Triple-decker Sandwich Complexes Research Articles

Electrophilic Functionalization of a Hexaphosphabenzene Ligand in [(Cp*Mo)2(μ,η6 : 6-P6)

The electrophilic functionalization of the triple-decker sandwich complex [{Cp*Mo}2(μ,η6:6-P6)] (A) and its mono-oxidized counterpart [{Cp*Mo}2(μ,η6:6-P6)][SbF6] (B) with reactive main-group electrophiles as well as radical scavengers is shown to be a reliable method for the selective functionalization of the hexaphosphabenzene ligand. Depending on the electrophile used, the regioselectivity of the functionalization can be adjusted. Using group 16 electrophiles, the trisubstituted compounds [{Cp*Mo}2{(μ,η3 : 3-P3)(μ,η1 : 1 : 1 : 1-1,3-(SePh)2-2-Br-P3)}][TEF] (1), [{Cp*Mo}2(μ,η3 : 3-P3)(μ,η1 : 1 : 1 : 1-1,2,3-(EPh)3-P3)][SbF6] (E=S (2), Se (3)) as well as the side product [{Cp*Mo}2(μ,η4:4-P4)(μ,η1 : 1-P(SPh)2)][SbF6] (4) are obtained. By switching to phosphenium ions as group 15 electrophiles, the ring-inserted products [{Cp*Mo}2(μ,η3 : 3 : 2 : 2-P7R2)][TEF] (R=Cy (5), iPr (6)) are isolated, showing an unprecedented P7R2 structural motif. Furthermore, the reaction with MeOTf yields the dimeric [{Cp*Mo}4(1,4-Me2-μ4,η1 : 1 : 1 : 1 : 1 : 1-P6)(μ,η3 : 3-P3)2][TEF]2 (7) as the first example of a complex featuring two interconnected cyclo-P6 middle deck ligands. Finally, by combination of the methylation step with Ph2Se2, the mixed group 14/16 complex [{Cp*Mo}2{(μ,η3 : 3-P3)(μ,η1 : 1 : 1 : 11,2-(SePh)2-3-Me-P3)}][OTf] (8) is obtained.

Hexagonal Planar [B6 H6 ] within a [B6 H12 ] Borate Complex: Structure and Bonding of [(Cp*Ti)2 (μ-ɳ6 : ɳ6 -B6 H6 )(μ-H)6

Isolation of planar [B6 H6 ] is a long-awaited goal in boron chemistry. Several attempts in the past to stabilize [B6 H6 ] were unsuccessful due to the domination of polyhedral geometries. Herein, we report the synthesis of a triple-decker sandwich complex of titanium [(Cp*Ti)2 (μ-η6 : η6 -B6 H6 )(μ-H)6 ] (1), which features the first-ever experimentally achieved nearly planar six-membered [B6 H6 ] ring, albeit within a [B6 H12 ] borate. The small deviation from planarity is a direct consequence of the predicted structural pattern of the middle ring in 24 Valence Electron Count (VEC) triple-decker complexes. The large ring size of [B6 H6 ] in 1 brings the metal-metal distance into the bonding range. However, significant electron delocalization from the M-M bonding orbital to the bridging hydrogen and B-B skeleton in the middle decreases its bond strength.

A homoleptic tris(diphosphacyclobutadiene) tripledecker sandwich complex.

The synthesis and characterisation of [Co2(η4-P2C2tBu2)2(μ:η4:η4-P2C2tBu2)] (1) is described, featuring two cobalt atoms and three diphosphacyclobutadiene ligands. This compound is the first triple-decker sandwich complex which exclusively contains cyclobutadiene ligands.

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.

