Kerstin Freitag

The Reactivity of [Zn2Cp*2]: Trapping Monovalent {.ZnZnCp*} in the Metal‐Rich Compounds [(Pd,Pt)(GaCp*)a(ZnCp*)4−a(ZnZnCp*)4−a] (a=0, 2)

Carmona s synthesis of [Zn2Cp*2] (Cp* = pentamethylcyclopentadienyl), the first molecular compound exhibiting a covalent Zn Zn bond, has generated much interest and stimulated research on low-coordinate (main-group) metal compounds. Other derivatives with the formula [M2L2], such as [Zn2{HC(CMeNAr)2}2] (Ar = 2,6-iPr2C6H3) or [Zn2Ar2] (Ar = 2,6-(2,6-iPr2C6H3)2C6H3) were subsequently obtained, and even magnesium analogues, such as [Mg2(DippNacnac)2] (DippNacnac = [(2,6-iPr2C6H3)N= CMe]2CH) have been reported. [4–7] Notably, Robinson s concept of using N-heterocyclic carbenes (NHCs) as neutral, soft, and very bulky ligands for stabilizing unusual bonding states, for example, [LDE=EDL] (E = Si, Ge; LD=DC[N(2,6-iPr2C6H3)CH]2) relates to this progress. [8] The quite well-developed coordination chemistry of the carbenoid Group 13 metal analogues of NHC ligands, ER (E = Al, Ga, In; R = Cp* and other bulky substituents) to metal centers complements this progress. 10] Nevertheless, not much is known on the chemistry of the compounds [M2L2] in general, [6,8] and only very few reports have appeared for reactions of the zinc dimers in particular. 5, 7] For example, [Zn2Cp*2] should behave as a natural source for the monovalent species CZnCp*, which in essence contains Zn. In fact, only a few transition metal (TM) complexes with one-electron ligands CZnR are known (R = Cp*, CH3). Recently, we established an access to very zinc-rich, highly coordinated [TM(ZnR)n] compounds (TM: Group 6–10 element, n = 8–12) bridging the gap between complexes, clusters, and Hume-Rothery intermetallic phases, with the icosahedral [Mo(ZnCp*)3(ZnMe)9] as prototype of a novel family. [11,12] The formation reaction starts from mononuclear complexes [TM(GaCp*)m] (m = 4–6) and ZnR2 (R = Me, Et) and involves Ga/Zn and Cp*/R exchange processes. In the course of the reaction, Zn is reduced to Zn by Ga, which ends up as Ga and causes the overall substitution of one two-electron GaCp* ligand by two one-electron ZnR ligands at the TM center. If inert co-ligands at TM are present, other unusual and high nuclearity clusters, such as [Mo4(CO)12Zn6(ZnCp*)4], may be formed, which reveal close similarities to structural motifs of Mo/Zn intermetallic phases. Herein, we present the first results of our ongoing study on reactions of [Zn2Cp*2] with [LaTMb(GaCp)*c]. Most interestingly, we found the fragment {ZnZnCp*} with the intact covalent Zn Zn linkage being trapped as a one-electron ligand in the coordination sphere of a transition metal. Treatment of [Pd(GaCp*)4] with four equivalents of [Zn2Cp*2] in toluene at 95 8C over a period of 2 h leads to the quantitative formation of a mixture of the six-coordinate complex [Pd(GaCp*)2(ZnCp*)2(ZnZnCp*)2] (1) and the eight-coordinate complex [Pd(ZnCp*)4(ZnZnCp*)4] (2) in a molar ratio of 6:1, as revealed by in situ NMR spectroscopy (Scheme 1). Orange crystals of 1 and red needle-shaped crystals of 2 deposit from a saturated toluene solution at

The σ‐Aromatic Clusters [Zn3]+ and [Zn2Cu]: Embryonic Brass

The triangular clusters [Zn3Cp*3](+) and [Zn2CuCp*3] were obtained by addition of the in situ generated, electrophilic, and isolobal species [ZnCp*](+) and [CuCp*] to Carmonas compound, [Cp*Zn-ZnCp*], without splitting the ZnZn bond. The choice of non-coordinating fluoroaromatic solvents was crucial. The bonding situations of the all-hydrocarbon-ligand-protected clusters were investigated by quantum chemical calculations revealing a high degree of σ-aromaticity similar to the triatomic hydrogen ion [H3](+). The new species serve as molecular building units of Cu(n)Zn(m) nanobrass clusters as indicated by LIFDI mass spectrometry.

