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A donor−π−acceptor dyad with a highly electron-deficient B(C6F5)2 group as the acceptor has been prepared. 5-Diphenylamino-5‘-bis(pentafluorophenyl)boryl-2,2‘-bithiophene (3) was fully characterized by multinuclear NMR spectroscopy, mass spectrometry, and X-ray crystallography. The solid-state structure of 3 shows the presence of multiple π-stacking interactions rather than Lewis acid−base bonding between boron and nitrogen. Cocrystallized benzene molecules are incorporated into a channel-like framework of 3. The electronic structure and photophysical properties were investigated by UV−visible absorption and emission spectroscopy and DFT calculations. The absorption and emission maxima experience a strong bathochromic shift relative to the non-fluorinated analogues, the origin of which has been further examined by DFT calculations.

Borane-end-functionalized polymers have been prepared through (i) atom transfer radical polymerization (ATRP) of styrene using a silylated initiator, 1-bromo-1-(4-trimethylsilylphenyl)ethane (PEB-SiMe3), (ii) exchange of the SiMe3 end groups with BBr3, and (iii) modification of the Lewis acidic boron centers with nucleophiles. Ditelechelic α,ω-borane-functionalized polymers were obtained through atom transfer radical coupling (ATRC) of the silane-end-functionalized polymers followed by exchange with BBr3 and subsequent reaction with nucleophiles. Self-assembly of the borane-functionalized mono- and ditelechelic polymers into supramolecular structures by means of reversible noncovalent and covalent interactions including Lewis acid−base complexation and boroxine formation has been explored.

The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration, and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene) (PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh· t Py is achieved by treatment with the stronger Lewis acid, B(C6F5)3, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts.

A set of monodisperse bent donor-acceptor-donor-type conjugated borazine oligomers, BnNn+1 (n=1-4), incorporating electron-rich triarylamine donor and electron-deficient triarylborane acceptor units has been prepared through an iterative synthetic approach that takes advantage of highly selective silicon-boron and tin-boron exchange reactions. The effect of chain elongation on the electrochemical, one- and two-photon properties and excited-state photodynamics has been investigated. Strong intramolecular charge transfer (ICT) from the arylamine donors to boryl-centered acceptor sites results in emissions with high quantum yields (Φfl >0.5) in the range of 400-500 nm. Solvatochromic effects lead to solvent shifts as large as ∼70���nm for the shortest member (n=1) and gradually decrease with chain elongation. The oligomers exhibit strong two-photon absorption (2PA) in the visible spectral region with 2PA cross sections as large as 1410 GM (n=4), and broadband excited-state absorption (ESA) attributed to long-lived singlet-singlet and radical cation/anion absorption. The excited-state dynamics also show sensitivity to the solvent environment. Electrochemical observations and DFT calculations (B3LYP/6-31G*) reveal spatially separated HOMO and LUMO levels resulting in highly fluorescent oligomers with strong ICT character. The BnNn+1 oligomers have been used to demonstrate the detection of cyanide anions with association constants of log K>7.

A modular one-pot approach for the synthesis of well-defined organoboron quinolate polymers and the tuning of their photoluminescence is reported. Highly selective borylation of poly(4-trimethylsilylstyrene) (PSSiMe3) followed by replacement of one of the bromine substituents in the resulting reactive polymer PSBBr2 with tert-butylphenyl groups led to the common intermediate PSBPhBr. A series of organoboron quinolate polymers PSBPhQ were then obtained in high isolated yields (65−85%) by in situ treatment of PSBPhBr with differently substituted 8-hydroxyquinoline derivatives. All the quinolate polymers were fully characterized by multinuclear NMR spectroscopy, elemental analysis, gel permeation chromatography in-line with multiangle laser light scattering (GPC-MALLS), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Luminescence measurements revealed distinct emission bands, ranging from the blue to the red region (486−615 nm), depending on the substitution pattern on the qu...

The ferrocene-containing polymer [-fc-B(Br)-] n ( 6 ) with an average chain length of ca. 20 repeat units ( n = 20) is readily accessible from fc(BBr 2 ) 2 and HSiEt 3 [fc = (C 5 H 4 ) 2 Fe] via a novel polycondensation reaction. Treatment of 6 with excess THF yields the highly soluble alkoxy-substituted derivative [-fc-B(O(CH 2 ) 4 Br)-] n ( 10 ; n = 20).

