Timo Bollermann

Twelve One‐Electron Ligands Coordinating One Metal Center: Structure and Bonding of [Mo(ZnCH3)9(ZnCp*)3]

The highest coordination number for metal complexes of monodentate ligands has been nine since the days of Alfred Werner. [1] The term “complex” refers to a molecule [MLm] that features a central metal atom M that bonds to ligator atoms E of ligands L by donor–acceptor interactions to yield a core structure MEn. [2] Metal atoms can also become captured inside an electron-precise cage En. These compounds obey the Wade–Mingos rules and are referred to as endohedral clusters M@En, typically with n> 9. Examples for the latter are the recently synthesized [M@Pb10] 2 and [M@Pb12] 2 (M=Ni, Pd, Pt). Herein we describe the synthesis of an unprecedented molecule containing a MoZn12 core, which offers a novel linkage between coordination compounds and cluster molecules (Figure 1). At first glance, the icosahedral structure of the title molecule [MoZn12Me9Cp*3] (1; Me=CH3, Cp*=C5Me5) is reminiscent of the endohedral clusters described above. The actual bonding situation is, however, intriguingly different. Quantum chemical analysis revealed a unique situation best described as a perfectly sd-hybridized molybdenum atom that engages in six Mo Zn two-electron-three-center bonds. There are six high-lying valence molecular orbitals (MOs) occupied by 12 electrons that can clearly be identified as Mo Zn bonding. Another six electrons are delocalized over the Zn cage, evoking only weak Zn Zn interactions (Figures 2 and 3). Before discussing these aspects in detail, we briefly report the synthesis and the analytical and structural properties of 1. The title compound [MoZn12Me9Cp*3] (1) was reproducibly obtained in 82% yield by the treatment of [Mo(GaCp*)6] (2) with 14 equivalents of ZnMe2 in toluene at 110 8C over a period of 2 h. Two mixed Ga–Zn compounds [MoZn4Ga4Me4Cp*4] (3) and [MoZn8Ga2Me6Cp*4] (4) are intermediates of this reaction and were isolated in nearly quantitative yields using 4 and 8 equivalents of ZnMe2 (Scheme 1).

Cyclopentadiene based low-valent group 13 metal compounds: ligands in coordination chemistry and link between metal rich molecules and intermetallic materials.

Ligands in Coordination Chemistry and Link between Metal Rich Molecules and Intermetallic Materials Sandra Gonzaĺez-Gallardo,† Timo Bollermann,‡ Roland A. Fischer,*,‡ and Ramaswamy Murugavel* †Karlsruhe Institute of Technology (KIT), Institute of Inorganic Chemistry, 76131 Karlsruhe, Germany ‡Lehrstuhl für Anorganische Chemie II, Organometallics & Materials Chemistry, Ruhr-University Bochum, D-44780 Bochum, Germany Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai−400076, India

Molecular Alloys, Linking Organometallics with Intermetallic Hume-Rothery Phases: The Highly Coordinated Transition Metal Compounds [M(ZnR)n] (n ≥ 8) Containing Organo-Zinc Ligands

This paper presents the preparation, characterization and bonding analyses of the closed shell 18 electron compounds [M(ZnR)(n)] (M = Mo, Ru, Rh, Ni, Pd, Pt, n = 8-12), which feature covalent bonds between n one-electron organo-zinc ligands ZnR (R = Me, Et, eta(5)-C(5)(CH(3))(5) = Cp*) and the central metal M. The compounds were obtained in high isolated yields (>80%) by treatment of appropriate GaCp* containing transition metal precursors 13-18, namely [Mo(GaCp*)(6)], [Ru(2)(Ga)(GaCp*)(7)(H)(3)] or [Ru(GaCp*)(6)(Cl)(2)], [(Cp*Ga)(4)RhGa(eta(1)-Cp*)Me] and [M(GaCp*)(4)] (M = Ni, Pd, Pt) with ZnMe(2) or ZnEt(2) in toluene solution at elevated temperatures of 80-110 degrees C within a few hours of reaction time. Analytical characterization was done by elemental analyses (C, H, Zn, Ga), (1)H and (13)C NMR spectroscopy. The molecular structures were determined by single crystal X-ray diffraction. The coordination environment of the central metal M and the M-Zn and Zn-Zn distances mimic the situation in known solid state M/Zn Hume-Rothery phases. DFT calculations at the RI-BP86/def2-TZVPP and BP86/TZ2P+ levels of theory, AIM and EDA analyses were done with [M(ZnH)(n)] (M = Mo, Ru, Rh, Pd; n = 12, 10, 9, 8) as models of the homologous series. The results reveal that the molecules can be compared to 18 electron gold clusters of the type M@Au(n), that is, W@Au(12), but are neither genuine coordination compounds nor interstitial cage clusters. The molecules are held together by strong radial M-Zn bonds. The tangential Zn-Zn interactions are generally very weak and the (ZnH)(n) cages are not stable without the central metal M.

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

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.

