Cyclopentadienyl−Hydrazido Titanium Complexes: Tuning of Coordination Modes of Hydrazido Ligands to the Titanium Center

Cyclopentadienyl−hydrazido titanium complexes [(η5-C5Me4)SiMe2(NNMe2)]TiR2 (R = NMe2 (2), Cl (3), Me (5)) and [(η5-C5Me4)SiMe2(NNMe2AlMe3)]TiMe2 (4) have been prepared and characterized. Single-crystal X-ray diffraction studies reveal that complexes 2−5 contain η1-hydrazido (2 and 4) and η2-hydrazido (3 and 5) groups depending on the electronic nature of the titanium center. The reaction of 2 with H2O produces a tetrameric organotitanoxane [(η5-C5Me4)(SiMe2NHNMe2)Ti]4O6 (6) with an adamantane-like cage structure

Reactions of AlR₃ (R = Me, Et) with H₂NCH₂CH₂NMe₂: Synthesis and Characterization of Amido- and Imidoalanes

The reactions of R3Al (R = Me, Et) with N,N-dimethylethylenediamine (DMEDA) in a 1:1 molar ratio produce adducts, R3Al·NH2C2H4NMe2 (1a, R = Me; 1b, R = Et), which upon heating in refluxing toluene result in alkane elimination to afford the chelated monomers (2a, R = Me; 2b, R = Et), respectively. Compounds 2a,b form adducts with 1 equiv of R3Al through the 3-coordinate nitrogen atom to produce (3a, R = Me; 3b, R = Et), which can be alternatively prepared by the reaction of R3Al with DMEDA in a 2:1 molar ratio by alkane elimination at room temperature. Thermolysis of 3a,b at 140 °C in sealed ampules produces a mixture of cis and trans isomers of tetrametallic imidoalanes, (4a, R = Me; 4b, R = Et). Slow recrystallization of the isomeric mixture affords crystals of only the cis isomer for both 4a and 4b, but in solution cis-4a and cis-4b equilibrate with the respective trans isomers. The cis → trans isomerization of 4a has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow reversible first-order kinetics with ΔH° = 1.67 ± 0.60 kJ mol-1 and ΔS° = 9.07 ± 2.80 J mol-1 K-1. The activation parameters for the cis → trans conversion are ΔH1 = 125.8 ± 9.3 kJ mol-1 and ΔS1 = 89.7 ± 1.2 J mol-1 K-1, and those for the reverse process are ΔH-1 = 124.2 ± 9.3 kJ mol-1 and ΔS-1 = 80.7 ± 1.2 J mol-1 K-1. Pyrolysis of 4a,b in the presence of 2 equiv of DMEDA at 190 °C in sealed ampules gives hexameric imidoalanes, (RAlNC2H4NMe2)6 (5a, R = Me; 5b, R = Et), by alkane elimination. Compounds 5a,b can be also prepared by pyrolysis of 2a,b under similar conditions, but in lower yields. The molecular structures of cis-4b and 5b have been determined by single-crystal X-ray diffraction. The molecular geometry of cis-4b involves one four-membered Al2N2 ring and two five-membered AlN2C2 rings of cis conformation, and it has approximate C2 symmetry with the C2 axis going through the center of the Al2N2 ring. The hexameric imidoalane 5b consists of a hexagonal prism of the (AlN)6 cage formed by two flat six-membered (AlN)3 rings linked together by six transverse Al−N bonds

Trans−Cis Isomerization and Structure of [R₂Ga(μ-NHSiEt₃)]₂ (R = Me, Et)

