Thomas Cadenbach

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).

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.

Methylgallium as a Terminal Ligand in [(Cp*Ga)4Rh(GaCH3)]+

As “exotic” ligands at transition-metal centers M, carbenoid Group 13 metal compounds ER (E=Al, Ga, In; R=bulky substituent: e.g. alkyl, aryl, C5Me5 (Cp*), bisketoiminates, amidinates, guanidinates) are attracting a great deal of attention because their properties can be compared with those of the related borylenes and N-heterocyclic carbenes (NHCs). In particular, complexes with ECp* ligands show interesting reactivity that is related to the soft binding properties and facile haptotropic shifts of the Cp* ring, which allows a modulation of the electrophilicity at the Group 13 center E. Accordingly, even selective protolysis of coordinated GaCp* is possible: the treatment of the complex [Pt(GaCp*)4] with [H(OEt2)2]BAr F 4 (Ar F = 3,5-(CF3)2C6H3) yields the dimer [Pt2H(Ga)(GaCp*)7] 2+ by elimination of Cp*H via the intermediate [GaCp*)4PtH] . By using the Ga transfer reagent [Ga2Cp*] , the [(GaCp*)4PtGa] + complex has been generated in which the bonding of naked Ga as a strong s/p-acceptor ligand without s-donor properties has been demonstrated. As part of our continuing work in this area, we set out to generate otherwise elusive GaR moieties by protolytic cleavage of Cp*H from coordinated Ga(R)Cp* groups. The choice of the R substituent for isolable and thus synthetically useful monovalent ER compounds is limited because of the inherent instability of E and its disproportionation into E and E. Methylgallium, for example, has to date only been studied by matrix studies at low temperatures. Very few complexes bearing ER ligands with sterically nondemanding groups R without p-donor/acceptor properties, such as the anion [{Fe(CO)4}2GaCH3] and the dimer [{Cp*IrAlEt}2], are known. [6,7] However, all these complexes feature the ER ligand in a bridging (tricoordinate) binding mode, which rules out direct comparisons with other dicoordinate (terminal) ER ligands. Analogously, the first terminal alkyl borylene complex, [Cp(CO2)MnBtBu], has been reported recently. The Mn BR (R= tBu) bond was described as weakly polar but with significant p-backbonding. The reaction of [Rh(CH3)(cod)(py)] with excess of GaCp* in hexane at room temperature leads to the substitution of the labile ligands pyridine (py) and 1,5-cyclooctadiene (cod), as well as to the insertion of the carbenoid GaCp* into the Rh CH3 s bond to give the all-Ga-coordinated neutral complex [(Cp*Ga)4Rh(h -Cp*GaCH3)] (1) in 89% yield (Scheme 1).

Structure and Bonding of Metal-Rich Coordination Compounds Containing Low Valent Ga(I) and Zn(I) Ligands

Recent developments in the field of metal-rich low valent metal complexes with gallium(I)/zinc(I) ligands and their structural features are reviewed together with related theoretical calculations. Some emphasis is given to sterically encumbering NHC analogous ligands as well as the naked ions E+. The chemistry of organo Zn(I) ligands at transition metals is reviewed in the light of the recently discovered synthetic approach via suitable organo Ga(I) complexes as starting materials.

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.

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.

The reaction of RhCp*(CH3)2 (L)(L = pyridine, dmso) with GaCp* and AlCp*: A new type of carbon–carbon bond activation reaction

Reaction of RhCp*(L)(CH(3))(2)(L = pyridine, dmso) with equimolar amounts of GaCp* at 60 degrees C quantitatively leads to the zwitterionic species [Cp*Rh(CpMe(4)GaMe(3))]. [Cp*Rh(CH(3))(2)(GaCp*)] could be isolated and identified as an intermediate in this reaction.

Accessing low denticity coordination modes of a high denticity tripodal ligand to complete its coordinative repertoire

New coordination complexes of the neutral tripodal tetra-amine Me(6)TREN with tBu(3)Ga or tBu(2)Zn have been synthesised and studied with their molecular structures revealing, for the first time, coordination to metal centres via an η(1) or η(2) mode, adding to previously reported η(3) and η(4) ligated examples.

Structural and magnetic diversity in alkali-metal Manganate chemistry: evaluating donor and alkali-metal effects in co-complexation processes

By exploring co-complexation reactions between the manganese alkyl Mn(CH2SiMe3)2 and the heavier alkali-metal alkyls M(CH2SiMe3) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4-dioxane, and 1,4-diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali-metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X-ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA)2 MMn(CH2SiMe3)3] (M=Na, 3; M=K, 4) to dimers [{KMn(CH2SiMe3)3 ⋅C6 H6}2] (2) and [{NaMn(CH2SiMe3)3}2 (dioxane)7] (5); and to more complex supramolecular networks [{NaMn(CH2SiMe3)3}∞] (1) and [{Na2Mn2 (CH2SiMe3)6 (DABCO)2}∞] (7)). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4-dioxane, as 1 produces coordination adduct 5, while 2 forms heteroleptic [{(dioxane)6K2Mn2 (CH2SiMe3)4(O(CH2)2OCH=CH2)2}∞] (6) containing two alkoxide-vinyl anions resulting from α-metalation and ring opening of dioxane. Compounds 6 and 7, containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways.

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.