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

Functionalization of Tetraphosphido Ligands by Heterocumulenes

Although numerous polyphosphido complexes have been accessed through the transition-metal-mediated activation and functionalization of white phosphorus (P4), the selective functionalization of the resulting polyphosphorus ligands in these compounds remains underdeveloped. In this study, we explore the reactions between cyclotetraphosphido cobalt complexes and heterocumulenes, leading to functionalized P4 ligands. Specifically, the reaction of carbon disulfide (CS2) with [K(18c-6)][(Ar*BIAN)Co(η4-P4)] ([K(18c-6)]1, 18c-6 = [18]crown-6) affords the adduct [K(18c-6)][(Ar*BIAN)Co(η3:η1-P4CS2)] ([K(18c-6)]3), in which CS2 is attached to a single phosphorus atom (Ar* = 2,6-dibenzhydryl-4-isopropylphenyl, BIAN = 1,2-bis(arylimino)acenaphthene diimine). In contrast, the insertion of bis(trimethylsilyl)sulfur diimide S(NSiMe3)2 into a P-P bond of [K(18c-6)]1 yields [K(18c-6)][(Ar*BIAN)Co(η3:η1-P4SN2(SiMe3)2)] (K(18c-6)]4). This salt further reacts with Me3SiCl to form [(Ar*BIAN)Co(η3:η1-P4SN2(SiMe3)3] (5), featuring a rare azatetraphosphole ligand. Moreover, treatment of the previously reported complex [(Ar*BIAN)Co(η3:η1-P4C(O)tBu)] (2) with isothiocyanates results in P-C bond insertion, yielding [(Ar*BIAN)Co(η3:η1-P4C(S)N(R)C(O)tBu)] (6a,b; R = Cy, Ph).

Synthesis and Characterization of Novel Cobalt Carbonyl Phosphorus and Arsenic Clusters

Phosphorus- and arsenic-containing cobalt clusters are an interesting class of compounds that continue to provide new structures with captivating bonding patterns. Although the first members of this family were reported 45 years ago, the number of such species is still limited within the broad family of transition metal complexes bearing pnictogen atoms. Herein, we present the reaction of Co2(CO)8 as a cobalt source with a number of phosphorus- and arsenic-containing compounds under variable reaction conditions. These reactions result in various known and novel cobalt phosphorus and cobalt arsenic clusters in which different nuclearity ratios between P/As and Co exist. All those clusters were characterized by X-ray structural analysis and partly by IR, 31P{1H} NMR, EI-MS and elemental analysis. This comprehensive study is the first detailed study in this field that reveals the richness of compounds that could be obtained only by modifying the ratio of used reactants and the involved reaction conditions.

Cobalt-Mediated [3+1] Fragmentation of White Phosphorus: Access to Acylcyanophosphanides

Despite the accessibility of numerous transition metal polyphosphido complexes through transition-metal-mediated activation of white phosphorus, the targeted functionalization of Pn ligands to obtain functional monophosphorus species remains challenging. In this study, we introduce a new [3+1] fragmentation procedure for cyclo-P4 ligands, leading to the discovery of acylcyanophosphanides and -phosphines. Treatment of the complex [K(18c-6)][(Ar*BIAN)Co(η4 -P4 )] ([K(18c-6)]3, 18c-6=[18]crown-6, Ar*=2,6-dibenzhydryl-4-isopropylphenyl, BIAN=1,2-bis(arylimino)acenaphthene diimine) with acyl chlorides results in the formation of acylated tetraphosphido complexes [(Ar*BIAN)Co(η4 -P4 C(O)R)] (R=tBu, Cy, 1-Ad, Ph; 4 a-d). Subsequent reactions of 4 a-d with cyanide salts yield acylated cyanophosphanides [RC(O)PCN]- (9 a-d- ) and the cyclo-P3 cobaltate anion [(Ar*BIAN)Co(η3 -P3 )(CN)]- (8- ). Further reactions of 4 a-d with trimethylsilyl cyanide (Me3 SiCN) and isocyanides provide insight into a plausible mechanism of this [3+1] fragmentation reaction, as these reagents partially displace the P4 C(O)R ligand from the cobalt center. Several potential intermediates of the [3+1] fragmentation were characterized. Additionally, the introduction of a second acyl substituent was achieved by treating [K(18c-6)]9b with CyC(O)Cl, resulting in the first bis(acyl)monocyanophosphine (CyC(O))2 PCN (10).