The bifunctional conjugated organoboranes Ar2B-bt-BAr2, which contain 2,2'-bithiophene (bt) linkers and different aryl substituents on boron (3: Ar = p-tBuC6H4; 4: Ar = C6F5; 5: Ar = C6F5, Fc; Fc = ferrocenyl), have been synthesized. The electronic communication between the boron centers and cooperativity effects in the binding of pyridine have been investigated by a comprehensive study using X-ray crystallography, DFT calculations, cyclic voltammetry, 1H and 19F NMR, and UV visible absorption and emission spectroscopy. A comparison of the single-crystal X-ray structures of 4 and 4Py2 revealed a strongly diminished bond alternation in the thiophene rings for 4, indicative of a high degree of electronic delocalization. DFT calculations are in good agreement with the structural features determined from the X-ray analysis and, consistent with the experimental absorption and emission data, predict a smaller HOMO-LUMO gap for green luminescent 4 in comparison to blue luminescent 3. The complexation of pyridine to the two boron centers was further investigated by 1H and 19F NMR for 4 and by 1H NMR and UV-visible absorption spectroscopy for 3. We found that binding of the first pyridine molecule to one of the boryl groups significantly lowers the Lewis acidity of the other boryl group. For 3, the interaction parameter a, which provides a measure of communication between the boron sites, was determined to be a = 0.23 by UV-visible titration and 0.21 by 1H NMR spectroscopy. Further enhanced electronic communication was observed for the more highly Lewis acidic fluorinated derivative 4, for which a = 0.025 according to 19F and 1H NMR spectroscopy.

[Structure: see text] A series of organoboron quinolates with emission colors ranging from blue to red have been prepared. In comparison to the respective AlQ3 derivatives a distinct blue-shift of the emission is observed. Theoretical calculations serve to provide insight into the nature of the frontier orbitals and the effect of the substituents in the 5-position of the quinolate ligands on the relative HOMO and LUMO energy levels. An efficient new blue emitting material with a pinacolborane substituent has been identified.

A new class of highly fluorescent triarylborane polymers has been prepared from trimethylsilyl-substituted polystyrene via a modular approach that involves selective polymer modification reactions with organometallic reagents. The photophysical properties, environmental stability, and the Lewis acidity of the boron sites have been tailored through modifications in the substitution pattern on boron. The photophysical properties are indicative of electronic communication between the chromophores attached to polystyrene, which has been exploited for the efficient probing of fluoride and cyanide in the micromolar concentration range.

The functionalization of polymeric materials with Lewis acidic boron sites has led to exciting new opportunities in diverse areas, ranging from new polymeric catalysts to the preparation of highly luminescent materials and the design of efficient sensor systems for nucleophiles. Recent advances in the preparation of these Lewis acidic boron polymers, their coordination behavior, and some of their intriguing applications are reviewed.

MesB(C6F5)2 (1) has been prepared from MesMgBr and FB(C6F5)2·OEt2, while Mes2B(C6F5) (2) is readily available from CuC6F5 and Mes2BBr. The reduction potential E° of 1 vs Cp2Fe0/+ in THF is −1.72 V, while that of 2 is −2.10 V, and that of Mes3B (3) is −2.73 V. 11B and 1H NMR show that neither 1 nor 2 binds THF significantly. These results have been used to estimate the reduction potential of B(C6F5)3 in THF as −1.17 V vs Cp2Fe0/+ or as −0.64 V vs SCE.

1,2-Disubstituted ferrocenes represent an interesting, yet underdeveloped class of redox-active bidentate Lewis acids. We describe here a new rational synthesis of 1,2-bis(trimethylstannyl)ferrocene (2) and its high yield conversion to 1,2-bis(chloromercury)ferrocene (3). X-ray crystal structures for complexes of the bidentate Lewis acid 3 with DMSO, [Bu4N]Cl, and [PPh4]Cl were obtained. In all cases the two Hg atoms form reverse chelates with the nucleophile. With DMSO a 1:1 complex is formed, in which DMSO is coordinated from the endo side of ferrocene. Two molecules of 3 are used in the binding to the chloride anion. Different modes are realized with the two different counterions. In the complex with [Bu4N]Cl the chloride ion is coordinated from the exo side of both ferrocenes, while with [PPh4]Cl the chloride ion is endo with respect to one and exo with respect to the other ferrocene moiety. Layered and channel-like supramolecular structures are realized with [Bu4N] and [Ph4P] counterions, respectively.

Their preparation generallyinvolves either direct polymerization of boron-function-alized monomers or functionalization of polymers withboron groups. Polymerization of boron monomers hasoverall received more attention for the placement ofboron substituents in the side chains of non-cross-linkedpolyolefins. The method of choice usually is standardfree radical polymerization due to the reasonably goodcompatibility with boron-carbon bonds and the rela-tively straightforward synthetic procedures involved.Thus, heat-induced or AIBN (2,2′-azobis(2-methylpro-pionitrile)) initiated free radical polymerization has beenapplied to the homo- and copolymerization of olefinscontaining boronic acid and boronic ester

Different preparative routes for the attachment of organoboron moieties to polyolefins and applications of such materials are reviewed. Preparation from boron-functionalized monomers represents one possible synthetic strategy with free radical polymerization, Ziegler–Natta polymerization, and ring-opening metathesis polymerization methods as the most thoroughly studied procedures. Recent advances in the preparation of boron-containing polymers through polymer modification reactions provide an interesting alternative that allows for the facile preparation of well-defined organoboron polymers of various architectures including homo polymers, random copolymers, block copolymers, and telechelic polymers. New opportunities for organoboron polymers as supported catalysts, sensors, luminescent materials, device components, and precursors to ceramics are briefly discussed.

