Functionalization of White Phosphorus Mediated by Low Valent Cobalt Complexes

This thesis reports on the synthesis and characterization of cobalt complexes and their application in the functionalization of white phosphorus. Chapter 1 reviews the versatile chemistry of transition metal-mediated P4 functionalization and categorizes this research field into systematic subunits. Chapter 2 addresses the synthesis of a novel heterobimetallic Co2Sn2 cluster and its reactivity toward white phosphorus. Chapter 3 reports on the cyanide-induced [3+2] fragmentation of pentaphosphido ligands, which were obtained by stepwise P4 activation and functionalization. In Chapter 4, the construction of polyphosphido complexes from a tetraphosphido cobaltate precursor is discussed. The final chapter 5 summarizes the results of this thesis and gives a brief outlook

[3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide

The activation of white phosphorus (P4) by transition‐metal complexes has been studied for several decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of rare diphosphan‐1‐ide anions from a P5 ligand by treatment with cyanide. Cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low‐valent diimine cobalt complex, white phosphorus, and diorganochlorophosphanes. The reactions of the complexes with tetraalkylammonium or potassium cyanide afford a cyclotriphosphido cobaltate anion 5 and 1‐cyanodiphosphan‐1‐ide anions [R2PPCN]− (6‐R). The molecular structure of a related product 7 suggests a novel reaction mechanism, where coordination of the cyanide anion to the cobalt center induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a phosphorus atom and release of the P2 fragment

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

[3+2]‐Fragmentierung von Pentaphosphidoliganden durch Cyanid. [3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide†

The activation of white phosphorus (P4) by transition‐metal complexes has been studied for several decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of rare diphosphan‐1‐ide anions from a P5 ligand by treatment with cyanide. Cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low‐valent diimine cobalt complex, white phosphorus, and diorganochlorophosphanes. The reactions of the complexes with tetraalkylammonium or potassium cyanide afford a cyclotriphosphido cobaltate anion 5 and 1‐cyanodiphosphan‐1‐ide anions [R2PPCN]− (6‐R). The molecular structure of a related product 7 suggests a novel reaction mechanism, where coordination of the cyanide anion to the cobalt center induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a phosphorus atom and release of the P2 fragment

Reaction of a 2,4,6-triphenylphosphinine ferrate anion with electrophiles: a new route to phosphacyclohexadienyl complexes

A novel, versatile route to phosphorus-and carbon-substituted eta(5)-phosphacyclohexadienyl complexes was developed. Reaction of the anionic 2,4,6-triphenylphosphinine iron complex [K([18]crown-6)(thf)(2)][(CpFe)-Fe-star(PC5Ph3H2)] (1) with selected main group element electrophiles afforded the new complexes [(CpFe)-Fe-star(2-endo-H-PC5Ph3H2)] (endo-3), [(CpFe)-Fe-star(2-exo-H-PC5Ph3H2)] (exo-3), [(CpFe)-Fe-star(1-Me-PC5Ph3H2)] (4), [(CpFe)-Fe-star(1-Me3Si-PC5Ph3H2)] (5), [(CpFe)-Fe-star(1-PPh2-PC5Ph3H2)] (6) and [(CpFe)-Fe-star(2-BCat-PC5Ph3H2)] (7, BCat = 2-benzo[d][1,3,2]dioxaborol-2-yl). Initial attack of the electrophile at phosphorus was observed, leading to a P-substitued phosphinine ligand. A subsequent rearragement occured in some cases, resulting in C-substituted phosphinine complexes endo-3, exo-3 and 7. The new complexes were characterized by H-1, P-31{H-1}, and C-13{H-1} NMR spectroscopy, UV-vis spectroscopy and elemental analysis; their molecular structures were determined by X-ray crystallography

[3+2] Fragmentation of a Pentaphosphido Ligand by Cyanide

The activation of white phosphorus (P4) by transition metal complexes has been studied for decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of unusal diphosphanides from a P5 ligand by treatment with cyanide. New cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low-valent dimine cobalt complex, white phosphorus and diorganochlorophosphanes. Reactions of such complexes with tetraalkylammonium or potassium cyanide afford the first cyclotriphosphido cobaltate anion 5 and rare 1-cyano-diphosphan-1-ide anions [R2PPCN]− (6-R). The molecular structure of a related product 7 suggests a novel reaction mechanism, where cyanide anion coordination to cobalt induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a P atom, releasing the P2 fragment. <br /

Formation of a Hexaphosphido Cobalt Complex through P−P Condensation

The reaction between diphosphorus derivatives [(ClImDipp)P2(Dipp)]OTf (1[OTf]) and [(ClImDipp)P2(Dipp)Cl] (1[Cl]) with the cyclotetraphosphido cobalt complex [K(18c-6)][(PHDI)Co(η4-cyclo-P4)] (2) leads to the formation of complex [(PHDI)Co{η4-cyclo-P6(Dipp)(ClImDipp)}] (3), which features an unusual hexaphosphido ligand [ClImDipp=4,5-dichloro-1,3-bis(2,6-diisopropylphenyl)imidazol-2-yl, Dipp=2,6-diisopropylphenyl, 18c-6=18-crown-6, PHDI=bis(2,6-diisopropylphenyl)phenanthrene-9,10-diimine]. Complex 3 was obtained as a crystalline material with a moderate yield at low temperature. Upon exposure to ambient temperature, compound 3 slowly transforms into two other compounds, [K(18c-6)][(PHDI)Co(η4-P7Dipp)] (4) and [(PHDI)Co{cyclo-P5(ClImDipp)}] (5). The novel complexes 3–5 were characterized using multinuclear NMR spectroscopy and single-crystal X-ray diffraction. To shed light on the formation of these compounds, a proposed mechanism based on 31P NMR monitoring studies is presented

Halide‐Substituted Phosphacyclohexadienyl Iron Complexes: Covalent Structures vs. Ion Pairs

Invited for the cover of this issue is the group of Robert Wolf from the University of Regensburg, Germany. The cover image shows the structure of the first transition metal complexes bearing pi-coordinated lambda(3)-halophosphacyclohexadienyl ligands, featuring polarized P-halogen bonds

Synthesis of a Cyclic Co2Sn2 Cluster Using a Co- Synthon.

[Ar'SnCo]2 (1, Ar' = C6H3-2,6{C6H3-2,6- iPr2}2), a rare metal-metal bonded cobalt-tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)0.2][Co(1,5-cod)2] (cod = 1,5-cyclooctadiene) with [Ar'Sn(μ-Cl)]2. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal Co2Sn2 core with strong metal-metal bonds between tin and cobalt and a weaker tin-tin interaction. Reaction of 1 with white phosphorus afforded [Ar'2Sn2Co2P4] (2), the first molecular cluster compound containing phosphorus, cobalt and tin