Pentaphosphametallocene

A lens-shaped supramolecule based on the bulky pentaphosphaferrocene [CpBIGFe(η5-P5)] and CuBr2

Besides inherent fullerene-like hollow spheres, the metallasupramolecular chemistry of pentaphosphaferrocenes and CuBr2 afforded a conceptually new product, a compact 3.2 nm sized supramolecule [{1d}6(CuBr)32(CH3CN)6] formed by six largest pentaphosphaferrocene units [CpBIGFe(η5-P5)] (1d: CpBIG = η5-C5(4-nBuC6H4)5) so far and a framework of 32 copper and 32 bromide ions.

Pentaphosphaferrocene-mediated synthesis of asymmetric organo-phosphines starting from white phosphorus

The synthesis of phosphines is based on white phosphorus, which is usually converted to PCl₃, to be afterwards substituted step by step in a non-atomic efficient manner. Herein, we describe an alternative efficient transition metal-mediated process to form asymmetrically substituted phosphines directly from white phosphorus (P₄). Thereby, P₄ is converted to [Cp*Fe(η⁵-P₅)] (1) (Cp* = η⁵-C₅(CH₃)₅) in which one of the phosphorus atoms is selectively functionalized to the 1,1-diorgano-substituted complex [Cp*Fe(η⁴-P₅R'R″)] (3). In a subsequent step, the phosphine PR'R″R‴ (R' ≠ R″ ≠ R‴ = alky, aryl) (4) is released by reacting it with a nucleophile R‴M (M = alkali metal) as racemates. The starting material 1 can be regenerated with P₄ and can be reused in multiple reaction cycles without isolation of the intermediates, and only the phosphine is distilled off.

The Missing Parent Compound [(C5 H5 )Fe(η5 -P5 )]: Synthesis, Characterization, Coordination Behavior and Encapsulation

The so far missing parent compound of the large family of pentaphosphaferrocenes [CpFe(η5 -P5 )] (1 b) was synthesized by the thermolysis of [CpFe(CO)2 ]2 with P4 using the very high-boiling solvent diisopropylbenzene. It was comprehensively characterized by, inter alia, NMR spectroscopy, single crystal X-ray structure analysis, cyclic voltammetry and DFT computations. Moreover, its coordination behavior towards CuI halides was explored, revealing the unprecedented 2D polymeric networks [{CpFe(η5:1:1:1:1 -P5 )}Cu2 (μ-X)2 ]n (2 a: X=Cl, 2 b: X=Br) and [{CpFe(η5:1:1 -P5 )}Cu(μ-I)]n (3) and even the first cyclo-P5 -containing 3D coordination polymer [{CpFe(η5:1:1 -P5 )}Cu(μ-I)]n (4). The sandwich complex 1 b can also be incorporated in nano-sized supramolecules based on [Cp*Fe(η5 -P5 )] (1 a) and CuX (X=Cl, Br, I): [CpFe(η5 -P5 )]@[{Cp*Fe(η5 -P5 )}12 (CuX)20-n ] (5 a: X=Cl, n=2.4; 5 b: X=Br, n=2.4; 5 c: X=I, n=0.95). Thereby, the formation of the CuI-containing fullerene-like sphere 5 c is found for the first time.

Mechanism for the Reaction of White Phosphorus with Cp2Cr2(CO)6 Leading Ultimately to the Triple-Decker Sandwich Cp2Cr2(μ-η5,η5-P5): A Theoretical Study

The experimentally known reaction of Cp₂Cr₂(CO)₆ with white phosphorus (P₄) to give CpCr(CO)₂(η³-P₃), Cp₂Cr₂(CO)₄(μ-η,²η²-P₂), and the triple-decker sandwich Cp₂Cr₂(μ-η,⁵η⁵-P₅) is of interest since the P₄ reactant having a tetrahedral cluster of four phosphorus atoms is converted to products having P₂, P₃, and P₅ ligands. The mechanism of this obviously complicated reaction can be dissected into three stages using a coupled cluster theoretical method that has been benchmarked with the P₂, Mn(CO)₅, and CpCr(CO)₃ dimerization processes. The first stage of the Cp₂Cr₂(CO)₆/P₄ reaction mechanism generates the unsaturated singlet intermediate Cp₂Cr₂(CO)₅ that combines with the P₄ reactant. Decarbonylation of the resulting Cp₂Cr₂(CO)₅(P₄) complex provides a singlet tetracarbonyl readily fragmenting into the stable triphosphacyclopropenyl complex CpCr(CO)₂(η³-P₃) and the chromium phosphide CpCr(CO)₂(P). The isomeric triplet tetracarbonyl Cp₂Cr₂(CO)₄(P₄), readily fragments into CpCr(CO)₂(η²-P₂), which can generate the stable diphosphaacetylene complex Cp₂Cr₂(CO)₄(η,²η²-P₂) as well as the pentamer [CpCr(CO)₂]₅(P₁₀). Combination of the coordinately unsaturated CpCr(CO)(η³-P₃) with CpCr(CO)₂(η²-P₂) can lead to a ring expansion. This generates the P₅ pentagonal ligand in a Cp₂Cr₂(CO)₃(P₅) precursor to the experimentally observed carbonyl-free triple-decker sandwich Cp₂Cr₂(μ-η,⁵η⁵-P₅) after three successive decarbonylations.

