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A convergent growth approach to ferrocenyl-rich dendritic macromolecules based on carbosilane and siloxane skeletons, which act as electrode modifiers.

The first thiol–yne coupling reactions of diferrocenylacetylene, which presents an internal CC bond and two ferrocenes, are investigated. The obtained vinyl thioether sulfide isomers have been isolated and show an interesting redox behavior.

The Grignard reagent, iPrMgCl and its lithium chloride-enhanced 'turbo' derivative iPrMgCl⋅LiCl have been employed to investigate the single iodo/magnesium exchange reactions of the trisubstituted arenes, 2,5-diiodo-N,N-diisopropylbenzamide 1, 1,4-diiodo-2-methoxybenzene 2, and 1,4-diiodo-2-(trifluoromethyl)benzene 3. These three arenes themselves were initially prepared by a double ortho-, meta'-deprotonation of N,N-diisopropylbenzamide, anisole and (trifluoromethyl)benzene, respectively, using the sodium magnesiate reagent [Na4 Mg2 (TMP)6 (nBu)2 ] (where TMP is 2,2,6,6-tetramethylpiperidide), and subsequent electrophilic quenching with iodine/THF solution. Thus, by following a combined deprotonation and magnesium/halogen exchange strategy, the simple monosubstituted arenes can be converted to trisubstituted diiodoarenes, which can ultimately be transformed into the corresponding mono-magnesiated arenes, in THF at -40 °C, within seconds in good yields. The other functional group (OMe, NiPr2 or CF3 respectively) present on the di-iodoarenes helps direct the exchange reaction to the ortho position, whereas subsequent addition of different electrophiles permits the preparation of hetero-poly-functional-arenes, with three different substituents in their structure. Intriguingly, if water is used as the electrophile, a new and facile route to prepare meta-substituted arenes, which cannot be easily obtained by conventional processes, is forthcoming. In contrast to directed ortho-metalation (DoM) chemistry, this reaction sequence can be thought of as InDirect meta-Metalation (IDmM). The scope of the chemistry has been tested further by exposing the initial unreacted iodo-functionality at the meta-position to a second Mg/I-exchange reaction and subsequent functionalization.

The titanium complex [TiCp*(thiosal)(thiosalH)] (1) has been synthesised by reaction of [TiCp*Me3], Cp* = η5-C5Me5, with thiosalicylic acid (H2thiosal). Complex 1 reacts with [M(μ-OH)(COD)]2 (M = Rh, Ir) to yield the corresponding early–late heterobimetallic complexes [TiCp*(thiosal)2M(COD)] (M = Rh (2); Ir (3)). Carbon monoxide replaces the COD ligand in 2 and 3 leading to the respective dicarbonyl complexes [TiCp*(thiosal)2M(CO)2] (M = Rh (4); Ir (5)). Compound 4 reacts with PPh3 to yield the monocarbonyl derivative [TiCp*(thiosal)2Rh(CO)(PPh3)] (6). The reaction of compound 1 with LinBu yields the tetrametallic complex [{TiCp*(thiosal)2Li}2(THF)3(H2O)] (7). Compound 7 reacts with [RuCp*Cl(COD)] yielding the heterometallic complex [TiCp*(thiosal)2RuCp*] (8). The molecular structures of compounds 4, 5 and 7 have been studied by X-ray diffraction. From cyclic voltammetric (CV) and square wave voltammetric (SWV) experiments, we observed that attachment of the titanium moiety of precursor 1 to a late transition metal moiety through the sulfur atoms has a significant influence on the reduction behaviour of the Ti(IV) metal centre. Thus, monometallic 1 exhibits an irreversible reduction process at −1.15 V vs. SCE, whereas the CVs of heterobimetallic compounds 2–6 are characterized by the reversible or quasi-reversible one-electron reduction of the Ti(IV)/Ti(III) system, suggesting a significant stabilization of the Ti(III) reduced species. Likewise, substitution of the M(COD) diolefin fragment in 2 and 3 by the M(CO)2 carbonyl-containing moiety (in compounds 4 and 5) leads to a significant anodic shift in the titanium E1/2 reduction redox potentials.