The binding properties of heteronuclear bidentate Lewis acids, in which an organoboron and an organotin moiety are attached adjacent to each other at one of the Cp rings of ferrocene, have been studied. Treatment of [1,2-fc(SnMe2Cl)(BClMe)] (1-Cl) (fc = ferrocenediyl) with one equivalent of pyridine or 4-dimethylaminopyridine (DMAP) resulted in diastereoselective complexation of boron. Adducts 2 and 3 have been studied by multinuclear NMR, and the stereoselectivity of complexation was further confirmed by single crystal X-ray diffraction of 2. The importance of cooperative effects that involve an intramolecular B-ClSn interaction on the diastereoselectivity is evident from comparison with binding studies on the phenyl-substituted analogue [1,2-fc(SnMe2Cl)(BPhMe)] (1-Ph). Complexation of 1-Ph led to diastereomeric mixtures of adducts 4 and 5, respectively, which were identified by multinuclear NMR including NOESY experiments. The solid-state structure of one of the diastereomers of 5 was confirmed by X-ray crystallography. Facile isomerization was found in solution and the barrier of activation was determined by VT NMR studies (4: Delta(#)(298) = 54.9+/-0.4 kJ mol(-1); 5: Delta(#)(298) = 70.3+/-0.1 kJ mol(-1)). Competitive binding of pyridine to 1-Cl and [FcB(Cl)Me] (Fc = ferrocenyl) showed that cooperative effects between tin and boron lead to significant Lewis acidity enhancement. Binding of a second nucleophile in the presence of excess of base occurred also at boron. The novel zwitterionic complexes [1,2-fc(BMe(py)2)(SnMe2Cl2)] (6) and [1,2-fc(BMe(dmap)(2))(SnMe(2)Cl2)] (7) formed, which consist of boronium cation and stannate anion moieties. The structure of 7 in the solid-state was confirmed by X-ray crystallography. Multinuclear NMR data and competition experiments indicate weak binding of chloride to tin in 7 and partial dissociation in solution.

The synthesis, characterization, and reactivity of novel carbogerma[2]ferrocenophanes, (η-C5Me4)Fe(η-C5H4)CH2GeR2, 11 (a, R = Ph; b, R = Me), and carbostanna[2]ferrocenophanes, (η-C5Me4)Fe(η-C5H4)CH2SnR2, 12 (a, R = tBu; b, R = Mes; c, R = Me), are reported. Compounds 11a,b and 12a−c were isolated as orange crystals from the reaction of (η-C5Me4)Fe(η-C5H4Li)CH2Li·xTMEDA with Cl2ER2 (E = Ge, R = Ph, Me or E = Sn, R = tBu, Mes, Me) and were characterized by 1H, 13C, and 119Sn NMR, UV/vis, MS, and in representative cases elemental analysis. X-ray diffraction analysis of these species revealed structures possessing moderate ring-tilt with values in the range α = 10.99(2)−11.81(5)° for 11a,b and α = 6.64(2)−7.5(1)° for 12a−c. The presence of a small or moderate degree of ring-strain was further substantiated through the observation of only a small (ca. 25−30 nm) bathochromic shift in the UV/vis absorption maxima when compared to pentamethylferrocene. Attempts to induce thermal ring-opening polymerization (ROP)...

We have developed a highly efficient new method for the introduction of Lewis acidic boron centers into the side chains of organic polymers. Our methodology involves three steps: (i) the controlled polymerization of the functional monomer 4-trimethylsilylstyrene (S−Si), (ii) the exchange of the silyl groups in poly(4-trimethylsilylstyrene) (PS−Si) with BBr3 to give the reactive polymer poly(4-dibromoborylstyrene) (PS−BBr), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers through substituent exchange reactions with nucleophiles. Treatment of PS−BBr with ethoxytrimethylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s PS−BOR (R = Et, 4-bromobutyl). The alkoxy groups in PS−BOR have been exchanged with pinacol to form the air-stable polymer PS−BPin (Pin = pinacolato). Treatment of PS−BBr with 2-thienyltrimethyltin and pentafluorophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers PS−BTh and PS−BPf (Th = 2-t...

The synthesis of well-defined luminescent organoboron polymers via a novel three-step procedure starting from silylated polystyrene is reported. Highly selective borylation of poly(4-trimethylsilylstyrene) (PS-Si), followed by replacement of the bromine substituents in poly(4-dibromoborylstyrene) (PS-BBr) with substituted thienyl groups (R = H, 3-hexyl, 5-hexyl), and final introduction of the 8-hydroxyquinolato moiety yields a series of new organoboron quinolate polymers in 67-83% isolated yield. The hexyl-substituted polymers are highly soluble and solution-processable yielding thin films that efficiently emit light at 513-514 nm upon excitation at 395 nm.