Au-Containing Coordination Polymers Based on Polyphosphorus Ligand Complexes

Whereas the self-assembly of pentaphosphaferrocenes [Cp^RFe(η⁵-P₅)] (Cp^R = Cp*, Cp^×, and Cp^Bn) with Cu and Ag salts has been well-studied in the past, the coordination chemistry toward Au complexes has been left untouched so far. Herein, the results of the self-assembly processes of [Cp^RFe(η⁵-P₅)] with Au salts of different anions (GaCl₄^-, SbF₆^-, and Al(OC(CF₃)₃)₄ (TEF^-)) are reported. Next to a variety of molecular coordination products, the first coordination polymers based on polyphosphorus ligand complexes and Au salts are also obtained. Thereby, a 2D coordination polymer comprising metal vacancies is isolated. In all products, the Au centers are coordinated in a linear or a trigonal planar environment. In solution, highly dynamic processes are observed. Variable-temperature NMR spectroscopy, solid-state NMR spectroscopy, and X-ray powder diffraction were applied to gain further insight into selected coordination compounds.

Stabilization of Pentaphospholes as η5 -Coordinating Ligands

Electrophilic functionalisation of [Cp*Fe(η5 -P5 )] (1) yields the first transition-metal complexes of pentaphospholes (cyclo-P5 R). Silylation of 1 with [(Et3 Si)2 (μ-H)][B(C6 F5 )4 ] leads to the ionic species [Cp*Fe(η5 -P5 SiEt3 )][B(C6 F5 )4 ] (2), whose subsequent reaction with H2 O yields the parent compound [Cp*Fe(η5 -P5 H)][B(C6 F5 )4 ] (3). The synthesis of a carbon-substituted derivative [Cp*Fe(η5 -P5 Me)][X] ([X]- =[FB(C6 F5 )3 ]- (4 a), [B(C6 F5 )4 ]- (4 b)) is achieved by methylation of 1 employing [Me3 O][BF4 ] and B(C6 F5 )3 or a combination of MeOTf and [Li(OEt2 )2 ][B(C6 F5 )4 ]. The structural characterisation of these compounds reveals a slight envelope structure for the cyclo-P5 R ligand. Detailed NMR-spectroscopic studies suggest a highly dynamic behaviour and thus a distinct lability for 2 and 3 in solution. DFT calculations shed light on the electronic structure and bonding situation of this unprecedented class of compounds.

Iodination of cyclo-E5 -Complexes (E=P, As)

In a high‐yield one‐pot synthesis, the reactions of [Cp*M(η⁵‐P₅)] (M=Fe (1), Ru (2)) with I₂ resulted in the selective formation of [Cp*MP₆I₆]⁺ salts (3, 4). The products comprise unprecedented all‐cis tripodal triphosphino‐cyclotriphosphine ligands. The iodination of [Cp*Fe(η⁵‐As₅)] (6) gave, in addition to [Fe(CH₃CN)₆]²⁺ salts of the rare [As₆I₈]²⁻ (in 7) and [As₄I₁₄]²⁻ (in 8) anions, the first di‐cationic Fe‐As triple decker complex [(Cp*Fe)₂(μ,η^5:5‐As₅)][As₆I₈] (9). In contrast, the iodination of [Cp*Ru(η⁵‐As₅)] (10) did not result in the full cleavage of the M−As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)₂(μ,η^5:5‐As₅)][As₆I₈]_0.5 (11) represents the first Ru‐As₅ triple decker complex, thus completing the series of monocationic complexes [(Cp^RM)₂(μ,η^5:5‐E₅)]⁺ (M=Fe, Ru; E=P, As). [(Cp*Ru)₂As₈I₆] (12) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)₂As₄I₄] (13) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.

