E4 Butterfly Complexes (E=P, As) as Chelating Ligands

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 Ternary Clusters Containing the [As16]10- Anion, [MM'As16]4- (M = Nb or Ta; M' = Cu or Ag)

The [Nb@As₈]^3- anion was first isolated from solution in 1986, and a number of isostructural [M@Pn₈]^n- clusters (M = Nb, Cr, or Mo; Pn = As or Sb; n = 2 or 3) have since been reported. We show here how anions of this class can be used as synthetic precursors that, in combination with sources of low-valent late transition metals (Cu and Ag), generate ternary polyarsenide cluster anions with unprecedented structural motifs. Chain type [MM'As₁₆]^4- (M = Nb or Ta; M' = Cu or Ag) units are found in compounds 2-5. These clusters contain a nortricyclane-like As₇ cage and a [M@As₈] crown, linked by a single As atom, and represent a fusion of two quite distinct branches of polyarsenide chemistry. Our analysis of the electronic structure confirms that the cluster retains many of the features of the component units. Electrospray ionization mass spectrometry reveals a series of smaller component ions containing 8-12 As atoms, the density functional theory-computed structures of which can be understood in terms of the pseudoelement concept. This work not only presents a new type of coordination mode for As clusters but also offers a point of entry for the rational design of multinary arsenic-based materials.

Substituted aromatic pentaphosphole ligands - a journey across the p-block

The functionalization of pentaphosphaferrocene [Cp*Fe(η5-P5)] (1) with cationic group 13-17 electrophiles is shown to be a general synthetic strategy towards P-E bond formation of unprecedented diversity. The products of these reactions are dinuclear [{Cp*Fe}2{μ,η5:5-(P5)2EX2}][TEF] (EX2 = BBr2 (2), GaI2 (3), [TEF]- = [Al{OC(CF3)3}4]-) or mononuclear [Cp*Fe(η5-P5E)][X] (E = CH2Ph (4), CHPh2 (5), SiHPh2 (6), AsCy2 (7), SePh (9), TeMes (10), Cl (11), Br (12), I (13)) complexes of hetero-bis-pentaphosphole ((cyclo-P5)2R) or hetero-pentaphosphole ligands (cyclo-P5R), the aromatic all-phosphorus analogs of prototypical cyclopentadienes. Further, modifying the steric and electronic properties of the electrophile has a drastic impact on its reactivity and leads to the formation of [Cp*Fe(μ,η5:2-P5)SbICp'''][TEF] (8) which possesses a triple-decker-like structure. X-ray crystallographic characterization reveals the slightly twisted conformation of the cyclo-P5R ligands in these compounds and multinuclear NMR spectroscopy confirms their integrity in solution. DFT calculations shed light on the bonding situation of these compounds and confirm the aromatic character of the pentaphosphole ligands on a journey across the p-block.

Insertion of Phosphenium Ions into a Bicyclo[1.1.0]Tetraphosphabutane Iron Complex

By reacting [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₄)] (1) with in situ generated phosphenium ions [Ph₂P][A] ([A]^- = [OTf]^- = [O₃SCF₃]^-, [PF₆]^-), a mixture of two main products of the composition [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₅(C₆H₅)₂)][PF₆] (2a and 3a) could be identified by extensive ³¹P NMR spectroscopic studies at 193 K. Compound 3a was also characterized by X-ray diffraction analysis, showing the rarely observed bicyclo[2.1.0]pentaphosphapentane unit. At room temperature, the novel compound [{Cp‴Fe}(µ,η^4:1-P₅Ph₂){Cp‴(CO)₂Fe}][PF₆] (4) is formed by decarbonylation. Reacting 1 with in situ generated diphenyl arsenium ions gives short-lived intermediates at 193 K which disproportionate at room temperature into tetraphenyldiarsine and [{Cp‴Fe(CO)₂}₄(µ₄,η^1:1:1:1-P₈)][OTf]₂ (5) containing a tetracyclo[3.3.0.0^2,7.0^3,6]octaphosphaoctane ligand.

