Intramolecular Phosphorus–Phosphorus Bond Formation within a Co2P4 Core

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).

Divalent metallocenes of the lanthanides - a guideline to properties and reactivity

Since the discovery in the early 1980s, the soluble divalent metallocenes of lanthanides have become a steadily growing field in organometallic chemistry. The predominant part of the investigation has been performed with samarium, europium, and ytterbium, whereas only a few reports dealing with other rare earth elements were disclosed. Reactions of these metallocenes can be divided into two major categories: (1) formation of Lewis acid-base complexes, in which the oxidation state remains +II; and (2) single electron transfer (SET) reductions with the ultimate formation of Ln(III) complexes. Due to the increasing reducing character from Eu(II) over Yb(II) to Sm(II), the plethora of literature concerning redox reactions revolves around the metallocenes of Sm and Yb. In addition, a few reactivity studies on Nd(II), Dy(II) and mainly Tm(II) metallocenes were published. These compounds are even stronger reducing agents but significantly more difficult to handle. In most cases, the metals are ligated by the versatile pentamethylcyclopentadienyl ligand: (C₅Me₅). Other cyclopentadienyl ligands are fully covered but only discussed in detail, if the ligand causes differences in synthesis or reactivity. Thus, the focus lays on three compounds: [(C₅Me₅)₂Sm], [(C₅Me₅)₂Eu] and [(C₅Me₅)₂Yb] and their solvates. We discuss the synthesis and physical properties of divalent lanthanide metallocenes first, followed by an overview of the reactivity rendering the full potential of these versatile reactants.

Molecular cyclo-P3 complexes of the rare-earth elements via a one-pot reaction and selective reduction

Synthesis of new organo-lanthanide polyphosphides with an aromatic cyclo-[P₄]^2- moiety and a cyclo-[P₃]^3- moiety is presented. For this purpose, the divalent Ln^II-complexes [(NON)Ln^II(thf)₂] (Ln = Sm, Yb) ((NON)^2- = 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene) and trivalent Ln^III-complexes [(NON)Ln^IIIBH₄(thf)₂] (Ln = Y, Sm, Dy) were used as precursors in the reduction process of white phosphorus. While using [(NON)Ln^II(thf)₂] as a one-electron reducing agent the formation of organo-lanthanide polyphosphides with a cyclo-[P₄]^2- Zintl anion was observed. For comparison, we investigated a multi-electron reduction of P₄ by a one-pot reaction of [(NON)Ln^IIIBH₄(thf)₂] with elemental potassium. As products molecular polyphosphides with a cyclo-[P₃]^3- moiety were isolated. The same compound could also be obtained by reducing the cyclo-[P₄]^2- Zintl anion within the coordination sphere of Sm^III in [{(NON)Sm^III(thf)₂}₂(μ-η⁴:η⁴-P₄)]. Reduction of a polyphosphide within the coordination sphere of a lanthanide complex is unprecedented. Additionally, the magnetic properties of the dinuclear Dy^III-compound bearing a bridging cyclo-[P₃]^3- moiety were investigated.

(thf)2Ln(Ge9{Si(SiMe3)3}3)2 (Ln = Eu, Sm): the first coordination of metalloid germanium clusters to lanthanides

We report the synthesis, structure and magnetic properties of the first rare earth complexes of metalloid group 14 clusters [(thf)2Ln(Ge9Hyp3)2] (Ln = Eu, Sm, Hyp = Si(SiMe3)3). X-Ray crystallographic analysis and DFT calculations reveal a novel η2-coordination mode of the Ge9Hyp3 units and a slight distortion of the Ge9 cage.

f-Block Phospholyl and Arsolyl Chemistry

The f-block chemistry of phospholyl and arsolyl ligands, heavier p-block analogues of substituted cyclopentadienyls (CpR , C5 R5 ) where one or more CR groups are replaced by P or As atoms, is less developed than for lighter isoelectronic C5 R5 rings. Heterocyclopentadienyl complexes can exhibit properties that complement and contrast with CpR chemistry. Given that there has been renewed interest in phospholyl and arsolyl f-block chemistry in the last two decades, coinciding with a renaissance in f-block solution chemistry, a review of this field is timely. Here, the syntheses of all structurally characterised examples of lanthanide and actinide phospholyl and arsolyl complexes to date are covered, including benzannulated derivatives, and together with group 3 complexes for completeness. The physicochemical properties of these complexes are reviewed, with the intention of motivating further research in this field.

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.

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.

Construction of alkyl-substituted pentaphosphido ligands in the coordination sphere of cobalt

Rare mono- and diorganopentaphosphido cobalt complexes are accessible by P-P condensation using the unprecedented, reactive cobalt-gallium tetraphosphido complex [K(dme)₂{(^MesBIAN)Co(μ-η⁴:η²-P₄)Ga(nacnac)}] (2). Compound 2 was prepared in good yield by reaction of [K(Et₂O){(^MesBIAN)Co(η⁴-1,5-cod)}] [1, BIAN = bis(mesitylimino)acenaphthene diimine, cod = 1,5-cyclooctadiene] with [Ga(nacnac)(η²-P₄)] (nacnac = CH[CMeN(2,6-iPr₂C₆H₃)]₂). Reactions with R₂PCl (R = iPr, tBu, and Cy) selectively afford [(^MesBIAN)Co(cyclo-P₅R₂)] (3a-c), which feature η⁴-coordinated 1,1-diorganopentaphosphido ligands. The mechanism of formation of these species has been studied by ³¹P{¹H} NMR spectroscopy and DFT calculations. In the case of 3a (R = iPr), it was possible to identify the intermediate [(^MesBIAN)Co(μ-η⁴:η²-P₅iPr₂)Ga(nacnac)] (4) by single-crystal X-ray diffraction. A related, monosubstituted organopentaphosphido cobalt complex [(^MesBIAN)Co(μ-η⁴:η¹-P₅ tBu)GaCl(nacnac)] (5) was isolated by reacting dichloroalkylphosphane tBuPCl₂ with 2. Heterobimetallic complexes such as 2 thus may enable the targeted construction of a range of new metal-coordinated polyphosphorus frameworks by P-P condensation.