Reactions of Et3SiNH2 with R3Ga in a 1:1 ratio have produced dimeric silylamidogallanes, [R2Ga(μ-NHSiEt3)]2 (1, R = Me, trans:cis = 1.5:1; 2, R = Et, trans:cis = 1.3:1), as a mixture of trans (a) and cis (b) isomers. Purification of 1 by either recrystallization or sublimation gives only trans isomer 1a as colorless crystals. Colorless liquid 2 has been obtained only as a mixture of the two isomers. The trans → cis isomerization of 1 has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow reversible first-order kinetics with ΔH° = − 0.64 ± 0.03 kJ mol-1 and ΔS° = − 4.4 ± 0.2 J K-1 mol-1. The activation parameters for the trans (1a) → cis (1b) conversion are ΔH1⧧ = 72.4 ± 1.3 kJ mol-1 and ΔS1⧧ = − 38.8 ± 4.5 J K-1 mol-1, and those for the reverse process are ΔH-1⧧ = 73.0 ± 0.4 kJ mol-1 and ΔS-1⧧ = − 34.4 ± 1.7 J K-1 mol-1. The isomerization is markedly accelerated in the presence of Lewis bases. A crossover experiment indicates that the isomer interconversion is a unimolecular process. The thermodynamic and kinetic data have been explained based on the solvent effect and the silyl substituent effect on the nitrogen atom. The molecular structure of 1a has been determined by a single-crystal X-ray diffraction study. The molecular geometry of 1a consists of a centrosymmetric and dimeric unit with two bridging (triethylsilyl)amido groups and two terminal methyl groups bound to each gallium atom. The two silyl groups are trans to each other with respect to the planar (Ga−N)2 ring framework. The coordination geometry of both gallium and nitrogen atoms is distorted tetrahedral

Synthesis and Characterization of η²-C₆₀ and μ₃-η²,η²,η²-C₆₀ Triosmium Cluster Complexes

Various η2-C60 and μ3-η2,η2,η2-C60 triosmium carbonyl cluster complexes Os3(CO)11(η2-C60) (1), Os3(CO)10(NCMe)(η2-C60) (2), Os3(CO)10(PPh3)(η2-C60) (3), Os3(CO)9(PR3)2(η2-C60) (4, R = Ph; 5, R = Me), Os3(CO)9(μ3-η2,η2,η2-C60) (6), and Os3(CO)8(PMe3)(μ3-η2,η2,η2-C60) (7) have been isolated as crystalline solids and characterized by spectroscopic (IR, MS, and 1H, 31P, and 13C NMR) and analytical data. The molecular structure of complex 1 has been determined by a single-crystal X-ray diffraction study. The structure of 1 is derived from that of Os3(CO)12 by replacing an equatorial carbonyl ligand with an η2-C60 ligand coordinated through a 6−6 ring fusion. The structural assignment of 2−7 is made on the basis of spectroscopic results. Compound 2 exists as two isomers in solution in a ratio of 2:1 (2a:2b). VT 13C NMR spectra of 2a and 5 indicate that both complexes undergo similar fluxional processes of restricted equilibration of in-plane equatorial C60 and carbonyl ligands via a triply bridged intermediate with identical values of ΔGc⧧ = 12.7 ± 0.1 kcal/mol. Thermolysis of 2 in refluxing chlorobenzene affords Os3(CO)9(μ3-η2,η2,η2-C60) (6) in 23% yield, which can be alternatively prepared in 32% yield from the reaction of Os3(CO)10(NCMe)2 (2 equiv) and C60 (1 equiv). Decarbonylation of 6 with Me3NO/MeCN reagent in the presence of excess PMe3 gives Os3(CO)8(PMe3)(μ3-η2,η2,η2-C60) (7) in a quantitative yield. VT 13C NMR spectra of both 6 and 7 reveal a localized-3-fold rotation of carbonyl and phosphine ligands on each osmium center

Two Organometallic Fragments Inclusioned in a 1,3-Alternate Calix[4]arene Tetraphosphane: Evidence for Transition Metal−Arene Interaction through the Cavity

