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

Reactivity of Sodium Pentaphospholide Na[ cyclo ‐P 5 ] towards C≡E (E=C, N, P) Triple Bonds

A diglyme solution of Na[cyclo-P₅ ] (1) reacts with alkynes and isolobal nitriles and phosphaalkynes to afford the otherwise elusive (aza)phospholide anions 2 a-c, 4 a,b, and 6. The reaction of Na[cyclo-P₅ ] with alkynes and nitriles was studied by means of DFT methods, which suggested a concerted mechanism for the formation of 2 a and 4 b. The anions 2 a-c, 4 a,b, and 6 coordinate in an η⁵ -fashion towards Fe^II to give the sandwich (aza)phosphametallocenes 3 a-c, 5 a,b and 7 in moderate to good yields. The new compounds were characterized by means of multinuclear NMR spectroscopy, single-crystal X-ray diffraction and cyclic voltammetry.

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.

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.

Versatile Coordination of AgI and CuI Ions towards cyclo-As5 Ligands

The reactions of the cyclo‐As₅ complex [Cp*Fe(η⁵‐As₅)] (B) with the Ag^I and Cu^I salts of the weakly coordinating anion (WCA) [FAl{OC₆F₁₀(C₆F₅)}₃]⁻ ([FAl]⁻) are studied. These reactions allow the synthesis of the mononuclear complexes [M(η⁵ : η²‐B)₂][FAl] (M=Ag (1), Cu (2)) when a ratio of B/M(FAl) 2 : 1 is used. Compound 1 shows an unusual disorder of the central Ag^I cation between two π‐coordinating cyclo‐As₅ ligands, which is absent in 2 pointing to a weak interaction of the Ag center towards the cyclo‐As₅ ligands in B. When the ratio of B/Ag(FAl) is changed to 3 : 1 or 1 : 1, the respective coordination compounds [Ag(η²‐B)₃][FAl] (3) and [Ag₂(η² : η²‐B)₂][FAl]₂ (4) are accessible. The coordination modes of the cyclo‐As₅ units in 1, 3 and 4 are all different, reflecting the adaptive coordination behavior of B towards Ag^I ions. The optimized geometries in the gas phase of 1–4 are determined by DFT calculations to support the bonding situation observed in their solid‐state structures.

Halogenation of Diphosphorus Complexes

A systematic study of diverse halogenation reactions of the tetrahedral Mo₂P₂ ligand complex [{CpMo(CO)₂}₂(μ,η²:η²-P₂)] (1) is reported. By reacting 1 with different halogenating agents, a series of complexes such as [(CpMo)₄(μ₄-P)(μ₃-PI)₂(μ-I)(I)₃(I₃)] (2), [{CpMo(CO)₂}₂(μ-PBr₂)₂] (3a), [{CpMo(CO)₂}(CpMoBr₂)(μ-PBr₂)₂] (4a), [{CpMo(CO)₂}₂(μ-PCl₂)₂] (3b), and [{CpMo(CO)₂}(CpMoCl₂)(μ-PCl₂)₂] (4b) were obtained. Whereas the reaction of 1 toward various bromine and chlorine sources leads to similar results, a different behavior is observed in the reaction with iodine in which 2 is formed. The products were comprehensively characterized by spectroscopic methods and single crystal X-ray diffraction, and the electronic structures of 2, 3a, and 4a were elucidated by DFT calculations.

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.

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.