Reactivity of [Cp*Fe(η5 -As5 )] towards Carbenes, Silylenes and Germylenes

The reaction behavior of [Cp*Fe(η5 -As5 )] (I) (Cp*=C5 Me5 ) towards carbenes and their heavier analogs was investigated. The reaction of I with NHCs (NHCs=N-heterocyclic carbenes) results in the first substitution products of polyarsenic ligand complexes by NHCs [Cp*Fe(η4 -As5 NHC)] (1 a: NHC=IMe=1,3,4,5-tetramethylimidazolin-2-ylidene, 1 b: NHC=IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene). In contrast, the reaction of I with Et CAAC (Et CAAC=2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene) leads to a fragmentation and the formation of an unprecedented As6 -sawhorse-type compound [As2 (AsEt CAAC)4 ] (2). The reaction of (LE)2 (L=PhC(Nt Bu)2 ; E=Si, Ge) with I resulted in a rearrangement and an insertion of LE fragments, forming unique silicon- (4: [Cp*Fe(η4 -As4 SiL)], 5 a: [Cp*Fe(η4 -As6 SiL)) and germanium-containing (5 b: [Cp*Fe(η4 -As6 GeL)) cyclic polyarsenic ligand complexes.

Activation of small molecules by cyclic alkyl amino silylenes (CAASis) and germylenes (CAAGes): a theoretical study

Quantum chemical calculations have been carried out on a series of skeletally modified cyclic alkyl amino silylenes (CAASis) and germylenes (CAAGes) to understand their ligand properties and reactivity towards the activation of a variety of small molecules. The installation of boron or silicon atoms into the ring framework of these silylenes/germylenes led to a dramatic increase in their σ-basicity while the incorporation of ylidic moieties resulted in a sharp reduction of their π-acidity although it did help in increasing the electron donation ability. The calculated values of energy barriers for the activation of H-H, N-H, C-H and Si-H bonds by many of the cyclic silylenes considered here are found to be comparable to those for experimentally evaluated systems, indicating the potential of these computationally designed molecules in small molecule activation and calling for synthetic efforts towards their isolation. Furthermore, activations employing CAAGes are found to be more demanding than those with CAASis which may be attributed to the significantly lower Lewis basicity of the former than the latter.

Different Reactivity of As4 towards Disilenes and Silylenes

The activation of yellow arsenic is possible with the silylene [PhC(NtBu)₂ SiN(SiMe₃ )₂ ] (1) and the disilene [(Me₃ Si)₂ N(η¹ -Me₅ C₅ )Si=Si(η¹ -Me₅ C₅ )N(SiMe₃ )₂ ] (3). The reaction of As₄ with 1 leads to the unprecedented As₁₀ cage compound [(LSiN(SiMe₃ )₂ )₃ As₁₀ ] (2; L=PhC(NtBu)₂ ) with an As₇ nortricyclane core stabilized by arsasilene moieties containing silicon(II)bis(trimethylsilyl)amide substituents. In contrast, the compound [Cp*{(SiMe₃ )₂ N}SiAs]₂ (4) containing a butterfly-like diarsadisilabicyclo[1.1.0]butane unit is formed by the reaction of As₄ with the disilene 3. Both compounds were characterized by single-crystal X-ray diffraction analysis, NMR spectroscopy, and mass spectrometry. The reaction outcomes demonstrate the different reaction behavior of yellow arsenic (As₄ ) compared to white phosphorus (P₄ ) in the reactions with the corresponding silylenes and disilenes.

The chemistry of cationic polyphosphorus cages--syntheses, structure and reactivity

The aim of this review is to provide a comprehensive view of the chemistry of cationic polyphosphorus cages.

The aim of this review is to provide a comprehensive view of the chemistry of cationic polyphosphorus cages. The synthetic protocols established for their preparation, which are all based on the functionalization of P₄, and their intriguing follow-up chemistry are highlighted. In addition, this review intends to foster the interest of the inorganic, organic, catalytic and material oriented chemical communities in the versatile field of polyphosphorus cage compounds. In the long term, this is envisioned to contribute to the development of new synthetic procedures for the functionalization of P₄ and its transformation into (organo-)phosphorus compounds and materials of added value.

Formation of cationic [RP5Cl](+)-cages via insertion of [RPCl](+)-cations into a P-P bond of the P4 tetrahedron

Fluorobenzene solutions of RPCl(2) and a Lewis acid such as ECl(3) (E = Al, Ga) in a 1:1 ratio are used as reactive sources of chlorophosphenium cations [RPCl](+), which insert into P-P bonds of dissolved P(4). This general protocol represents a powerful strategy for the synthesis of new cationic chloro-substituted organophosphorus [RP(5)Cl](+)-cages as illustrated by the isolation of several monocations (21a-g(+)) in good to excellent yields. For singular reaction two possible reaction mechanisms are proposed on the basis of quantum chemical calculations. The intriguing NMR spectra and structures of the obtained cationic [RP(5)Cl](+)-cages are discussed. Furthermore, the reactions of dichlorophosphanes and the Lewis acid GaCl(3) in various stoichiometries are investigated to obtain a deeper understanding of the species involved in these reactions. The formation of intermediates such as RPCl(2)·GaCl(3) (14) adducts, dichlorophosphanylchlorophosphonium cations [RPCl(2)-RPCl](+) (16(+)) and [RPCl(2)-RPCl-GaCl(3)](+) (17(+)) in reaction mixtures of RPCl(2) and GaCl(3) in fluorobenzene strongly depends on the basicity of the dichlorophosphane RPCl(2) (R = tBu, Cy, iPr, Et, Me, Ph, C(6)F(5)) and the reaction stoichiometry.

Activation of phosphorus by group 14 elements in low oxidation states

The activation of phosphorus remains a popular and competitive area of research driven by the dual goals of finding ways to avoid the environmentally questionable P-Cl compounds applied in many industrial processes and the target of catalytic functionalization of P(4). In recent years the activation, degradation, fragmentation, and functionalization of white phosphorus by compounds with heavier main group elements have become a fertile area of research. The isolation of various carbenes and functionalized silylenes has prompted chemists to investigate their reactions with white phosphorus. The most intriguing fact in these reactions is the subtle change in the substituents may afford strikingly different compounds. For example, from the reaction of P(4) with PhC(NtBu)(2)SiCl a cyclic Si(2)P(2) derivative is obtained, whereas the analogous reaction with PhC(NtBu)(2)SiN(SiMe(3))(2) resulted in an acyclic Si(2)P(4) framework. Similar phenomena have also been observed in the carbene mediated P(4) activation. Apart from these, a new entry point into phosphorus chemistry is the gentle activation of P(4) by an alkyne analogue of tin. In this feature article we have covered the activation of phosphorus by compounds with low valent group 14 elements with special concern to the recent developments in this topic.

Stable singlet carbenes as mimics for transition metal centers

This perspective summarizes recent results, which demonstrate that stable carbenes can activate small molecules (CO, H(2), NH(3) and P(4)) and stabilize highly reactive intermediates (main group elements in the zero oxidation state and paramagnetic species). These two tasks were previously exclusive for transition metal complexes.

Zwitterionic and cationic P(5)-clusters from four-membered phosphorus-nitrogen-metal heterocycles

A general route for the functionalization of P(4) mediated by four-membered phosphorus-nitrogen-metal heterocycles is introduced yielding novel phosphorus-rich clusters.