Theoretical studies on ferromagnetic behavior of [Cr(C5(CH3)5)2]+[TCNE]− and [Mn(C5(CH3)5)2]+[TCNQ]−

By using broken-symmetry hybrid-DFT (UB3LYP and UB2LYP) calculation, the effective exchange integrals (J values) of [Cr(C₅(CH₃)₅)₂]⁺[TCNE]⁻[Cr(C₅(CH₃)₅)₂]⁺ and [Mn(C₅(CH₃)₅)₂]⁺[TCNQ]⁻[Mn(C₅(CH₃)₅)₂]⁺ were determined theoretically. Those calculated models were reduced to 3-spin-sites models from X-ray crystallographic data of charge transfer 3D crystal. The calculated results showed that effective exchange integrals were positive and the signs of spin densities on the cyclopentadienyl rings were negative. These results supported the so-called McConnell I mechanism for ferromagnetism proposed by Kollmar et al. and our previous calculations. Natural orbital analysis made it clear that the orbital overlap between SOMO on metals and SOMO on TCNE or TCNQ cations was nearly zero. These results indicated that orbital orthogonality was an important key factor for explaining the ferromagnetism of those systems.     

[C5H5Fe(CO)2]LnCl2·nTHF和[C5H5Fe(CO)2][C5H4(SiMe3)]LnCl·nTHF双核配合物的合成

合成了稀土铁双核配合物:(C₅H₅Fe(CO)₂)LnCl₂·nTHF(Ln=Nd,Sm,Gd;n=1,2)和(C₅H₅Fe(CO)₂)(C₅H₄(SiMe₃))·LnCl·nTHF(Ln=Nd,Sm,Gd;n=0,1,2)。元素分析,热分析,红外光谱和质谱分析确认了这两种配合物。红外光谱数据表明铁与稀土原子是以羰基桥连接。晶体结构分析表明((C₅H₅Fe(CO)₂)Na·4THF是(C₅H₅Fe(CO)₂)LnCl₂·nTHF合成的中间体。     

Fluorine for hydrogen exchange in the hydrofluorobenzene derivatives C6H(x)F(6-x), where x = 2, 3, 4 and 5 by monomeric [1,2,4-(Me3C)3C5H2]2CeH: the solid state isomerization of [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,5-C6HF4) to [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,6-C6HF4)

The reaction between monomeric bis(1,2,4-tri-tert-butylcyclopentadienyl)cerium hydride, Cp'2CeH, and several hydrofluorobenzene derivatives is described. The aryl derivatives that are the primary products, Cp'2Ce(C6H(5-x)F(x)) where x = 1,2,3,4, are thermally stable enough to be isolated in only two cases, since all of them decompose at different rates to Cp'2CeF and a fluorobenzyne; the latter is trapped by either solvent when C6D6 is used or by a Cp'H ring when C6D12 is the solvent. The trapped products are identified by GC/MS analysis after hydrolysis. The aryl derivatives are generated cleanly by reaction of the metallacycle, Cp'((Me3C)2C5H2C(Me2)CH2)Ce, with a hydrofluorobenzene, and the resulting arylcerium products, in each case, are identified by their (1)H and (19)F NMR spectra at 20 degrees C. The stereochemical principle that evolves from these studies is that the thermodynamic isomer is the one in which the CeC bond is flanked by two ortho-CF bonds. This orientation is suggested to arise from the negative charge that is localized on the ipso-carbon atom due to C(o)(delta+)F(o)(delta-) polarization. The preferred regioisomer is determined by thermodynamic rather than kinetic effects; this is illustrated by the quantitative, irreversible solid-state conversion at 25 degrees C over two months of Cp'2Ce(2,3,4,5-C6HF4) to Cp'2Ce(2,3,4,6-C6HF4), an isomerization that involves a CeC(ipso) for C(ortho)F site exchange.     

