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The introduction of unconventional elements into π-conjugated systems has been studied to manipulate the electronic states and properties of compounds. Herein, boron- and germanium-containing hybrid macrocycles, as a new class of element-hybrid conjugated systems, have been synthesized. The palladium-catalyzed Stille cross coupling of bis(bromothienyl)borane and bis(trimethylstannylthienyl)- or bis(trimethylstannylphenyl)-substituted dithienogermoles as the boron- and germanium-containing building blocks, respectively, produced a mixture of several macrocyclic compounds. Single-crystal X-ray analysis of the 2:2 coupling product revealed a planar structure with a cavity inside the macrocycle. The optical properties of the macrocyclic products indicated rather small electronic interactions between the building units. However, intramolecular photoenergy transfer from the dithienogermole unit to the boron unit was clearly observed with respect to the fluorescence spectra.

The extension of conjugated organoboranes from monomeric species to oligomers, macrocycles, and polymers offers access to a plethora of fascinating new materials. The p-π* conjugation between empty orbitals on boron and the conjugated linkers not only affects the electronic structure and optical properties, but also enables mutual interactions between electron-deficient boron centers. The unique properties of these electron-deficient π-conjugated systems are exploited in highly luminescent materials, organic optoelectronic devices, and sensing applications.

We introduce a new boron-doped cyclophane, the hexabora[16 ]cyclophane B6-F Mes, in which six tricoordinate borane moieties alternate with short conjugated p-phenylene linkers. Exocyclic 2,4,6-tris(trifluoromethyl)phenyl (F Mes) groups serve not only to further withdraw electron density but at the same time sterically shield the boron atoms, resulting in a macrocycle that is both highly electron-deficient and stable. The optical and electronic properties are compared with those of related linear oligomers and the electronic structure is further evaluated by computational methods. The studies uncover unique properties of B6-F Mes, including a low-lying and extensively delocalized LUMO and a wide HOMO-LUMO gap, which arise from the combination of a cyclic π-system, strong electronic communication between the closely spaced borons, and the attachment of electron-deficient pendent groups. The binding of small anions to the electron-deficient macrocycle and molecular model compounds is investigated and emissive exciplexes are detected in aromatic solvents.

The functionalization of polycyclic aromatic hydrocarbons (PAHs) via B←N Lewis pair formation offers an opportunity to judiciously fine-tune the structural features and optoelectronic properties, to suit the demands of applications in organic electronic devices, bioimaging, and as sensitizers for singlet oxygen. We demonstrate that the N-directed electrophilic borylation of 2,6-di(pyrid-2-yl)anthracene offers access to linearly extended acene derivatives Py-BR (R = Et, Ph, C6F5). In comparison to indeno-fused 9,10-diphenylanthracene, the formal "BN for CC" replacement in Py-BR selectively lowers the LUMO, resulting in a much reduced HOMO-LUMO gap. An even more extended conjugated system with seven six-membered rings in a row (Qu-BEt) is obtained by borylation of 2,6-di(quinolin-8-yl)anthracene. Fluorinated Py-BPf shows particularly advantageous properties, including low-lying HOMO and LUMO levels, strong yellow-green fluorescence, and effective singlet oxygen sensitization, while resisting self-sensitized conversion to its endoperoxide.

Given that pyrene represents one of the most versatile chromophores, the development of new selective routes for its functionalization and tuning of its emission properties is highly desirable. Pyrene-based BN Lewis pair (LP)-functionalized polycyclic aromatic hydrocarbons (PAHs) were prepared by regioselective Lewis base-directed electrophilic aromatic substitution. The requisite 1,6-dipyridylpyrene ligands were accessed by Suzuki-Miyaura cross-coupling of 1,6-bis(pinacolatoboryl)pyrenes with 2-bromopyridine derivatives. Subsequent electrophilic borylation with BCl3 in the presence of AlCl3 and 2,6-di-tert-butylpyridine as a hindered base produced the dichloroborane complexes, which were then in situ reacted with diphenyl or diethyl zinc. The presence or absence of alkyl chains in the 3,8-positions of the pyrene moiety determined the position of the B-C bond formation (2,7 in the non-K region versus 5,10 in the K region) and thereby also the size of the BN heterocycle (five- versus six-membered). The impact of the regioisomeric borylation on the electrochemical, photophysical and structural properties was investigated and the conclusions supported by theoretical calculations. The rapid synthesis of derivatives that are borylated in the K region also suggests strong potential for the development of pyrene derivatives that are otherwise difficult to access.

