Triple-decker transition metal complexes bridged by a single carbocyclic ring

Triple-decker complexes incorporating three distinct deck architectures

The reactivity of the dilithioplumbole ([Li₂(thf)₂(μ,η⁵-L^Pb)], L^Pb = 1,4-bis-tert-butyl-dimethylsilyl-2,3-bis-phenyl-plumbolyl) towards the reactive pnictogen precursors P₄, pentaphosphaferrocene, and pentaarsaferrocene ([Cp*Fe(η⁵-E₅)] (Cp* = η⁵-C₅Me₅, E = P, As)) is reported. The reaction with P₄ afforded a phospholyl lithium complex, via lead-phosphorus exchange, while the reactions with [Cp*Fe(η⁵-E₅)] yielded the first examples of Pb-Fe-Li heterotrimetallic triple-decker polypnictogenides with three different deck motifs.

The Archetypal Homoleptic Lanthanide Quadruple-Decker-Synthesis, Mechanistic Studies, and Quantum Chemical Investigations

Reduction of [SmIII (COT1,4-SiiPr3 )(BH4 )(thf)] (COT1,4-SiiPr3 =1,4-(i Pr3 Si)3 C8 H6 ) with KC8 resulted in [SmIII/II/III (COT1,4-SiiPr3 )4 ], the first example of a homoleptic lanthanide quadruple-decker. As indicated by an analysis of the bond metrics in the solid-state, the inner Sm ion is present in the divalent oxidation state, while the outer ones are trivalent. This observation could be confirmed by quantum chemical calculations. Mechanistic studies revealed not only insight into possible formation pathways of [SmIII/II/III (COT1,4-SiiPr3 )4 ] but also resulted in the transformation to other mixed metal sandwich complexes with unique structural properties. These are the 1D-polymeric chain structured [KSmIII (COT1,4-SiiPr3 )]n and the hexametallic species [(tol)K(COT1,4-SiiPr3 )SmII (COT1,4-SiiPr3 )K]2 which were initially envisioned as possible building blocks as part of different retrosynthetically guided pathways that we developed.

Triple-Decker Sandwich Complexes of Tungsten with Planar and Puckered Middle Decks

A triple-decker complex of tungsten, [(Cp*W)₂{μ-η⁶:η⁶-B₄H₄Co₂(CO)₅}(H)₂] (1; Cp* = η⁵-C₅Me₅), with a planar middle deck has been isolated by thermolysis of an in situ formed intermediate from the reaction of Cp*WCl₄ and LiBH₄ with Co₂(CO)₈. In addition, we have also isolated another triple-decker complex, [(Cp*W)₂{μ-η⁶:η⁶-B₅H₅Fe(CO)₃}(H)₂] (4), having a puckered central ring, from a similar reaction with Fe₂(CO)₉. Clusters 1 and 4 are unprecedented examples of a triple-decker complex having a 24-valence electron with bridging hydrogen atoms.

Zirconium arene triple-decker sandwich complexes: synthesis, electronic structure and bonding

Reduction of a permethylpentalene zirconium(iv) chloride complex [η⁸-Pn*Zr(μ-Cl)_3/2]₂(μ-Cl)₂Li·THF_x with KC₈ in benzene results in activation of the aromatic solvent to yield an "inverted sandwich" complex, [η⁸-Pn*Zr]₂(μ-η⁶:η⁶-C₆H₆) (1). The reactions in toluene, cumene, o-xylene and m-xylene also yield analogous solvent activated triple-decker sandwich complexes, which have been structurally characterised by single-crystal X-ray diffraction. Edge energies in the Zr K-edge XANES spectra are not distinguishable between 1 and formally Zr(ii) and Zr(iv) reference compounds, suggesting a broad edge structure. DFT calculations best describe the bonding in 1 as highly covalent with frontier molecular orbitals showing almost equal contributions from benzene and the Zr-permethylpentalene fragments.

Triple decker sandwiches and related compounds of the first row transition metals with cyclopentadienyl and hexafluorobenzene rings: remarkable effects of fluorine substitution