First Dinuclear Copper/Gallium Complexes: Supporting Cu0 and CuI Centres by Low‐Valent Organogallium Ligands

The synthesis and structural characterisation of low-valent dinuclear copper(I) and copper(0) complexes supported by organogallium ligands has been accomplished for the first time by the reductive coordination reaction of [GaCp*] (Cp*=pentamethylcyclopentadienyl) and [Ga(ddp)] (ddp=HC(CMeNC(6)H(3)-2,6-iPr(2))(2) 2-diisopropylphenylamino-4-diisopropylphenylimino-2-pentene) with readily available copper(II) and copper(I) precursors. The treatment of CuBr(2) and Cu(OTf)(2) (OTf=CF(3)SO(3)) with [Ga(ddp)] under mild conditions resulted in elimination of [Ga(L)(2)(ddp)] (L=Br, OTf) and afforded the novel gallium(I)/copper(I) compounds [{(ddp)GaCu(L)}(2)] (L=Br (1), OTf (2)). The single-crystal X-ray structure determinations of 1 and 2 reveal that these molecules are composed of {(ddp)GaCu(L)} dimeric units, with planar Cu(I)-Ga(I) four-membered rings and short Cu(I)...Cu(I) distances, with 2 exhibiting the shortest Cu(I)Cu(I) contact reported to date of 2.277(3) A. The all-gallium coordinated dinuclear [Cu(2)(GaCp*)(mu-GaCp*)(3)Ga(OTf)(3)] (3) is formed when Cu(OTf)(2) is combined with [GaCp*] instead of [Ga(ddp)]. Notably, in the course of this redox reaction Lewis acidic Ga(OTf)(3) is formed, which coordinates to one of the electron-rich copper(0) centres. Compound 3 is suggested as the first case of a structurally characterised complex of copper(0). By changing the copper(II) to a copper(I) source, that is, [Cu(cod)(2)][OTf] (cod=1,5-cyclooctadiene), the salt [Cu(2)(GaCp*)(3)(mu-GaCp*)(2)][OTf](2) (4) is formed, the cationic part of which is related to previously described isoelectronic dinuclear d(10) complexes of the type [M(2)(GaCp*)(5)] (M=Pd, Pt).

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.

Syntheses and crystal structures of ruthenium and rhodium olefin complexes containing GaCp.

The reactivity of olefin containing complexes of the d(8) metals Ru(0) and Rh(I) toward GaCp* and AlCp* is presented. [Ru(eta(4)-butadiene)(PPh(3))(3)] reacts with GaCp* to give the substitution product [Ru(eta(4)-butadiene)(PPh(3))(2)(GaCp*)] (1), which proved to be stable in the presence of GaCp* even under hydrogenolytic conditions. In contrast, the bis-styrene complex [Ru(PPh(3))(2)(styrene)(2)] undergoes full substitution of the olefin ligands to give [Ru(PPh(3))(2)(GaCp*)(3)] (2), whereas reaction of [Ru(eta(2),eta(2)-COD)(eta(6)-COT)] (COD = 1,5-cyclooctadiene, C(8)H(12), COT = 1,3,5-cyclooctatriene, C(8)H(10)) and GaCp* leads to [Ru(eta(2),eta(2)-COD)(GaCp*)(3)] (3) under mild hydrogenolytic conditions. Analogously, the Rh(I) compounds [{Rh(eta(2),eta(2)-NBD)(PCy(3))(2)}{BAr(F)}] (NBD = norbornadiene) and [{Rh(eta(2),eta(2)-COD)(2)}{BAr(F)}] ({BAr(F)}= B{[C(6)H(3)(CF(3))(2)](4)) yield the complexes [{Rh(eta(2),eta(2)-NBD)(PCy(3))(GaCp*)(2)}{BAr(F)}] (4), [{Rh(eta(2),eta(2)-COD)(GaCp*)(3)}{BAr(F)}] (5), and [{Rh(eta(2),eta(2)-COD)(AlCp*)(3)}{BAr(F)]}] (6) upon reaction with the appropriate ECp* ligand (E = Al, Ga). All new complexes have been characterized by means of (1)H and (13)C NMR spectroscopy and elemental analysis, as well as X-ray single crystal structure analysis in the case of 1-5.