Transformations of the cyclo-P4 ligand in [Cp'''Co(η4-P4)]

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated. By using K[CpFe(CO)₂], a selective reduction to the dianionic complex [(Cp′′′Co)₂(μ,η³:η³-P₈)]²⁻ (2) was achieved. The reaction of 1 with ^tBuLi and LiCH₂SiMe₃ as carbon-based nucleophiles yielded [Cp′′′Co(η³-P₄R)]⁻ (R = ^tBu (4), CH₂SiMe₃ (7)), which, depending on the reaction conditions, undergo subsequent reactions with another equivalent of 1 to form [(Cp′′′Co)₂(μ,η³:η³-P₈R)]⁻ (R = ^tBu (5), CH₂SiMe₃ (8)). In the case of 4, a different pathway was observed, namely a dimerisation followed by a fragmentation into [Cp′′′Co(η³-P₅^tBu₂)]⁻ (6) and [Cp′′′Co(η³-P₃)]⁻ (3). With OH⁻ as an oxygen-based nucleophile, the synthesis of [Cp′′′Co(η³-P₄(O)H)]⁻ (9) was achieved. All compounds were characterized by X-ray crystal structure analysis, NMR spectroscopy and mass spectrometry. Their electronic structures and reaction behavior were elucidated by DFT calculations.

The reactivity of the cyclo-P₄ ligand complex [Cp′′′Co(η⁴-P₄)] (1) (Cp′′′ = 1,2,4-tri-tert-butyl-cyclopentadienyl) towards reduction and main group nucleophiles was investigated.

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.

Organometallic-Organic Hybrid Polymers Assembled from Pentaphosphaferrocene, Bipyridyl Linkers, and CuI Ions

A multicomponent approach of the P n ligand complex [Cp*Fe(η5-P5)] (1: Cp* = η5-C5Me5) with the ditopic organic linkers 4,4'-bipyridine (2) or trans-1,2-di(pyridine-4-yl)ethene (3) in the presence of CuI salts of the anions [BF4]- and [PF6]- or the coordinating anion Br-, leads to the formation of four novel organometallic-organic hybrid polymers: the cationic 1D polymeric compounds [Cu4{Cp*Fe(µ3,η5:1:1-P5)}2(µ,η1:1-C10H8N2)4(CH3CN)4] n [BF4]4n (4) and [Cu4{Cp*Fe(µ3,η5:1:1-P5)}2(µ,η1:1-C10H8N2)4(CH3CN)4] n [PF6]4n (5) as well as the unique neutral threefold 2D → 2D interpenetrated networks [Cu2Cl2{Cp*Fe(µ3,η5:1:1-P5)}(µ,η1:1-C12H10N2)] n (6) and [Cu2Br2{Cp*Fe(µ3,η5:1:1-P5)}(µ,η1:1-C10H8N2)] n (7).

Rotating Iron and Titanium Sandwich Complexes

The origin for the rotational barrier of organometallic versus inorganic sandwich complexes has remained enigmatic for the past decades. Here, we investigate in detail what causes the substantial barrier for titanodecaphosphacene through spin-state consistent density functional theory. Orbital interactions are shown to be the determining factor.

Synthesis and Reactivity of an End-Deck cyclo-P4 Iron Complex

Reduction of the Fe^II complex [(^Ph PP₂^Cy )FeCl₂ ] (2) generated an electron-rich and unsaturated Fe⁰ species, which was reacted with white phosphorus. The resulting new complex, [(^Ph PP₂^Cy )Fe(η⁴ -P₄ )] (3), is the first iron cyclo-P₄ complex and the only known stable end-deck cyclo-P₄ complex outside Group V. Complex 3 features an Fe^II center, as shown by Mössbauer spectroscopy, associated to a P₄^2- fragment. The distinct reactivity of complex 3 was rationalized by analysis of the molecular orbitals. Reaction of complex 3 with H⁺ afforded the unstable complex [(^Ph PP₂^Cy )Fe(η⁴ -P₄ )(H)]⁺ (4), whereas with CuCl and BCF, the complexes [(^Ph PP₂^Cy )Fe(η⁴ :η¹ -P₄ )(μ-CuCl)]₂ (5) and [(^Ph PP₂^Cy )Fe(η⁴ :η¹ -P₄ )B(C₆ F₅ )₃ ] (6) were formed.

