Syntheses, Structures and Reactivity of Terminal Phosphido Complexes of Iron(II) Supported by a β-Diketiminato Ligand

Binary interpnictogen compounds bearing diaryl bismuth fragments bound to all lighter pnictogens

Multiple interpnictogen compounds with covalent single bonds between a diarylbismuth fragment and all lighter pnictogens were prepared from the corresponding diarylhalido bismuthanes. The aminobismuthanes Ph₂BiNMe₂ (1) and Mes₂BiNMe₂ (2) (Mes = 2,4,6-trimethylphenyl-) have been obtained via a salt metathesis reaction and compound 2 was successfully reacted with tBuNH₂ in a condensation reaction to yield Mes₂BiNHtBu (3). The bismuthanyl phosphanes Ar₂BiPtBu₂ (Ar = Ph: 4 and Ar = Mes: 5) and arsanes Ar₂BiAstBu₂ (Ar = Ph: 8 and Ar = Mes: 9) were also obtained via salt metathesis. Through a trimethylsilyl halide abstraction reaction of the diaryl halido bismuthanes and EtBu(SiMe₃)₂ (E = P and As), the bismuthanyl phosphanes Ar₂BiPtBu(SiMe₃) (Ar = Ph: 6; Ar = Mes: 7) and the arsanes Ar₂BiAstBu(SiMe₃) (Ar = Ph: 10; Ar = Mes: 11) have been prepared. Bismuthanyl stibanes were accessed via a condensation reaction of Mes₂SbH with 1 or 2, respectively. The compound Ph₂BiSbMes₂ (12), which has different substituents at the bismuth and antimony atoms, was isolated and fully characterised. In contrast, the isolation of Mes₂BiSbMes₂ (13) was not possible due to a dynamic equilibrium with Mes₄Bi₂ and Mes₄Sb₂ which was investigated via low-temperature ¹H-NMR spectroscopy in solution. The isolated compounds with a single bond between bismuth and the heavy pnictogens arsenic and antimony are rare examples of their kind. All isolated compounds (1-12) were characterised by NMR and IR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction.

Reversible P-P bond cleavage at an iridium(III) metal centre

Treatment of a κ¹-P-monodentate bicyclic diphosphane iridium(III) complex with a labile gold(I) precursor afforded an unusual Ir^III/Au^I complex in which the P-P single bond has been cleaved. This reaction was cleanly reversed upon addition of tertiary phosphine. Carbon-carbon bond activation, across neighbouring P₂C₂N rings of the coordinated bicyclic diphosphane, occurred upon thermolysis of the Ir^III/Au^I complex.

Monomeric Triphosphinoboranes: Intramolecular Lewis Acid–Base Interactions between Boron and Phosphorus Atoms

Herein, we present the synthesis of the first fully characterized monomeric triphosphinoboranes. The simple reaction of boron tribromide with 3 equiv of bulky lithium phosphide tBu₂PLi yielded triphosphinoborane (tBu₂P)₃B. Triphosphinoboranes with diversified phosphanyl substituents were obtained via a two-step reaction, in which isolable bromodiphosphinoborane (tBu₂P)₂BBr is first formed and then reacts with 1 equiv of less bulky phosphide R₂PLi (R₂P = Cy₂P, iPr₂P, tBuPhP, or Ph₂P). By utilizing this method, we obtained a series of triphosphinoboranes with the general formula (tBu₂P)₂BPR₂. On the basis of structural and theoretical studies, two main types of triphosphinoborane structures can be distinguished. In the first type, all three electron lone pairs interact with the formally empty p orbital of the central boron atom, resulting in delocalized π bonding, whereas in the second type, one localized P=B bond and two P–B bonds are observed. The Lewis acidic–basic properties of triphosphinoboranes during the reaction of (tBu₂P)₂BPiPr₂ with H₃B·SMe₂ were analyzed. The P–B bond-containing compound mentioned above not only formed an adduct with BH₃ but also activated the B–H bond of the borane molecule, resulting in the incorporation of the BH₂ unit into two phosphorus atoms and migration of a hydride to the boron atom of the parent triphosphinoborane. The structures of the triphosphinoboranes were confirmed by single-crystal X-ray analysis, multinuclear nuclear magnetic resonance spectroscopy, and elemental analysis.

The synthesis and structural analysis of the first fully characterized monomeric triphosphinoboranes are presented.