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox-active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2-fc(PPh2 )(SnMe3 ) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n-Bu4 N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg-Cl→Hgfc2 (2.9929(13) A) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2 )2 ⋅HgCl2 where the bridging mercury atom acts as a σ-acceptor. Furthermore, a bis-[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) A. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10-2 and 1.4×10-2 e/a03 at the bond critical points.

p-π conjugation with embedded heteroatoms offers unique opportunities to tune the electronic structure of conjugated polymers. An approach is presented to form highly electron-deficient p-π conjugated polymers based on triarylboranes, demonstrate their n-type behavior, and explore device applications. By combining alternating [2,4,6-tris(trifluoromethyl)phenyl]di(thien-2-yl)borane (FBDT) and electron-deficient isoindigo (IID)/pyridine-flanked diketopyrrolopyrrole (DPPPy) units, we achieve low-lying lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels, high electron mobilities, and broad absorptions in the visible region. All-polymer solar cells with these polymers as electron acceptors exhibit encouraging photovoltaic performance with power conversion efficiencies of up to 2.83 %. These results unambiguously prove the n-type behavior and demonstrate the photovoltaic applications of p-π conjugated polymers based on triarylborane.

The importance of scorpionate ligands in modern coordination chemistry continues to increase, because of their outstanding versatility, tunability and user-friendliness. Herein, we provide a short overview of recent developments in the classes of scorpionate ligands, derived from pyrazoles, triazoles, imidazoles, oxazolines, thioimidazoles and other similar systems, followed by an in-depth discussion of a new type of robust and tunable scorpionate ligand, tris(2-pyridyl)borates. The structure and synthesis of tris(2-pyridyl)borate (Tpyb) ligands are discussed, and key features of coordination of Tpyb ligands with metal ions, as well as supramolecular crystal packing, transmetallation and applications in metallo-supramolecular polymer chemistry are addressed.

The regioregular synthesis of the first azaborine oligomers and a corresponding conjugated polymer was accomplished by Suzuki-Miyaura coupling methods. An almost perfectly coplanar syn arrangement of the heterocycles was deduced from an X-ray crystal structure of the dimer, which also suggested that NH⋅⋅⋅π interactions play an important role. Computational studies further supported these experimental observations and indicated that the electronic structure of the longer azaborine oligomers and polymer resembles that of poly(cyclohexadiene) more than poly(p-phenylene). A comparison of the absorption and emission properties of the polymer with those of the oligomers revealed dramatic bathochromic shifts upon chain elongation, thus suggesting highly effective extension of conjugation.

A new class of Janus-like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4-SnP and 4-BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single-crystal X-ray studies. In addition, the ligands are redox-responsive and the Lewis acidic borane moiety in 4-BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska-type Rh(I) complex 5-BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.

A facile and versatile approach was developed to access ambipolar boron-containing macrocycles. Two examples of new conjugated cyclic motifs are presented with carbazole moieties as donors and borane moieties as acceptors embedded into the ring system. They were first predicted using computational methods. Possible targets with appropriately shaped π-conjugated bridges that minimize the overall ring strain were identified and their geometry was optimized by DFT methods. The synthetic demonstration was then accomplished using organometallic condensation reactions under high dilution conditions. The resulting monodisperse macrocycles provide important insights into the design principles necessary for the preparation of new unstrained macrocycles with interesting optical and electronic characteristics. The current research also offers a more general approach to conjugated ambipolar B/N macrocycles as a promising new family of (opto)electronic materials.