Direct Synthesis of Phosphoryltriacetates from White Phosphorus via Visible Light Catalysis

Organophosphorus compounds (OPCs) are widely used in many fields. However, traditional synthetic routes in the industry usually involve multistep and hazardous procedures. Therefore, it's of great significance to construct such compounds in an environmentally-friendly and facile way. Herein, a photoredox catalytic method has been developed to construct novel phosphoryltriacetates. Using fac-Ir(ppy)3 (ppy=2-phenylpyridine) as the photocatalyst and blue LEDs (456 nm) as the light source, white phosphorus can react with α-bromo esters smoothly to generate phosphoryltriacetates in moderate to good yields. This one-step approach features mild reaction conditions and simple operational process without chlorination.

Formation of a Hexaphosphido Cobalt Complex through P-P Condensation

The reaction between diphosphorus derivatives [(Cl ImDipp )P2 (Dipp)]OTf (1[OTf]) and [(Cl ImDipp )P2 (Dipp)Cl] (1[Cl]) with the cyclotetraphosphido cobalt complex [K(18c-6)][(PHDI)Co(η4 -cyclo-P4 )] (2) leads to the formation of complex [(PHDI)Co{η4 -cyclo-P6 (Dipp)(Cl ImDipp )}] (3), which features an unusual hexaphosphido ligand [Cl ImDipp =4,5-dichloro-1,3-bis(2,6-diisopropylphenyl)imidazol-2-yl, Dipp=2,6-diisopropylphenyl, 18c-6=18-crown-6, PHDI=bis(2,6-diisopropylphenyl)phenanthrene-9,10-diimine]. Complex 3 was obtained as a crystalline material with a moderate yield at low temperature. Upon exposure to ambient temperature, compound 3 slowly transforms into two other compounds, [K(18c-6)][(PHDI)Co(η4 -P7 Dipp)] (4) and [(PHDI)Co{cyclo-P5 (Cl ImDipp )}] (5). The novel complexes 3-5 were characterized using multinuclear NMR spectroscopy and single-crystal X-ray diffraction. To shed light on the formation of these compounds, a proposed mechanism based on 31 P NMR monitoring studies is presented.

Photochemical Benzylation of White Phosphorus

Organophosphorus compounds (OPCs) have wide application in organic synthesis, material sciences, and drug discovery. Generally, the vast majority of phosphorus atoms in OPCs are derived from white phosphorus (P4). However, the large-scale preparation of OPCs mainly proceeds through the multistep and environmentally toxic chlorine route from P4. Herein, we report the direct benzylation of P4 promoted by visible light. The cheap and readily available benzyl bromide was used as a benzylation reagent, and tetrabenzylphosphonium bromide was directly synthesized from P4. In addition, the metallaphotoredox catalysis strategy was applied to functionalize P4 for the first time, which significantly improved the application range of the substituted benzyl bromide.