Spin States, Bonding and Magnetism in Mixed-Valence Iron(0)-Iron(II) Complexes

"Xenophilic" complexes offer metal-metal bonds between disparate metal sites, but the nature of the metal-metal bonding is often unclear. Here, we describe two novel complexes with unsupported Fe-Fe bonds, Lx Fe-Fp (LX = β-aldiminate or β-diketiminate; Fp = Fe(CO)2 Cp), that offer insight into Fe-Fe bonding. Mössbauer, magnetism, and DFT analysis indicate that the most accurate electronic structure description is LFeII ←Fe0 (CO)2 Cp, in which the Fe(CO)2 Cp is low-spin iron(0) and acts as an X-type ligand toward the high-spin iron(II) of the LFe fragment. This largely electrostatic interaction has a bond order of only 0.5. The three-coordinate high-spin iron(II) site has large zero-field splitting, and in addition its Mössbauer parameters can be used to rank the Fp- "metalloligand" as a donor; it is nearly as strong a donor as phosphides and alkyls.

Phosphine-catalysed reductive coupling of dihalophosphanes

Classically tetraaryl 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. To show that this protocol is more widely applicable, we show that Ph₂PCl and Mes₂PX (X = Cl, Br) are efficiently coupled using 10 mol% of PEt₃ to give (Ph₂P)₂ and (Mes₂P)₂, respectively. Control experiments show that [BrPEt₃]Br is a potential oxidation product in the catalytic cycle, which can be debrominated by Zn dust as a sacrificial reductant.

Hydrogen/Halogen Exchange of Phosphines for the Rapid Formation of Cyclopolyphosphines

The hydrogen/halogen exchange of phosphines has been exploited to establish a truly useable substrate scope and straightforward methodology for the formation of cyclopolyphosphines. Starting from a single dichlorophosphine, a sacrificial proton "donor phosphine" makes the rapid, mild synthesis of cyclopolyphosphines possible: reactions are complete within 10 min at room temperature. Novel (aryl)cyclopentaphosphines (ArP)₅ have been formed in good conversion, with the crystal structures presented. The use of catalytic quantities of iron(III) acetylacetonate provides significant improvements in conversion in the context of diphosphine (Ar₂P)₂ and alkyl-substituted cyclotetra- or cyclopentaphosphine ((AlkylP)_n, where n = 4 or 5) formation. Both iron-free and iron-mediated reactions show high levels of selectivity for one specific ring size. Finally, investigations into the reactivity of Fe(acac)₃ suggest that the iron species is acting as a sink for the hydrochloric acid byproduct of the reaction.

Synthesis of a carborane-substituted bis(phosphanido) cobaltate(i), ligand substitution, and unusual P4 fragmentation

Oxidative addition of the P-P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C2(PMes)2B10H10) (Mes = 2,4,6-Me3C6H2) to cobalt(-i) and nickel(0) sources affords the first heteroleptic complexes of a carborane-bridged bis(phosphanido) ligand. The complexes also incorporate labile ligands suitable for further functionalisation. Thus, the cobalt(i) complex [K([18]crown-6)][Co{1,2-(PMes)2C2B10H10}(cod)] (cod = 1,5-cyclooctadiene) bearing a labile cyclooctadiene ligand undergoes facile ligand exchange reactions with isonitriles and tert-butyl phosphaalkyne with retention of the bis(phosphanido) ligand. However, in the reaction with one equivalent of P4, the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P3 chain, while the remaining three P atoms derived from P4 form an η3-coordinating cyclo-P3 ligand. In contrast, when the same reaction is performed with two equivalents of the cobalt(i) complex, a dinuclear product is formed which features an unusual P4 chain in its molecular structure.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the β-diketiminato complex [(Dippnacnac)FeCl₂Li(dme)₂] (Dippnacnac = HC[(CMe)N(C₆H₃-2,6-iPr₂)]₂) or [FeBr₂(thf)₂] with an excess of phosphides R₂PLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBu₂PLi precursor led to an anionic diiron complex 1 encompassing a planar Fe₂P₂ core with two bridging and two terminal phosphido ligands. An analogous reaction employing less sterically demanding phosphides, tBuPhPLi and Cy₂PLi yielded diiron anionic complexes 2 and 3, respectively, featuring a short Fe-Fe interaction supported by three bridging phosphido groups and one additional terminal R₂P^- ligand at each iron center. Further tuning of the P-substrates bulkiness gave a neutral phosphido complex 4 possessing a tetrahedral Fe₄ cluster core held together by six bridging iPr₂P moieties. Moreover, we also describe the first homoleptic phosphanylphosphido iron complex 5, which features an iron center with low coordination provided by three tBu₂P-P(SiMe₃)^- ligands. The structures of compounds 1-5 were determined by single-crystal X-ray diffraction and 1-3 by ¹H NMR spectroscopy. Moreover, the electronic structures of 1-3 were interrogated using zero-field Mössbauer spectroscopy and DFT methods.

