Synthesis, Structural Characterization, and Olefin Polymerization Behavior of Group 4 Metal Complexes with Constrained-Geometry Carborane Ligands

[closo-B10H8-1-CN-10-Azinium]- Anions: Photoactive Heteroditopic Ligands for Metal Complexes

A new class of rigid, photoactive heteroditopic anionic ligands based on the 1,10-disubstituted [closo-B10H10]2- anion was designed and six of these compounds were obtained from [closo-B10H10]2- in three steps with yields in the range of 25-30%. The design includes two apical substituents, a metal coordinating cyano group and an azinium (4-cyanopyridinium, 4,4'-bipyridinium, pyrazinium, pyrimidinium, and pyridazinium), which provides a secondary binding site. The azinium substituent is involved in an efficient intramolecular charge transfer process and compensates one of the two delocalized negative charges of the boron cluster. The compounds exhibit intramolecular CT bands with maxima in the range of 340-410 nm (MeCN) and two are weakly fluorescent with significant Stokes shifts. A highly colored bis-zwitterionic byproduct with two clusters, [closo-1-CN-B10H8-10-(pyrazinium-1,4-diyl)-10'-B10H8-1'-CN-closo]2-, was also obtained in a low yield. The ligands were structurally characterized (XRD) and their geometrical and photophysical properties were compared to those of the analogues lacking the CN group and the parent pyridinium derivative. A comparative analysis of experimental data was augmented with DFT and TD-DFT results. Two of the ligands (with the 4,4'-bipyridinium and pyrazinium) were converted to (η5-Cp)(dppe)Fe complexes and one of them was used to obtain a heterodinuclear complex with Cu(pdc)(H2O)3 to demonstrate the ditopic function of the ligand. All three iron complexes were characterized by the XRD method.

Conformation-Dependent Electron Donation of Nido-Carborane Substituents and Its Influence on Phosphorescence of Tris(2,2′-bipyridyl)ruthenium(II) Complex

In this work, we report the synthesis of the nido-carborane-substituted ruthenium complexes and the substituent effects of nido-carboranes on the optical properties. Initially, from the optical measurements, it is shown that deep-red phosphorescence was obtained from the synthesized molecule, and the phosphorescent quantum yields were significantly improved by loading onto a polyethylene glycol film. This result represents that nido-carborane can work as a strong electron donor and should be an effective unit for enhancing the solid-state phosphorescence of ruthenium complexes. Further, it is suggested that the electron-donating properties of the nido-carborane units and subsequently the optical properties can be tuned by controlling the conformation of the nido-carborane units with the steric substituents. We demonstrate in this study the potential of nido-carborane as a building block for constructing optical materials as well as fundamental information regarding electronic interactions with π-conjugated systems.

Electron-donating abilities and luminescence properties of tolane-substituted nido-carboranes

The luminescence properties of nido-carborane-substituted tolane derivatives were investigated.

New ligand platforms featuring boron-rich clusters as organomimetic substituents

200 years of research with carbon-rich molecules have shaped the development of modern chemistry. Research pertaining to the chemistry of boron-rich species has historically trailed behind its more distinguished neighbor (carbon) in the periodic table. Notably, a potentially rich and, in many cases, unmatched field of coordination chemistry using boronrich clusters remains fundamentally underdeveloped. Our work has been devoted to examining several basic concepts related to the functionalization of icosahedral boron-rich clusters and their use as ligands, aimed at designing fundamentally new hybrid molecular motifs and materials. Particularly interesting are icosahedral carboranes, which can be regarded as 3D analogs of benzene. These species comprise a class of boron-rich clusters that were discovered in the 1950s during the "space race" while researchers were developing energetic materials for rocket fuels. Ultimately, the unique chemical and physical properties of carborane species, such as rigidity, indefinite stability to air and moisture, and 3D aromaticity, may allow one to access a set of properties not normally available in carbon-based chemistry. While technically these species are considered as inorganic clusters, the chemical properties they possess make these boron-rich species suitable for replacing and/or altering structural and functional features of the organic and organometallic molecules-a phenomenon best described as "organomimetic". Aside from purely fundamental features associated with the organomimetic chemistry of icosahedral carboranes, their use can also provide new avenues in the development of systems relevant to solving current problems associated with energy production, storage, and conversion.

Synthesis, structural characterization, and reactivity of Group 4 metallacarboranes bearing the ligand [H2C(C5Me4)(C2B9H10)]3-

A new organic-inorganic hybrid ligand H(2)C(C(5)Me(4)H)(C(2)B(10)H(11)) (2) has been prepared. A selective deboration reaction with piperidine in ethanol resulted in the isolation of [Me(3)NH][H(2)C(C(5)Me(4)H)(C(2)B(9)H(11))] (3). An amine-elimination reaction of 3 with [Zr(NMe(2))(4)] produced a neutral metal-amide complex [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr(NMe(2))(NHMe(2)) (4). The double-ring-opening reaction of 4 with tetrahydrofuran (THF) afforded [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr (OCH(2)CH(2)CH(2)CH(2))(2)N(CH(3))(2) (5). Treatment of the trianionic salt of 3 with [MCl(4)(thf)(2)] gave complexes [{η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))}M(μ-Cl)(2)][Li(thf)(2)] (M=Zr (6), Hf (7)). Reaction of 6 with LiCH(2)TMS generated the ionic species [{η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))}Zr(CH(2)TMS)(2)][Li(thf)(3)] (9). Interaction of complex 6 with KCH(2)(NMe(2))-o-C(6)H(4) led to the formation of the neutral metal alkyl complex [η(5):η(5)-H(2)C(C(5)Me(4))(C(2)B(9)H(10))]Zr[σ:σ-CH(2)(NMe(2))-o-C(6)H(4)] (10). All complexes have been fully characterized by various spectroscopic techniques and elemental analyses. Some were further confirmed by single-crystal X-ray analyses.

Synthesis, Structural Characterization, Reactivity, and Thermal Stability of [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2)

Reaction of [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]TiCl(NMe2) (1) with 1 equiv of PhCH2K, MeMgBr, or Me3SiCH2Li gave corresponding organotitanium alkyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2) (R = CH2Ph (2), CH2SiMe3 (4), or Me (5)) in good yields. Treatment of 1 with 1 equiv of n-BuLi afforded the decomposition product {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe)(mu:sigma-CH2NMe) (3). Complex 5 slowly decomposed to generate a mixed-valence dinuclear species {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe2)(mu:sigma-CH2NMe) (6). Complex 1 reacted with 1 equiv of PhNCO or 2,6-Me2C6H3NC to afford the corresponding monoinsertion product [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-OC(NMe2)NPh] (7) or [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-C(NMe2)=N(2,6-Me2C6H3)] (8). Reaction of 4 or 5 with 1 equiv of R'NC gave the titanium eta(2)-iminoacyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(NMe2)[eta(2)-C(R)=N(R')] (R = CH2SiMe3, R' = 2,6-Me2C6H3 (9) or tBu (10); R = Me, R' = 2,6-Me2C6H3 (11) or tBu (12)). The results indicated that the unsaturated molecules inserted into the Ti-N bond only in the absence of the Ti-C(alkyl) bond and that the Ti-C(cage) bond remained intact. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 2, 3, 6-8, and 10-12 were further confirmed by single-crystal X-ray analyses.