The formation of a family of silicon- and siloxane-bridged multiferrocenyl derivatives carrying different functional groups attached to silicon, including Fc2(CH3)3C(CH2)2SiCH[double bond, length as m-dash]CH2 (5), Fc2(CH2[double bond, length as m-dash]CH-O)SiCH[double bond, length as m-dash]CH2 (6), Fc2(OH)SiCH[double bond, length as m-dash]CH2 (7), Fc2(CH2[double bond, length as m-dash]CH-O)Si-O-Si(O-CH[double bond, length as m-dash]CH2)Fc2 (8) and Fc2(CH2[double bond, length as m-dash]CH-O)Si-O-SiFc3 (9) is described. Silyl vinyl ether molecules 6, 8 and 9 and the heteroleptic vinylsilane 5 resulted from the competing metathesis reaction of lithioferrocene (FcLi), CH2[double bond, length as m-dash]CH-OLi or (CH3)3C(CH2)2Li with the corresponding multifunctional chlorosilane, Cl3SiCH[double bond, length as m-dash]CH2 or Cl3Si-O-SiCl3. The last two organolithium species have been likely formed in situ by fragmentation of the tetrahydrofuran solvent. Diferrocenylvinyloxyvinylsilane 6 is noteworthy since it represents a rare example of a redox-active silyl mononomer in which two different C[double bond, length as m-dash]C polymerisable groups are directly connected to silicon. The molecular structures of the silicon-containing multiferrocenyl species 5, 6, 8 and 9 have been investigated by single-crystal X-ray diffraction studies, demonstrating the capture and storage processes of two ring fragments resulting from the cleavage of cyclic THF in redox-active and stable crystalline organometallic compounds. From electrochemical studies we found that by changing the anion of the supporting electrolyte from [PF6]- to [B(C6F5)4]-, the redox behaviour of tetrametallic disiloxane 8 can be switched from a poorly resolved multistep redox process to four consecutive well-separated one-electron oxidations, corresponding to the sequential oxidation of the four ferrocenyl moieties.

The ability of diferrocenylsilanediol, Fc2Si(OH)2 (5), and 1,1,3,3-tetraferrocenyldisiloxane-1,3-diol, Fc2(HO)Si–O–Si(OH)Fc2 (6), to act as new electroactive anion receptors for either acetate or chloride anions has been investigated in solution, in the solid state, and in the gas phase. 1H NMR spectroscopic titrations with anions reveal that the binding interaction causes chemical-shift perturbations not only in the Si–OH hydrogen-bonding donor motif but also in the ferrocenyl protons of receptors 5 and 6. Square-wave voltammetric studies evidence that multiferrocenyl silanols 5 and 6 exhibit higher ability for electrochemical sensing of acetate than chloride, since the corresponding half-wave potentials (E1/2) for the successive ferrocene oxidations display a higher cathodic shift in the presence of such an anion. Furthermore, single-crystal X-ray diffraction analyses of the tetrabutylammonium salts of complexes [Fc2Si(OH)2·CH3COO]− (8), [Fc2Si(OH)2·Cl]− (9), [Fc2(HO)Si–O–Si(OH)Fc2·CH3COO]− (10), [{Fc2(...

The potential of structurally new ferrocene-functionalized guanidines as redox-active precursors for the synthesis of heterometallic platinum(II)–guanidine complexes with anticancer activity was studied. To this end, an atom-economical catalytic approach was followed by using ZnEt2 to catalyze the addition of aminoferrocene and 4-ferrocenylaniline to N,N′-diisopropylcarbodiimide. Furthermore, reaction of a platinum(II) source with the newly obtained guanidines Fc–N═C(NHiPr)2 (3) and Fc(1,4-C6H4)–N═C(NHiPr)2 (4) provided access to the heterometallic complexes [PtCl2{Fc–N═C(NHiPr)2}(DMSO)] (5), [PtCl2{Fc(1,4-C6H4)–N═C(NHiPr)2}(DMSO)] (6), and [PtCl2{Fc(1,4-C6H4)–N═C(NHiPr)2}2] (7). Electrochemical studies evidence the remarkable electronic effect played by the direct attachment of the guanidine group to the ferrocene moiety in 3, making its one-electron oxidation extremely easy. Guanidine-based Fe–Pt complexes 5 and 6 are active against all human cancer cell lines tested, with GI50 values in the range 1.4–2...

The application of 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane [(CH2═CH)FcMeSi]2O (1) as an efficient electroactive vinylsilane precursor for thiol–ene radical reactions is described. In order to determine if steric or electronic limitations due to the redox-active metallocene moiety might affect the bis(hydrothiolation) of the bifunctional vinylsilane, a model reaction was initially performed between 1 and 2-mercaptoethanol, resulting in the formation of the newly sulfur-containing carbosiloxane 2 in excellent yield. The bis(thiol–ene) reaction of 1 was successfully extended to 2,2′-(ethylenedioxy)diethanethiol, affording a series of novel precisely defined, redox-active oxathiacrown macrocycles (3 and 4n) and sulfur-bearing linear oligo-carbosiloxanes (5n and 6n) with a backbone in which the −S(CH2)2–O(CH2)2O–(CH2)2S– chain and the −Si–O–Si– bond, bearing pendant ferrocenes, are alternately linked by ethylene bridges. These reactions have been initiated either thermally (in toluene solution with...