A comparative study on the reactivity and selectivity of arylcopper species in reactions with boron halides was performed. Mesitylcopper reacts with BX 3 (X=Cl, Br) in toluene at low temperature under highly selective formation of the monosubstituted boranes MesBX 2 . The dimesitylboranes Mes 2 BX are gradually formed with a twofold excess of the organocopper reagent at elevated temperature. In contrast, pentafluorophenylcopper shows a tendency for formation of B(C 6 F 5 ) 3 in reactions with BX 3 irrespective of the stoichiometry used, suggesting a strong impact of electronic factors on the selectivity of the aryl transfer reaction. New procedures for the synthesis of the pentafluorophenylboron halides C 6 F 5 BX 2 (X=Cl: 57%; X=Br: 62%) and of tris(pentafluorophenyl)borane (80%) and related mixed-substituted triarylboranes from the base-free isolable pentafluorophenylcopper precursor have been developed.

The binding behavior of arenes toward pentafluorophenylcopper was investigated. Crystallization of pentafluorophenylcopper from a mixture of 1,2-dichloroethane and cyclohexane affords the homoleptic tetrameric complex [Cu(C6F5)]4, whereas a π-complex, [Cu(C6F5)]4(η2-toluene)2, is obtained from toluene solution. The unique coordination of two toluene molecules in [Cu(C6F5)]4(η2-toluene)2 leads to major structural changes as the regular square planar tetramer is distorted toward a butterfly structure with one short and one long diagonal Cu···Cu distance of 2.5935(3) and 3.955(1) A, respectively. The toluene molecules are bound in an unsymmetrical η2-coordination mode with the shortest contacts observed between copper and the meta carbon atoms (d(Cu−C) = 2.271(2), 2.298(2) A) and slightly longer distances to the para positions (d(Cu−C) = 2.339(2), 2.455(4) A). Multinuclear NMR studies show that complexation to the intact tetrameric cluster species also occurs in neat solution of the aromatic species. Strongl...

The first hypercoordinate sila[1]ferrocenophanes [fcSiMe(2-C 6 H 4 CH 2 NMe 2 )] (5a) and [fcSi(CH 2 Cl)(2-C 6 H 4 CH 2 NMe 2 )] (5 b) (fc = (η 5 -C 5 H 4 )Fe(η 5 -C 5 H 4 )) were synthesized by low-temperature (-78°C) reactions of Li[2-C 6 H 4 CH 2 NMe 2 ] with the appropriate chlorinated sila[1]ferrocenophanes ([fcSiMeCl] (la) and [fcSi(CH 2 Cl)Cl] (1d), respectively). Single-crystal X-ray diffraction studies revealed pseudotrigonal bipyramidal structures for both 5a and 5b, with one of the shortest reported Si...N distances for an sp 3 -hybridized nitrogen atom interacting with a tetraorganosilane detected for Sa (2.776(2) A). Elongated Si-C i p s o bonds trans to the donating NMe 2 arms (1.919(2) and 1.909(2) A for 5a and 5b, respectively) were observed relative to both the non-trans bonds (5a: 1.891(2); 5b: 1.879(2) A) and the Si-C i p s o bonds of the non-hypercoordinate analogues ([fcSiMePh] (1b): 1.879(4), 1.880(4) A; [fcSi(CH 2 Cl)Ph] (1e): 1.881(2), 1.884(2)). Solution-state fluxionality of 5 a and 5b, suggestive of reversible coordination of the NMe 2 group to silicon, was demonstrated by means of variable-temperature NMR studies. The ΔG of the fluxional processes for 5 a and 5b in CD 2 Cl 2 were estimated to be 35.0 and 37.6 kJ mol - 1 , respectively (35.8 and 38.3 kJ mol - 1 in [D 8 ]toluene). The quaternization of 5a and 5b by MeOTf, to give [fcSiMe(2-C 6 H 4 CH 2 NMe 3 )][OTf] (7a-OTf) and [fcSi(CH 2 Cl)(2-C 6 H 4 CH 2 NMe 3 )][OTf] (7b-OTf), respectively, supported the reversibility of NMe 2 coordination at the silicon center as the source of fluxionality for 5a and 5b. Surprisingly, low room-temperature stability was detected for 5b due to its tendency to intramolecularly cyclize and form the spirocyclic [fcSi(cyclo-CH 2 NMe 2 CH 2 C 6 H 4 )]Cl (9-Cl). This process was observed in both solution and the solid state, and isolation and X-ray characterization of 9-Cl was achieved. The model compound, [Fc 2 Si(2-C 6 H 4 CH 2 NMe 2 ) 2 ] (8), synthesized through reaction of [Fc 2 SiCl 2 ] with two equivalents of Li[2-C 6 H 4 CH 2 NMe 2 ] at -78°C, showed a lack of hypercoordination in both the solid state and in solution (down to- 80 °C). This suggests that either the reduced steric hindrance around Si or the unique electronics of the strained sila[1]ferrocenophanes is necessary for hypercoordination to occur.

