Neue vanadium-komplexe mit substituentenfreien phosphorliganden

Haptotropism in a Nickel Complex with a Neutral, π‐Bridging cyclo ‐P 4 Ligand Analogous to Cyclobutadiene

Dedicated to Professor Manfred Scheer on the occasion of his 65th birthday

The reaction of (1)Ni(η²‐cod), 2, incorporating a chelating bis(N‐heterocyclic carbene) 1, with P₄ in pentane yielded the dinuclear complex [(2)Ni]₂(μ₂,η² : η²‐P₄), 3, formally featuring a cyclobutadiene‐like, neutral, rectangular, π‐bridging P₄‐ring. In toluene, the butterfly‐shaped complex [(1)Ni]₂(μ₂,η² : η²‐P₂), 4, with a formally neutral P₂‐unit was obtained from 2 and either P₄ or 3. Computational studies showed that a haptotropic rearrangement involving two isomers of the μ₂,η² : η²‐P₄ coordination mode and a low‐energy μ₂,η⁴ : η⁴‐P₄ coordination mode, as previously predicted for related nickel cyclobutadiene complexes, could explain the coalescence observed in the low‐temperature NMR spectra of 3. The insertion of the (1)Ni fragment into a P−P bond of P₇(SiMe₃)₃, forming complex 5 with a norbornane‐like P₇ ligand, was also observed.

Low-oxidation state cobalt-magnesium complexes: ion-pairing and reactivity

Magnesium cobaltates (Arnacnac)MgCo(COD)2 (1-3) were synthesised by reacting (Arnacnac)MgI(OEt2) with K[Co(η4-COD)2] (COD = 1,5-cyclooctadiene) [Arnacnac = CH(ArNCMe)2; Ar = 2,4,6-Me3-C6H2 (Mes), 2,6-Et2-C6H3 (Dep), 2,6-iPr2-C6H3Mes (Dipp)]. Compounds 1-3 form contact ion-pairs in toluene, while solvent separated ion-pairs are formed in THF. The effect of ion-pairing on the reactivity is illustrated by reaction of 2 with tert-butylphosphaalkyne, which affords distinct 1,3-diphosphacyclobutadiene complexes. The heteroleptic sandwich complex [(Depnacnac)MgCo(P2C2tBu2)]2 (4) is selectively formed in toluene, while the homoleptic bis(1,3-diphosphacyclobutadiene) complex [(Depnacnac)Mg(THF)3][Co(P2C2tBu2)2] (5) is obtained in THF. Complex 4 is a precursor to further unusual phosphaorganometallic compounds. Substitution of the labile COD ligand in 4 by white phosphorus (P4) enabled the synthesis of the phosphorus-rich sandwich compound [(Depnacnac)MgCoP4(P2C2tBu2)]2 (6). The heterobimetallic complex (Cp*NiP2C2tBu2)Co(COD) (7) was isolated after treatment of 4 with Cp*Ni(acac) (Cp* = C5Me5, acac = acetylacetonate).

E4 Transfer (E=P, As) to Ni Complexes

The use of [Cp''2 Zr(η1:1 -E4 )] (E=P (1 a), As (1 b), Cp''=1,3-di-tert-butyl-cyclopentadienyl) as phosphorus or arsenic source, respectively, gives access to novel stable polypnictogen transition metal complexes at ambient temperatures. The reaction of 1 a/1 b with [CpR NiBr]2 (CpR =CpBn (1,2,3,4,5-pentabenzyl-cyclopentadienyl), Cp''' (1,2,4-tri-tert-butyl-cyclopentadienyl)) was studied, to yield novel complexes depending on steric effects and stoichiometric ratios. Besides the transfer of the complete En unit, a degradation as well as aggregation can be observed. Thus, the prismane derivatives [(Cp'''Ni)2 (μ,η3:3 -E4 )] (2 a (E=P); 2 b (E=As)) or the arsenic containing cubane [(Cp'''Ni)3 (μ3 -As)(As4 )] (5) are formed. Furthermore, the bromine bridged cubanes of the type [(CpR Ni)3 {Ni(μ-Br)}(μ3 -E)4 ]2 (CpR =Cp''': 6 a (E=P), 6 b (E=As), CpR =CpBn : 8 a (E=P), 8 b (E=As)) can be isolated. Here, a stepwise transfer of En units is possible, with a cyclo-E4 2- ligand being introduced and unprecedented triple-decker compounds of the type [{(CpR Ni)3 Ni(μ3 -E)4 }2 (μ,η4:4 -E'4 )] (CpR =CpBn , Cp'''; E/E'=P, As) are obtained.