A series of vinyl-silyl-functionalized biferrocenyl compounds were very recently synthesized and studied by our group through cyclic (CV) and square-wave (SWV) voltammetric techniques, showing two well-resolved one-electron transfer oxidation processes. This fact might reflect a certain degree of electronic communication between ferrocenyl centers, but solvent or electrolyte effects could have an influence in the splitting. Gas-phase theoretical studies were carried out in order to determine the degree of iron–iron communication in absence of undesired environmental effects, revealing through the analysis of the topology of the electron density with different methods that organosilicon bridges between ferrocenyl units have mainly a steric but not an electronic-linking role, which is however of crucial importance, as they allow non-covalent paths for electronic communication between iron centers.

The formation of a family of silicon- and siloxane-bridged multiferrocenyl derivatives carrying different functional groups attached to silicon, including Fc

The application of ethynylferrocene, FcC≡CH (1), as a highly efficient electroactive precursor for the thiol–yne click reaction is presented. For this purpose, a wide range of functionalized thiols, namely 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropionic acid, 4-aminothiophenol, and benzene-1,3-dithiol as well as tetrathiol pentaerythritol tetrakis(3-mercaptopropionate), were investigated. This facile thiol–ethynylferrocene radical reaction has resulted in the quantitative formation and isolation of the newly ferrocenyl–vinyl sulfides FcCH═CHS(CH2)2OH (2Z and 2E), FcCH═CHSCH2CH(OH)CH2OH (3Z and 3E), FcCH═CHS(CH2)2COOH (4Z and 4E), FcC(CH2)S(1,4-C6H4)NH2 (5α), FcCH═CHS(1,3-C6H4)SCH═CHFc (6), and [FcCH═CHS(CH2)2COOCH2]4C (7). Thiol–ethynylferrocene reactions have been initiated either by heat, in toluene with AIBN, or by UV light irradiation in THF in the presence of DMPA as photoinitiator. The outcome of the hydrothiolation of ethynylferrocene strongly depends on the thiol structure and on the initia...

The potential of vinylferrocene Fc(CH═CH2) (1) as redox-active ene functional precursor for thiol–ene radical reaction has been successfully investigated for the first time. To this end, we initially studied thiol–ene model reactions of 1 with a variety of functionalized monothiols, including 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropionic acid, (3-mercaptopropyl)trimethoxysilane, 2-aminoethanethiol hydrochloride, dithiol 2,2′-(ethylenedioxy)diethanethiol, and the tetrafunctional thiol pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). These reactions afforded the newly ferrocenyl-hydrothiolated small-molecule models Fc(CH2)2S(CH2)2OH (2), Fc(CH2)2S(CH2)2COOH (3), Fc(CH2)2S(CH2)CH(OH)(CH2)OH (4), Fc(CH2)2S(CH2)3Si(OMe)3 (5), bimetallic Fc(CH2)2S(CH2)2O(CH2)2O(CH2)2S(CH2)2Fc (6), and tetrametallic [Fc(CH2)2S(CH2)2COOCH2]4C (7) in relatively high yields. Furthermore, the hydrothiolation of the C═C bond of vinylferrocene was successfully extended to the S–H-polyfunctionalized poly[(3-mercaptoprop...

Triferrocenylsilane (Fc)3SiH (1) and the unexpected Si–H-functionalized diferrocenyl(3,3-dimethylbutyl)silane (Fc)2(CH3)3C(CH2)2SiH (3) have been synthesized via the salt metathesis reaction of monolithioferrocene and trichlorosilane. The mysterious heteroleptic hydrosilane 3 resulted from the competitive reaction of FcLi and 3,3-dimethylbutyllithium with Cl3SiH. The organolithium species (CH3)3C(CH2)2Li has been generated in situ via the carbolithiation reaction of ethene, which was formed by the α-deprotonation and subsequent reverse [3 + 2] cycloaddition of the tetrahydrofuran solvent. Compound 3 is noteworthy since, for the first time, a ring fragment resulting from the cleavage of cyclic ether THF has been captured and stored in a redox-active and stable crystalline compound. The Si–H bond of hydrosilane 1 oxidatively adds to the Co(0) metal center of Co2(CO)8 to give (Fc)3Si–Co(CO)4 (4), which is exceptionally air-stable and shows a good thermal stability. The molecular structures of multiferrocenes 1, 3 and 4 have been investigated by single-crystal X-ray diffraction studies. From electrochemical studies we observed that, using either [PF6]− (in CH2Cl2/CH3CN 3:0.5) or [B(C6F5)4]− (in CH2Cl2) as supporting electrolyte anions of different coordinating ability, the newly synthesized multiferrocenylsilyl derivatives exhibit a three (for 1 and 4) or two (for 3) well-resolved one electron waves, indicating appreciable electronic interactions between the silicon-bridged ferrocenyl moieties.