We have developed a highly efficient new method for the introduction of Lewis acidic boron centers into the side chains of organic polymers. Our methodology involves three steps: (i) the controlled polymerization of a functional monomer, (ii) the exchange of the functional group for Lewis acidic boron centers, and (iii) the fine-tuning of the Lewis acidity of the individual centers through substituent exchange reactions with nucleophiles. This approach gives access to a family of new well-defined organoboron polymers including moderately Lewis acidic poly(arylboronates) and the first examples of highly Lewis acidic fluorinated triarylborane polymers.

Recent advances in the synthesis of organoborane polymers are reviewed in this chapter. The last decade has witnessed new approaches for the direct polymerization of functional borane monomers as well as the use of innovative polymer modification techniques. Powerful new methods that allow for positioning of functional borane moieties at well-defined positions in the polymer chain have also been developed. The resulting organoborane polymers have been investigated as luminescent and electro-active materials, electrolytes for batteries, supported Lewis acid catalysts, sensors for anions and biologically relevant molecules, building blocks of stimuli-responsive and dynamic (supramolecular) materials, and for biomedical applications.

A new type of ferrocene-based heteronuclear bidentate Lewis acid with both Lewis acidic centers attached to the same cyclopentadienyl (Cp) ring is reported. Borylation of 1,1‘-bis(trimethylstannyl)ferrocene (1) with BCl3 in hexanes at −78 °C occurs with high selectivity at the α-position to give 1-(Me3Sn)-2-(Cl2B)fc (2a-Cl; fc = ferrocenediyl) as the major product in ca. 87% spectroscopic yield. Only minor amounts of the two other isomers, the 1-stannyl-3-boryl- (2b-Cl) and the 1-stannyl-1‘-borylferrocene (2c-Cl), are observed. The reaction rate and selectivity strongly depend on the steric and electronic properties of the electrophile. With the bulkier electrophile C6F5BCl2 larger amounts of the 1,3-product, 1-(Me3Sn)-3-(C6F5ClB)fc (2b-Pf; ca. 40%), form in addition to the 1,2-isomer 1-(Me3Sn)-2-(C6F5ClB)fc (2a-Pf; ca. 60%). Use of the weaker electrophile PhBCl2 results in a significantly lower reaction rate. Treatment of 1 with excess borane in hexanes yields 1-(ClMe2Sn)-2-(Cl2B)fc (3a-Cl) and 1-(ClMe2S...

To obtain mechanistic insight, detailed studies of the intriguing "spontaneous" ambient temperature ring-opening polymerization (ROP) of tin-bridged [1]ferrocenophanes Fe(eta-C(5)H(4))(2)SnR(2) 3a (R = t-Bu) and 3b (R = Mes) in solution have been performed. The investigations explored the influence of non-nucleophilic additives such as radicals and radical traps, neutral and anionic nucleophiles, Lewis acids, protic species, and other cationic electrophiles. Significantly, two novel methodologies and mechanisms for the ROP of strained [1]ferrocenophanes are proposed based on this study. First, as the addition of amine nucleophiles such as pyridine was found to strongly accelerate the polymerization rate in solution, a new nucleophilicallyassisted ROP methodology was proposed. This operates at ambient temperature in solution even in the presence of chlorosilanes but, unlike the anionic polymerization of ferrocenophanes, does not involve cyclopentadienyl anions. Second, the addition of small quantities of the electrophilic species H(+) and Bu(3)Sn(+) was found to lead to a cationic ROP process. These studies suggest that the "spontaneous" ROP of tin-bridged [1]ferrocenophanes may be a consequence of the presence of spurious, trace quantities of Lewis basic or acidic impurities. The new ROP mechanisms reported are likely to be of general significance for the ROP of other metallocenophanes (e.g., for thermal ROP in the melt) and for other metallacycles containing group 14 elements.

Introduced herein is a series of conjugated thienylboranes, which are inert to air and moisture, and even resist acids and strong bases. X-ray analyses reveal a coplanar arrangement of the thiophene rings, an arrangement which facilitates p-π conjugation through the boron atoms despite the presence of highly bulky 2,4,6-tri-tert-butylphenyl (Mes*) or 2,4,6-tris(trifluoromethyl)phenyl ((F)Mes) groups. Short B⋅⋅⋅F contacts, which lead to a pseudotrigonal bipyramidal geometry in the (F)Mes species, have been further studied by DFT and AIM analysis. In contrast to the Mes* groups, the highly electron-withdrawing (F) Mes groups do not diminish the Lewis acidity of boron toward F(-) anions. These compounds can be lithiated or iodinated under electrophilic conditions without decomposition, thus offering a promising route to larger conjugated structures with electron-acceptor character.

Reaction of Co2(CO)8 with the Si−H-functionalized sila[1]ferrocenophane Fe(η-C5H4)2SiMeH (1a) was found to result in metalation of silicon and ring-opening of the ferrocenophane, affording the oran...

