Bonding in Diborane–Metal Complexes: A Quantum‐Chemical and Experimental Study of Complexes Featuring Early and Late Transition Metals

The coordination chemistry of the doubly base‐stabilised diborane(4), [HB(hpp)]₂ (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido‐[1,2‐a]pyrimidinate), was extended by the synthesis of new late transition‐metal complexes containing Cu^I and Rh^I fragments. A detailed experimental study was conducted and quantum‐chemical calculations on the metal–ligand bonding interactions for [HB(hpp)]₂ complexes of Group 6, 9, 11 and 12 metals revealed the dominant B? H? M interactions in the case of early transition‐metal fragments, whereas the B? B? M bonding prevails in the case of the late d‐block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]₂ and model reactions between [B₂H₄ ? 2NMe₃] and [Rh(μ‐Cl)(C₂H₄)₂] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B? B bond. However, the formation of σ‐complexes is thermodynamically favoured. The results point to the selective B? H or B? B bond‐activation of diborane compounds by complexation, depending on the chosen transition‐metal fragment.     

Factors Controlling β‐Elimination Reactions in Group 10 Metal Complexes

Trends in reactivity of β‐chloride and β‐hydride elimination reactions involving Group 10 transition‐metal complexes have been computationally explored and analyzed in detail by DFT. These reactions do not require the initial formation of a vacant coordination site; they proceed concertedly without a prior ligand‐dissociation step. Whereas β‐chloride elimination is associated with relatively moderate activation barriers, the high barriers calculated for analogous β‐hydride eliminations suggest that the latter process is unfeasible for this type of compounds. This differential behavior is analyzed within the activation strain model, which provides quantitative insight into the physical factors controlling these β‐elimination reactions. The effects of the nature of the Group 10 transition metal (Ni, Pd, Pt), as well as the substituents attached to the β‐eliminating fragment (R₂C?CR₂X; R, X=H, Cl) on the transformation have also been considered and are rationalized herein.     

Selective Reduction of CO2 to a Formate Equivalent with Heterobimetallic Gold‐ ‐ ‐Copper Hydride Complexes

A series of heterobimetallic complexes containing three‐center, two‐electron Au−H−Cu bonds have been prepared from addition of a parent gold hydride to a bent d¹⁰ copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu−H−Cu and M−H−M⁺ moieties (M=Cu, Ag). The well‐defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO₂ into HCO₂Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric Group 11 complexes.     

Hetero‐ and homo‐leptic Ru(II) catalyzed synthesis of cyclic carbonates from CO2; Synthesis,spectroscopic characterization and electrochemical properties

Based on the a ligand BDPPZ [(9a,13a‐dihydro‐4,5,9,14‐tetraaza‐benzo[b]triphenylene‐11‐yl)‐phenyl‐methanone] (1) and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes, [Ru(bpy)₂L](PF₆)₂ (2), [Ru(phen)₂L](PF₆)₂ (3), [Ru(dafo)₂L](PF₆)₂ (4), [Ru(dcbpy)₂L](PF₆)₂ (5) and [RuL₃](PF₆)₂ (6) (where, L = ligand, bpy = 2,2′‐bipyridine, phen = 1,10‐phenantroline, dafo = 4,5‐diazafluoren‐9‐one and dcbpy = 3,3′‐dicarboxy‐2,2′‐bipyridine), have been synthesized and characterized by elemental analysis, UV–vis, FT‐IR, ¹H and ¹³C‐NMR spectra (for ligand), molar conductivity measurements and X‐ray powder techniques. The electrochemical parameters of the substituted ligand and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes are reported by cyclic voltammetry. UV–vis spectroscopy is used to compare the differences between the conjugated π systems in this ligand and its Ru(II) metal complexes. The polypyridyl hetero‐ and homoleptic Ru(II) metal complexes also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [Ru(L)₃](PF₆)₂ (6) complex is more efficient than the other Ru(II) complexes for the formation of cyclic organic carbonates from carbon dioxide. Copyright © 2010 John Wiley & Sons, Ltd.     

