Beiträge zur Chemie der Pniktogene: Pnictanylidenphosphorane und Cyclotripnictane

Diese Arbeit beschreibt Aspekte der Chemie der Phosphanylidenphosphorane, Triphosphirane und von Mehrfachbindungssystemen der Gruppe 13 und 15. Es wird gezeigt, dass Phosphanylidenphosphorane sowohl potente Phosphiniden-Überträger darstellen, als auch eine Phosphiniden-artige Reaktivität zeigen. Triphosphirane mit Aryl-Substituenten können selektiv hergestellt werden, und deren Reaktivtät gegenüber Titanocen-Vorstufenkomplexen wird diskutiert. Darüber hinaus wird gezeigt, dass die analogen Triarsirane synthetisiert werden können und vielfältige Reagenzien in der Molekülchemie darstellen.This thesis describes aspects of the chemistry of phosphanylidene phosphoranes, triphosphiranes and of group 13/15 multiple bond systems. It is shown that phosphanylidene phosphoranes are both potent phosphinidene transfer agents and exhibit phosphinidene-like reactivity. Triphosphiranes with aryl substituents can be selectively prepared and their reactivity towards titanocene precursor complexes is discussed. Furthermore, it is shown that the analogous triarsiranes can be synthesised and are versatile reagents in molecular chemistry

Synthetic strategies to bicyclic tetraphosphanes using P1, P2 and P4 building blocks

Different reactions of Mes* substituted phosphanes (Mes* = 2,4,6-tri-tert-butylphenyl) led to the formation of the bicyclic tetraphosphane Mes*P4Mes* (5) and its unknown Lewis acid adduct 5·GaCl3. In this context, the endo–exo isomer of 5 was fully characterized for the first time. The synthesis was achieved by reactions involving “self-assembly” of the P4 scaffold from P1 building blocks (i.e. primary phosphanes) or by reactions starting from P2 or P4 scaffolds (i.e. a diphosphene or cyclic tetraphosphane). Furthermore, interconversion between the exo–exo and endo–exo isomer were studied by 31P NMR spectroscopy. All compounds were fully characterized by experimental as well as computational methods

On the Reactivity of Phosphaalumenes towards C−C Multiple Bonds

Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2-phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe3 gave 1,4-phosphaaluminabarrelenes. Using styrene saturated 1,2-phosphaalumates were formed, which reacted further with additional styrene to give different regio-isomers of 1,4-aluminaphosphorinanes. Using ethylene, a 1,4-aluminaphosphorinane is obtained, while with 1,3-butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles

Cyclische Dipnictadialane

Bei Umsetzungen der AlI-Verbindung Cp3tAl mit Triphosphiranen (PAr)3 (Ar=Mes, Dip, Tip) ist es gelungen, Lewis-basenfreie cyclische Diphosphadialane herzustellen, bei denen sowohl das Al- als auch das P-Atom drei Substituenten tragen. Mit den sterisch anspruchsvolleren Dip- und Tip-Substituenten wurden die ersten 1,2-Diphospha-3,4-dialuminacyclobutane erhalten, während mit Mes-Substituenten [Cp3tAl(μ-PMes)]2 gebildet wird. Diese abweichende Reaktivität wurde durch DFT-Studien bestätigt, die auf eine thermodynamische Präferenz für die 1,2-Diphospha-3,4-dialuminacyclobutane für sterisch anspruchsvollere Gruppen am Phosphor hinwiesen. Mithilfe von Cp*Al konnten wir dieses Konzept auf die entsprechenden cyclischen Diarsadialane [Cp*Al(μ-AsAr)]2 (Ar=Dip, Tip) ausdehnen und zusätzlich die Phosphorvarianten [Cp*Al(μ-PAr)]2 (P=Mes, Dip, Tip) synthetisieren. Die Reaktivität von [Cp3tAl(μ-PPh)]2 gegenüber NHCs wurde untersucht und führte zu doppelt NHC-stabilisiertem [Cp3t(IiPr2)Al(μ-PPh)]2

On 1,3-phosphaazaallenes and their diverse reactivity

1,3-Phosphaazaallenes are heteroallenes of the type RP-C-NR′ and little is known about their reactivity. In here we describe the straightforward synthesis of ArPCNR (Ar = Mes*, 2,4,6-tBu-C6H2;MesTer, 2.6-(2,4,6-Me3C6H2)-C6H3;DipTer, 2.6-(2,6-iPr2C6H2)-C6H3; R =tBu; Xyl, 2,6-Me2C6H3) starting from phospha-Wittig reagents ArPPMe3and isonitriles CNR. It is further shown that ArPCNtBu are thermally labile with respect to the loss of iso-butene and it is shown that the cyanophosphines ArP(H)CN are synthetically feasible and form the corresponding phosphanitrilium borates with B(C6F5)3, whereas deprotonation ofDipTerP(H)CN was shown to give an isolable cyanidophosphide. Lastly, the reactivity of ArPCNR towards Pier's borane was investigated, showing hydroboration of the C-N bond in Mes*PCNtBu to give a hetero-butadiene, while withDipTerPCNXyl the formation of the Lewis acid-base adduct with a B-P linkage was observed. © The Royal Society of Chemistry 2021