Synthesis and Reactivity of a Cyclooctatetraene-Like Polyphosphorus Ligand Complex [Cyclo-P8 ]

The thermolysis of Cp'''Ta(CO)₄ with white phosphorus (P₄ ) gives access to [{Cp'''Ta}₂ (μ,η^{2 : 2 : 2 : 2 : 1 : 1} -P₈ )] (A), representing the first complex containing a cyclooctatetraene-like (COT) cyclo-P₈ ligand. While ring sizes of n >6 have remained elusive for cyclo-P_n structural motifs, the choice of the transition metal, co-ligand and reaction conditions allowed the isolation of A. Reactivity investigations reveal its versatile coordination behaviour as well as its redox properties. Oxidation leads to dimerization to afford [{Cp'''Ta}₄ (μ₄ ,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1} -P₁₆ )][TEF]₂ (4, TEF=[Al(OC{CF₃ }₃ )₄ ]^- ). Reduction, however, leads to the fission of one P-P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand]₂ [{Cp'''Ta}₄ (μ₄ ,η^{2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1} -P₁₆ )] (5), which features an unprecedented chain-type P₁₆ ligand. Lastly, A serves as a P₂ synthon, via ring contraction to the triple-decker complex [{Cp'''Ta}₂ (μ,η^6 : 6 -P₆ )] (B).

Halogenation and Nucleophilic Quenching: Two Routes to E−X Bond Formation in Cobalt Triple‐Decker Complexes (E=As, P; X=F, Cl, Br, I)

The oxidation of [(Cp’’’Co)₂(μ,η² : η²‐E₂)₂] (E=As (1), P (2); Cp’’’=1,2,4‐tri(tert‐butyl)cyclopentadienyl) with halogens or halogen sources (I₂, PBr₅, PCl₅) was investigated. For the arsenic derivative, the ionic compounds [(Cp’’’Co)₂(μ,η⁴ : η⁴−As₄X)][Y] (X=I, Y=[As₆I₈]_0.5 (3 a), Y=[Co₂Cl_6‐nI_n]_0.5 (n=0, 2, 4; 3 b); X=Br, Y=[Co₂Br₆]_0.5 (4); X=Cl, Y=[Co₂Cl₆]_0.5 (5)) were isolated. The oxidation of the phosphorus analogue 2 with bromine and chlorine sources yielded the ionic complexes [(Cp’’’Co)₂(μ‐PBr₂)₂(μ‐Br)][Co₂Br₆]_0.5 (6 a), [(Cp’’’Co)₂(μ‐PCl₂)₂(μ‐Cl)][Co₂Cl₆]_0.5 (6 b) and the neutral species [(Cp’’’Co)₂(μ‐PCl₂)(μ‐PCl)(μ,η¹ : η¹‐P₂Cl₃] (7), respectively. As an alternative approach, quenching of the dications [(Cp’’’Co)₂(μ,η⁴ : η⁴‐E₄)][TEF]₂ (TEF=[Al{OC(CF₃)₃}₄]⁻, E=As (8), P (9)) with KI yielded [(Cp’’’Co)₂(μ,η⁴ : η⁴‐As₄I)][I] (10), representing the homologue of 3, and the neutral complex [(Cp’’’Co)(Cp’’’CoI₂)(μ,η⁴ : η¹‐P₄)] (11), respectively. The use of [(CH₃)₄N]F instead of KI leads to the formation of [(Cp’’’Co)₂(μ‐PF₂)(μ,η² : η¹ : η¹‐P₃F₂)] (12) and 2, thereby revealing synthetic access to polyphosphorus compounds bearing P−F groups and avoiding the use of very strong fluorinating reagents, such as XeF₂, that are difficult to control.

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.

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.

Redox Chemistry of Heterobimetallic Polypnictogen Triple-Decker Complexes - Rearrangement, Fragmentation and Transfer

