A new and selective one-step synthesis was developed for the first activation stage of white phosphorus by organic radicals. The reactions of NaCp(R) with P4 in the presence of CuX or FeBr3 leads to the clean formation of organic substituted P4 butterfly compounds Cp(R)2P4 (Cp(R): Cp(BIG)=C5(4-nBuC6H4)5 (1 a), Cp'''=C5H2tBu3 (1 b), Cp*=C5Me5 (1 c) und Cp(4iPr)=C5HiPr4 (1 d)). The reaction proceeds via the activation of P4 by Cp(R) radicals mediated by transition metals. The newly formed organic derivatives of P4 have been comprehensively characterized by NMR spectroscopy and X-ray crystallography.

The molecular structures, chemical bonding and magnetochemistry of the three-coordinate iron(II) NHC complexes [(NHC)Fe{N(SiMe 3 ) 2 } 2 ] (NHC = IPr, 2; NHC = IMes, 3) are reported.N-Heterocyclic carbene (NHC) complexes of late transition metals such as ruthenium, palladium and gold are an intensely studied class of compound owing to their applications in catalysis. [1][2][3] In contrast, studies of iron NHC complexes are less widespread. A series of recent reports has, however, shown that NHC complexes of iron do have considerable potential for development in a range of carbon-carbon and carbonheteroatom bond forming reactions. 4 In most cases, the nature of the active iron NHC complex is not known, but it is probable that low-coordinate iron NHC complexes play an important role.

As you like it: [Ag(η2‐As4)2]+[pftb]− can be used to store yellow arsenic (As4). From it, As4 can be easily released to give concentrated, light‐stable solutions. These As4 solutions, and those of white phosphorus (P4), allowed molecular As4 and P4 to be encapsulated inside giant, spherical aggregates and polymeric matrices, enabling the first determination of their EE (E=P, As) bond lengths by diffraction methods.

Dedicated to Professor Dieter Fenske on the occasion of his 70th birthdayIn the last decades, the activation of white phosphorus by main-group elements [1] and transition metals [2] has become an area of ongoing interest in chemistry. Its heavier homologue, arsenic, is well-known for its toxicity and is mainly used as additive in metal alloys and in GaAs 13/15 semiconductors. Yellow arsenic is isostructural with white phosphorus and was first described by Bettendorff almost 150 years ago. [3] It consists of tetrahedral As 4 units, which was determined in the 1960s by electron diffraction. [4] Yellow arsenic is made in a time-consuming synthesis by heating gray arsenic to 750 8C. The emerging As 4 is removed in a constant flow of carrier gas, and it is discharged in a solvent to yield a diluted As 4 solution. Yellow arsenic is very unstable at ambient conditions. Especially when exposed to light, it immediately decomposes to gray arsenic. Moreover, smallest traces of gray arsenic accelerate the autodecomposition of As 4 , even in solution. Therefore, As 4 is not storable as a solid or in solution as it is possible for the lighter homologue P 4 and a certain stoichiometry during reactions is hard to fulfill. Thus, only few results regarding the use of As 4 in main-group [5] and in transition-metal chemistry [6] have been published to date. Furthermore, no studies concerning the coordination behavior of the intact [7] As 4 tetrahedron are available. So far, the physical properties of As 4 could only be investigated under gas-phase conditions [4] or in thin films deposited on cooled substrates, which allowed spectroscopic and calorimetric investigations. [8] To overcome all of these problems, we intended to develop an appropriate source of yellow arsenic. Herein we present the synthesis of [Ag(h 2 -As 4 ) 2 ] + (1) as an unprecedented homoleptic complex possessing intact As 4 tetrahedra as ligands. It is light-stable and can be stored under inert conditions without decomposition. Moreover, this complex can be used as an effective source of intact As 4 , as exemplified by the synthesis of [(PPh 3 )Au(h 2 -As 4 )] + (2).The reaction of freshly prepared As 4[9] with the weakly coordinated silver(I) salt [Ag(CH 2 Cl 2 )][pftb] (pftb = [Al{OC(CF 3 ) 3 } 4 ]) [10] leads to the formation of the first homoleptic metal-arsenic complex [Ag(h 2 -As 4 ) 2 ][pftb] (1) in excellent yields [Eq. (1)]. Compound 1 is obtained as an airand moisture-sensitive colorless powder, which is interestingly stable to light and can be stored under an argon atmosphere at À30 8C without decomposition. It has good solubility in polar solvents, especially in dichloromethane, but is insoluble in hexane.The ESI mass spectrum in the cation mode of 1 shows the molecular ion peak as well as a peak for the As 4 released fragment [Ag(As 4 )] + . In the anion mode, the complete [Al{OC(CF 3 ) 3}4 ] À ion is detected. The Raman spectrum of 1 in solid state reveals three bands at 210, 265, and 343 cm À1 . Theoretical calculations predict six Raman-active vibr...