Homoleptic Tetrakis(silyl) Complexes of Pd0 and Pt0 Featuring Metal‐Centred Heterocubane Structures: Evidence for the Existence of the Corresponding Mononuclear PdI and PtI Complexes

We report on the first homoleptic tetrakis(silyl) complexes of zerovalent Group 10 metals. The compounds [MLi₄{Si(3,5‐Me₂pz)₃}₄] (M=Pd and Pt; 3,5‐Me₂pz=3,5‐dimethylpyrazolyl) exhibit very appealing metal‐centred heterocubane structures with the central d¹⁰ metal atoms surrounded by four silicon and four lithium atoms. Both compounds were characterised in detail, including X‐ray crystal‐structure analysis and 2D NMR spectroscopic methods such as ⁷Li,²⁹Si and ⁷Li,¹⁹⁵Pt HMQC. Cyclic voltammetry studies, in combination with density functional theory (DFT) calculations, revealed that the corresponding mononuclear cationic d⁹‐M^I and dicationic d⁸‐M^II complexes are accessible by stepwise one‐electron oxidation of the title compounds. Electron paramagnetic resonance (EPR) investigations provided evidence for the existence of the corresponding paramagnetic palladium(I) and platinum(I) complexes.     

Magnesium(II) Complexes with High Emission: The Distinct Charge‐Transfer Process from Transition Metal

Generally, the first‐row transition‐metal complexes are notorious in luminescence materials because of their metal‐ligand charge transfer in emission process. Herein, we rationally used magnesium instead the first‐row transition metal to coordinate with 2‐(anthracen‐9‐yl)‐1H‐imidazo[4,5‐f][1,10]phenanthroline (AIP) in the construction of luminescent complexes. Further investigation revealed AIP could work as detector for quantitative determination of Mg²⁺ cation. Comparing to other divalent cations, this fluorescence sensor exhibited high selectivity for the quantitative determination of Mg²⁺ with the low limit of detection (5 × 10^–7 m ). Through X‐ray single crystal diffraction, the crystal structures of [Mg(AIP₂)(NO₃)₂ · (H₂O)₄] ( 1 ), [Mn(AIP)(NO₃) · EtOH] ( 2 ), and [Co₂(AIP)₂Cl₄ · (MeOH)₂] ( 3 ) were observed in various arrangements. The theory calculations based on crystal structures indicated the Mg^II complex undergoes distinct charge‐transfer process from other transition‐metals based compounds, in which charge‐transfer excited‐state lifetimes were deactivated rapidly through metal‐to‐ligand charge‐transfer (MLCT) process. This study provided insight into construction of luminescence compounds by using d⁰ metals in main groups instead of transition metals.     

Exploring Coordination Modes: Late Transition Metal Complexes with a Methylene‐bridged Macrocyclic Tetra‐NHC Ligand

A tetranuclear silver(I) N‐heterocyclic carbene (NHC) complex bearing a macrocyclic, exclusively methylene‐bridged, tetracarbene ligand was synthesized and employed as transmetalation agent for the synthesis of nickel(II), palladium(II), platinum(II), and gold(I) derivatives. The transition metal complexes exhibit different coordination geometries, the coinage metals being bound in a linear fashion forming molecular box‐type complexes, whereas the group 10 metals adapt an almost ideal square planar coordination geometry within the ligand's cavity, resulting in saddle‐shaped complexes. Both the Ag^I and the Au^I complexes show ligand‐induced metal–metal contacts, causing photoluminescence in the blue region for the gold complex. Distinct metal‐dependent differences of the coordination behavior between the group 10 transition metals were elucidated by low‐temperature NMR spectroscopy and DFT calculations.     

Filling a Gap: The Coordinatively Saturated Group 4 Carbonyl Complexes TM(CO)8 (TM=Zr,Hf) and Ti(CO)7

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight-coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six-coordinate Ti(CO)₆⁺ and seven-coordinate Ti(CO)₇. Titanium octacarbonyl Ti(CO)₈ is unstable as a result of steric repulsion between the CO ligands. The 20-electron Zr(CO)₈ and Hf(CO)₈ complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18-electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)₈ and Hf(CO)₈ are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)₇ and Hf(CO)₇. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable.     

Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ²‐N(PPh₂(BH₃))₂}Li(THF)₂] ( 2 ) and [{κ³‐N(PPh₂(BH₃))₂}₂M(THF)₂] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH₃ group in κ²‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ³‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described.     

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis,Structure, Reactivity,and Cytotoxicity

Cobaltocenium carboxylate is an unusual betaine that functions as a formally neutral carboxylate ligand with late transition metal centers comprising Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Rh⁺. Structurally, a rich coordination chemistry is observed – from simple monomeric homoleptic complexes to heteroleptic dimeric, trimeric, and polymeric compounds, as shown by X‐ray diffraction of 11 compounds. Chemically, thermal decarboxylation was investigated aiming at the formation of cobaltocenium‐carbene transition metal complexes, in analogy to such chemistry of imidazolium carboxylate betaines. Cytotoxicity studies of cobaltocenium carboxylate transition metal complexes were performed to evaluate the medicinal bioorganometallic potential of these compounds. While cobaltocenium carboxylate was inactive, its complexes with Ag⁺, Cd²⁺, and Hg²⁺ triggered significant cytotoxic effects.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

Structure and Isotope Effects of the β‐H Agostic (α‐Diimine)Nickel Cation as a Polymerization Intermediate

Single‐crystal X‐ray characterization of cationic (α‐diimine)Ni‐ethyl and isopropyl β‐agostic complexes, which are key intermediates in olefin polymerization and oligomerization, are presented. The sharp Ni‐C_α‐C_β angles (75.0(3)° and 74.57(18)°) and short C_α−C_β distances (1.468(7) and 1.487(5) Å) provide unambiguous evidence for a β‐agostic interaction. An inverse equilibrium isotope effect (EIE) for ligand coordination upon cleavage of the agostic bond highlights the weaker bond strength of Ni−H relative to the C−H bond. An Eyring plot for β‐hydride elimination–olefin rotation–reinsertion is constructed from variable‐temperature NMR spectra with ¹³C‐labeled agostic complexes. The enthalpy of activation (ΔH ^≠) for β‐H elimination is 13.2 kcal mol⁻¹. These results offer important mechanistic insight into two critical steps in polymerization: ligand association upon cleavage of the β‐agostic bonds and chain‐migration via β‐H elimination.     

Transition‐metal compatibilization of poly(4‐bromostyrene) and polybutadiene via palladium(0) catalyzed reactions

Immiscible blends of 1,2‐polybutadiene and poly(4‐bromostyrene) can be compatibilized by rather low concentrations of Pd⁽⁰⁾[P(C₆H₅)₃]₄ at ambient temperature and 60 °C under argon. Two distinct glass‐transition temperatures merge into a single glass‐transition temperature at high enough concentrations of Pd⁽⁰⁾ (i.e., 2 or 3 mol %). Compatibilization does not occur if Pd⁽⁰⁾ is absent, triphenylphosphine is added without Pd⁽⁰⁾, or polystyrene is not functionalized. The methodology described herein is also useful for inducing melting‐point depression of 2,7‐dibromofluorene in ternary complexes with 1,2‐polybutadiene and Pd⁽⁰⁾. A 72/28 complex of poly(4‐bromostyrene) and 1,2‐polybutadiene with 5.5 mol % Pd⁽⁰⁾ exhibits a reinforced rubbery response with a modulus of 1.2 × 10⁷ N/m², a fracture strain of 235%, and a single glass‐transition temperature. Mechanical properties of these compatibilized ternary systems compare well with those of styrene–butadiene block copolymers, particularly above 100% strain. A five‐step mechanism that includes oxidative addition, olefin coordination, migratory insertion, β‐hydride elimination, and reductive elimination in the coordination sphere of the transition metal is proposed to illustrate how either poly(4‐bromostyrene) or 2,7‐dibromofluorene is linked covalently to alkene side groups in the diene polymer via the Heck reaction. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 677–688, 2001     

