Transition Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

Abstract

A covalently-linked salen-C60 (H2L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C60 cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen-C60 introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal-salen-C60 complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene-containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single-, double- and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen-C60 complexes in heterogeneous catalysis.

Chemical reactions at the graphitic step-edge: changes in product distribution of catalytic reactions as a tool to explore the environment within carbon nanoreactors

“…The activity of the fullerene containing catalyst, 1, in solution (38 % conversion) is more than double that of the non-fullerene catalyst, 2 (18 %), which is attributed to the electron withdrawing effect of the fullerene group. [ 20 ] When confined inside the GNF in a heterogeneous system, both catalysts show significant increase in conversion to 49 % and 31 % for 1@GNF and 2@GNF respectively. This is attributed to an increased local concentration of reactants within the nanoreactor, a well-known effect for carbon nanotubes and nanofibers, Comparison of the selectivities of the reactions carried out in solution, on the GNF outer surface and on the GNF step-edge ( Figure 2) shows preferential formation of trans-stilbene in each case, with small amounts of cis-stilbene and geminal coupling products formed (Table 1).…”

“…We prepared two Pd(II)Salen catalysts for the Heck reaction according to our previously reported procedure [ 20 ] ( Figure 1), 1, which contains a fullerene group to provide high affinity to the graphitic surface of the carbon nanoreactor, and 2, which doesn't have the fullerene spacer group but has been shown to bind to the GNF nanoreactor through similar van der Waals interactions, albeit with less affinity. Comparison of the infrared spectra of the composite 1@GNF and 2@GNF and the corresponding molecular catalysts (see Figure S2 in the SI) show that the spectrum is dominated by the C=C stretches of the GNF.…”

“…The Heck reaction -an arylhalide-arylalkene cross-coupling reaction catalysed by Pd catalysts [ 18 ] -gives a distribution of several isomeric coupling products, the selectivity of which depends strongly on the electronic and steric environment of the catalytic centre, [ 19 ] and is therefore an ideal reaction system to investigate the local reaction environment of catalyst materials. Variation of the size and shape of the reactant molecules by incorporating bulky planar and non-planar substituents, as well as modifying the size and shape of the catalyst molecule by using a square planar Pd(II)Salen complex and a modified Pd(II)Salen-C60, in which a bulky, spherical C60 cage is appended to the otherwise identical Pd(II)Salen complex, [ 20 ] results in notable changes of the catalyst activity and selectivity. The observed product distribution in each case reveals both important information about the role that the GNF nanoreactor plays in the catalytic process and unprecedented detail regarding the location and orientation of the fullerene-containing and fullerene-free catalyst molecules inside the GNF unavailable by any spectroscopic or microscopic techniques.…”

Coordination chemistry on carbon surfaces

“…DFT calculations have predicted that Pt and PtRu clusters have the highest and lowest stability on boron-doped graphene and pristine graphene, respectively [570]. Even the Pt 32 metal cluster, [551] N N Re CO OC OC Cl [552] Adapted from Ref. [560].…”

New Pathway for Heterogenization of Molecular Catalysts by Non-covalent Interactions with Carbon Nanoreactors

“…[14] We have synthesised the fullerenetagged Cu(II) salen complex 1 ( Figure 1) in six steps according to our recently reported procedure. [15] The analogous fullerene-free complex 2 was prepared for comparison.…”