Metallocenophanes bridged by group 13 elements

Hybrid materials comprising ferrocene and diaminoborane moieties: linear concatenation versus macrocyclization

Combination of borane and diaminoferrocene monomers by Si/B exchange condensation reactions afforded either diazabora-[3]ferrocenophanes or, via stepwise processes, larger macrocycles and a series of linear oligomers. Additional incorporation of p-phenylene moieties in the backbone yielded alternating concatenation.

Multistimuli-Responsive [3]Dioxaphosphaferrocenophanes with Orthogonal Switches

Novel multistimuli‐responsive phosphine ligands comprising a redox‐active [3]dioxaphosphaferrocenophane backbone and a P‐bound imidazolin‐2‐ylidenamino entity that allows switching by protonation are reported. Investigation of the corresponding metal complexes and their redox behaviour are reported and show the sensitivity of the system towards protonation and metal coordination. The experimental findings are supported by DFT calculations. Protonation and oxidation events are applied in Rh‐catalysed hydrosilylations and demonstrate a remarkable influence on reactivity and/or selectivity.

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Role of torsional strain in the ring-opening polymerisation of low strain [n]nickelocenophanes

Ring-opening polymerisation (ROP) of strained [1]- and [2]metallocenophanes and related species is well-established, and the monomer ring-strain is manifest in a substantial tilting of the cyclopentadienyl ligands, giving α angles of ∼14-32°. Surprisingly, tetracarba[4]nickelocenophane [Ni(η5-C5H4)2(CH2)4] (2) undergoes ROP (pyridine, 20 °C, 5 days) to give primarily insoluble poly(nickelocenylbutylene) [Ni(η5-C5H4)2(CH2)4] n (12), despite the lack of significant ring-tilt. The exoenthalpic nature of the ROP was confirmed by DFT calculations involving the cyclic precursor and model oligomers (ΔH0ROP = -14 ± 2 kJ mol-1), and is proposed to be a consequence of torsional strain present in the ansa bridge of 2. The similarly untilted disila-2-oxa[3]nickelocenophanes [Ni(η5-C5H4)2(SiMe2)2O] (13) and [Ni(η5-C5H4)2(SiMePh)2O] (14) were found to lack similar torsional strain and to be resistant to ROP under the same conditions. In contrast, 1-methyltricarba[3]nickelocenophane {Ni(η5-C5H4)2(CH2)2[CH(CH3)]} (15) with a significant tilt angle (α ∼ 16°) was found to undergo ROP to give soluble polymer {Ni(η5-C5H4)2(CH2)2[CH(CH3)]} n (18). The reversibility of the process in this case allowed for the effects of temperature and reaction concentration on the monomer-polymer equilibrium to be explored and thereby thermodynamic data to be elucidated (ΔH0ROP = -8.9 kJ mol-1, ΔG0ROP = -3.1 kJ mol-1). Compared to the previously described ROP of the unsubstituted analogue [Ni(η5-C5H4)2(CH2)3] (1) (ΔH0ROP = -10 kJ mol-1, ΔG0ROP = -4.0 kJ mol-1), the presence of the additional methyl substituent in the ansa bridge appears to marginally disfavour ROP and leads to a corresponding decrease in the equilibrium polymer yield.

Enantiopure Phospha[1]ferrocenophanes: Textbook Examples of Through-Space Nuclear Spin-Spin Coupling

Three enantiopure phospha[1]ferrocenophanes (2^R ) equipped with either a phenyl, an isopropyl, or a tert-butyl group at the bridging phosphorus atom were synthesized by a salt-metathesis approach in isolated yields between 52 and 63 %. The chirality in these strained sandwich compounds stems from the planar-chiral ferrocene moiety, which is symmetrically equipped with two iPr groups adjacent to phosphorus. Surprisingly, all three phospha[1]ferrocenophanes show an uncommon through-space nuclear ¹ H-³¹ P coupling. As a result of the embedded symmetry, these new compounds are ideal examples to differentiate between through-space and through-bond coupling mechanisms in NMR spectroscopy.

PBP bridged [3]ferrocenophane: a bisphosphanylborane with a redox trigger

Stereospecific access to the unprecedented P-B-P bridged [3]ferrocenophane Fe(C₅H₄PtBu)₂BMes is presented. In contrast to acyclic ferrocenylphosphanes, we find evidence for a shift of spin-density from Fe to P upon pyramidal inversion of the P centers in the mono-cation; the latter has a lifetime of τ = 0.31(4) s.