Remarkable Tuning of the Coordination and Photophysical Properties of Lanthanide Ions in a Series of Tetrazole‐Based Complexes

A series of seven new tetrazole‐based ligands (L1, L3–L8) containing terpyridine or bipyridine chromophores suited to the formation of luminescent complexes of lanthanides have been synthesized. All ligands were prepared from the respective carbonitriles by thermal cycloaddition of sodium azide. The crystal structures of the homoleptic terpyridine–tetrazolate complexes [Ln(Li)₂]NHEt₃ (Ln=Nd, Eu, Tb for i=1, 2; Ln=Eu for i=3, 4) and of the monoaquo bypyridine–tetrazolate complex [Eu(H₂O)(L7)₂]NHEt₃ were determined. The tetradentate bipyridine–tetrazolate ligand forms nonhelical complexes that can contain a water molecule coordinated to the metal. Conversely, the pentadentate terpyridine–tetrazolate ligands wrap around the metal, thereby preventing solvent coordination and forming chiral double‐helical complexes similarly to the analogue terpyridine–carboxylate. Proton NMR spectroscopy studies show that the solid‐state structures of these complexes are retained in solution and indicate the kinetic stability of the hydrophobic complexes of terpyridine–tetrazolates. UV spectroscopy results suggest that terpyridine–tetrazolate complexes have a similar stability to their carboxylate analogues, which is sufficient for their isolation in aerobic conditions. The replacement of the carboxylate group with tetrazolate extends the absorption window of the corresponding terpyridine‐ (≈20 nm) and bipyridine‐based (25 nm) complexes towards the visible region (up to 440 nm). Moreover, the substitution of the terpyridine–tetrazolate system with different groups in the ligand series L3–L6 has a very important effect on both absorption spectra and luminescence efficiency of their lanthanide complexes. The tetrazole‐based ligands L1 and L3–L8 sensitize efficiently the luminescent emission of lanthanide ions in the visible and near‐IR regions with quantum yields ranging from 5 to 53 % for Eu^III complexes, 6 to 35 % for Tb^III complexes, and 0.1 to 0.3 % for Nd^III complexes, which is among the highest reported for a neodymium complex. The luminescence efficiency could be related to the energy of the ligand triplet states, which are strongly correlated to the ligand structures.     

Chemistry of Guanidinate‐Stabilised Diboranes: Transition‐Metal‐Catalysed Dehydrocoupling and Hydride Abstraction

Herein, we analyse the catalytic boron–boron dehydrocoupling reaction that leads from the base‐stabilised diborane(6) [H₂B(hpp)]₂ (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate) to the base‐stabilised diborane(4) [H₂B(hpp)]₂. A number of potential transition‐metal precatalysts was studied, including transition‐metal complexes of the product diborane(4). The synthesis and structural characterisation of two further examples of such complexes is presented. The best results for the dehydrocoupling reactions were obtained with precatalysts of Group 9 metals in the oxidation state of +I. The active catalyst is formed in situ through a multistep process that involves reduction of the precatalyst by the substrate [H₂B(hpp)]₂, and mechanistic investigations indicate that both heterogeneous and (slower) homogeneous reaction pathways play a role in the dehydrocoupling reaction. In addition, hydride abstraction from [H₂B(hpp)]₂ and related diboranes is analysed and the possibility for subsequent deprotonation is discussed by probing the protic character of the cationic boron–hydrogen compounds with NMR spectroscopic analysis.     

Polybismuthide Anions as Ligands: The Homoleptic Complex [(Bi7)Cd(Bi7)]4− and the Ternary Cluster [(Bi6)Zn3(TlBi5)]4−