Boron- and silicon-containing conjugated homo- and copolymers could be synthesized using acyclic diene metathesis (ADMET) condensation of bis-styryl monomers. Both, tri-and tetra-coordinated boron monomers were successfully polymerized forming homopolymers, or random copolymers (if polymerized together with a silicon containing co-monomer). Polymer molecular weights Mn were measured at ∼6000 to 15,000 g/mol (NMR end group analysis) with molecular weight distributions Mw/Mn ∼1.8 to 2.2. The polymers absorbed at λmax ∼317 to 406 nm and emitted at λmax ∼370 to 494 nm with fluorescent quantum efficiencies ∼24 to 48%. The copolymer with tri-coordinate boron showed highly efficient fluorescence quenching in the presence of fluoride ions at ratios boron/fluoride ∼5/1, demonstrating its potential as anion sensor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1707–1718

A new type of smart borinic acid polymer with luminescence and multiple stimuli-responsive properties is reported. In DMSO with small amounts of water, the homopolymer PBA shows a tunable upper critical solution temperature (UCST). As the amount of water increases from 0 to 2.5 % (v/v), the UCST rises linearly from 20 °C to 100 °C (boiling point of water). Thus, the thermal responsive behavior can be tuned over a wide temperature range. Furthermore, polymer solutions in DMSO show a reversible response to fluoride ions, which can be correlated to the presence of the Lewis acidic borinic acid groups. Upon addition of fluoride, the polymer becomes soluble because the functional R2BOH groups are converted into ionic [R2BF2](-) groups, but turns insoluble again upon addition of H2O, which reverses this process.

This perspective highlights recent progress on the design, synthesis and applications of thienylboranes as building blocks for new functional materials. Well-controlled synthetic protocols, such as boron–tin and boron–silicon exchange reactions, hydroboration of alkynyl groups, and electrophilic borylations provide opportunities to access thiophene-boranes that are chemically robust and display desirable photophysical properties, redox characteristics, and solid-state assembly behavior. Diverse protocols for further functionalization allow for facile integration into larger conjugated structures and even polymeric systems. Moreover, the strong Lewis acid character that is characteristic of trivalent boranes facilitates intra- and intermolecular Lewis acid–base interactions that can further enrich the chemical and electronic properties of thiophene-borane materials. Recent advances with respect to applications in sensing, organic electronics, and the development of molecular switches are also discussed.

Boratabenzene-derived metallocene analogues are introduced as versatile new building blocks for metallopolymers. Bis(borinato)iron(II) complexes of the type Fe(C(5)H(5)B-R)(2) (R: C≡CH, C≡CSiMe(3), 4-(1-benzyl-1,2,3-triazolyl) were synthesized and spectroscopically, structurally, and electrochemically characterized. Polymerization via Sonogashira-Hagihara coupling of the alkynyl-substituted derivative Fe(C(5)H(5)B-C≡CH)(2) with 2,5-bis(dodecyloxy)-1,4-diiodobenzene yields a film-forming polymer in 50-69% yield. Polymer batches were obtained with number-average molecular weights (M(n)) of 11.7 and 20.5 kDa and polydispersity indices (PDI) of 1.55 and 2.65, respectively, as determined by gel permeation chromatography relative to polystyrene standards. Click-type polymerization of Fe(C(5)H(5)B-C≡CH)(2) through azide-alkyne cycloaddition with 1,4-bis(4-azidobutoxy)benzene gives the corresponding metallopolymer with an M(n) of 5.7 kDa and a PDI of 2.29 in 87% yield.