A General Pathway to Heterobimetallic Triple‐Decker Complexes

A systematic study on the reactivity of the triple‐decker complex [(Cp’’’Co)2(μ,η4:η4‐C7H8)] (A) (Cp’’’=1,2,4‐tritertbutyl‐cyclopentadienyl) towards sandwich complexes containing cyclo‐P3, cyclo‐P4, and cyclo‐P5 ligands under mild conditions is presented. The heterobimetallic triple‐decker sandwich complexes [(Cp*Fe)(Cp’’’Co)(μ,η5:η4‐P5)] (1) and [(Cp’’’Co)(Cp’’’Ni)(μ,η3:η3‐P3)] (3) (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) were synthesized and fully characterized. In solution, these complexes exhibit a unique fluxional behavior, which was investigated by variable temperature NMR spectroscopy. The dynamic processes can be blocked by coordination to {W(CO)5} fragments, leading to the complexes [(Cp*Fe)(Cp’’’Co)(μ3,η5:η4:η1‐P5){W(CO)5}] (2 a), [(Cp*Fe)(Cp’’’Co)(μ4,η5:η4:η1:η1‐P5){(W(CO)5)2}] (2 b), and [(Cp’’’Co)(Cp’’’Ni)(μ3,η3:η2:η1‐P3){W(CO)5}] (4), respectively. The thermolysis of 3 leads to the tetrahedrane complex [(Cp’’’Ni)2(μ,η2:η2‐P2)] (5). All compounds were fully characterized using single‐crystal X‐ray structure analysis, NMR spectroscopy, mass spectrometry, and elemental analysis.

Ring Contraction by NHC-Induced Pnictogen Abstraction.

The reaction of [Cp'''Co(η4 -P4 )] (1) (Cp'''=1,2,4-tBu3 C5 H2 ) with Me NHC (Me NHC=1,3,4,5-tetramethylimidazol-2-ylidene) leads through NHC-induced phosphorus cation abstraction to the ring contraction product [(Me NHC)2 P][Cp'''Co(η3 -P3 )] (2), which represents the first example of an anionic CoP3 complex. Such NHC-induced ring contraction reactions are also applicable for triple-decker sandwich complexes. The complexes [(Cp*Mo)2 (μ,η6:6 -E6 )] (3 a, 3 b) (Cp*=C5 Me5 ; E=P, As) can be transformed to the complexes [(Me NHC)2 E][(Cp*M)2 (μ,η3:3 -E3 )(μ,η2:2 -E2 )] (4 a, 4 b), with 4 b representing the first structurally characterized example of an NHC-substituted AsI cation. Further, the reaction of the vanadium complex [(Cp*V)2 (μ,η6:6 -P6 )] (5) with Me NHC results in the formation of the unprecedented complexes [(Me NHC)2 P][(Cp*V)2 (μ,η6:6 -P6 )] (6), [(Me NHC)2 P][(Cp*V)2 (μ,η5:5 -P5 )] (7) and [(Cp*V)2 (μ,η3:3 -P3 )(μ,η1:1 -P{Me NHC})] (8).

The "Wanderlust" of Me3Si groups in rare-earth triple-decker complexes: a combined experimental and computational study.

The migration of Me3Si groups ("Wanderlust") in rare-earth triple-decker sandwich complexes of the type Ln2(COT'')3 (COT'' = bis(trimethylsilyl)cyclooctatetraenyl) has been elucidated by a combined experimental and computational study. For the first time, two isomers of a Ln2(COT'')3 triple-decker have been isolated and characterized in the case of Y2(COT'')3.

Scandium-Mediated Formation of a Bis(tetrahydropentalene).

The reactivity of Li[Sc(COT'')2 ] (1; COT''=1,4-bis(trimethylsilyl)cyclooctatetraenyl) towards CoCl2 is considerably different from that of related lanthanide triple-decker sandwich complexes. In addition to the expected triple-decker complex Sc2 (COT'')3 (2), the complex Sc2 {μ-BTHP}(COT'')2 (3) is formed, which comprises the novel BTHP2- ligand (BTHP2- =bis(3,5-bis(trimethylsilyl)-1,3a,6,6a-tetrahydropentalene-1-yl)diide or bis(2,7-bis(trimethylsilyl)bicyclo[3.3.0]octa-2,7-dien-4-yl)diide, C16 H10 (SiMe3 )42- ). The formation of 3 is likely facilitated by the fact that scandium prefers η8 ,η3 coordination rather than highly symmetric η8 ,η8 coordination, and the η3 -coordinated COT'' ligand in 1 is activated owing to a loss of aromaticity. Acid hydrolysis of 3 leads to air-stable H2 BTHP (4).

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·THFx 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.