The binding interactions between a novel ferrocenylguanidinium derivative (FcG+) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. 1H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG+, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG+ complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments. The association equilibrium constants (K) were determined from NMR competition experiments. The measured K values were 3.5 × 109 and 2.5 × 108 M–1 for CB7 and CB8, respectively, in 50 mM sodium acetate-d3 D2O solution (pD 4.7). DFT computational studies confirmed the 1:1 stoichiometry and the inclusion character of both complexes. Voltammetric experiments were carried out to measure the complexation-induced shifts on the half-wave potentials for the one-electron oxidation of the ferrocenyl moiety. Complexation by CB7 led to a 12 mV an...

Redox-active, highly symmetrical cubic octasilsesquioxanes (OS) peripherally decorated with 24 ferrocenyl units, linked in threes around the periphery of a cubic cage, namely, [Fc3Si(CH2)2Me2SiO]8Si8O12 (6) and [Fc3Si(CH2)2]8Si8O12 (7) (Fc = (η5-C5H4)Fe(η5-C5H5)), have been synthesized. Such integrally ferrocenyl-functionalized cubic macromolecules 6 and 7, as well as the related small-molecule models hexaferrocenyldisiloxane [Fc3Si(CH2)2Me2Si]2O (4) and dodecaferrocenyl cyclotetrasiloxane [Fc3Si(CH2)2MeSiO]4 (5), have been prepared by covalently linking, via Karstedt’s-catalyzed hydrosilylation, triferrocenylvinylsilane (CH2═CH)Si(Fc)3 (3) around the surface of octasilsesquioxane cages T8(OSiMe2H)8 and T8H8 and linear [Me2SiH]2O and cyclic [MeSiHO]4 siloxane scaffolds, respectively. All new polyferrocenyl oligosiloxanes have been thoroughly characterized using a combination of elemental analysis, multinuclear (1H, 13C, 29Si) NMR spectroscopy, FT-IR, and MALDI-TOF mass spectrometry. The molecular structur...

A series of novel, precisely defined, redox-active macrocyclic and linear co-oligocarbosiloxanes containing pendant ferrocenyl moieties attached to the carbosiloxane backbones, have been synthesized via hydrosilylation reactions of the bifunctional 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane [(CH2═CH)(Fc)MeSi]2O (6) (Fc = (η5-C5H4)Fe(η5-C5H5)). Specifically, 6 was reacted with 1,1,3,3-tetramethyldisiloxane, in the presence of Karstedt’s catalyst, to afford both the cyclic species 7, 8 and 9n (n = 3–6) and several linear co-oligomeric carbosiloxanes 10 and 11n (n = 2–5), containing a backbone in which the −Me2Si–O–SiMe2– moiety and the ferrocenyldisiloxane unit −MeFcSi–O–SiFcMe– are alternately linked by −(CH2)2– bridges. Ferrocenyl cyclocarbosiloxanes 7 and 8, as well as linear 10, were isolated by column chromatography. The crude reaction mixtures, as well as pure macrocycles and oligocarbosiloxanes have been thoroughly characterized by elemental analysis, multinuclear (1H, 13C, 29Si) NMR spectro...