The preparation of an 1,3-alternate calix[4]arene tetraphosphane ligand, 25,26,27,28-tetrakis{2-(diphenylphosphino)ethoxy}calix[4]arene (4), is described. Ligand 4 is obtained in four steps in 17% overall yield. Reaction of 4 with AgBF4 produced the encapsulated two silver complex [Ag2{(P,P,P,P)-tetraphencalix[4]arene}](BF4)2. The solid-state structure shows that the encapsulated silver undergoes a substantial π-interaction by two opposite arene rings. Rhodation of 4 employing [Rh(cot)2]BF4 yielded the encapsulated complex with a bent coordination mode. Two organometallic fragments inclusioned inside a 1,3-alternate calix[4]arene tetraphosphane was also achieved by the reaction of 4 with [PtH(PPh3)2(thf)]+. Full characterization includes X-ray structural studies of compounds 4−6

Two Organometallic Fragments Inclusioned in a 1,3-Alternate Calix[4]arene Tetraphosphane: Evidence for Transition Metal−Arene Interaction through the Cavity

The preparation of an 1,3-alternate calix[4]arene tetraphosphane ligand, 25,26,27,28-tetrakis{2-(diphenylphosphino)ethoxy}calix[4]arene (4), is described. Ligand 4 is obtained in four steps in 17% overall yield. Reaction of 4 with AgBF4 produced the encapsulated two silver complex [Ag2{(P,P,P,P)-tetraphencalix[4]arene}](BF4)2. The solid-state structure shows that the encapsulated silver undergoes a substantial π-interaction by two opposite arene rings. Rhodation of 4 employing [Rh(cot)2]BF4 yielded the encapsulated complex with a bent coordination mode. Two organometallic fragments inclusioned inside a 1,3-alternate calix[4]arene tetraphosphane was also achieved by the reaction of 4 with [PtH(PPh3)2(thf)]+. Full characterization includes X-ray structural studies of compounds 4−6

Heterogeneous Binuclear Complexation of 1,3-Alternate Calix[4]-Bis<i>-</i>Crown Bearing Two Different Crown Rings

Heterogeneous Binuclear Complexation of 1,3-Alternate Calix[4]-Bis-Crown Bearing Two Different Crown Ring

Steric Influence on the Reactivity of Silyl-<i>o</i>-carboranes: Oxidative-Addition Reactions Involving Si−H and B−H Activation

The reactivity of mono(silyl)- and bis(silyl)-o-carboranes (HSiR2)n(C2B10H12-n) (n = 1, R = Me, 1a; n = 1, R = Et, 1b; n = 2, R = Me, 3a; n = 2, R = Et, 3b) toward six-coordinate iridium [(Cp*IrCl2)2] and nine-coordinate rhenium [ReH7(PPh3)2] complexes has been investigated. Reactions between the mono(silyl)-o-carboranes (1a,b) and (Cp*IrCl2)2 resulted in the formation of four-membered, cyclic seven-coordinate iridium complexes Cp*IrH2[η1:η1-(SiR2)BC2B9H10-Si,B] (R = Me, 2a; R = Et, 2b), where Si−H activation in the mono(silyl)-o-carborane (1) is accompanied by the concomitant B−H activation of a neighboring boron hydride. The X-ray structure of 2a reveals that the iridium center is coordinated to both silicon and boron in a four-legged piano-stool arrangement. In the reaction between the bis(silyl)-o-carboranes (3a,b) and (Cp*IrCl2)2, silylation occurs at both Si−H sites, giving rise to the complexes Cp*IrH2[η1:η1-(SiR2)2C2B10H10-Si,Si‘] (R = Me, 4a; R = Et, 4b), in which the metal center forms part of a five-membered metallacycle (Ir−Si−C−C−Si). Interestingly, the reaction of 3a with ReH7(PPh3)2 afforded the kinetically stabilized intermediate (PPh3)2ReH5[η1-SiMe2C2B10H10(SiMe2H)-Si] (8), in which only one of the Si−H groups is coordinated, as determined by X-ray crystallography

Steric Influence on the Reactivity of Silyl-<i>o</i>-carboranes: Oxidative-Addition Reactions Involving Si−H and B−H Activation