Unexpected Reactivity of [(η(5) -1,2,4-tBu3 C5 H2 )Ni(η(3) -P3 )] towards Main Group Nucleophiles and by Reduction.

The reduction of [Cp'''Ni(η(3) -P3 )] (1; Cp'''=η(5) -1,2,4-tBu3 C5 H2 ) with potassium produces the complex anion [(Cp'''Ni)2 (μ,η(2:2) -P8 )](2-) (2), which contains a realgar-like P8 unit. The anionic triple-decker sandwich complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )](-) (3) with a cyclo-P3 middle deck is obtained when 1 is treated with NaNH2 as a nucleophile. Na[3] can subsequently be oxidized with AgOTf to the neutral triple-decker complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )] (4). In contrast, 1 reacts with LiPPh2 to give the anionic compound [(Cp'''Ni)2 (μ,η(2:2) -P6 PPh2 )](-) (5), a complex containing a bicyclic P7 fragment capped by two Cp'''Ni units. Protonation of Li[5] with HBF4 leads to the neutral complex [(Cp'''Ni)2 (μ,η(2:2) -(HP6 PPh2 )] (6). Adding LiNMe2 to 1 results in [Cp'''Ni(η(2) -P3 NMe2 )](-) (7) becoming accessible, a complex which forms as a result of nucleophilic attack at the cyclo-P3 ring of 1. The complexes K2 [2], Na[3], 4, 6, and Li[7] were fully characterized and their structures determined by single-crystal X-ray diffraction.

Triple-decker sandwich complexes with a bent cyclo-P5 middle-deck.

New types of triple-decker complexes with an organo-substituted P5 middle-deck were synthesized by the reaction of [Cp*Fe(η4-P5R)]- (1a: R = CH2SiMe3; 1b: R = NMe2) with halogeno-bridged transition metal dimers [Cp'''MX]2 (M = Cr, Fe, Co, Ni; X = Cl, Br). By oxidation of [(Cp*Fe)(Cp'''Co)(μ,η4:3-P5CH2SiMe3)] 2a with [Cp2Fe][PF6], the cationic complex [(Cp*Fe)(Cp'''Co)(μ,η5:4-P5CH2SiMe3)]+ was isolated. The electronic structure of the synthesized complexes was elucidated by DFT calculations.

An electron-poor di-molybdenum triple-decker with a puckered [B4Ru2] bridging ring is an oblato-closo cluster

An unprecedented, 22-valence-electron triple-decker sandwich complex [(Cp*Mo)2{μ-η(6):η(6)-B4H4Ru2(CO)6}], 2, has been prepared. In an effort to generate analogous triple-deckers with group 6 metal carbonyl fragments in the middle deck, we have isolated [(Cp*MoCO)2(μ-H)2B4H4], 3, that provides the first direct evidence for the missing link between [(Cp*MoCl)2B3H7] and [(Cp*Mo)2B5H9] clusters.

Metal–ligand bonding and metal atom dynamics in Fe–Fe and Ru–Fe triple-decker sandwich complexes

Three structurally related bimetallic triple-decker complexes of iron and ruthenium have been studied by temperature-dependent 57Fe Mössbauer Effect (ME) spectroscopy and their redox-behavior has been elucidated. The triple-decker compounds are [Cp′FeCp′FeCp′]BF4, [CpRuCp′FeCp′]PF6 and [Cp*RuCp′FeCp′]PF6 where Cp = C5H5, Cp′ = C5Me4H and Cp* = C5Me5. The metal atom (Fe) root-mean-square-vibrational-amplitude has been determined over the temperature range ∼90 < T < 300 K, and is found to be essentially isotropic in all three cases. The ME spectrum for [Cp′FeCp′FeCp′]BF4 is similar to the spectra for the two Ru–Fe compounds indicating that the substitution of Ru for Fe has only a minor effect on the hyperfine and associated parameters. Similarly, analysis of the metal atom dynamics for [CpRuCp′FeCp′]PF6 and [Cp*RuCp′FeCp′]PF6 shows that ring substitution has a negligible effect on the bonding parameters. A comparison of the three triple-decker compounds with the mono-iron diamagnetic compound Cp*FeCp* and the paramagnetic [Cp′FeCp′]BF4 compound is also detailed.