The complete series of Cp2M2(μ-C6F6) (M = Ti, V, Cr, Mn, Fe, Co, Ni) structures have been examined theoretically for comparison with their unsubstituted Cp2M2(μ-C6H6) analogues. The singlet triple decker sandwich titanium complex Cp2Ti2(η(6),η(6)-C6F6) with a closed shell electronic structure and a non-planar C6F6 ring is preferred energetically by a wide margin (>20 kcal mol(-1)) over other isomers and spin states. This is in contrast to the hydrogen analogue for which related triplet spin state structures are clearly preferred. A similar low-energy triple-decker sandwich Cp2V2(η(6),η(6)-C6F6) structure is found for vanadium but with a quintet spin state. The later transition metals from Cr to Ni energetically prefer the so-called "rice-ball" cis-Cp2M2(μ-C6F6) structures with varying hapticities of metal-ring bonding, a range of formal orders of metal-metal bonding, and varying spin states depending on the metal atom. Thus the lowest energy Cp2Cr2(μ-C6F6) structures are triplet and quintet structures with pentahapto-trihapto η(5),η(3)-μ-C6F6 rings and formal Cr=Cr double bonds. This contrasts with the structure of Cp2Cr2(μ-C6H6) having a bis(tetrahapto) η(4),η(4)-C6H6 ring and a formal Cr-Cr quadruple bond. The lowest energy Cp2Mn2(μ-C6F6) structures are trans and cis quintet spin state structures. This contrasts with Cp2Mn2(μ-C6H6) for which a closed-shell singlet triple decker sandwich structure is preferred. The lowest energy Cp2Fe2(μ-C6F6) structure is a triplet cis structure with a tetrahapto-dihapto η(4),η(2)-μ-C6F6 ring and a formal Fe-Fe single bond. The lowest energy Cp2Co2(μ-C6F6) structures are singlet spin state structures with formal M-M single bonds and either bridging bis(trihapto) η(3),η(3)-C6F6 or tetrahapto-dihapto η(4),η(2)-C6F6 rings. For Cp2Ni2(μ-C6F6) low energy singlet cis and trans structures are both found. The singlet cis-Cp2Ni2(μ-C6F6) structure has a Ni-Ni single bond of length ∼2.5 Å and a bridging bis(dihapto) η(2),η(2)-C6F6 ligand with an uncomplexed C=C double bond. The singlet trans-Cp2Ni2(μ-C6F6) structure has a bis(trihapto) η(3),η(3)-C6F6 ligand.

Distortions of π-coordinated arenes with anionic character

A qualitative analysis of the distortions that operate on the π system of bridging arenes with anionic character is presented and substantiated by computational studies at the density functional B3LYP and CASSCF levels. The observed effects of bonding to two metal atoms and of the negative charge are an expansion of the arene ring due to the partial occupation of π* orbitals, an elongation or compression distortion accompanied by a loss of the equivalence of carbon-carbon bonds due to a Jahn-Teller distortion of the arene dianions, and a ring puckering due to a second-order Jahn-Teller distortion that may appear independently of the existence of the first-order effect. The workings of the orbital mixing produced by these distortions have been revealed in a straightforward way by a pseudosymmetry analysis of the HOMOs of the distorted conformations. The systems studied include Li(I) and Y(III) adducts of benzene, as well as trimethylsilyl-substituted derivatives in the former case. An analysis of the structural data of a variety of purported di- and tetraanionic arene ligands coordinated to transition metals in several bridging modes has reproduced the main geometrical trends found in the computational study for the benzene and trimethylsilyl-substituted benzene dianions, allowing a classification of the variety of structural motifs found in the literature.

The organometallic chemistry of cycloheptatrienyl zirconium complexes

This tutorial review summarizes the organometallic chemistry derived from the half-sandwich complex [(η(7)-C(7)H(7))ZrCl(tmeda)], which was used as an efficient and versatile starting material for the incorporation of monoanionic ligands into the cycloheptatrienyl zirconium coordination sphere by conventional salt metathesis reactions. A broad variety of ligands was employed, affording novel and previously inaccessible cycloheptatrienyl (sandwich) complexes of the type [(η(7)-C(7)H(7))Zr(Y)]; Y comprises pentadienyl, cyclopentadienyl, allyl, phospholyl, boratabenzene, imidazolin-2-iminato and amido systems. The cycloheptatrienyl ring in these systems usually acts as an "innocent spectator ligand", but reactivity can arise from the second ligand Y or the Lewis acidity of the, formally, Zr(+iv) center, which was probed in selected examples and put in perspective to related studies. The corresponding results emphasize why the use of [(η(7)-C(7)H(7))ZrCl(tmeda)] is clearly an advancement in the chemistry of the still fairly unexplored area of cycloheptatrienyl transition metal complexes.

Hexaferrocenylbenzene

Hexaferrocenylbenzene has been synthesized by six-fold Negishi type ferrocenylation of hexabromo- or hexaiodobenzene.

Hypercarbons in polyhedral structures

Though carbon is mostly tetravalent and tetracoordinated, there are several examples where the coordination number exceeds four. Structural varieties that exhibit hypercarbons in polyhedral structures such as polyhedral carboranes, sandwich complexes, encapsulated polyhedral structures and novel planar aromatic systems with atoms embedded in the middle are reviewed here. The structural variety anticipated with hypercoordinate carbon among carboranes is large as there are many modes of condensation that could lead to large number of new patterns. The relative stabilities of positional isomers of polyhedral carboranes, sandwich structures, and endohedral carboranes are briefly described. The mno rule accounts for the variety of structural patterns. Wheel-shaped and planar hypercoordinated molecules are recent theoretical developments in this area.

Group 14 triple-decker cations

The triple-decker cations trans-[(Cp*Sn)(2)(mu-eta(5):eta(5)-Cp*)](+) and trans-[(Cp*Pb)(2)(mu-eta(5):eta(5)-Cp*)](+) have been prepared and structurally characterized as their [B(C(6)F(5))(4)](-) salts from the reactions of [Cp*M][B(C(6)F(5))(4)](M = Sn, Pb) with the appropriate decamethylmetallocene. Both triple-decker cations adopt a cisoid arrangement of terminal Cp* groups, whereas the two known triple-decker main-group anions possess a transoid arrangement of terminal Cp groups. The reason for this conformational difference has been probed on the basis of DFT calculations.