The redox chemistry of the heterobimetallic triple‐decker complexes [(Cp*Fe)(Cp′′′Co)(μ,η⁵:η⁴‐E₅)] (E=P (1), As (2), Cp*=1,2,3,4,5‐pentamethyl‐cyclopentadienyl, Cp′′′=1,2,4‐tri‐tertbutyl‐cyclopentadienyl) and [(Cp′′′Co)(Cp′′′Ni)(μ,η³:η³‐E₃)] (E=P (10), As (11)) was investigated. Compound 1 and 2 could be oxidized to the monocations 3 and 4 and further to the dications 5 and 6, while the initially folded cyclo‐E₅ ligand planarizes upon oxidation. The reduction leads to an opposite change in the geometry of the middle deck, which is now folded stronger into the direction of the other metal fragment (formation of monoanions 7 and 8). For the arsenic compound 8, a different behavior is found since a fragmentation into an As₆ (9) and As₃ ligand complex occurs. The Co and Ni triple‐decker complexes 10 and 11 can be oxidized initially to the heterometallic monocations 12 and 13, which are not stable in solution and convert selectively into the homometallic nickel complexes 14 and 15 and the cobalt complexes 16 and 17. This behavior was further proven by the oxidation of [(Cp′′′Co)(Cp′′Ni)(μ,η³:η²‐P₃)] (19, Cp′′=1,3‐di‐tertbutyl‐cyclopentadienyl) comprising two different Cp ligands. The transfer of {Cp^RM} fragments can be suppressed when a {W(CO)₅} unit is coordinated to the P₃ ligand (20) prior to the oxidation and the mixed cobalt and nickel cation 21 can be isolated. The reduction of 10 and 11 yields the heterometallic monoanions 22 and 23, where no transfer of the {Cp^RM} fragments is observed.

Reactivity of Cu(I) Nacnac Complexes Toward Polypnictogen Compounds

The nacnac Cu(I) compound [LCu(MeCN)] (2) (L = [{N(C₆H₃Me₂-2,6)C(Me)}₂CH]^-) was reacted with complexes containing aromatic cyclo-E₅ ([Cp*Fe(η⁵-E₅)], E = P (1a), As (1b), Cp* = η⁵-C₅Me₅), cyclo-P₄ ([Cp‴Co(η⁴-P₄)] (3), Cp‴ = η⁵-C₅H₂^tBu₃) and cyclo-E₃ ligands ([Cp‴Ni(η³-E₃)], E = P (4a), As (4b)) yielding the heterometallic complexes [(Cp*Fe)(μ,η^5:2-E₅)(LCu)] (E = P (5a), As (5b)), [(Cp*Fe)(μ₃,η^5:2:1-E₅)(LCu)₂] (E = P (6a), As (6b)), [(Cp‴Co)(μ,η^4:2-P₄)(LCu)] (7), [(Cp‴Co)(μ₃,η^4:2:1-P₄)(LCu)₂] (8), and [(Cp‴Ni)(μ,η^3:2-E₃)(LCu)] (E = P (9a), As (9b)). These complexes are rare examples of the coordination of a group 11 metal to aromatic cyclo-E_n (E = P, As; n = 3-5) ligands. All products were comprehensively characterized by crystallographic and spectroscopic methods. Their dynamic behavior in solution was studied by VT (variable-temperature) NMR spectroscopy, and their electronic structures were elucidated by DFT calculations.

Coordination Behavior of a P4 -Butterfly Complex towards Transition Metal Lewis Acids: Preservation versus Rearrangement

The reactivity of the P4 butterfly complex [{Cp'''Fe(CO)2 }2 (μ,η1:1 -P4 )] (1, Cp'''=η5 -C5 H2 tBu3 ) towards divalent Co, Ni and Zn salts is investigated. The reaction with the bromide salts leads to [{Cp'''Fe(CO)2 }2 (μ3 ,η2:1:1 -P4 ){MBr2 }] (M=Co (2Co), Ni (2Ni), Zn (2Zn)) in which the P4 butterfly scaffold is preserved. The use of the weakly ligated Co complex [Co(NCCH3 )6 ][SbF6 ]2 , results in the formation of [{(Cp'''Fe(CO)2 )2 (μ3 ,η4:1:1 -P4 )}2 Co][SbF6 ]3 (3), which represents the second example of a homoleptic-like octaphospha-metalla-sandwich complex. The formation of the threefold positively charged complex 3 occurs via redox processes, which among others also enables the formation of [{Cp'''Fe(CO)2 }4 (μ5 ,η4:1:1:1:1 -P8 ){Co(CO)2 }][SbF6 ] (4), bearing a rare octaphosphabicyclo[3.3.0]octane unit as a ligand. On the other hand, the reaction with [Zn(NCCH3 )4 ][PF6 ]2 yields the spiro complex [{(Cp'''Fe(CO)2 )2 (μ3 ,η2:1:1 -P4 )}2 Zn][PF6 ]2 (5) under preservation of the initial structural motif.

