Search

The synthesis of multiwalled carbon nanotubes (MWCNTs) and carbon balls (CBs) catalyzed by ferrocene (Fc), Mo(CO)5L (L = CO, ^tBuNC), and bimetallic catalyst systems (Fc/M(CO)5^tBuNC; M = W or Mo) was investigated. These reactions were carried out in flowing 5% H2 in Ar in the temperature range 700−900 °C. Under the reaction conditions, Fc yielded CNTs and CBs, while the M(CO)5L complexes yielded little carbonaceous material. Depending on the temperature and weight ratio of the metals used, mixtures of Fc and M(CO)5L generated varying amounts of CNTs and CBs. EDS and TEM analysis revealed the formation of large particles of Mo/Fe alloys. It was observed that the diameters of the CNTs catalyzed by Fc are smaller while the diameters of CBs are larger relative to the diameters of CNTs and CBs produced by the bimetallic catalyst systems. In all instances MWCNTs were produced, which contrasts with the single-walled CNTs produced by Fe/Mo-supported heterogeneous catalyst systems.

The reaction between solid (η⁵-C5H5)M(CO)3CH3 and solid phosphines is shown to occur in the melt phase (optical microscopy), and a DRIFTS study of the melt reveals a well-behaved reaction following pseudo-first-order kinetics.

Migratory insertion reactions of organometallic complexes have been shown to occur in the absence of solvent and, more significantly, between solid reagents. Reaction between (η⁵-C5H5)M(CO)3Me (M = Mo, W) or (η⁵-C5H5)Fe(CO)2Me and PPh3 (no solvent) took place at temperatures between 40 and 90 °C and gave the products (η⁵-C5H5)M(CO)2(PPh3)COMe and (η⁵-C5H5)Fe(CO)(PPh3)COMe in moderate to good yield (60−99%). The Mo and W complexes reacted in the solid state when T < 80 °C. The decarbonylation of (η⁵-C5H5)Mo(CO)2(PPh3)COMe to yield (η⁵-C5H5)Mo(CO)2(PPh3)Me also occurred in the solid state (120 °C). Reaction of (η⁵-C5H5)Mo(CO)3Me with a range of ligands, L (L = PPh3, P(p-MeOC6H4)3, PCy3, PEt3, AsPh3, POPh3, P(OEt)3; 1:1 reagent ratio, 90 °C, 15 min), in the absence of solvent gave (η⁵-C5H5)Mo(CO)2(L)COMe (7−100% yield) and, on extended reaction, (η⁵-C5H5)Mo(CO)2(L)Me in varying yields. A kinetic study of the solid-state reaction between (η⁵-C5H5)Mo(CO)3Me and PPh3 yielded rate constants, e.g. k = 5.18 × 10^-5 s^-1 (Mo:P = 1:10; 50 °C), which compares with the literature solution data in toluene (k = (0.8−2.5) × 10^-5 s^-1, 50 °C) using similar metal to ligand ratios. The data are consistent with a pseudo-first-order reaction in the presence of PPh3. Diffusional effects on the reaction rate are detected at low temperature and low PPh3 ratios.

The reaction of tert-butyldichlorophosphine with freshly prepared lithium indene is shown to exhibit an unusual solvent dependence. In diethyl ether the reaction proceeds to the achiral tert-butylbis(3-indenyl)phosphine via a series of chiral intermediates. The reaction is catalyzed in-situ by the presence of solvent-separated indenyl ions in the solution. In toluene, tert-butyl(n-butyl)indenylphosphine is formed because of the selective precipitation of an unusual mixed indenyl-butyllithium aggregate prior to the addition of tert-butyldichlorophosphine. These mechanisms explain the solvent dependence of a range of related reactions.

Cone (θ) and solid (Ω) angle data for the alkyl phosphite ligands P(OR)3 (R = Me, Et, ⁱPr) were determined from structural data in the Cambridge Structural Database (CSD). The results for the P(OMe)3 and P(OEt)3 ligands are indicative of more than one preferred cone (or solid) angle, suggesting that geometric measurements of steric parameters for these ligands need to be used with care, as is shown in the analysis of some linear free energy relationships.

The complexes [Mo(η⁵-C5H5)(CO)2(L)I] (L = P(OMe)3, P(OEt)3, P(OⁱPr)3, P(OⁱBu)3, P(OⁿPn)3) were prepared and characterized by X-ray crystallography. Crystallographic cone (θC) and solid (ΩC) angles for the phosphite ligands were calculated from the ligand conformations in the crystal structures and compared with the available literature data. The steric data are shown to be influenced by the surrounding ligand environment. The effects of the ligand conformation on the steric measurements are discussed, and the results applied to the analysis of equilibrium cis−trans isomer ratios in [Mo(η⁵-C5H5)(CO)2(L)I].

The complex [Re(η⁵-C5H4Me)(CO)(P(OPh3)Br2] (1) isomerizes from the diag→lat (trans→cis) isomer in the solid state, while [Re(η⁵-C5H4^tBu)(CO)2Br2] (2) does not isomerize, although 2 is found to isomerize in the melt. Both complexes isomerize from the lat→diag isomer in solution. The crystal structures of both isomers of 1 and 2 have been determined by single-crystal X-ray diffraction. The crystal structures of 1 are analyzed to determine the structural forces driving the solid-state isomerization. For 2, the crystal structures are analyzed and compared with those of [Re(η⁵-C5H4Me)(CO)2Br2] (3), which does isomerize in the solid state.