Reactivity of P4 butterfly complexes towards NHCs - generation of a metal-bridged P2 dumbbell complex

The reactivity of the P₄ butterfly complexes [{Cp'''Fe(CO)₂}₂(μ,η^1:1-P₄)] (A, Cp''' = C₅H₂^tBu₃) and [{Cp*Cr(CO)₃}₂(μ,η^1:1-P₄)] (B, Cp* = C₅(CH₃)₅) towards the N-heterocyclic carbene IMe (1,3,4,5-tetramethyl-imidazol-2-ylidene) is reported. The reaction of A affords [P(IMe)₂][Fe(CO)₂Cp'''] (1) or [P(IMe)₂][{Cp'''Fe}₂(μ,η^3:3-P₃)] (2), the latter possessing a P₃-allylic moiety. In contrast, the reaction of B yields [P(IMe)₂][Cr(CO)₃Cp*] (3) and [{Cp*Cr(CO)₂}(η²-P₂IMe₂)][Cr(CO)₃Cp*] (4), featuring a novel metal-bridged P₂ dumbbell.

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.

Transition-Metal-Mediated Functionalization of White Phosphorus

Recently there has been great interest in the reactivity of transition-metal (TM) centers towards white phosphorus (P4 ). This has ultimately been motivated by a desire to find TM-mediated alternatives to the current industrial routes used to transform P4 into myriad useful P-containing products, which are typically indirect, wasteful, and highly hazardous. Such a TM-mediated process can be divided into two steps: activation of P4 to generate a polyphosphorus complex TM-Pn , and subsequent functionalization of this complex to release the desired phosphorus-containing product. The former step has by now become well established, allowing the isolation of many different TM-Pn products. In contrast, productive functionalization of these complexes has proven extremely challenging and has been achieved only in a relative handful of cases. In this review we provide a comprehensive summary of successful TM-Pn functionalization reactions, where TM-Pn must be accessible by reaction of a TM precursor with P4 . We hope that this will provide a useful resource for continuing efforts that are working towards this highly challenging goal of modern synthetic chemistry.

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.

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.

A soft molecular 2Fe-2As precursor approach to the synthesis of nanostructured FeAs for efficient electrocatalytic water oxidation

An unprecedented molecular 2Fe-2As precursor complex was synthesized and transformed under soft reaction conditions to produce an active and long-term stable nanocrystalline FeAs material for electrocatalytic water oxidation in alkaline media. The 2Fe2As-centred β-diketiminato complex, having an unusual planar Fe2As2 core structure, results from the salt-metathesis reaction of the corresponding β-diketiminato FeIICl complex and the AsCO- (arsaethynolate) anion as the monoanionic As- source. The as-prepared FeAs phase produced from the precursor has been electrophoretically deposited on conductive electrode substrates and shown to act as a electro(pre)catalyst for the oxygen evolution reaction (OER). The deposited FeAs undergoes corrosion under the severe anodic alkaline conditions which causes extensive dissolution of As into the electrolyte forming finally an active two-line ferrihydrite phase (Fe2O3(H2O) x ). Importantly, the dissolved As in the electrolyte can be fully recaptured (electro-deposited) at the counter electrode making the complete process eco-conscious. The results represent a new and facile entry to unexplored nanostructured transition-metal arsenides and their utilization for high-performance OER electrocatalysis, which are also known to be magnificent high-temperature superconductors.