From a P4 butterfly scaffold to cyclo- and catena-P4 units

The reactivity of [{Cp'''Fe(CO)2}2(μ,η1 : 1-P4)] (1) towards half-sandwich complexes of Ru(ii), Rh(iii), and Ir(iii) is studied. The coordination of these Lewis acids leads to a rearrangement of the P4 butterfly unit to form complexes with either an aromatic cyclo-P4R2 unit (R = Cp'''Fe(CO)2) or a catena-tetraphosphaene entity.

Fragmentation Mechanism of White Phosphorus: A Theoretical Insight into Multiple Cleavage/Formation of P-P and P-C Bonds

Molecular-level understanding of metal-mediated white phosphorus (P₄ ) activation is meaningful but challenging because of its direct relevance to the conversion of P₄ into useful organophosphorus compounds as well as the complicated and unforeseeable cleavage process of P-P bonds. The related study, however, has still rarely been achieved to date. Here, a theoretical insight into the step-by-step process of three P-P bond cleavage/four P-C bond formation for [P₃ +P₁ ]-fragmentation of P₄ mediated by lutetacyclopentadienes is reported. The unique charge-separated intermediate and the intermolecular cooperation between two lutetacyclopentadienes play a vital role in the subsequent P-P/P-C bond breaking/forming. It is found that, although the first P-C formation is involved in the assembly of the cyclo-P₃ [R₄ C₄ P₃ ]^- unit, the construction of the aromatic five-membered P₁ heterocycle [R₄ C₄ P]^- is completed prior to the cyclo-P₃ formation. The reaction mechanism has been carefully elucidated by analyses of the geometric structure, frontier molecular orbitals, bond index, and natural charge, which greatly broaden and enrich the general knowledge of the direct functionalization of P₄ .

Iron-Gallium and Cobalt-Gallium Tetraphosphido Complexes

The synthesis and characterization of two heterobimetallic complexes [K([18]crown-6){(η4-C14H10)Fe(μ-η4:η2-P4)Ga(nacnac)}] (1) (C14H10 = anthracene) and [K(dme)2{(η4-C14H10)Co(μ-η4:η2-P4)Ga(nacnac)}] (2) with strongly reduced P4 units is reported. Compounds 1 and 2 are prepared by reaction of the gallium(III) complex [(nacnac)Ga(η2-P4)] (nacnac = CH[CMeN(2,6-iPr2C6H3)]2) with bis(anthracene)ferrate(1-) and -cobaltate(1-) salts. The molecular structures of 1 and 2 were determined by X-ray crystallography and feature a P4 chain which binds to the transition metal atom via all four P atoms and to the gallium atom via the terminal P atoms. Multinuclear NMR studies on 2 suggest that the molecular structure is preserved in solution.

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.