Hypoelectronic Dimetallaheteroboranes of Group 6 Transition Metals Containing Heavier Chalcogen Elements

We have synthesized and structurally characterized several dimetallaheteroborane clusters, namely, nido-[(Cp*Mo)2B4SH6], 1; nido-[(Cp*Mo)2B4SeH6], 2; nido-[(Cp*Mo)2B4TeClH5], 3; [(Cp*Mo)2B5SeH7], 4; [(Cp*Mo)2B6SeH8], 5; and [(CpW)2B5Te2H5], 6 (Cp* = η(5)-C5Me5, Cp = η(5)-C5H5). In parallel to the formation of 1-6, known [(CpM)2B5H9], [(Cp*M)2B5H9], (M = Mo, W) and nido-[(Cp*M)2B4E2H4] compounds (when M = Mo; E = S, Se, Te; M = W, E = S) were isolated as major products. Cluster 6 is the first example of tungstaborane containing a heavier chalcogen (Te) atom. A combined theoretical and experimental study shows that clusters 1-3 with their open face are excellent precursors for cluster growth reactions. As a result, the reaction of 1 and 2 with [Co2(CO)8] yielded clusters [(Cp*Mo)2B4H4E(μ3-CO)Co2(CO)4], 7-8 (7: E = S, 8: E = Se) and [(Cp*Mo)2B3H3E(μ-CO)3Co2(CO)3], 9-10 (9: E = S, 10: E = Se). In contrast, compound 3 under the similar reaction conditions yielded a novel 24-valence electron triple-decker sandwich complex, [(Cp*Mo)2{μ-η(6):η(6)-B3H3TeCo2(CO)5}], 11. Cluster 11 represents an unprecedented metal sandwich cluster in which the middle deck is composed of B, Co, and Te. All the new compounds have been characterized by elemental analysis, IR, (1)H, (11)B, (13)C NMR spectroscopy, and the geometric structures were unequivocally established by X-ray diffraction analysis of 1, 2, 4-7, and 9-11. Furthermore, geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state structure determinations. We have analyzed the discrepancy in reactivity of the chalcogenato metallaborane clusters in comparison to their parent metallaboranes with the help of a density functional theory (DFT) study.

Novel Triple-Decker Sandwich Complex with a Six-Membered [B3Co2(μ4-Te)] Ring as the Middle Deck

Thermolysis of nido-[(Cp*Mo)2B4TeClH5], with an excess of Co2(CO)8 at room temperature, afforded a triple-decker sandwich complex [(Cp*Mo)2{μ-η(6):η(6)-B3H3TeCo2(CO)5}] (4), which represents an unsaturated 24-valence-electron sandwich cluster in which the middle deck is composed of B, Co, and a heavy group 16 element.

Steric Effects in Lanthanide Sandwich Complexes Containing Bulky Cyclooctatetraenyl Ligands

This paper gives a full account of the complex reaction system LnCl3/(COT″)2– (COT″ = 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion). Four different series of organolanthanide complexes of this bulky COT ligand have been reported: (1) anionic sandwich complexes containing [Ln(COT″)2]− anions, (2) dimeric chloro-bridged mono(COT″) complexes, (3) cluster-centered multidecker-sandwich complexes, and (4) linear triple-decker sandwich complexes. In order to get a more complete picture of the reaction system LnCl3/(COT″)2– and to examine possible steric effects exerted by the COT″ ligand, four new rare-earth-metal COT″ complexes have been prepared: [Li(DME)3][Ce(COT″)2] (1), [Li(THF)4][Nd(COT″)2] (2), [(COT″)Nd(μ-Cl)(THF)]2 (4), and (COT″)Yb(DIPPForm)(THF) (5,; DIPPForm = [HC(NAr)2]−, Ar = 2,6-diisopropylphenyl). For comparison, the COTTBS derivative [Li(DME)3][Ce(COTTBS)2] (3; COTTBS = 1,4-bis(tert-butyldimethylsilyl)cyclooctatetraenyl dianion) has also been synthesized. It was found that the steric effect...