Current mechanisms for the transition metal-catalyzed ring-opening polymerization (ROP) of [1]ferrocenophanes and related strained species such as cyclic carbosilanes invoke a homogeneous mechanism...

Selective functionalization of polystyrene with weakly coordinating organoborate functionalities BAr(4)(-) (Ar = Ph, C(6)F(5)) has been accomplished by a polymer modification strategy. The first examples of perfluoroarylborate block copolymers have been prepared; light scattering and TEM studies confirm the formation of reverse micelles, in which the weakly coordinating anion sites are covered by a shell of "inert" polystyrene. The core of the micelles was successfully loaded with a cationic rhodium complex.

Functionalized organometallic polymers are reported. Direct substitution reactions on poly(ferrocenylsilanes) using nucleophiles with protected amines led to amine-functionalized polymers. The use of protecting group and monomer substitution strategies were found to be compatible with ring-opening polymerization protocols allowing the synthesis of high polymers with amino, bromo, ester, or quarternary ammnonium functionalities

Water-soluble poly(ferrocenylsilane) (PFS) and poly(styrenesulfonate) (PSS) of alternating charge are shown to self-assemble in a layer-by-layer fashion on primed Au, Si, and quartz substrates to create the first examples of organic−organometallic electrostatic superlattices from polymers with ferrocene units in the backbone. The layer-by-layer assembly of these electrostatic superlattices has been monitored through frequency changes with layer deposition using a quartz-crystal microbalance (QCM), a regular film thickness increase observed using ellipsometry, and step-wise absorbance increases observed using ultraviolet−visible (UV−vis) spectroscopy. As well, structural information was obtained using X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). These superlattices are of interest as possible precursors to patterned magnetic and redox active multilayers.

The reactivity of strained [1]ferrocenophanes, [Fe(eta-C5H4)2ERx] (ERx = SiMe2, 1a: SiMePh, 1b; SnR2, 1c), towards boron halides has been investigated and has been shown to provide a facile pathway to ferrocene derivatives functionalized with Lewis acidic boron centers. The boron halides RBX2 (R = Cl, Ph, fc; X = Cl, Br) (fc = Fe(eta-C5H4)2) lead to selective cleavage of the Si-Cp bonds in 1a and 1b to give, depending on the reaction stoichiometry, functionalized mono- or diferrocenylboranes RnB [(eta-C5H4)Fe(eta-C5H4SiMe2Cl)](3-n) (2a: R = Cl, n = 2; 2b: R = Cl, n = 1; 2c: R = Ph, n = 1) and RnB[(eta-C5H4)Fe(eta-C5H4SiMePhCl)](3-n) (2d: R = Cl, n = 2) in high yields. Compounds 2a-d were characterized by multinuclear NMR spectroscopy, mass spectrometry, and by single-crystal X-ray diffraction (for 2b). Most likely due to steric constraints, a triferrocenylborane was not obtained even from the reaction of BCl3 with an excess of 1a, whereas facile formation of the diferrocenylphenylborane 2c from PhBCl2 and two equivalents of 1a was observed. Selective hydrolysis of the B-Cl bonds of chlorodiferrocenylborane 2b in the presence of trace amounts of water led to the silylated tetranuclear ferrocene complex [(ClMe2Sifc)2B-O-B(fcSiMe2Cl)2] (3) without cleavage of the Si-Cl bonds. The structure of 3 was confirmed by an X-ray diffraction study. Studies of the reactivity of the higher Group 14 homologue of 1a and 1b, the tin-bridged [1]ferrocenophane 1c, revealed that facile addition of B-Cl bonds occurs across the Sn-Cp bonds to yield the 1-stannyl-1'-borylferrocenes [(ClMes2Sn)fc(BClR)] (4a: R = Cl; 4b: R = Ph; Mes = 2,4,6-Me3C6H2). The new synthetic methodology can be extended to bifunctional Lewis acids such as the bis(boryl)ferrocene 1,1'-fc(BBr2)2, which affords the linear boron-bridged ferrocene trimer 1,1'-[fc[B(Br)fcSiMe2Br]2] 5 in 54% isolated yield. In order to incorporate the functionalized ferrocenylboranes into polymer structures, compound 2c was reduced with Li[BEt3H] to give the silicon-hydride functionalized species [PhB[(eta-C5H4)Fe(eta-C5H4SiMe2H)]2] (6), which was then used as a capping reagent in the transition metal catalyzed polymerization of 1a. This process leads to the incorporation of the ferrocenylborane unit into the main chain of a poly(ferrocenylsilane) to afford [PhB-[(fcSiMe2)(n-1)fcSiMe2H]2] (7).

A series of poly(ferrocenylsilane)s containing chloroalkyl side chains of increasing length is reported. By reacting fcLi2· $$\tfrac{2}{3}$$ tmeda with Cl2SiMeR, the corresponding [1]ferrocenophanes were prepared (2a, R=CH2Cl; 2b, R=CH2CH2Cl; and 2c, R=CH2CH2CH2Cl). Transition metal-catalyzed or thermal ring-opening polymerization (ROP) of these monomers yielded the polyferrocenes 3a, 3b, and 3c. The chlorine substituents of polymers 3a and 3b were unreactive toward nucleophilic substitution. In contast, polymer 3c could be reacted with 4-dimethylaminopyridine in DMF to afford the water-soluble poly(ferrocenylsilane) 4. This represents a new method for the preparation of water-soluble polyferrocenes.