Selective Oxidative Cleavage of Cp* from Coordinated GaCp*: Naked Ga+ in [GaNi(GaCp*)4]+ and [(μ2-Ga)nM3(GaCp*)6]n+ †

The coordination chemistry of monovalent compounds comprising a Group 13 element E and an organic group R at a metal center M offers a unique molecular access to novel compounds linking metal-rich complexes and clusters with the solid-state chemistry of metal alloys. In particular, the soft chemical synthesis of M–E Hume–Rothery phases (NiAl, NiGa, PtGa, CuAl, CuGa, etc.) as colloidal nanoparticles or as powders were achieved by using combinations [LnM] (L = hydrocarbon) and ER of precursors or by employing tailored single-source precursors with direct M E bonds. Similarly, a-,b-,g-Cu/Zn colloids, “nano-brass”, were obtained from [CpCuL] with ZnCp*2 as precursors (Cp = C5H5, Cp* = C5Me5). [3] Furthermore, Cp*–CH3 and Zn–Ga exchange reactions allow the formation of the unusual compounds [Mo(ZnMe)9(ZnCp*)3] and [(CO)16Mo4Zn6(ZnCp*)4] from [(CO)6 nMo(GaCp*)n] (n = 0, 2) and ZnMe2. Both Mo–Zn compounds represent molecular cut-outs of the solid-state structure of Mo–Zn intermetallics. The cleavage of the “protecting” Cp* group from transition-metal bound ECp* ligands is a pertinent aspect of this novel chemistry. For example, the selective protolysis of [Pt(GaCp*)4] by [H(OEt2)2](BAr F 4) yields [GaPt(GaCp*)4](BAr4) and [Pt2H(Ga)(GaCp*)7](BAr F 4)2 (BAr F 4 = B[3,5-(CF3)2C6H3]4). [5] Also, the hydrogenation of [Ru(cod)(cot)] (cod = 1,4-cyclooctadiene, cot = 1,3,5-cyclooctatriene) in the presence of GaCp* gives the highly fluxional diruthenium complex [Ru2(Ga)(GaCp*)7(H)3], featuring a linear Ru–Ga–Ru unit. Herein we now report a new and selective method for a facile cleavage of Ga–Cp* bonds. The treatment of [M(GaCp*)]4 (M = Ni, Pd, Pt) [7] with [Fe(C5H5)2](BAr F 4) leads to a surprisingly selective oxidative cleavage of the Cp* group leaving the oxidation state of Ga and M unchanged and yields the products shown in Scheme 1, Figure 1, and Figure 2. The cation [GaNi(GaCp*)4] + (1) was obtained as its BAr4 salt by treatment of [Ni(GaCp*)4] with an equimolar amount of [Fe(C5H5)2](BAr F 4) in fluorobenzene at 25 8C in reproducible yields (80 %), and characterised by H NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The H NMR spectrum shows two broad signals arising from the cation 1 indicating fluxional GaCp* ligands. In situ NMR experiment of the reaction mixture reveals one characteristic signal for decamethylfulvalene (Cp*2), while the other signals for this by-product are masked by broad peaks from GaCp*. No other side products were detected that would indicate either the oxidation of Ga or of the transitionmetal center. Also no Ga-F species were formed. This unexpected selectivity of the reaction for oxidative cleavage of the Cp* is quite surprising. Compound 1BAr4 crystallizes in the monoclinic space group P21/c. The cation 1 exhibits a slightly distorted trigonalbipyramidal structure with the Ga ligand in an axial position (Supporting Information, Figure S1), as in the homologous [GaPt(GaCp*)4] . The equatorial GaCp* ligands are bent towards the terminal Ga ligand (Ga1) and the Ga1-Ni-Ga(n) angles (n = 3, 4, 5) are closer to 808 than 908. The equatorial Ni Ga bond lengths average to 2.246 and are thus slightly longer than those of the parent complex [Ni(GaCp*)4] (average = 2.219 ). Interestingly, the Ga1 Ni bond length (2.361(1) ) is close to the value for the axial Cp*Ga Ni bond (2.320(1) ), both bonds being slightly elongated with respect to the equatorial ones. The bonding situation of substituent-free (“naked”), terminally coordinated Ga was elucidated in detail and can be described as a main-groupmetal equivalent of the proton H. Note that Ga exhibits Scheme 1. Reaction of [M(GaCp*)4] (M= Ni, Pt) with [Fe(C5H5)2](BAr4).

Reactions of cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ with GaCp*: novel gallium complexes of iron, cobalt, copper and silver

The reactions of the cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ (m = 2: M = Fe, Co and m = 1: M = Cu, Ag) with GaCp* were investigated. The reaction of [Fe(CH3CN)6][BArF]2 (BAr(F) = [B{C6H3(CF3)2}4) with GaCp* leads to [Cp*Fe(GaCp*)3][BAr(F)] (1) via a redox neutral Cp* transfer and [Ga2Cp*][BAr(F)] as a by-product while the formation of [Cp*Co(GaCp*)3][BAr(F)]2 (2) from [Co(CH3CN)6][BAr(F)]2 is accompanied by oxidation of Co(II) to Co(III) with GaCp* as the oxidant. The reactions of [Cu(CH3CN)4][BAr(F)] and Ag[BPh4] with GaCp* lead to the formation of the homoleptic compounds [Cu(GaCp*)4][BAr(F)] (4) and [Ag(GaCp*)4][BPh4] (5), while treatment of Ag[CF3SO3] with GaCp* leads to the dimeric complex [Ag2(GaCp*)3(micro-GaCp*)2][CF3SO3]2 (6). All compounds were characterized by NMR spectroscopy, single crystal X-ray diffraction and elemental analysis.