTHI), 6.10 (s, 1 H, Zr-H), 5.38 (d, J = 2.5 Hz, 1 H, EBTHI), 4.99 (d, J = 2.8 Hz, 1 H, EBTHI), 1.5-3.5 (broad m, EBTHI,NMe2,C2BgHn).…”

“…If the transition state for hydride complex, (EBTHI)HfCl2 (2), has also been prepared, although in low yield.6 As part of an ongoing project in which the utility of such compounds in asymmetric synthesis is being examined, we have prepared several derivatives of 1 and 2. Herein we report the syntheses of the bridged hydride dimers [( ) (µ-)]2 (M = Zr, 3; = Hf, 4) and the dimethylhafnium compound (EB-THI) HfMe2 (5). Protonation of 3 or 4 with the weak acid, [PhMe2NH] [Co(C2B9Hn)2], gives the corresponding cationic monomeric hydride species [(EBTHI)M(H)-(PhNMe2)][Co(C2B9Hn)2] ( = Zr, 6; = Hf, 7); the former, when enantiomerically enriched, catalyzes the asymmetric hydrogenation of -ethylstyrene.…”

ansa-Metallocene derivatives XX. An assignment of 1H- and 13C-NMR signals in ansa-metallocene complexes with 16-electron and 18-electron configuration

“…Complexes Ib [12], 2a [13] and 3 [14] were prepared by published procedures. Complex 4 [6,7] was obtained by reaction of (CH3)4C2(C5H4MgClh• 4THF [12] with FeCl 2 in THF.…”

Equilibria and kinetics in the CO-induced, reversible disproportionation of ((C5H5)2TiCl)2 to (C5H5)2TiCl2 and (C5H52Ti(CO)2. An IR study at elevated CO gas pressures

“…The CO solubility data thus obtained show an evident saturation at higher CO pressures, which is particularly pronounced at lower temperatures. At each temperature, the data are reproduced, within experimental error, by the two-term equation 13, with values of a and 13 as indicated in Tab. 1.…”

“…Such a reaction could occur either via an outer-sphere electron transfer to yield Cp2Ti(CO)Cl-and Cp2TiCl+, from which the final products could then be formed by rapid ligand exchange, or via an inner-sphere halogen transfer from Cp2Ti(CO)Cl to Cp2TiCl. Electrochemical studies on the oxidation of Cp2TiCl and the reduction of Cp2Ti(CO)Cl [12,13] indicate that an electron transfer between these species would be endothermic by ca. 100-150 kJ/mol in THF solution (and hence even more so in toluene), which would let an outer-sphere path appear rather unlikely.…”