New reactivity at the silicon bridge in sila[1]ferrocenophanes

We describe two new types of reactivity involving silicon-bridged [1]ferrocenophanes. In an attempt to form a [1]ferrocenophane with a bridging silyl cation, the reaction of sila[1]ferrocenophane [Fe(η-C₅H₄)₂Si(H)TMP] (12) (TMP = 2,2,6,6-tetramethylpiperidyl) towards the hydride-abstraction reagent trityl tetrakis(pentafluorophenyl)borate ([CPh₃][B(C₆F₅)₄]) was explored. This yielded the unusual dinuclear species [Fe(η-C₅H₄)₂Si(TMP·H)(η-C₅H₃)Fe(η-C₅H₄)Si(H)TMP][B(C₆F₅)₄] [13][B(C6F5)4] in low yield. The formation of [13]+ is proposed to involve abstraction of hydride from the silicon bridge in 12 with subsequent C-H bond cleavage of a cyclopentadienyl group by the resulting electrophilic transient silyl cation intermediate. We also explored the reaction of dimethylsila[1]ferrocenophane [Fe(η-C₅H₄)₂SiMe₂] (1) with the Au(i) species AuCl(PMe₃). This was found to result in addition of the Au-Cl bond across the Cp_ipso-Si bond to yield the ring-opened species [1'-(chlorodimethylsilyl)-ferrocenyl](trimethylphosphine)gold(i), [Fe(C₅H₄SiMe₂Cl){C₅H₄Au(PMe₃)}] (14). This represents the first example of ring-opening addition of a metallocenophane with a reagent possessing a transition metal-halogen bond.

Synthesis and characterization of metal-rich phosphonium polyelectrolytes and their use as precursors to nanomaterials

Upon efficient quaternization and salt metathesis of stable triethyl ferrocene/ruthenocene phosphines, styrene-based phosphonium triflate monomers with four different stoichiometric ratios of Fe/Ru were synthesized. Free-radical polymerization of the monomers afforded four polyelectrolytes (M_n: 38 650-69 100 g mol^-1, Đ: 3.16-4.10) that retained many of the spectroscopic and electrochemical properties of the ferrocene/ruthenocene units. TGA studies demonstrated the thermal stability (onset of decomposition: ∼310 °C) and high char yields (33-54% at 1000 °C) of the polyelectrolytes. Pyrolysis in N₂/H₂ (95/5) (film thickness of ∼6 μm, 1000 °C, 3 h) yielded crystalline, mixed-phase nanomaterials containing iron, ruthenium, and phosphorus with compositions influenced by the structure of the parent polyelectrolytes.

Strained azabora[2]ferrocenophanes

The first BN-bridged [2]ferrocenophanes were synthesized and their structures and strain enthalpies were investigated.

Control over cyclisation sequences of 1,1′-bifunctional octamethylferrocenes to ferrocenophanes

This paper describes the facile synthesis of a number of electron rich octamethyl[1.4]ferrocenophanes with unsaturated handles from 1,1′-bis(1-chlorovinyl)octamethylferrocene.

Palladium complexes of ferrocene-based phosphine ligands as redox-switchable catalysts in Buchwald–Hartwig cross-coupling reactions

Redox-switchable catalysis: Palladium(ii) complexes of two differently substituted [1]phosphaferrocenophanes FcPR (R = Mes, biaryl) and of diphenylferrocenyl phosphine Ph₂PFc were applied in redox-switchable Buchwald–Hartwig cross-coupling reactions.

[n]Ferrocenophanes (n = 2, 3) with Nitrogen and Phosphorus in Bridging Positions

The in situ prepared dilithio derivative of the known species 1-bromo-1'-(trimethylsilylamino)ferrocene (1) reacted with tBuPCl2 to form the first example of a [2]ferrocenophane ([2]FCP) bridged by nitrogen and phosphorus (2). Sulfurization of 2 followed by column chromatography on silica gel gave the expected [2]FCP with a tBu(S)PN(SiMe3) bridging moiety (3a) and its desilylated counterpart with a tBu(S)PNH bridging moiety (3b). The molecular structure of 3b was determined by single-crystal X-ray analysis (α = 18.40(11)°). Using a common synthetic methodology, two new 1-amino-1'-bromoferrocene derivatives were prepared, one species with a PhCH2 (6a) and another with a tBuCH2 group (6b) on nitrogen. Dilithiation of 6a followed by addition of tBuPCl2 gave a mixture of three constitutional isomers: the targeted [2]FCP (7a), the 1,1'-disubstituted ferrocene derivative (tBuPH)(PhCH═N)fc (8a), and the [3]FCP bridged by a (NH)(CHPh)PtBu moiety (9a). NMR spectroscopy revealed that 8a is the precursor for 9a. The salt-metathesis reaction of the dilithio derivative of 6b with tBuPCl2 exclusively gave the 1,1'-disubstituted ferrocene derivative (tBuPH)(tBuCH═N)fc (8b), which does not isomerize to the respective [3]FCP. DFT calculations at the M06/6-311+G(d,p) level were used to better rationalize these unexpected results.

Polyferrocenylsilanes: synthesis, properties, and applications

This comprehensive review covers polyferrocenylsilanes (PFSs), a well-established, readily accessible class of main chain organosilicon metallopolymer. The focus is on the recent advances involving PFS homopolymers and block copolymers and the article covers the synthesis, properties, and applications of these fascinating materials.