The use of mesitylcopper, a soluble, thermally stable arylcopper compound, was investigated as an alternative to less selective organolithium and Grignard reagents or toxic mercury, tin, and organozinc compounds. [CuMes]5·toluene (1) was found to readily react with various main group metal halides MXn and RMXn (M = B, Sn; X = Cl, Br; R = nBu, Ph, 1,1‘-fc) to give, depending on the stoichiometry of the reactions, monoarylated, diarylated, or mixed substituted species MesMXn-1, Mes2MXn-2, and MesRMXn-1 (2−5) in high yields.

The Lewis acidity of boron in diboradiferrocene 1 is strongly enhanced through oxidation of the iron atoms as evident from examination of X-ray structural parameters of the mixed-valent cation 1(+)PF(6) and further confirmed from the strong complexation of MeCN to the dication in 2(2+)(I(3))(2).

Novel tin-bridged [1]ferrocenophanes (1) undergo ring-opening polymerization to yield unusual bimetallic high-molecular-weight poly(ferrocenylstannane)s (2). They also undergo insertion of platinum to afford a 1-stanna-2-platina[2]ferrocenophane (3).

In an effort to develop a new class of redox-active chiral Lewis pairs, pyridine and borane moieties with different steric and electronic properties were introduced onto a planar chiral 1,2-disubstituted ferrocene framework. Metathesis of lithiated, stannylated, or mercuriated pyridylferrocenes with boron halides afforded (pR)-2-[bis(pentafluorophenyl)boryl]-1-(3,5-dimethylpyrid-2-yl)ferrocene (4-Pf), (pR)-2-[dimesitylboryl]-1-(3,5-dimethylpyrid-2-yl)ferrocene (4-Mes), (pS)-2-(bis(pentafluorophenyl)boryl)-1-(2-trimethylsilylpyrid-6-yl)ferrocene (5-Pf), or (pS)-2-[dimesitylboryl]-1-(2-trimethylsilylpyrid-6-yl)ferrocene (5-Mes). The borylated products were analyzed by multinuclear NMR spectroscopy, HRMS, and single-crystal X-ray diffraction. Chiral HPLC and optical-rotation measurements were employed to assess the stereoselectivity of the borylation process and to establish the correct stereochemical assignments. The strength of the B-N interactions were investigated in solution and in the solid state. Compounds 4-Pf and 4-Mes formed robust 'closed' B-N heterocyclic systems that proved to be perfectly stable to air and moisture, whereas 5-Pf established a dynamic equilibrium, in which the B-N heterocycle was observed exclusively at room temperature, but opened up at high temperature according to (19)F NMR exchange spectroscopy data. As a consequence, 5-Pf reacted readily with a molecule of water to generate a ring-opened pyridinium borate. The combination of bulky borane and bulky pyridyl groups in 5-Mes led to a completely 'open' frustrated Lewis pair system with uncomplexed pyridine and borane groups, even at room temperature. Electrochemical studies were performed and the effect of preparative ferrocene oxidation on the structural features was also explored.

Starting from readily available diborylferrocenes 1,1‘-fc[B(Br)R]2 (fc = (C5H4)Fe(C5H4); R: Br (1a), Me (1b), OEt (1d)), ferrocenophanes 1,1‘-fc[B(μ-PPh2)R]2 (R = Br (2a), Me (2b), PPh2 (2d)) and ...

A one-step high-yield synthesis of donor−acceptor complexes [1A]X to [1D]X, [2A]X2, and [4A]X4 with one, two, and four cationic [B(R)bipy]+ acceptors (R = Me, Br, OEt, NC4H8; X = Br, PF6; bipy = 2,2‘-bipyridine) covalently attached to a ferrocene donor is described. Apart from 2,2‘-bipyridine, 1,10-phenanthroline and 2,2‘-bipyrimidine have also been used as chelating amines. With the exception of R = Br, water-stable compounds are obtained in all cases. In DMF solution and under an inert atmosphere, [1A]PF6, [2A](PF6)2, and [4A](PF6)4 behave as reversible three-step redox systems, capable of storing three, five, and nine electrons, respectively. In their cationic state, the complexes possess an intense purple color, which can be attributed to charge-transfer interactions between the ferrocene unit and the electron-poor B(R)bipy substituent(s). This is confirmed by the ESR spectrum of the monoreduced species [1A]0, which features a line shape indicating considerable admixture of the ligand and metal orbitals.

