cyclo‐P₅ as Complex Ligand—the Phosphorus Analogue of the Cyclopentadienyl Ligand

Abstract

A milestone for the chemistry of phosphorus‐containing complexes is the synthesis of the black‐red cyclo‐P5 complex 1, which is metallic in appearance. In light of the overwhelming significance of the cyclopentadienyl ligand in organometallic chemistry, the isovalent isoelectronic cyclo‐P5 would appear to hold much promise. ESR investigations indicate that 1 is a mixed valence complex (d4/d5 system), which can be readily oxidized and reduced.

Iron- and Ruthenium-Containing Triple-Decker Complexes with a Central Pentaphospholyl Ligand − X-ray Structures of [(η-C5H5)Fe(μ-η:η-P5)Ru(η-C5Me5)]PF6 and [(η-C5Me5)Ru(μ-η:η-P5)Ru(η-C5Me5)]PF6

“…A further irreversible oxidation, not shown in Figure 3, almost completely overlaps the solvent discharge. Consistent with the behaviour of the related complexes [(triphos)MP 3 M(triphos)] nϩ (M ϭ Ni, Co), [27] Cp* MP 6 MCp* (M ϭ V, Mo, W), [28] Cp*Fe(As 2 Se 2 )FeCp*, [29] and in particular Cp*CrP 5 CrCp*, [2] controlled potential coulometry performed in correspondence to the first cathodic step (E w ϭ Ϫ1.2 V) consumed one electron per molecule, thus supporting the involvement of one-electron transfers in all the redox processes. This means that the oxidation processes should correspond to the Fe II Fe II /Fe II Fe III /Fe IIIFe III sequence, whereas the reduction steps should correspond to the Fe II Fe II /Fe II Fe I /Fe I Fe I sequence.…”

“…In this connection, a K com ϭ 4 ϫ 10 17 has been calculated for Cp*CrP 5 CrCp*, which, also supported by EPR spectroscopic measurements, was classified as a delocalized Cr II Cr I system. [2] It should be noted finally that, in spite of the chemical reversibility of the Fe II Fe II /Fe II Fe III and Fe II Fe II / Fe II Fe I redox changes on the cyclic voltammetric timescale, cyclic voltammetric tests performed after the exhaustive Fe II Fe II /Fe II Fe I reduction show that the mixed-valent neutral species undergoes slow decomposition over the long timescales of macroelectrolysis.…”

“…[1] The first complexes of this type, (η-C 5 R 5 )Cr(µ-η:η-P 5 )Cr(η-C 5 R 5 ) (R ϭ H, Me), were synthesized by Scherer [2] and other authors [3] by treatment of [(η-C 5 R 5 )Cr(CO) x ] 2 (x ϭ 2, 3) with P 4 . Scheer has prepared the similar complex (η-C 5 H 4 tBu)Cr(µ-η:η-P 5 )Cr(η-C 5 H 4 tBu) by treatment of K[(η-C 5 H 4 tBu)Cr(CO) 3 ] with Cr(CO) 5 PCl 3 .…”

Rearrangement of a P4 Butterfly Complex—The Formation of a Homoleptic Phosphorus–Iron Sandwich Complex

“…Single-crystal X-ray diffraction reveals that the central Fe atom in 3 is coordinated by two planar cyclo-P 4 units ( Figure 2). Each cyclo-P 4 unit is substituted by two bulky [Cp'''Fe(CO) 2 ]f ragments.T he P-P distances vary from 2.1406(10) to 2.1547 (10) and are between aP -P single (2.20-2.25 )a nd aP -P double bond (2.00-2.05 ), which compares well to the P-P distances found in the isolated P 4 2À anion in Cs 2 P 4 ·2NH 3 (2.146(1) and 2.1484 (9) ). [20] The cyclo-P 4 R 2 (R = Cp'''Fe(CO) 2 )units in 3 are slightly distorted from the symmetric square geometry with P-P-P bond angles of 82.76(4)8 8/82.88(4)8 8 and 97.11(4)8 8/97.24(4)8 8.D ue to the geometry analogy of the two cyclo-P 4 units in 3 and Cs 2 P 4 ·2NH 3 ,w ep ropose that the cyclo-P 4 units in 3 can be formally described as aromatic 6p-electron-containing R 2 P 4 ligands.The two cyclo-P 4 planes in 3 are parallel to each other but twisted along the P 4cent.…”

Ringkontraktion durch NHC‐induzierte Pnictogen‐Abstraktion

“…438 8 zu erwarten ist, da dieser eine effektive Überlappung des p-Systems der NHC-Fragmente mit den p-Orbitalen des Arsens verhindert. [18] Wasd en anionischen Te il angeht, obgleich das As 5 -Mitteldeck über drei Positionen mit Besetzungen von 0.62:0.26:0.12 (siehe Hintergrundinformationen) fehlgeordnet ist, kann wiederum zwischen kürzeren (zwischen 2.289(14) und 2.463(4) ) und längeren (zwischen 2.729 (15) Der Komplex [{Cp*V} 2 (m,h 6:6 -P 6 )] (5)i st eines von nur wenigen Beispielen fürV anadium-Komplexe,d ie Polyphosphor-Liganden [19] Die Molekülstrukturen von 6 und 7 werden in Abbildung 3w iedergegeben. AusG r ünden der Übersichtlichkeit werden die sich überlagernden Mitteldecks als getrennte Moleküle dargestellt.…”