Neutral two-dimensional organometallic–organic hybrid polymers based on pentaphosphaferrocene, bipyridyl linkers and CuCl

The reaction of the P_n ligand complex [Cp*Fe(η⁵-P₅)] (1: Cp* = η⁵-C₅Me₅) with CuCl in the presence of 4,4′-bipyridine or 1,2-di(4-pyridyl)ethylene leads to the formation of three unprecedented neutral 2D organometallic–organic hybrid networks.

Rearrangement of a P4 Butterfly Complex-The Formation of a Homoleptic Phosphorus-Iron Sandwich Complex

The versatile coordination behavior of the P₄ butterfly complex [{Cp'''Fe(CO)₂ }₂ (μ,η^1:1 -P₄ )] (1, Cp'''=η⁵ -C₅ H₂^t Bu₃ ) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr₂ ⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp'''Fe(CO)₂ }₂ (μ₃ ,η^1:1:2 -P₄ ){FeBr₂ }] (2), whereas, in the reaction with [Fe(CH₃ CN)₆ ][PF₆ ]₂ , an unprecedented rearrangement of the P₄ butterfly structural motif leads to the cyclo-P₄ moiety in {(Cp'''Fe(CO)₂ )₂ (μ₃ ,η^1:1:4 -P₄ )}₂ Fe][PF₆ ]₂ (3). Complex 3 represents the first fully characterized "carbon-free" sandwich complex containing cyclo-P₄ R₂ ligands in a homoleptic-like iron-phosphorus-containing molecule. Alternatively, 2 can be transformed into 3 by halogen abstraction and subsequent coordination of 1. The additional isolated side products, [{Cp'''Fe(CO)₂ }₂ (μ₃ ,η^1:1:2 -P₄ ){Cp'''Fe(CO)}][PF₆ ] (4) and [{Cp'''Fe(CO)₂ }₂ (μ₃ ,η^1:1:4 -P₄ ){Cp'''Fe}][PF₆ ] (5), give insight into the stepwise activation of the P₄ butterfly moiety in 1.

The Cobalt cyclo-P4 Sandwich Complex and Its Role in the Formation of Polyphosphorus Compounds

A synthetic approach to the sandwich complex [Cp′′′Co(η⁴‐P₄)] (2) containing a cyclo‐P₄ ligand as an end‐deck was developed. Complex 2 is the missing homologue in the series of first‐row cyclo‐P_n sandwich complexes, and shows a unique tendency to dimerize in solution to form two isomeric P₈ complexes [(Cp′′′Co)₂(μ,η⁴:η²:η¹‐P₈)] (3 and 4). Reactivity studies indicate that 2 and 3 react with further [Cp′′′Co] fragments to give [(Cp′′′Co)₂(μ,η²:η²‐P₂)₂] (5) and [(Cp′′′Co)₃P₈] (6), respectively. Furthermore, complexes 2, 3, and 4 thermally decompose forming 5, 6, and the P₁₂ complex [(Cp′′′Co)₃P₁₂] (7). DFT calculations on the P₄ activation process suggest a η³‐P₄ Co complex as the key intermediate in the synthesis of 2 as well as in the formation of larger polyphosphorus complexes via a unique oligomerization pathway.

Viability of aromatic all-pnictogen anions

Aromaticity in novel cyclic all-pnictogen heterocyclic anions, P2N3(-) and P3N2(-), and in their heavier analogues is studied using quantum mechanical computations. All geometrical parameters from optimized geometry, bonding, electron density analysis from quantum theory of atoms in molecules, nucleus-independent chemical shift, and ring current density plots support their aromaticity. The aromatic nature of these molecules closely resembles that of the prototypical aromatic anion, C5H5(-). These singlet C2v symmetric molecules are comprised of five distinct canonical structures and are stable up to at least 1000 fs without any significant distortion. Mechanistic study revealed a plausible synthetic pathway for P3N2(-) - a click reaction between N2 and P3(-), through a C2v symmetric transition state. Besides this, the possibility of P3N2(-) as a η(5)-ligand in metallocenes is studied and the nature of bonding in metallocenes is discussed through the energy decomposition analysis.