Systematic DFT Studies on Binary Pseudo-tetrahedral Zintl Anions: Relative Stabilities and Reactivities towards Protons, Trimethylsilyl Groups, and Iron Complex Fragments

Binary pseudo-tetrahedral Zintl anions composed of (semi)metal atoms of the p-block elements have proven to be excellent starting materials for the synthesis of a variety of heterometallic and intermetalloid transition metal-main group metal cluster anions. However, only ten of the theoretically possible 48 anions have been experimentally accessed to date as isolable salts. This brings up the question whether the other species are generally not achievable, or whether synthetic chemists just have not succeeded in their preparation so far. To contribute to a possible answer to this question, global minimum structures were calculated for all anions of the type (TrTt3 )5- , (TrPn3 )2- , and (Tt2 Pn2 )2- , comprising elements of periods 3 to 6 (Tr: triel, Al⋅⋅⋅Tl; Tt: tetrel, Si⋅⋅⋅Pb; Pn: pnictogen, P⋅⋅⋅Bi). By analyzing the computational results, a concept was developed to predict which of the yet missing anions should be synthesizable and why. Additionally, the results of an electrophilic attack by protons or trimethylsilyl groups or a nucleophilic attack by transition metal complex fragments are described. The latter yields butterfly-like structures that can be viewed as a new form of adaptable tridentate chelating ligands.

The Butterfly Complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] as a Versatile Ligand and Its Unexpected P1 /P3 Fragmentation

The versatile coordination behavior of the P4 butterfly complex [{Cp*Cr(CO)3 }2 (μ,η1:1 -P4 )] (1) towards Lewis acidic pentacarbonyl compounds of Cr, Mo and W is reported. The reaction of 1 with [W(CO)4 (nbd)] (nbd=norbornadiene) yields the complex [{Cp*Cr(CO)3 }2 (μ3 ,η1:1:1:1 -P4 ){W(CO)4 }] (2) in which 1 serves as a chelating P4 butterfly ligand. In contrast, reactions of 1 with [M(CO)4 (nbd)] (M=Cr (a), Mo (b)) result in the step-wise formation of [{Cp*Cr(CO)2 }2 (μ3 ,η3:1:1 -P4 ){M(CO)5 }] (3 a,b) and [{Cp*Cr(CO)2 }2 -(μ4 ,η3:1:1:1 -P4 ){M(CO)5 }2 ] (4 a,b) which contain a folded cyclo-P4 unit. Complex 4 a undergoes an unprecedented P1 /P3 -fragmentation yielding the cyclo-P3 complex [Cp*Cr(CO)2 (η3 -P3 )] (5) and the as yet unknown phosphinidene complex [Cp*Cr(CO)2 {Cr(CO)5 }2 (μ3 -P)] (6). The identity of 6 is confirmed by spectroscopic methods and by the in situ formation of [{Cp*Cr(CO)2 (tBuNC)}P{Cr(CO)5 }2 (tBuNC)] (7). DFT calculations throw light on the bonding situation of the reported products.

Highly soluble Cu(i)-acetonitrile salts as building blocks for novel phosphorus-rich organometallic-inorganic compounds

The synthesis of the air-stable and highly soluble Cu(i)-acetonitrile salts [Cu(CH3CN)3.5][FAl] (1) ([FAl] = FAl{OC(C6F10)(C6F5)}3) and [Cu(CH3CN)4][TEF] (2) ([TEF] = Al{OC(CF3)3}4) is presented. Compound 1 reacts with the organometallic polyphosphorus complexes [Cp2Mo2(CO)4(η2-P2)] (A) and [(Cp*Fe(η5-P5)] (B) and salt 2 reacts with B to form one new (3) and three unprecedented (4-6) phosphorus-rich Cu(i) dimers with the general formulas [Cu2(μ,η1:η1-A)2(η2-A)2][FAl]2 (3), [Cu2(μ,η1:η1-A)2(η1-CH3CN)4][FAl]2 (4), [Cu2(μ,η1:η1-B)2(η1-CH3CN)4][FAl]2 (5) and [Cu2(μ,η1:η1-B)2(η1-CH3CN)4][TEF]2 (6).

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.