Solvent Impact on the Diversity of Products in the Reaction of Lithium Diphenylphosphide and a Ti(III) Complex Supported by a tBu2P-P(SiMe3) Ligand

We present two important trends in the reactivity of the titanium complex [^MeNacNacTi(Cl){η²-P(SiMe₃)-PtBu₂}] (^MeNacNac^- = [Ar]NC(Me)CHC(Me)N[Ar]; Ar = 2,6-iPr₂Ph) with nucleophilic reagents RLi (R = Ph₂P, tBuO, (Me₃Si)₂N, and tBu₂N) depending on the reaction medium. Reaction in nonpolar solvent (toluene) leads to three main products: via an autoredox process and nucleophilic substitution at the Ti-atom to afford the Ti(IV) complex [^MeNacNacTi(R){η²-P-PtBu₂}] (1 for R = PPh₂), via the elimination of Me₃SiR to afford Ti(III) complex [^MeNacNacTi(Cl){η²-P-PtBu₂}]^-[Li(12-crown-4)₂]⁺ (2), and via 2e^- reduction process to afford new ionic complex [{ArNC(Me)CHC(Me)}Ti═NAr{η¹-P(SiMe₃)-PtBu₂}]^-[Li(12-crown-4)₂]⁺ (3). Quite differently, the complex [^MeNacNacTi(Cl){η²-P(SiMe₃)-PtBu₂}] reacts with Ph₂PLi in THF, unexpectedly yielding two new, four-coordinate Ti(IV) imido complexes 4a [{ArNC(Me)═CHC(H)(Me)-P(PtBu₂)}Ti═NAr(Cl)]^-[Li(12-crown-4)₂]⁺·(toluene)₂ and 4b [{ArNC(CH₂)CH═C(Me)-P(PtBu₂)}Ti═NAr(Cl)]^-[Li(12-crown-4)₂]⁺·(Et₂O). Complex 2 dissolved in THF converts to 4a and 4b. 1, 2, 3, 4a, and 4b were characterized by X-ray diffraction. 1, 4a, and 4b were also fully characterized by multinuclear NMR spectroscopy.

Structural and spectroscopic analysis of a new family of monomeric diphosphinoboranes

We present a series of amino- and aryl(diphosphino)boranes R₂PB(R'')PR'₂, where R₂P, R'₂P = tBu₂P, tBuPhP, Ph₂P, Cy₂P, and R'' = iPr₂N, Ph, which were obtained via the metathesis reaction of iPr₂NBBr₂ or PhBBr₂ with selected lithium phosphides. The structures of isolated diphosphinoboranes were characterized in the solid state and in solution by means of X-ray diffraction and NMR spectroscopy, respectively. The utility of these P-B-P species as ligands for transition metal complexes was tested in the reaction with [(COD)PtMe₂]. Moreover, we carried out DFT calculations to elucidate bonding interactions and philicity of the reactive centers as well as to analyze conformations of the studied species. Electronic and steric properties of substituents on P and B atoms were found to have a strong influence on the structures of the obtained compounds. Three main types of diphosphinoboranes were distinguished, based on the strength of P-B π-interaction within the molecule: (i) application of strong electron-donating substituents on P-atoms and electron-accepting phenyl groups on B atoms led to the structure with one double P[double bond, length as m-dash]B and one single P-B bond and diverse planar and pyramidal geometry of phosphanyl groups; (ii) reduction of the donor ability of phosphanyl groups gave diphosphanylboranes with delocalized P-B-P π-interactions; (iii) introduction of amino groups with strong donor abilities on B atoms canceled P-B π-interactions and allowed compounds with two very long P-B bonds and two pyramidal phosphanyl groups to be obtained.

Symmetrical and unsymmetrical diphosphanes with diversified alkyl, aryl, and amino substituents

Synthesis, classification, and analysis of the structural, electronic and spectroscopic properties of a series of novel diphosphanes with diversified substituents.