The reactivity of mono(silyl)- and bis(silyl)-o-carboranes (HSiR2)n(C2B10H12-n) (n = 1, R = Me, 1a; n = 1, R = Et, 1b; n = 2, R = Me, 3a; n = 2, R = Et, 3b) toward six-coordinate iridium [(Cp*IrCl2)2] and nine-coordinate rhenium [ReH7(PPh3)2] complexes has been investigated. Reactions between the mono(silyl)-o-carboranes (1a,b) and (Cp*IrCl2)2 resulted in the formation of four-membered, cyclic seven-coordinate iridium complexes Cp*IrH2[η1:η1-(SiR2)BC2B9H10-Si,B] (R = Me, 2a; R = Et, 2b), where Si−H activation in the mono(silyl)-o-carborane (1) is accompanied by the concomitant B−H activation of a neighboring boron hydride. The X-ray structure of 2a reveals that the iridium center is coordinated to both silicon and boron in a four-legged piano-stool arrangement. In the reaction between the bis(silyl)-o-carboranes (3a,b) and (Cp*IrCl2)2, silylation occurs at both Si−H sites, giving rise to the complexes Cp*IrH2[η1:η1-(SiR2)2C2B10H10-Si,Si‘] (R = Me, 4a; R = Et, 4b), in which the metal center forms part of a five-membered metallacycle (Ir−Si−C−C−Si). Interestingly, the reaction of 3a with ReH7(PPh3)2 afforded the kinetically stabilized intermediate (PPh3)2ReH5[η1-SiMe2C2B10H10(SiMe2H)-Si] (8), in which only one of the Si−H groups is coordinated, as determined by X-ray crystallography

Carborane-Based Optoelectronically Active Organic Molecules: Wide Band Gap Host Materials for Blue Phosphorescence

Carborane-based host materials were prepared to fabricate deep blue phosphorescence organic light-emitting diodes (PHOLEDs), which constituted three distinctive geometrical structures stemming from the corresponding three different isomeric forms of carboranes, namely, <i>ortho</i>-, <i>meta</i>-, and <i>para</i>-carboranes. These materials consist of two carbazolyl phenyl (CzPh) groups as photoactive units on each side of the carborane carbons to be bis­[4-(<i>N</i>-carbazolyl)­phenyl]­carboranes, <b><i>o</i>-Cb</b>, <b><i>m</i>-Cb</b>, and <b><i>p</i>-Cb</b>. To elaborate on the role of the carboranes, comparative analogous benzene series (<b><i>o</i>-Bz</b>, <b><i>m</i>-Bz</b>, and <b><i>p</i>-Bz</b>) were prepared, and their photophysical properties were compared to show that advantageous photophysical properties were originated from the carborane structures: high triplet energy. Unlike <b><i>m</i>-Bz</b> and <b><i>p</i>-Bz</b>, carborane-based <b><i>m</i>-Cb</b> and <b><i>p</i>-Cb</b> showed an unconjugated nature between two CzPh units, which is essential for the blue phosphorescent materials. Also, the carborane hosts showed high glass transition temperatures (<i>T</i>_g) of 132 and 164 °C for <b><i>m</i>-Cb</b> and <b><i>p</i>-Cb</b>, respectively. Albeit <b><i>p</i>-Cb</b> exhibited slightly lower hole mobility when compared to <b><i>p</i>-Bz</b>, it still lies at the high end hole mobility with a value of 1.1 × 10^–3 cm²/(V s) at an electric field of 5 × 10⁵ V/cm. Density functional theory (DFT) calculations revealed that triplet wave functions were effectively confined and mostly located at either side of the carbazolyl units for <b><i>m</i>-Cb</b> and <b><i>p</i>-Cb</b>. Low-temperature PL spectra indeed provided unequivocal data with higher triplet energy (<i>T</i>₁) of 3.1 eV for both <b><i>m</i>-Cb</b> and <b><i>p</i>-Cb</b>. <b><i>p</i>-Cb</b> was successfully used as a host in deep blue PHOLEDs to provide a high external quantum efficiency of 15.3% and commission internationale de l’elcairage (CIE) coordinates of (0.15, 0.24)