josiphos ligand. fuel additives ferrocene and its derivatives are antiknock agents used in the fuel for petrol engines. they are safer than previously used tetraethyllead. petrol additive solutions containing ferrocene can be added to unleaded petrol to enable its use in vintage cars designed to run on leaded petrol. the iron-containing deposits formed from ferrocene can form a conductive coating on spark plug surfaces. ferrocene polyglycol copolymers, prepared by effecting a polycondensation reaction between a ferrocene derivative and a substituted dihydroxy alcohol, has promise as a component of rocket propellants. these copolymers provide rocket propellants with heat stability, serving as a propellant binder and controlling propellant burn rate. ferrocene has been found to be effective at reducing smoke and sulfur trioxide produced when burning coal. the addition by any practical means, impregnating the coal or adding ferrocene to the combustion chamber, can significantly reduce the amount of these undesirable byproducts, even with a small amount of the metal cyclopentadienyl compound. pharmaceuticals ferrocene derivatives have been investigated as drugs, with one compound ferrocerone approved for use in the ussr in the 1970s, though it is no longer marketed today. only one drug has entered clinical trials in recent years, ferroquine (7-chloro-n-(2-((dimethylamino)methyl)ferrocenyl)quinolin-4-amine), an antimalarial, which has reached phase iib trials. ferrocene-containing polymer-based drug delivery systems have been investigated. ferroquine the anticancer activity of ferrocene derivatives was first investigated in the late 1970s, when derivatives bearing amine or amide groups were tested against lymphocytic leukemia. some ferrocenium salts exhibit anticancer activity, but no compound has seen evaluation in the clinic. ferrocene derivatives have strong inhibitory activity against human lung cancer cell line a549, colorectal cancer cell line hct116, and breast cancer cell line mcf-7. an experimental drug was reported which is a ferrocenyl version of tamoxifen. the idea is that the tamoxifen will bind to the estrogen binding sites, resulting in cytotoxicity. ferrocifens are exploited for cancer applications by a french biotech, feroscan, founded by pr. gerard jaouen. solid rocket propellant ferrocene and related derivatives are used as powerful burn rate catalysts in ammonium perchlorate composite propellant. derivatives and variations ferrocene analogues can be prepared with variants of cyclopentadienyl. for example, bisindenyliron and bisfluorenyliron. various ferrocene derivatives where cyclopentadienyl has been replaced by related ligands carbon atoms can be replaced by heteroatoms as illustrated by fe(η5-c5me5)(η5-p5) and fe(η5-c5h5)(η5-c4h4n) ("azaferrocene"). azaferrocene arises from decarbonylation of fe(η5-c5h5)(co)2(η1-pyrrole) in cyclohexane. this compound on boiling under reflux in benzene is converted to ferrocene. because of the ease of substitution, many structurally unusual ferrocene derivatives have been prepared. for example, the penta(ferrocenyl)cyclopentadienyl ligand, features a cyclopentadienyl anion derivatized with five ferrocene substituents. penta(ferrocenyl)cyclopentadienyl ligand structure of hexaferrocenylbenzene in hexaferrocenylbenzene, c66, all six positions on a benzene molecule have ferrocenyl substituents (r). x-ray diffraction analysis of this compound confirms that the cyclopentadienyl ligands are not co-planar with the benzene core but have alternating dihedral angles of +30° and −80°. due to steric crowding the ferrocenyls are slightly bent with angles of 177° and have elongated c-fe bonds. the quaternary cyclopentadienyl carbon atoms are also pyramidalized. also, the benzene core has a chair conformation with dihedral angles of 14° and displays bond length alternation between 142.7 pm and 141.1 pm, both indications of steric crowding of the substituents. the synthesis of hexaferrocenylbenzene has been reported using negishi coupling of hexaiodidobenzene and diferrocenylzinc, using tris(dibenzylideneacetone)dipalladium(0) as catalyst, in tetrahydrofuran: the yield is only 4%, which is further evidence consistent with substantial steric crowding around the arene core. materials chemistry strands of an uncharged ferrocene-substituted polymer are tethered to a hydrophobic silica surface. oxidation of the ferrocenyl groups produces a hydrophilic surface due to electrostatic attractions between the resulting charges and the polar solvent. ferrocene, a precursor to iron nanoparticles, can be used as a catalyst for the production of carbon nanotubes. the vinylferrocene can be made by a wittig reaction of the aldehyde, a phosphonium salt, and sodium hydroxide. the vinyl ferrocene can be converted into a polymer (polyvinylferrocene, pvfc), a ferrocenyl version of polystyrene (the phenyl groups are replaced with ferrocenyl groups). another polyferrocene which can be formed is poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate), pfcma. in addition to using organic polymer backbones, these pendant ferrocene units have been attached to inorganic backbones such as polysiloxanes, polyphosphazenes, and polyphosphinoboranes, (–ph(r)–bh2–)n, and the resulting materials exhibit unusual physical and electronic properties relating to the ferrocene / ferrocinium redox couple. both pvfc and pfcma have been tethered onto silica wafers and the wettability measured when the polymer chains are uncharged and when the ferrocene moieties are oxidised to produce positively charged groups. the contact angle with water on the pfcma-coated wafers was 70° smaller following oxidation, while in the case of pvfc the decrease was 30°, and the switching of wettability is reversible. in the pfcma case, the effect of lengthening the chains and hence introducing more ferrocene groups is significantly larger reductions in the contact angle upon oxidation.