An Inverted-Sandwich Diuranium μ-η5:η5-Cyclo-P5 Complex Supported by U-P5 δ-Bonding

Reaction of [U(TrenTIPS)] [1, TrenTIPS=N(CH2CH2NSiiPr3)3] with 0.25 equivalents of P4 reproducibly affords the unprecedented actinide inverted sandwich cyclo-P5 complex [{U(TrenTIPS)}2(μ-η5:η5-cyclo-P5)] (2). All prior examples of cyclo-P5 are stabilized by d-block metals, so 2 shows that cyclo-P5 does not require d-block ions to be prepared. Although cyclo-P5 is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P5)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo-P5 charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P5 compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals.

An Inverted-Sandwich Diuranium μ-η(5):η(5)-Cyclo-P5 Complex Supported by U-P5 δ-Bonding

Reaction of [U(Tren^TIPS)] [1, Tren^TIPS=N(CH₂CH₂NSiiPr₃)₃] with 0.25 equivalents of P₄ reproducibly affords the unprecedented actinide inverted sandwich cyclo-P₅ complex [{U(Tren^TIPS)}₂(μ-η⁵:η⁵-cyclo-P₅)] (2). All prior examples of cyclo-P₅ are stabilized by d-block metals, so 2 shows that cyclo-P₅ does not require d-block ions to be prepared. Although cyclo-P₅ is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P₅)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P₅ unit to give a cyclo-P₅ charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P₅ compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals.

Revisiting the 1,2,4-Triaza-3,5-diborolyl Ligand: σ and π Coordination Modes in the Alkali Metal and Rhodium Complexes of a Planar, 6-π-Electron B2N3- Ring

Lithium (2a), sodium (2b), and potassium (2c) salts of 1-methyl-3,5-diphenyl-4-methylamino-1,2,4-triaza-3,5-diborolyl were prepared by deprotonation of the ring nitrogen in neutral precursor 1. The alkali metal derivatives were characterized by multinuclear NMR, mass spectrometry, and single-crystal X-ray diffraction. The structural determinations revealed extended 2D structures for 2a and 2b and an extended 1D structure for 2c. All three solvent-free structures are dominated by sigma interactions, and pi interactions are also present for the potassium derivative. Addition of triphenylborane to 2a, 2b, and 2c produced the adducts 3a, 3b, and 3c, respectively, and these were characterized by multinuclear NMR and mass spectrometry. Structural determinations have been performed for the lithium and potassium salt, showing that Ph3B coordinates at the 2 position of the ring, whereas the alkali metal is coordinated by the pendant methylamino group. The lithium ion is additionally coordinated by three acetonitrile molecules in the monomeric structure of 3a, whereas the potassium ion is coordinated by three phenyl groups, forming the 1D polymeric structure of 3c. Reaction of 2a with [Rh(cod)Cl]2 yielded the dimeric 4, containing two 1,2,4-triaza-3,5-diborolyl rings bridging two Rh(cod) fragments through the substituent-free ring nitrogen atoms.

Electronic structure and bonding studies on triple-decker sandwich complexes with a P6middle ring

DFT and hybrid HF-DFT studies of structure and bonding of CpMP6MCp triple-decker sandwich complexes, ranging from 18-28 valence electrons (VE) with M=Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, show that the middle P6 ring complexes adopt symmetric planar (28 valence electron count [VEC]), asymmetric planar (26 VEC), and puckered (24 VEC) geometries. According to the mno Rule, 50 skeletal electrons are needed for these triple-decker cluster frameworks. For 28 VEC, this corresponds to 10 electrons more than the 50 electrons of the mno Rule if all VE of the metal are included. These additional electrons control the distortion of a P6 middle ring and other finer structural details. Completely filled 2a* and 2b* orbitals in 28 VE complexes lead to a planar symmetrical P6 middle ring, while the occupancy in either 2a* or 2b* alone explains the in-plane distortions (asymmetric) in 26 VE complexes. In comparison with 28 VE complexes, the puckering of P6 middle ring in 24 VE complexes is due to the greater stabilization of 5a and the extra stabilization of the +4 oxidation state of Ti. The quintet state of 22 VE complexes is planar as 2a* and 2b* are half filled. Similar geometrical and bonding patterns of CpScP6ScCp and C2P3H2ScC3P3H3ScC2P3H2 support the carbon-phosphorus analogy further. The 18 VE systems, CpScC3B3H6ScCp+ and CpScP3B3H3ScCp+, have the 50 skeletal electrons as stipulated by the mno Rule. Corresponding anions have 52 skeletal electrons (20 VE); the middle rings here are distorted in the plane.