Homoleptic Hexa and Penta Gallylene Coordinated Complexes of Molybdenum and Rhodium

The reactions of molybdenum(0) and rhodium(I) olefin containing starting materials with the carbenoid group 13 metal ligator ligand GaR (R = Cp*, DDP; Cp* = pentamethylcyclopentadienyl, DDP = HC(CMeNC(6)H(3)-2,6-(i)Pr(2))(2)) were investigated and compared. Treatment of [Mo(η(4)-butadiene)(3)] with GaCp* under hydrogen atmosphere at 100 °C yields the homoleptic, hexa coordinated, and sterically crowded complex [Mo(GaCp*)(6)] (1) in good yields ≥50%. Compound 1 exhibits an unusual and high coordinated octahedral [MoGa(6)] core. Similarly, [Rh(GaCp*)(5)][CF(3)SO(3)] (2) and [Rh(GaCp*)(5)][BAr(F)] (3) (BAr(F) = B{C(6)H(3)(CF(3))(2)}(4)) are prepared by the reaction of GaCp* with the rhodium(I) compound [Rh(coe)(2)(CF(3)SO(3))](2) (coe = cyclooctene) and subsequent anion exchange in case of 3. Compound 2 features a trigonal bipyramidal [RhGa(5)] unit. In contrast, reaction of excess Ga(DDP) with [Rh(coe)(2)(CF(3)SO(3))](2) does not result in a high coordinated homoleptic complex but instead yields [(coe)(toluene)Rh{Ga(DDP)}(CF(3)SO(3))] (4). The common feature of 2 and 4 in the solid state structure is the presence of short CF(3)SO(2)O···Ga contacts involving the GaCp* or rather the Ga(DDP) ligand. Compounds 1, 2, and 4 have been fully characterized by single crystal X-ray diffraction, variable temperature (1)H and (13)C NMR spectroscopy, IR spectroscopy, mass spectrometry, as well as elemental analysis.

Oligonuclear Molecular Models of Intermetallic Phases: A Case Study on [Pd2Zn6Ga2(Cp*)5(CH3)3]

The synthesis, characterization, and theoretical investigation by means of quantum-chemical calculations of an oligonuclear metal-rich compound are presented. The reaction of homoleptic dinuclear palladium compound [Pd(2)(μ-GaCp*)(3)(GaCp*)(2)] with ZnMe(2) resulted in the formation of unprecedented ternary Pd/Ga/Zn compound [Pd(2)Zn(6)Ga(2)(Cp*)(5)(CH(3))(3)] (1), which was analyzed by (1)H and (13)C NMR spectroscopy, MS, elemental analysis, and single-crystal X-ray diffraction. Compound 1 consisted of two C(s)-symmetric molecular isomers, as revealed by NMR spectroscopy, at which distinct site-preferences related to the Ga and Zn positions were observed by quantum-chemical calculations. Structural characterization of compound 1 showed significantly different coordination environments for both palladium centers. Whilst one Pd atom sat in the central of a bi-capped trigonal prism, thereby resulting in a formal 18-valence electron fragment, {Pd(ZnMe)(2)(ZnCp*)(4)(GaMe)}, the other Pd atom occupied one capping unit, thereby resulting in a highly unsaturated 12-valence electron fragment, {Pd(GaCp*)}. The bonding situation, as determined by atoms-in-molecules analysis (AIM), NBO partial charges, and molecular orbital (MO) analysis, pointed out that significant Pd-Pd interactions had a large stake in the stabilization of this unusual molecule. The characterization and quantum-chemical calculations of compound 1 revealed distinct similarities to related M/Zn/Ga Hume-Rothery intermetallic solid-state compounds, such as Ga/Zn-exchange reactions, the site-preferences of the Zn/Ga positions, and direct M-M bonding, which contributes to the overall stability of the metal-rich compound.

Dizinc Cation [Zn2]2+ Trapped In A Homoleptic Metalloid Coordination Environment Stabilized by Dispersion Forces: [Zn2(GaCp*)6][BAr4F]2

The synthesis and characterization of the cationic mixed metal Ga/Zn cluster [Zn2(GaCp*)6](2+) (1) is presented. The reaction of [Zn2Cp*2] with [Ga2Cp*][BAr4(F)] leads to the formation of the novel complex being the first example of a [Zn2](2+) core exclusively ligated by metalloid group-13 organyl-ligands. Compound 1 exhibits two different coordination modes: In the solid state, two of the six GaCp* ligands occupy bridging positions, whereas VT (1)H NMR indicates the coexistence of a second isomer in solution featuring six terminal GaCp* ligands. Quantum chemical calculations have been carried out to assign the gallium and zinc positions; the bonding situation in 1 is characterized and the importance of dispersion forces is discussed.