Selective [3+1] Fragmentations of P4 by "P" Transfer from a Lewis Acid Stabilized [RP4 ]- Butterfly Anion

Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P₄ ⋅ BPh₃ ] (Mes*=2,4,6-tBu₃ C₆ H₂ ) are reported. The reactions proceed by extrusion of a P₁ fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P₃ , which was isolated as a dimer and trapped by 1,3-cyclohexadiene as a Diels-Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P₁ - and P₃ -containing organophosphorus compounds in two simple steps from white phosphorus.

Insertion of phenyl isothiocyanate into a P-P bond of a nickel-substituted bicyclo[1.1.0]tetraphosphabutane

A new reaction mode for bicyclo[1.1.0]tetraphosphabutanes is reported. The C[double bond, length as m-dash]S and C[double bond, length as m-dash]N bonds of phenyl isothiocyanate reversibly insert into a P-P bond of [{CpNi(IMes)}2(μ-η(1):η(1)-P4)] (, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), forming isomers and . X-ray crystallography and (31)P{(1)H} NMR spectroscopy revealed similar bicyclo[3.1.0]heterohexane structures for these compounds.

Pentaarylcyclopentadienyl Iron, Cobalt, and Nickel Halides

The preparation of new stable half-sandwich transition metal complexes, having a bulky cyclopentadienyl ligand C5(C6H4-4-Et)5 (Cp(Ar1)) or C5(C6H4-4-nBu)5 (Cp(Ar2)), is reported. The tetrahydrofuran (THF) adduct [Cp(Ar1)Fe(μ-Br)(THF)]2 (1a) was synthesized by reacting K[Cp(Ar1)] with [FeBr2(THF)2] in THF, and its molecular structure was determined by X-ray crystallography. Complex 1a easily loses its coordinated THF molecules under vacuum to form the solvent-free complex [Cp(Ar1)Fe(μ-Br)]2 (1b). The analogous complexes [Cp(Ar1)Co(μ-Br)]2 (2), [Cp(Ar1)Ni(μ-Br)]2 (3), and [Cp(Ar2)Ni(μ-Br)]2 (4) were synthesized from CoBr2 and [NiBr2(1,2-dimethoxyethane)]. The mononuclear, low-spin cobalt(III) and nickel(III) complexes [Cp(Ar2)MI2] (5, M = Co; 6, M = Ni) were prepared by reacting the radical Cp(Ar2) with NiI2 and CoI2. The complexes were characterized by NMR and UV-vis spectroscopies and by elemental analyses. Single-crystal X-ray structure analyses revealed that the dimeric complexes 1a, 1b, and 3 have a planar M2Br2 core, whereas 2 and 4 feature a puckered M2Br2 ring.

Low temperature isolation of a dinuclear silver complex of the cyclotetraphosphane [ClP(μ-PMes*)]2

The reaction of the cyclotetraphosphane [ClP(μ-PMes*)]2 (, Mes* = 2,4,6-tri-tert-butylphenyl) with Ag[Al(OR(F))4] (R(F) = CH(CF3)2) resulted in a labile, dinuclear silver complex of , which eliminates AgCl above -30 °C. Its properties were investigated by spectroscopic methods, single crystal X-ray diffraction and DFT calculations.

Functionalization of P4 in the coordination sphere of coinage metal cations

Selective functionalization of white phosphorus is achieved by addition of ArLi to unique cationic coinage metal η²–P₄ complexes.

Stabilization and Transfer of the Transient [Mes*P4](-) Butterfly Anion Using BPh3

The transient bicyclo[1.1.0]tetraphosphabutane anion, generated from white phosphorus (P4) and Mes*Li (Mes*=2,4,6-tBu3C6H2), can be trapped by BPh3 in THF. This Lewis acid stabilized anion can be used as an [RP4](-) transfer agent, reacting cleanly with neutral Lewis acids (B(C6F5)3, BH3, and W(CO)5) to afford unique singly and doubly coordinated butterfly anions, and with the trityl cation to form a neutral, nonsymmetrical, all-carbon-substituted P4  derivative. This reaction path enables a simple, stepwise functionalization of white phosphorus.