Nucleophilic Activation of Red Phosphorus for Controlled Synthesis of Polyphosphides

Reactions between red phosphorus (P_red) and potassium ethoxide in various organic solvents under reflux convert this rather inert form of the element to soluble polyphosphides. The activation is hypothesized to proceed via a nucleophilic attack by ethoxide on the polymeric structure of P_red, leading to disproportionation of the latter, as judged from observation of P(OEt)₃ in the reaction products. A range of solvents has been probed, revealing that different polyphosphide anions (P₇^3-, P₁₆^2-, P₂₁^3-, and P₅^-) can be stabilized depending on the combination of the boiling point and dielectric constant (polarity) of the solvent. The effectiveness of activation also depends on the nature of nucleophile, with the rate of reaction between P_red and KOR increasing in the order t-Bu < n-Hex < Et < Me, which is in agreement with the increasing order of nucleophilic strength. Thiolates and amides were also examined as potential activators, but the reaction with these nucleophiles were substantially slower; nonetheless, all reactions between P_red and NaSR yielded exclusively P₁₆^2- as a soluble polyphosphide product.

Element-Element Bond Formation upon Oxidation and Reduction

The redox chemistry of [(Cp′′′Co)₂(μ,η²:η²‐E₂)₂] (E=P (1), As (2); Cp′′′=1,2,4‐tri(tert‐butyl)cyclopentadienyl) was investigated. Both compounds can be oxidized and reduced twice. That way, the monocations [(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)][X] (E=P, X=BF₄ (3 a), [FAl] (3 b); E=As, X=BF₄ (4 a), [FAl] (4 b)), the dications [(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)][TEF]₂ (E=P (5), As (6)), and the monoanions [K(18‐c‐6)(dme)₂][(Cp′′′Co)₂(μ,η⁴:η⁴‐E₄)] (E=P (7), As (8)) were isolated. Further reduction of 7 leads to the dianionic complex [K(18‐c‐6)(dme)₂][K(18‐c‐6)][(Cp′′′Co)₂(μ,η³:η³‐P₄)] (9), in which the cyclo‐P₄ ligand has rearranged to a chain‐like P₄ ligand. Further reduction of 8 can be achieved with an excess of potassium under the formation of [K(dme)₄][(Cp′′′Co)₂(μ,η³:η³‐As₃)] (10) and the elimination of an As₁ unit. Compound 10 represents the first example of an allylic As₃ ligand incorporated into a triple‐decker complex.

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.

Direct functionalization of white phosphorus with anionic dicarbenes and mesoionic carbenes: facile access to 1,2,3-triphosphol-2-ides

A series of unique C₂P₃-ring compounds [(ADC^Ar)P₃] (4) are readily accessible in an almost quantitative yield by the direct functionalization of white phosphorus (P₄) with appropriate anionic dicarbenes [Li(ADC^Ar)].

A series of unique C₂P₃-ring compounds [(ADC^Ar)P₃] (ADC^Ar = ArC{(DippN)C}₂; Dipp = 2,6-iPr₂C₆H₃; Ar = Ph 4a, 3-MeC₆H₄4b, 4-MeC₆H₄4c, and 4-Me₂NC₆H₄4d) are readily accessible in an almost quantitative yield by the direct functionalization of white phosphorus (P₄) with appropriate anionic dicarbenes [Li(ADC^Ar)]. The formation of 1,2,3-triphosphol-2-ides (4a–4d) suggests unprecedented [3 + 1] fragmentation of P₄ into P₃⁺ and P^–. The P₃⁺ cation is trapped by the (ADC^Ar)^– to give 4, while the putative P^– anion reacts with additional P₄ to yield the Li₃P₇ species, a useful reagent in the synthesis of organophosphorus compounds. Remarkably, the P₄ fragmentation is also viable with the related mesoionic carbenes (iMICs^Ar) (iMIC^Ar = ArC{(DippN)₂CCH}, i stands for imidazole-based) giving rise to 4. DFT calculations reveal that both the C₃N₂ and C₂P₃-rings of 4 are 6π-electron aromatic systems. The natural bonding orbital (NBO) analyses indicate that compounds 4 are mesoionic species featuring a negatively polarized C₂P₃-ring. The HOMO–3 of 4 is mainly the lone-pair at the central phosphorus atom that undergoes σ-bond formation with a variety of metal-electrophiles to yield complexes [{(ADC^Ar)P₃}M(CO)_n] (M = Fe, n = 4, Ar = Ph 5a or 4-Me-C₆H₄5b; M = Mo, n = 5, Ar = Ph 6; M = W, n = 5, Ar = 4-Me₂NC₆H₄7).

Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO)₅ }₂ ] (1 a) (Cp*=C₅ Me₅ ) with the anionic cyclo-P_n ligand complex [(η³ -P₃ )Nb(ODipp)₃ ]^- (2, Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)₅ }₂ {μ₃ ,η^3:1:1 -P₄ Cp*}Nb(ODipp)₃ ]^- (3), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)₅ }₂ ] (E=P: 1 a, As: 1 b) with the neutral complex [Cp'''Co(η⁴ -P₄ )] (Cp'''=1,2,4-tBu₃ C₅ H₂ ) led to a cyclo-P₄ E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P₄ ligand. Starting from 1 a, the two isomers [Cp'''Co(μ₃ ,η^4:1:1 -P₅ Cp*){W(CO)₅ }₂ ] (5 a,b), and from 1 b, the three isomers [Cp'''Co(μ₃ ,η^4:1:1 -AsP₄ Cp*){W(CO)₅ }₂ ] (6 a-c) with unprecedented cyclo-P₄ E ligands (E=P, As) were isolated. The complexes 6 a-c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P₄ As ligands. The possible reaction pathways for the formation of 5 a,b and 6 a-c were investigated by a combination of temperature-dependent ³¹ P{¹ H} NMR studies and DFT calculations.

The Chemistry of Yellow Arsenic

The generation and handling of the light-sensitive and metastable yellow arsenic (As₄) is extremely challenging. In view of recent breakthroughs in synthesizing As₄ storage materials and transfer reagents, the more intensive use of yellow arsenic as a source for further reactions can be expected. Given these aspects, the current stage of knowledge of the direct use of As₄ is comprehensively summarized in the present review, which lists the activation of As₄ by main group elements as well as transition metal compounds (including the f-block elements). Moreover, it also partly compares the reaction outcomes in relation to the corresponding reactions of P₄. The possibility of using alternative sources for generating arsenic moieties and compounds is also discussed. The release of As₄ molecules from precursor compounds and the use of transfer reagents for polyarsenic entities open up new synthetic pathways to avoid the direct generation of yellow arsenic solutions and to ensure its smooth usage for subsequent reactions.

Synthesis of a Cyclic Co2Sn2 Cluster Using a Co- Synthon

[Ar'SnCo]2 (1, Ar' = C6H3-2,6{C6H3-2,6- iPr2}2), a rare metal-metal bonded cobalt-tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)0.2][Co(1,5-cod)2] (cod = 1,5-cyclooctadiene) with [Ar'Sn(μ-Cl)]2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co2Sn2 core with strong metal-metal bonds between tin and cobalt and a weaker tin-tin interaction. Reaction of 1 with white phosphorus afforded [Ar'2Sn2Co2P4] (2), the first molecular cluster compound containing phosphorus, cobalt and tin.

Mono- and dinuclear tetraphosphabutadiene ferrate anions

Reduction of [Cp^ArFe(μ-Br)]₂ (1, Cp^Ar = C₅(C₆H₄-4-Et)₅) by potassium napthalenide, followed by the addition of white phosphorus, affords [K(18-c-6){Cp^ArFe(η⁴-P₄)}] (2, 18-c-6 = [18]crown-6), which features a planar cyclo-P₄^2- ligand. The related diiron complex [Na₂(THF)₅(Cp^ArFe)₂(μ,η^4:4-P₄)] (3) was obtained by reducing 1 with sodium amalgam in the presence of P₄. Protonation of 3 affords [Na(THF)₃][(Cp^ArFe)₂(μ,η^4:4-P₄)(H)] (4), while the reaction of 3 with trimethylchlorosilane gives the nortricyclane compound P₇(SiMe₃)₃ as the main product.

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.