The stability of ferrocenophanes ansa-1,1‘-Fc[B(R)(μ-pzR#)]2 (2) with pyrazabole bridges depends to a large extent on the substitution pattern of boron (R) and pyrazole (R#). Cyclic voltammetry measurments on 17 derivatives of 2, with R and R# covering a wide spectrum of electronic features, revealed a pronounced influence of these substituents on the E°‘0/+ values of the Fe(II)/Fe(III) redox couple. The electronic effects of R and R# thus appear to be transmitted to a great degree along the pyrazabole framework. π donors R and electron acceptors R# lead to a gradual ansa-bridge weakening and finally opening, if R = pyrrolidinyl and R# = 3,5-CF3 or 3,4,5-COOEt (NMR spectroscopy; X-ray crystal structure analyses of 2c (R = Me; R# = 3,4,5-H), 2d (R = Me; pzR# = indazolyl), 2n (R = pyrrolidinyl; R# = 3,4,5-H), 2p (R = pyrrolidinyl; pzR# = triazolyl)). Cyclic voltammetry indicates ansa-bridge opening to occur without major alterations of the charge density at boron. In the case of R = pyrrolidinyl there is ev...

The reaction of (dibromoboryl)ferrocene (1a) with pyrazole/NEt3 gave the ferrocenyltri-1-pyrazolylborate ligand 2. Its thallium(I) derivative 2-Tl provides the first example of a polymeric structure with bridging tri-1-pyrazolylborate units in the solid state. The trinuclear iron complex 2-Fe, which is related to 1,1′-terferrocene, was obtained by reaction of 2 with FeCl2. The bis(polydentate) ligand 1,1′-ferrocenediyl-bis(tri-1-pyrazolylborate) (3-Li) was prepared from 1,1′-bis-[bis(dimethylamino)boryl]ferrocene (1c) and a mixture of lithium pyrazolide/pyrazole in refluxing toluene/THF. 3-Li reacts with TlNO3 to give the thallium(I) complex 3-Tl.

A variety of stereorigid ansa-ferrocenes 2 with o-phenylene-type bridges have been obtained by the reaction of 1,1‘-diborylferrocenes (1,1‘-Fc(BBrR)2; Fc = ferrocenyl; R = CH3, Br, OEt, NC4H8) with selected pyrazole derivatives. Subsequent intramolecular B−N adduct formation establishes the interannular bridges. The synthetic approach is based on the replacement of certain critical carbon−carbon links by the isoelectronic, self-assembling, dative boron−nitrogen bonds and thus follows the principles of noncovalent synthesis. The pyrazabole bridge does not seem to cause any significant distortion of the ferrocene core. Most substituents at boron or pyrazole lead to an ansa-ferrocene structure. However, the presence of both strong electron donors (i.e. pyrrolidine) at boron and strongly electron-withdrawing pyrazole substituents (i.e. ester groups) results in an open chain structure 2i with three-coordinate boron atoms. The tetravalent boron centers in ansa-1,1‘-Fc[B(Br)(μ-pz)]2, 2a, show an unusually high t...

The geometry and electronic structure of borylferrocenes, FcBR2, have been investigated by X-ray structure analysis (R = Br) and density functional theory (DFT) calculations (R = H). An interaction...

This chapter provides an overview of the most significant developments in the area of boron-containing polymers over the past about 10 years. We describe the synthesis, characterization, and applications of new polymeric materials that feature boron as an integral component with a clear effect on the chemical or physical properties. These include (1) organoborane polymers, (2) polymers that contain conjugated boron heterocyles, such as borazane, pyrazabole, bipyridylboronium, boron quinolate, boron diketonate, and 4,4-difluoro-4-bora-3a,4a-diaza- s -indacene moieties, (3) boronic acid and boronic ester-functionalized polymers and related materials, and (4) polymers that feature carboranes and other boron clusters.

The facile formation of boron-nitrogen bridges allows the one-step assembly of oligonuclear organometallic complexes. By the reaction of 1-(dibromoboryl)ferrocene (1a) and 1,1′-bis(dibromoboryl)ferrocene (1b) with 1-[(dimethylamino)methyl]ferrocene (2) and (η6-aniline)tricarbonylchromium derivatives (3, 4) dinuclear to pentanuclear units (5–10) were obtained. The homodimetallic compound FcBBr2-NMe2CH2Fc (5, Fc: ferrocene) closely resembles a propylene-bridged complex. Its dative B-N link is stable at temperatures as high as 100°C. Each of the heterooligonuclear aggregates 7–10 is tied together by covalent B-N bonds, which are isoelectronic with ethylene bridges. In FcB(Br)-N(Me)Bct [7, Bct: (η6-C6H5)Cr(CO3)] and 1,1′-Fc[B(Br)-N(Me)Bct]2 (9) B-N π bonding dominates over the N-Bct π interaction as indicated by spectroscopical data and an X-ray analysis of 9. The N-lithiated compounds BctNRLi (4a, b; R = H, Me) possess a remarkably increased N-Bct π donation compared to the protonated parent compounds, which results in a further perturbation of the local C3v symmetry of the (C6H5)Cr(CO3) framework.