Synthesis and Reactivity of Monocyclic Homoleptic Oligophosphanes

This Minireview outlines the synthesis and reactivity of homoleptic, cyclic oligophosphanes, which have been known for more than 150 years. We will discuss a variety of (PR)n (n = 3,4,5,6) species and outline approaches towards their syntheses in the first part of this review. Then the unique reactivity of these inorganic ring systems will be discussed in detail with a focus on recent findings within the last 20 years. First ring expansion reactions will be described, which are mainly restricted to cyclotriphosphanes. Secondly, ring fragmentation will be highlighted, including phosphinidene transfer reactions. Furthermore, cyclooligophosphanes can be functionalized while retaining the parent ring structures. As oligophosphanes offer multiple donor sites, in a last part the coordination chemistry of these species is highlighted. We hope that this Minireview will spark further interest in this underexplored class of compounds as reagents in inorganic and organic synthesis, as well as the design of new P-containing materials

On the ambiphilic character of phosphanylidenephosphoranes and manipulation of phosphinidenoid reactivity with Lewis acids

Phosphanylidenephosphoranes of the type R−P(PR’3), also known as phospha-Wittig reagents, can be utilized in a variety of bond activation reactions pursuing their phosphinidenoid reactivity. In here, we thoroughly show that a facile PMe3 for H2O exchange gives access to various primary phosphine oxides of the general formula RP(H)2O (R = Mes*, MesTer, DipTer). The molecular structure of DipTerP(H)2O was determined and provided the first picture of such species in the solid state. However, phosphanylidenephosphoranes are described to be highly nucleophilic as well. We show that the attachment of main group Lewis acids such as GaCl3 and GaI3 to2 R−P(PMe3) yielded highly sensitive, yet stable coordination compounds [RP(GaX3)PMe3] (R = Mes*, DipTer) or [(RPPMe3)2GaCl2]GaCl4 (R = MesTer). In contrast to the free phosphanylidenephosphoranes, these species reacted differently with H2O which was demonstrated for [(Mes*PPMe3)GaI3]. Here the formation of the phosphinophosphonium cation [Mes*P(H)PMe3]+ and different anions was observed with combined NMR spectroscopic and SC-XRD (SC-XRD = single crystal diffraction analysis) studies. This work demonstrates that the ambiphilic character of phosphanylidenephosphoranes can be utilized to manipulate the reactivity of R−P(PMe3) towards water, giving primary phosphine oxides, whereas the Lewis acid adducts [(RPPMe3)GaX3] gave phosphino-phosphonium species

Titanocene Pnictinidene Complexes

The phospha-Wittig reagent MesTerPPMe3 (MesTer = 2,6-{2,4,6-Me3-C6H2}-C6H3) and arsa-Wittig reagent DipTerAsPMe3 (DipTer = 2,6-{2,6-iPr2-C6H3}-C6H3) have been employed to synthesize the titanocene complexes Cp2Ti(PMe3)PnAr (Pn = P, As) with terminal phosphinidene or arsinidene ligands, respectively. Ab initio studies show that the description as singlet biradicaloids in their ground state is warranted.<br /

Phosphine-catalysed reductive coupling of Dihalophosphanes

Classically, tetraorgano diphosphanes have been synthesized through Wurtz-type reductive coupling of halophosphanes R2PX or more recently, through the dehydrocoupling of phosphines R2PH. Catalytic variants of the dehydrocoupling reaction have been reported but are limited to R2PH compounds. Using PEt3 as a catalyst, we now show that TipPBr2 (Tip = 2,4,6-iPr3C6H2) is selectively coupled to give the dibromodiphosphane (TipPBr)2 (1), a compound not accessible using classic Mg reduction. Surprisingly, when using DipPBr2 (Dip = 2,6-iPr3C6H3) in the PEt3-catalysed reductive coupling the diphosphene (PDip)2 (2) with a P=P double was formed selectively. In benzene solutions (PDip)2 has a half life-time of ca. 28 days and can be utilized with NHCs to access NHC-phosphinidene adducts. Control experiments show that [BrPEt3]Br is a potential oxidation product in the catalytic cycle, which can be then debrominated by using Zn dust as sacrificial reductant

Aryl-substituted Triarsiranes: Synthesis and Reactivity

Cyclotriarsanes are rare and limited synthetic approaches have hampered reactivity studies on these systems. Described in here is a scalable synthetic protocol towards (AsAr)3 (Ar = Dip, 2,6-iPr2-C6H3; Tip, 2,4,6-iPr3-C6H2), which allowed to study their reactivity towards [Cp2Ti(C2(SiMe3)2], affording titanocene diarsene complexes and towards N-heterocyclic carbenes (NHCs) to give straightforward access to a variety of NHC-arsinidene adducts. The electronic structure of the titanium diarsene complxes has been studied and they are best described as Ti(IV) species with a doubly reduced As2Ar2 ligand. These findings will make (AsAr)3 valuable precursors in the synthetic inorganic and organic chemistry