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.

The reaction behavior of [Cp2Mo2(CO)4(μ,η2:2-P2)] and [Cp′′Ta(CO)2(η4-P4)] towards hydroxide and tert-butyl nucleophiles

The reaction behavior of [Cp₂Mo₂(CO)₄(μ,η^2:2-P₂)] (1) and [Cp′′Ta(CO)₂(η⁴-P₄)] (2), respectively, towards the anions OH⁻ and ^tBu⁻ are reported, which leads to a selective functionalisation of one P atom.

[3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide

The activation of white phosphorus (P4 ) by transition-metal complexes has been studied for several decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of rare diphosphan-1-ide anions from a P5 ligand by treatment with cyanide. Cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low-valent diimine cobalt complex, white phosphorus, and diorganochlorophosphanes. The reactions of the complexes with tetraalkylammonium or potassium cyanide afford a cyclotriphosphido cobaltate anion 5 and 1-cyanodiphosphan-1-ide anions [R2 PPCN]- (6-R). The molecular structure of a related product 7 suggests a novel reaction mechanism, where coordination of the cyanide anion to the cobalt center induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a phosphorus atom and release of the P2 fragment.

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.

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.

Redox and Coordination Behavior of the Hexaphosphabenzene Ligand in [(Cp*Mo)2 (μ,η(6) :η(6) -P6 )] Towards the "Naked" Cations Cu(+) , Ag(+) , and Tl(.)

Although the cyclo-P₆ complex [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] (1) was reported 30 years ago, little is known about its chemistry. Herein, we report a high-yielding synthesis of 1, the complex 2, which contains an unprecedented cyclo-P₁₀ ligand, and the reactivity of 1 towards the “naked” cations Cu⁺, Ag⁺, and Tl⁺. Besides the formation of the single oxidation products 3 a,b which have a bisallylic distorted cyclo-P₆ middle deck, the [M(1)₂]⁺ complexes are described which show distorted square-planar (M=Cu(4 a), Ag(4 b)) or distorted tetrahedral coordinated (M=Cu(5)) M⁺ cations. The choice of solvent enabled control over the reaction outcome for Cu⁺, as proved by powder XRD and supported by DFT calculations. The reaction with Tl⁺ affords a layered two-dimensional coordination network in the solid state.

The synthesis of the heterocubane cluster [{CpMn}4(μ3-P)4] as a tetrahedral shaped starting material for the formation of polymeric coordination compounds

Thermolysis of [CpMn(η⁶-cht)] with P₄ in 1,3-diisopropylbenzene leads to the formation of the heterocubane [Cp₄Mn₄P₄] (1) in high yields, as a rare example of ‘naked’ phosphorus containing complexes of manganese.