We present the results from a reactivity study of the binary anion (TlBi₃)^2? towards Group 12 metal compounds MPh₂ (M=Zn, Cd, Hg) to gain access to coordination compounds of polycyclic polypnictide molecules such as Bi₇^3? or Bi₁₁^3?. The coordination chemistry of these polybismuthide cages has been unprecedented to date, while it has been known for a long time for the lighter Group 15 anions Pn₇^3? (Pn=P, As, Sb). The use of (TlBi₃)^2?, previously shown to release Tl under certain conditions in situ, resulted in the formation of the first heterometallic polyanion in which a nortricyclane‐type polybismuthide coordinates a transition‐metal atom, [(Bi₇)Cd(Bi₇)]^4?. Reactions with the lighter Group 12 metal precursor yielded the uncommon ternary cluster [(Bi₆)Zn₃(TlBi₅)]^4?, most likely representing a reaction intermediate, and at the same time hinting at the formation of the nortricyclane‐shaped cage. Quantum‐chemical studies provide deeper insight into the stability trends of the [(E₇)M(E₇)]^4? anion family and reveal a complex bonding situation in [(Bi₆)Zn₃(TlBi₅)]^4?, which features both localized and multi‐center bonding.     

Insertion of Molecular Oxygen in Transition‐Metal Hydride Bonds,Oxygen‐Bond Activation,and Unimolecular Dissociation of Metal Hydroperoxide Intermediates. Short Communication

Thermal activation of molecular oxygen is observed for the late‐transition‐metal cationic complexes [M(H)(OH)]⁺ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal? hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H₂O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O‐atoms of the neutrals expelled originate almost exclusively from the substrate O₂. In comparison to the [M(H)(OH)]⁺ cations, the ion? molecule reactions of the metal hydride systems [MH]⁺ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H₂O)]⁺ (M=Fe, Co, Ni), the reaction with O₂ involving O? O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]⁺/O₂ couple.     

A Simple Homoleptic Gallium(I) Olefin Complex: Mimicking Transition‐Metal Chemistry at a Main‐Group Metal?

The earth‐metal olefin complex [Ga ^I (COD)₂]⁺[Al(OR^F)₄]^? (COD=1,5‐cyclooctadiene; R^F=C(CF₃)₃) constitutes the first homoleptic olefin complex of any main‐group metal accessible as a bulk compound. It is straight forward to prepare in good yield and constitutes an olefin complex of a main‐group metal that—similar to many transition‐metals—may adopt the +1 and +3 oxidation states opening potential applications. Crystallographic‐, vibrational‐ and computational investigations give an insight to the atypical bonding between an olefin and a main‐group metal. They are compared to classical transition‐metal relatives.     

Coordination chemistry of neutral quinolyl- and aminophenylcyclopentadiene derivatives

The cyclopentadiene and indene derivatives 1–4 being functionalised by a dimethylaniline and quinolyl group, respectively, were treated with metal carbonyl complexes. Whereas cyclopentadienes (C₅R₅H) normally loose one hydrogen atom prior or during metal complex formation, leading to negatively charged cyclopentadienide ligands, the compounds 1–4 are able to act as neutral ligands without hydrogen loss. Consequently transition metal complexes with coordination of the nitrogen donor and a CC double bond of the five membered ring have been obtained. In some cases a hydrogen atom is eliminated and the expected η⁵-(C₅R₅) complexes are formed. Reaction of Ru₃(CO)₁₂ with 2 leads to the binuclear η⁶-fulvene complex 8. The octahedral molybdenum complex 9 and the square planar rhodium(I) complexes 10 and 11 which were obtained from Mo(CO)₆ and [Rh(CO)₂Cl]₂, respectively, are rare examples of η²-(C₅R₅H) coordination to metal atoms.     

Exohedral Complexation of B40, C60 and Arenes with Transition Metals: A Comparative DFT Study

Holes are inevitable in borospherenes. The surface topography of B₄₀ and its π MOs isolobal to benzene allow for better η⁷‐, η⁶‐ and η³‐ exohedral complexation with transition metal fragments than it is possible with C₆₀ and arenes. η⁷‐complexes of B₄₀ is lower in energy than the η⁶‐complexes for metal fragments such as C₅H₅Mn, C₄H₄Fe, and C₃H₃Co that have relatively diffuse frontier orbitals. The fragment C₆H₆Cr prefers η⁶‐coordination. Near‐isodesmic equations based on density functional theory computations of the transition metal complexes of B₄₀, C₆₀ and C₆H₆ support these anticipations. Transition metal complexation increases the stability of B₄₀.