Synthesis, solid-state structure, and bonding analysis of the beryllocenes [Be(C5Me4H)2], [Be(C5Me5)2], and [Be(C5Me5)(C5Me4H)

The beryllocenes [Be(C(5)Me(4)H)(2)] (1), [Be(C(5)Me(5))(2)] (2), and [Be(C(5)Me(5))(C(5)Me(4)H)] (3) have been prepared from BeCl(2) and the appropriate KCp' reagent in toluene/diethyl ether solvent mixtures. The synthesis of 1 is facile (20 degrees C, overnight), but generation of decamethylberyllocene 2 demands high temperatures (ca. 115 degrees C) and extended reaction times (3-4 days). The mixed-ring beryllocene 3 is obtained when the known [(eta(5)-C(5)Me(5))BeCl] is allowed to react with K[C(5)Me(4)H], once more under somewhat forcing conditions (115 degrees C, 36 h). The structures of the three metallocenes have been determined by low-temperature X-ray studies. Both 1 and 3 present eta5/eta1 geometries of the slip-sandwich type, whereas 2 exhibits an almost regular, ferrocene-like, sandwich structure. In the mixed-ring compound 3, C(5)Me(5) is centrally bound to beryllium and the eta(1)-C(5)Me(4)H ring bonds to the metal through the unique CH carbon atom. This is also the binding mode of the eta(1)-ring of 1. To analyze the nature of the bonding in these molecules, theoretical calculations at different levels of theory have been performed on compounds 2 and 3, and a comparison with the bonding in [Be(C(5)H(5))(2)] has been made. As for the latter molecule, energy differences between the eta5/eta5 and the eta5/eta1 structures of 2 are very small, being of the order of a few kcal mol(-1). Constrained space orbital variations (CSOV) calculations show that the covalent character in the bonding is larger for [Be(C(5)Me(5))(2)] than for [Be(C(5)H(5))(2)] due to larger charge delocalization and to increased polarizability of the C(5)Me(5) fragment.     

Synthesis of (C5Me5)2(C5Me4H)UMe, (C5Me5)2(C5H5)UMe, and (C5Me5)2UMe[CH(SiMe3)2] from cationic metallocenes for the evaluation of sterically induced reduction

To probe the correlation of unusual (C5Me5)(1-) reactivity with steric crowding in complexes such as (C5Me5)3UMe and (C5Me5)3UCl, slightly less crowded (C5Me5)2(C5Me4H)UX analogues (X = Me, Cl) were synthesized and their reactivity was evaluated. The utility of the cationic precursors [(C5Me5)2UMe](1+), 1, and [(C5Me5)2UCl](1+), 2, in the synthesis of (C5Me5)2(C5Me4H)UMe, 3, and (C5Me5)2(C5Me4H)UCl, 4, was also explored. Since the use of precursor [(C5Me5)2UMe][MeBPh3], 1a, is complicated by the equilibrium between 1a and (C5Me5)2UMe2/BPh3, the reactivity of [(C5Me5)2UMe(OTf)]2, 1b, (OTf = O3SCF3) prepared from (C5Me5)2UMe2 and AgOTf, was also studied. Both 1a and 1b react with KC5Me4H to form 3. Complex 4 readily forms by addition of KC5Me4H to [(C5Me5)2UCl][MeBPh3], generated in situ from (C5Me5)2UMeCl and BPh3. Complex 1b was preferred to 1a for the synthesis of (C5Me5)2(C5H5)UMe, 5, and (C5Me5)2UMe[CH(SiMe3)2], 6, from KC5H5 and LiCH(SiMe3)2, respectively. Complex 6 is the first example of a mixed alkyl uranium metallocene complex. Sterically induced reduction (SIR) reactivity was not observed with 3-6 although the methyl displacements from the (C5Me5)(1-) ring plane for 3 are the closest observed to date to those of SIR-active complexes. The (1)H NMR spectra of 3 and 4 are unusual in that all of the (C5Me4H)(1-) methyl groups are inequivalent. This structural rigidity is consistent with density-functional theory calculations.