Transition-Metal-Stabilized Heavy Tetraphospholide Anions.

Phosphorus analogues of the ubiquitous cyclopentadienyl (Cp) are a rich and diverse family of compounds, which have found widespread use as ligands in organometallic complexes. By contrast, phospholes incorporating heavier group 14 elements (Si, Ge, Sn, and Pb) are hardly known. Here, we demonstrate the isolation of the first metal complexes featuring heavy cyclopentadienyl anions SnP42- and PbP42-. The complexes [(η4-tBu2C2P2)2Co2(µ,η5:η5-P4Tt)] [Tt = Sn (6), Pb (7)] are formed by reaction of white phosphorus (P4) with cyclooctadiene cobalt complexes [Ar'TtCo(η4-P2C2tBu2)(η4-COD)] [Tt = Sn (2), Pb (3), Ar' = C6H3-2,6{C6H3-2,6-iPr2}2, COD = cycloocta-1,5-diene] and Tt{Co(η4-P2C2tBu2)(COD)}2 [Tt = Sn (4), Pb (5)]. While the SnP42- complex 6 was isolated as a pure and stable compound, compound 7 eliminated Pb(0) below room temperature to afford [(η4-tBu2C2P2)2Co2(µ,η4:η4-P4) (8), which is a rare example of a tripledecker complex with a P42- middle deck. The electronic structures of 6-8 are analyzed using theoretical methods including an analysis of intrinsic bond orbitals and magnetic response theory. Thereby, the aromatic nature of P5- and SnP42- was confirmed, while for P42-, a specific type of symmetry-induced weak paramagnetism was found that is distinct from conventional antiaromatic species.

Photochemical transformation of chlorobenzenes and white phosphorus into arylphosphines and phosphonium salts.

Chlorobenzenes are important starting materials for the preparation of commercially valuable triarylphosphines and tetraarylphosphonium salts, but their use for the direct arylation of elemental phosphorus has been elusive. Here we describe a simple photochemical route toward such products. UV-LED irradiation (365 nm) of chlorobenzenes, white phosphorus (P4) and the organic superphotoreductant tetrakis(dimethylamino)ethylene (TDAE) affords the desired arylphosphorus compounds in a single reaction step.

Photocatalytic Arylation of P4 and PH3 : Reaction Development Through Mechanistic Insight.

Detailed 31 P{1 H} NMR spectroscopic investigations provide deeper insight into the complex, multi-step mechanisms involved in the recently reported photocatalytic arylation of white phosphorus (P4 ). Specifically, these studies have identified a number of previously unrecognized side products, which arise from an unexpected non-innocent behavior of the commonly employed terminal reductant Et3 N. The different rate of formation of these products explains discrepancies in the performance of the two most effective catalysts, [Ir(dtbbpy)(ppy)2 ][PF6 ] (dtbbpy=4,4'-di-tert-butyl-2,2'-bipyridine) and 3DPAFIPN. Inspired by the observation of PH3 as a minor intermediate, we have developed the first catalytic procedure for the arylation of this key industrial compound. Similar to P4 arylation, this method affords valuable triarylphosphines or tetraarylphosphonium salts depending on the steric profile of the aryl substituents.

A Phosphinine-Derived 1-Phospha-7-Bora-Norbornadiene: Frustrated Lewis Pair Type Activation of Triple Bonds.

Invited for the cover of this issue are the groups of Ruth M. Gschwind and Robert Wolf (University of Regensburg), Christian Müller (Freie Universität Berlin), and J. Chris Slootweg (University of Amsterdam). The image depicts playing cards representing the reported reactions involving 1-phospha-7-bora-norbornadiene. Read the full text of the article at 10.1002/chem.202000266.

A Phosphinine-Derived 1-Phospha-7-Bora-Norbornadiene: Frustrated Lewis Pair Type Activation of Triple Bonds.

Salt metathesis of 1-methyl-2,4,6-triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1-phospha-7-bora-norbornadiene derivative 2. The C≡N triple bonds of nitriles insert into the P-B bond of 2 with concomitant C-B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ4 -phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus-boron bond in 2, which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P-B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4-addition.

Direct catalytic transformation of white phosphorus into arylphosphines and phosphonium salts.

Phosphorus compounds are ubiquitous in the chemical sciences, finding applications throughout industry and academia. Of particular interest to synthetic chemists are organophosphorus compounds, which contain P-C bonds. However, state-of-the-art processes for the synthesis of these important materials rely on an inefficient, stepwise methodology involving initial oxidation of white phosphorus (P4) with hazardous chlorine gas and the subsequent displacement of chloride ions. Catalytic P4 organofunctionalisation reactions have remained elusive, as they require multiple P-P bond breaking and P-C bond formation events to break down the P4 core, all of which must occur in a controlled manner. Herein, we describe an efficient transition metal-catalyzed process capable of forming P-C bonds from P4. Using blue light photocatalysis, this method directly affords valuable triarylphosphines and tetraarylphosphonium salts in a single reaction step.

Facile C=O Bond Splitting of Carbon Dioxide Induced by Metal-Ligand Cooperativity in a Phosphinine Iron(0) Complex.

New iron complexes [Cp*FeL]- (1-σ and 1-π, Cp*=C5 Me5 ) containing the chelating phosphinine ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (L) have been prepared, and found to undergo facile reaction with CO2 under ambient conditions. The outcome of this reaction depends on the coordination mode of the versatile ligand L. Interaction of CO2 with the isomer 1-π, in which L binds to Fe through the phosphinine moiety in an η5 fashion, leads to the formation of 3-π, in which CO2 has undergone electrophilic addition to the phosphinine group. In contrast, interaction with 1-σ-in which L acts as a σ-chelating [P,N] ligand-leads to product 3-σ in which one C=O bond has been completely broken. Such CO2 cleavage reactions are extremely rare for late 3d metals, and this represents the first such example mediated by a single Fe centre.