Samarium Polystibides Derived from Highly Activated Nanoscale Antimony

Zintl ions in molecular compounds are of fundamental interest for basic research and application. Two reactive antimony sources are presented that allow direct access to molecular polystibide compounds. These are Sb amalgam (Sb/Hg) and ultrasmall Sb⁰ nanoparticles (d=6.6±0.8 nm), which were used independently as precursors for the synthesis of the largest f-element polystibide, [(Cp*₂ Sm)₄ Sb₈ ]. Whereas the reaction of the nanoparticles with [Cp*₂ Sm] directly led to [(Cp*₂ Sm)₄ Sb₈ ], Sm/Sb/Hg intermediates were isolated when using Sb/Hg as the precursor. These Sm/Sb/Hg intermediates [{(Cp*₂ Sm)₂ Sb}₂ (μ-Hg)] and [{(Cp*₂ Sm)₃ (μ⁴ ,η^1:2:2:2 -Sb₄ )}₂ Hg] were synthetically trapped and structurally characterized, giving insight in the formation mechanism of polystibide compounds.

Sterically induced reductive linkage of iron polypnictides with bulky lanthanide complexes by ring-opening of THF

Reduction of [Cp*Fe(η⁵-E₅)] (E = P, As) with divalent lanthanide reagents usually leads to reduction of [Cp*Fe(η⁵-E₅)] followed by a Ln-E bond formation. In contrast, by using the sterically encumbered reagent [(DippForm)₂Sm(thf)₂] (DippForm = {(2,6-ⁱPr₂C₆H₃)NC(H)[double bond, length as m-dash]N(2,6-ⁱPr₂C₆H₃)}^-), ring-opening of thf and reduction of the polypnictide is observed. This leads to two new 3d/4f polyphosphide or polyarsenide complexes [(DippForm)₂Sm(Cp*Fe)E₅{(CH₂)₄O}{(DippForm)₂Sm(thf)}], in which [(DippForm)₂Sm(thf)₂] and [Cp*Fe(η⁵-E₅)] are linked by a ring-opened thf molecule and no Ln-E bond formation is observed.

Stepwise Formation of a 1,3-Butadiene Analogue of Mixed Heavier Group 15 Elements

The reaction of the phosphinidene complex [Cp*P{W(CO)5}2] (1 a) with di-tert-butylcarboimidophosphene leads to the P-C cage compound 6 and the Lewis acid-base adduct [Cp*P{W(CO)5}2(CNtBu)] (2 a). In contrast, the arsinidene complex shows a different reactivity. At low temperatures, the arsaphosphene complex [{W(CO)5}{η(2)-(Cp*)As=P(tBu)}{W(CO)5}] (3) is formed. At these temperatures, 3 reacts further with a second equivalent of carboimidophosphene to form [{W(CO)5}{η(2)-{(Cp*)(tBu)P}As=P(tBu)}{W(CO)5}] (5), probably by the insertion of a phosphinidene unit (tBuP) into an As-C bond. In contrast, at room temperature 3 reacts further by a radical-type reaction to form [{(tBu)P=As-As=P(tBu)}{W(CO)5}4] (4). Compound 4 is the first example of a neutral, 1,3-butadiene analogue containing only mixed heavier Group 15 elements. It consists of two P=As double bonds connected by arsenic atoms.

Samarocene oxide: from an undesired decomposition product to a new reagent

Samarocene oxide [Cp*₂Sm-O-SmCp*₂], which is mostly considered as an undesired decomposition product, may act as a mild oxide base and thus is a valuable synthetic equivalent for “O²⁻”.

The approach to 4d/4f-polyphosphides

The first 4d/4f polyphosphides were obtained from reactions of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. New aggregation of the central phosphorus scaffold in combination with P–P bond formation within the coordination sphere of the transition metal was observed.

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. Treatment of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] gave the 16-membered bicyclic compounds [(Cp₂*Ln)₂P₂(CpMo(CO)₂)₄] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P₄ complex [(Cp*₂Sm)₂P₄(CpMo(CO)₂)₂] and the cyclic P₅ complex [(Cp*₂Sm)₃P₅(CpMo(CO)₂)₃] were also obtained as minor products. In each reaction, the P₂ unit is reduced and a rearrangement occurred. In dedicated cases, a P–P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [Cp*Mo(CO)₂P₃] a new P–P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*₂Ln)₂P₆(Cp*Mo(CO)₂)₂] (Ln = Sm, Yb) were obtained.

Metal-free Lewis acid mediated dehydrocoupling of phosphines and concurrent hydrogenation

The stoichiometric reaction of trityl cation with two equivalents of Ph₂PH affords the phosphine stabilized phosphenium salt [Ph₂(H)PPPh₂][B(C₆F₅)₄] via hydride abstraction, while catalytic amounts of B(p-HC₆F₄)₃ effects catalytic phosphine dehydrocoupling with the liberation of H₂.

Selective dehydrocoupling of phosphines by lithium chloride carbenoids

The development of a simple, transition-metal-free approach for the formation of phosphorus-phosphorus bonds through dehydrocoupling of phosphines is presented. The reaction is mediated by electronically stabilized lithium chloride carbenoids and affords a variety of different diphosphines under mild reaction conditions. The developed protocol is simple and highly efficient and allows the isolation of novel functionalized diphosphines in high yields.