The selective formation of the dinuclear butterfly complexes [{Cp'''Fe(CO)2}2(μ,η(1:1)-E4)] (E = P (1 a), As (1 b)) and [{Cp*Cr(CO)3}2(μ,η(1:1)-E4)] (E = P (2 a), As (2 b)) as new representatives of this rare class of compounds was found by reaction of E4 with the corresponding dimeric carbonyl complexes. Complexes 1 b and 2 b are the first As4 butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1 b and 2 b are presented, revealing the formation of the unprecedented As8 cuneane complexes [{Cp'''Fe(CO)2}2{Cp'''Fe(CO)}2(μ4,η(1:1:2:2)-As8)] (3 b) and [{Cp*Cr(CO)3}4(μ4,η(1:1:1:1)-As8)] (4). The compounds are fully characterized by NMR and IR spectroscopy as well as by X-ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E4 butterfly to the corresponding cuneane structural motif.

White phosphorus, yellow arsenic, and AsP3 have been successfully activated by a complex with a CrCr quintuple bond in one step leading to the formation of rare terminally bound cyclo‐P42−, cyclo‐As42−, and cyclo‐AsP3 units. The subsequent reaction with an excess of [W(CO)5(thf)] leads to the coordination of one {W(CO)5} fragment in the thermodynamically most stable form according to DFT calculations.

The coordination properties of new types of bidentate phosphane and arsane ligands with a narrow bite angle are reported. The reactions of [{Cp'''Fe(CO)2 }2 (μ,η(1:1) -P4 )] (1 a) with the copper salt [Cu(CH3 CN)4 ][BF4 ] leads, depending on the stoichiometry, to the formation of the spiro compound [{{Cp'''Fe(CO)2 }2 (μ3 ,η(1:1:1:1) -P4 )}2 Cu](+) [BF4 ](-) (2) or the monoadduct [{Cp'''Fe(CO)2 }2 (μ3 ,η(1:1:2) -P4 ){Cu(MeCN)}](+) [BF4 ](-) (3). Similarly, the arsane ligand [{Cp'''Fe(CO)2 }2 (μ,η(1:1) -As4 )] (1 b) reacts with [Cu(CH3 CN)4 ][BF4 ] to give [{{Cp'''Fe(CO)2 }2 (μ3 ,η(1:1:1:1) -As4 )}2 Cu](+) [BF4 ](-) (5). Protonation of 1 a occurs at the "wing tip" phosphorus atoms, which is in line with the results of DFT calculations. The compounds are characterized by spectroscopic methods (heteronuclear NMR spectroscopy and IR spectrometry) and by single-crystal X-ray diffraction studies.

The versatile coordination behavior of the P butterfly complex [{Cp'''Fe(CO) } (μ,η -P )] (1, Cp'''=η -C H Bu ) towards different iron(II) compounds is presented. The reaction of 1 with [FeBr ⋅dme] (dme=dimethoxyethane) leads to the chelate complex [{Cp'''Fe(CO) } (μ ,η -P ){FeBr }] (2), whereas, in the reaction with [Fe(CH CN) ][PF ] , an unprecedented rearrangement of the P butterfly structural motif leads to the cyclo-P moiety in {(Cp'''Fe(CO) ) (μ ,η -P )} Fe][PF ] (3). Complex 3 represents the first fully characterized "carbon-free" sandwich complex containing cyclo-P R 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) } (μ ,η -P ){Cp'''Fe(CO)}][PF ] (4) and [{Cp'''Fe(CO) } (μ ,η -P ){Cp'''Fe}][PF ] (5), give insight into the stepwise activation of the P butterfly moiety in 1.