The amphiphilic organoboron block copolymer poly (styreneboronic acid)-block-polystyrene (PSBA-b-PS )h as been prepared through a postpolymerization modification route from the silicon-functionalized block copolymer poly(4- trimethylsilylstyrene)-block-polystyrene (PSSi-b-PS). PSBA-b- PS is obtained through highly selective reaction of PSSi-b- PS with BBr3 at room temperature and subsequent hydroly- sis of the BBr2-functionalized intermediate. Transmission electron microscopy studies demonstrate that PSBA-b-PS undergoes pH dependent micellization in aqueous solution. Different morphologies could be realized by using different mixtures of water and organic solvents. V C 2010 Wiley Period- icals, Inc. J Polym Sci Part A: Polym Chem 48: 2438-2445, 2010

A luminescent main chain donor-π-acceptor-type polymer (4) was prepared via organometallic polycondensation reaction followed by post modification. With both electron-rich amine and electron-deficient borane moieties embedded in the main chain, 4 exhibits an interesting ambipolar character: it can be reduced and oxidized electrochemically at moderate potentials and shows a strong solvatochromic effect in the emission spectra. Complexation studies show that 4 selectively binds to fluoride and cyanide; quantitative titration with cyanide reveals a two-step binding process.

A new class of amphiphilic organometallic block copolymers with cationic organoboron pendant groups was developed. Selective replacement of one of the bromine substitutents on each boryl group of the block copolymer PSBBr2-b-PS with an organometallic reagent ArM (ArM = 2,4,6-trimethylphenyl copper, 4-t-butylphenyltrimethyl tin) followed by treatment with 2,2′-bipyridine gave the novel block copolymers [3Ar](Br)n as light yellow solid materials that show good stability in air and moisture and high solubility in most organic solvents. Their structure and composition were confirmed by multinuclear NMR, GPC, and elemental analysis. Highly regular micellar aggregates form in block-selective solvents (e.g., MeOH, toluene) as demonstrated by 1H NMR, dynamic light scattering, and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6612–6618, 2009

Building bridges: The title compound forms an unprecedented polymeric structure with bridging B-H-B three-center two-electron bonds in the solid state. This organoborane serves as an efficient precursor for the preparation of boron-doped pi-conjugated polymers by hydroboration polymerization with a functionalized 1,4-diethynylbenzene (see picture). These polymers form thin films that show intense green luminescence.

A series of mixed-valent (MV) complexes [(FeCp) 2 (μ-C 10 H 6 -(BPh) 2 )] + X ([1 + ]X; X=I 5 , PF 6 , SbF 6 , B(C 6 F 5 ) 4 ) were prepared by oxidation of diboradiferrocene [(FeCp) 2 (μ-C 10 H 6 -(BPh) 2 )] (1) with I 2 , AgPF 6 , and AgSbF 6 , respectively, and through anion exchange of the I 5 - salt with [Li-(Et 2 O) x ][B(C 6 F 5 ) 4 ] in the case of X=B-(C 6 F 5 ) 4 . The MV state of the cation was investigated in solution by multi-nuclear NMR spectroscopy, CV, and UV/Vis-NIR absorption spectroscopy, and in the solid state by IR spectroscopy, single-crystal X-ray crystallography, and Mossbauer spectroscopy. The cyclic voltammogram of 1 shows two distinct redox waves with a large redox splitting of ΔE=510 mV in CH 2 Cl 2 and the NIR spectrum for the mono-oxidized species displays an intervalence charge-transfer band at around 1500 to 1700 nm depending on the specific counterion present. The X-ray crystal structures of [1 + ]X show inversion-symmetric cations with X=I 5 and B-(C 6 F 5 ) 4 and unsymmetric valence-trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF 6 and SbF 6 . Mossbauer data for X=PF 6 are consistent with valence trapping at all temperatures between 90 and 343 K. In comparison, fast electron transfer is evident on the Mossbauer timescale for X=I 5 and temperature-dependent behavior is observed for X=B(C 6 F 5 ) 4 . The anion dependence of the X-ray structural and Mossbauer data is discussed in the context of crystal symmetry and the possibility of static and dynamic disorder effects is considered.

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 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.

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

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).

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).

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.

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.