A neutral tetraphosphacyclobutadiene ligand in cobalt(I) complexes

The unusual reactivity of the newly synthesized β-diketiminato cobalt(I) complexes, [(L(Dep)Co)2] (2 a, L(Dep)=CH[C(Me)N(2,6-Et2C6H3)]2) and [L(Dipp)Co⋅toluene] (2 b, L(Dipp)=CH[CHN(2,6-(i)Pr2C6H3)]2), toward white phosphorus was investigated, affording the first cobalt(I) complexes [(L(Dep)Co)2(μ2:η(4),η(4)-P4)] (3 a) and [(L(Dipp)Co)2(μ2:η(4),η(4)-P4)] (3 b) bearing the neutral cyclo-P4 ligand with a rectangular-planar structure. The redox chemistry of 3 a and 3 b was studied by cyclic voltammetry and their chemical reduction with one molar equivalent of potassium graphite led to the isolation of [(L(Dep)Co)2(μ2:η(4),η(4)-P4)][K(dme)4] (4 a) and [(L(Dipp)Co)2(μ2:η(4),η(4)-P4)][K(dme)4] (4 b). Unexpectedly, the monoanionic Co2P4 core in 4 a and 4 b, respectively, contains the two-electron-reduced cyclo-P4(2-) ligand with a square-planar structure and mixed-valent cobalt(I,II) sites. The electronic structures of 3 a, 3 b, 4 a, and 4 b were elucidated by NMR and EPR spectroscopy as well as magnetic measurements and are in agreement with results of broken-symmetry DFT calculations.

Addition of pnictogen atoms to chromium(ii): synthesis, structure and magnetic properties of a chromium(iv) phosphide and a chromium(iii) arsenide

Chromium(ii) chloride reacts with LiCp* (Cp* = C₅Me₅) and LiE (SiMe₃)₂ (E = P or As) to give the chromium(iv) phosphide [(η⁵-Cp*Cr)(μ₃-P)]₄ (1) or the chromium(iii) arsenide [(η⁵-Cp*Cr)₃(μ₃-As)₂] (2), respectively.

Nature of the Chemical Bond in Polypnictides: The Lone Pair Aromatic Anions P42- and As42-

The nature of the chemical bond in inorganic 6pi aromatic systems such as P4(2-), S4(2+), or S2N2 is a matter of particular interest because the phenomenon of aromaticity is not as well established in these compounds as it is in the classic aromatic hydrocarbons. Here we present the synthesis, NMR spectra, and crystal structures of bis(potassium(18-crown-6))cyclotetraphosphide-ammonia(1/2) (K@18-crown-6)2P4 x 2 NH3, bis(rubidium(18-crown-6))cyclotetraphosphide-cyclotetraarsenide-ammonia(1/3) (Rb@18-crown-6)2(P4)0.85(As4)0.15 x 3 NH3, both containing the 6pi aromatic cyclotetraphosphide anion, P4(2-), and the synthesis and crystal structure of bis(potassium(18-crown-6))cyclotetraarsenide (K@18-crown-6)2As4. As a common motive, all three compounds feature neutral molecules with a tripledecker-like coordination of the cyclotetrapnictide anion between two crown ether-coordinated alkali metal cations. With ab initio calculations on the HF level and by employing the concept of the electron localization function ELF, we established that the cyclotetraarsenide anion, As4(2-), shows electron delocalization primarily through the lone pairs, as does P4(2-), and may consequently also be described as lone pair aromatic.

The Chemical Bond in Polyphosphides: Crystal Structures, the Electron Localization Function, and a New View of Aromaticity in P42− and P5−

The incongruent solvation of M(I)4P6 species (M(I) = K, Rb, Cs) in liquid ammonia leads to a broad variety of polyphosphides such as P7(3-), P11(3-), and the putatively aromatic P4(2-) and P5(-), which we investigated by using NMR spectroscopy and single-crystal X-ray structure analysis. The structures of Cs2P4 x 2 NH3, (K@[18]crown-6)3K3(P7)2 x 10 NH3, Rb3P7 x 7 NH3, and (Rb@[18]crown-6)3P7 x 6 NH3 are discussed and compared. The electron localization function ELF is used in a comparison of the chemical bonding of various phosphorus species. The variances of the basin populations provide a well-established measure for electron delocalization and therefore aromaticity. While comparable variance is calculated for P4(2-) and P5(-) it is observed in the lone pairs rather than in the basin populations of the bonds as in the prototypical aromatic hydrocarbons such as benzene or the cyclopentadienide anion. For this behavior, the term "lone pair aromaticity" is proposed.