On the Suppression Mechanism of the Pseudo-Jahn–Teller Effect in Middle E6 (E = P, As, Sb) Rings of Triple-Decker Sandwich Complexes

Quantum chemical calculations of the CpMoE(6)MoCp (E = P, As, Sb) triple-decker sandwich complexes showed that E(6) fragments in the central decks of the complexes are planar. Analysis of molecular orbitals involved in vibrational coupling demonstrated that filling the unoccupied molecular orbitals involved in vibronic coupling with electron pairs of Mo atoms suppresses the PJT effect in the CpMoE(6)MoCp (E = P, As, Sb) sandwich, with the E(6) ring becoming planar (D(6h)) upon complex formation. The AdNDP analysis revealed that bonding between C(5)H(5)(-) units and Mo atoms has a significant ionic contribution, while bonding between Mo atoms and E(6) fragment becomes appreciably covalent through the δ-type M → L back-donation mechanism.

Size‐Determining Dependencies in Supramolecular Organometallic Host–Guest Chemistry

Treatment of the pentaphosphaferrocene [Cp*Fe(η(5)-P(5))] with Cu(I) halides in the presence of different templates leads to novel fullerene-like spherical molecules that serve as hosts for the templates. If ferrocene is used as the template the 80-vertex ball [Cp(2)Fe]@[{Cp*Fe(η(5)-P(5))}(12){CuCl}(20)] (4), with an overall icosahedral C(80) topological symmetry, is obtained. This result shows the ability of ferrocene to compete successfully with the internal template of the reaction system [Cp*Fe(η(5)-P(5))], although the 90-vertex ball [{Cp*Fe(η(5):η(1):η(1):η(1):η(1):η(1)-P(5))}(12)(CuCl)(10)(Cu(2)Cl(3))(5){Cu(CH(3)CN)(2)}(5)] (2 a) containing pentaphosphaferrocene as a guest is also formed as a byproduct. With use of the triple-decker sandwich complex [(CpCr)(2)(μ,η(5)-As(5))] as a template the reaction between [Cp*Fe(η(5)-P(5))] and CuBr leads to the 90-vertex ball [(CpCr)(2)(μ,η(5)-As(5))]@[{Cp*Fe(η(5)-P(5))}(12){CuBr}(10){Cu(2)Br(3)}(5){Cu(CH(3) CN)(2)}(5)] (6), in which the complete molecule acts as a template. However, if the corresponding reaction is instead carried out with CuCl, cleavage of the triple-decker complex is found and the 80-vertex ball [CpCr(η(5)-As(5))]@[{Cp*Fe(η(5)-P(5))}(12){CuCl}(20)] (5) is obtained. This accommodates as its guest [CpCr(η(5)-As(5))], which has only 16 valence electrons in a triplet ground state and is not known as a free molecule. The triple-decker sandwich complex [(CpCr)(2)(μ,η(5)-As(5))] requires 53.1 kcal mol(-1) to undergo cleavage (as calculated by DFT methods) and therefore this reaction is clearly endothermic. All new products have been characterized by single-crystal X-ray crystallography. A favoured orientation of the guest molecules inside the host cages has been identified, which shows π⋅⋅⋅π stacking of the five-membered rings (Cp and cyclo-As(5)) of the guests and the cyclo-P(5) rings of the nanoballs of the hosts.

ChemInform Abstract: Multiple‐Decker Sandwich Complexes of f‐Elements

AbstractReview: 86 refs.

Multiple-decker sandwich complexes of f-elements

Extended sandwich structures (triple-deckers, tetra-deckers etc.) containing d-transition metals are well established for more than 30 years. In contrast, similar complexes containing lanthanide or actinide elements are still rare. In recent years, however, significant progress has been made in this area. This has mainly been achieved with the use of sterically demanding π-ligands such as pentamethylcyclopentadienyl (=Cp*) or silyl-substituted cyclooctatetraenyl dianions like [C8H5(SiMe3)3-1,3,6]2− (=COT‴). Suitable combinations of such ligands in the coordination sphere of f-elements allowed the synthesis and structural characterization of bent and linear triple-decker sandwich complexes as well as the first tetra-deckers and novel cluster-centered multidecker sandwich complexes. This NJC Perspective article gives an overview on recent achievements in this field and looks forward to future developments.