A new family of heterometallic compounds 3-6 containing ferrocenyl and platinum(II) centers has been synthesized by reaction of 1-β-aminoethylferrocene (1) and 1,1'-bis(β-aminoethyl)ferrocene (2) with Pt(II) precursors. Using K(2)[PtCl(4)] as the Pt(II) source, the cis-square-planar neutral compounds [Fe{η(5)-C(5)H(4)(CH(2))(2)NH(2)}(2)PtCl(2)] (3) and [{Fe(η(5)-C(5)H(4)(CH(2))(2)NH(2))(η(5)-C(5)H(5))}(2)PtCl(2)] (5) were obtained. Reaction of cis-[PtCl(2)(dmso)(2)] with 1 and 2 resulted in the displacement of dmso and chloride ligands from the platinum coordination sphere, affording the cationic and neutral compounds [Fe{η(5)-C(5)H(4)(CH(2))(2)NH(2)}(2)Pt(dmso)Cl]Cl (4) and [Fe(η(5)-C(5)H(4)(CH(2))(2)NH(2))(η(5)-C(5)H(5))Pt(dmso)Cl(2)] (6). Compounds 3-6 were thoroughly characterized using multinuclear ((1)H, (13)C, (195)Pt) NMR, IR spectroscopy, ESI mass spectrometry and elemental analysis. Single-crystal X-ray analysis of heterometallic 6 confirmed the cis geometry of the molecule and revealed that the platinum atom is held in a perfect square-planar geometry. The electrochemical behaviour of the heterometallic compounds 3-6, which has been examined by cyclic (CV) and square wave (SWV) voltammetries in dichloromethane and dmso solution, is characterized by the reversible one-electron oxidation of the ferrocene moieties. The results of the biological activity studies revealed that the organometallic complex 5 is active against all cell lines with GI(50) values in the range 1.7-2.3 μM. When compared to the standard anticancer drug cisplatin, heterotrimetallic 5, possessing two aminoethylferrocenyl units coordinated to the Pt(II) center, showed a greater activity profile in the colon cancer cell line. Cell cycle studies revealed that the new mixed compound exhibits a mechanism of action different to cisplatin.

Novel highly functionalized polysiloxanes have been synthesized, which bear small pendant dendritic wedges containing two different redox-active organometallic moieties, namely the electron-donating ferrocenyl group and the electron withdrawing (η6-aryl)tricarbonylchromium entity. Hydrosilylations of vinylsilyl-functionalized (CH2═CH)MePhSiFc (1) and allylsilyl-terminated dendron (CH2═CHCH2)PhSi[(CH2)2MePhSiFc]2 (3), with the Si–H-containing polysiloxane backbones (Me3SiO)(MeSiHO)n(Me2SiO)m(SiMe3) (n = 30–35%, m = 65–70%), and (Me3SiO)(MeSiHO)n(SiMe3) (n ∼ 35) successfully afforded the novel siloxane-based copolymers 8 and 9 and homopolysiloxanes 10 and 11 possessing appended organometallic dendritic side chains. Thermal treatment of 8 with Cr(CO)6 and reaction of 10 with (CH3CN)3Cr(CO)3 further increased metal density of the polymers affording polysiloxanes 12 and 13 carrying (η5-C5H4)Fe(η5-C5H5) and (η6-C6H5)Cr(CO)3 moieties hanging from their polysiloxane chain. Similar reactions, starting from 1,1,3,3...

A new series of vinyl-functionalized polyferrocenyl organosilicon compounds, including triferrocenylvinylsilane, (CH2═CH)Si(Fc)3 (7) (Fc = (η5-C5H4)Fe(η5-C5H5)), 1,3-divinyl-1,1,3,3-tetraferrocenyldisiloxane, [(CH2═CH)(Fc)2Si]2O (8), and 1,3-divinyl-1,3-dimethyl-1,3-diferrocenyldisiloxane, [(CH2═CH)(Fc)MeSi]2O (9), have been synthesized via the low-temperature salt metathesis reaction of monolithioferrocene and the chlorosilanes (CH2═CH)SiCl3 and [(CH2═CH)(Cl)MeSi]2O. Compounds 7−9 were characterized by elemental analysis, multinuclear (1H, 13C, 29Si) NMR spectroscopy, and MALDI-TOF mass spectrometry. The molecular structures of the vinyl-functionalized silane 7 and divinyldisiloxanes 8 and 9 in the solid state have been determined by single-crystal X-ray analysis. Whereas tetraferrocenyl compound 8 possesses a linear disiloxane skeleton (Si−O−Si bond angle of 180.0(2)°), biferrocenyl 9 shows a bent arrangement of the disiloxane linkage (Si−O−Si angle of 143.2(2)°). The oxidation electrochemical behavior ...

A new heterometallic electroactive compound having the ferrocenyl moiety attached to the platinum atom through an amidine functionality has been prepared via Pt(II)-mediated nucleophilic addition of β-aminoethylferrocene to a benzonitrile ligand. This neutral receptor shows remarkable electrochemical anion-sensing redox response to H(2)PO(4)(-).

Simple manual grinding of solid cyanomethylferrrocene (1) and silica gel provides a facile one-pot access route to prepare unexpected and highly electron-poor metallocene, 1-cyanocarbonylferrocene (2). Electrochemical measurements supported by computational studies reveal that 2 exhibits the highest Fe(II)/Fe(III) oxidation potential reported for mono-substituted ferrocenes.