Consecutive Insertion of a Silylene into the P4 Tetrahedron: Facile Access to Strained SiP4 and Si2P4 Cage Compounds

Ferrocene-Based N-Heterocyclic Silylenes: Monomeric Silanechalcogenones, Silanimines, Silirenes, and Insertion Products with P4

The stable ferrocene-based N-heterocyclic silylenes fc[(N{B})2Si] (A; fc=1,1'-ferrocenylene, {B}=(HCNDipp)2B, Dipp=2,6-diisopropylphenyl) and fc[(NDipp)2Si] (B) are compared in a study focussing on their reactivity towards a range of small to moderately sized molecular substrates, viz. P4, S8, Se8, MesN3 (Mes=mesityl), RC≡CH, and RC≡CR (R=Ph, SiMe3). The Dipp-substituted congener B exhibits a more pronounced ambiphilicity and is sterically less congested than its 1,3,2-diazaborolyl-substituted relative A, in line with the higher reactivity of the former. The difference in reactivity is obviously due more to electronic than to steric reasons, as is illustrated by the fact that both A and B react with the comparatively bulky substrate MesN3 under mild conditions to afford the corresponding silanimine fc[(N{B})2Si=NMes] and fc[(NDipp)2Si=NMes], respectively. The heavier ketone analogues fc[(N{B})2Si=E] (E=S, Se, Te) are readily available from A and the corresponding chalcogen. In contrast, the reaction of the more reactive silylene B with elemental sulfur or selenium is unspecific, affording product mixtures. However, fc[(NDipp)2Si=Se] is selectively prepared from B and (Et2N)3PSe; the Te analogue is also accessible, but crystallises as head-to-tail dimer.

Applications of low-valent compounds with heavy group-14 elements

Over the last two decades, the low-valent compounds of group-14 elements have received significant attention in several fields of chemistry owing to their unique electronic properties. The low-valent group-14 species include tetrylenes, tetryliumylidene, tetrylones, dimetallenes and dimetallynes. These low-valent group-14 species have shown applications in various areas such as organic transformations (hydroboration, cyanosilylation, N-functionalisation of amines, and hydroamination), small molecule activation (e.g. P4, As4, CO2, CO, H2, alkene, and alkyne) and materials. This review presents an in-depth discussion on low-valent group-14 species-catalyzed reactions, including polymerization of rac-lactide, L-lactide, DL-lactide, and caprolactone, followed by their photophysical properties (phosphorescence and fluorescence), thin film deposition (atomic layer deposition and vapor phase deposition), and medicinal applications. This review concisely summarizes current developments of low-valent heavier group-14 compounds, covering synthetic methodologies, structural aspects, and their applications in various fields of chemistry. Finally, their opportunities and challenges are examined and emphasized.

N2 cleavage by silylene and formation of H2Si(μ-N)2SiH2

Fixation and functionalisation of N2 by main-group elements has remained scarce. Herein, we report a fixation and cleavage of the N ≡ N triple bond achieved in a dinitrogen (N2) matrix by the reaction of hydrogen and laser-ablated silicon atoms. The four-membered heterocycle H2Si(μ-N)2SiH2, the H2SiNN(H2) and HNSiNH complexes are characterized by infrared spectroscopy in conjunction with quantum-chemical calculations. The synergistic interaction of the two SiH2 moieties with N2 results in the formation of final product H2Si(μ-N)2SiH2, and theoretical calculations reveal the donation of electron density of Si to π* antibonding orbitals and the removal of electron density from the π bonding orbitals of N2, leading to cleave the non-polar and strong NN triple bond.

Controlled Ring Opening of a Tetracyclic Tetraphosphane with Twofold Metallocene Bridging

A direct route to a doubly ferrocene bridged tetracyclic tetraphosphane 1 was developed via reductive coupling of Fe(CpPCl2)2 (2 a), where a chlorine terminated linear P4-compound 3 could be identified as an intermediate. Selective P-P bond activation was further achieved by reacting 1 with elemental selenium or [Cp*Al]4, where regioselective insertion of Se or Al atoms resulted in ferrocenylene bridged [P4Se] (4) or [P4Al] (7) moieties. Compound 7 can be transformed to a hydrogen terminated linear P4 species, 8, with protic solvents. Methylation of compound 1 with MeOTf, proceeds via intermediate formation of monomethylated species 5, which gradually produced Me2-terminated dicationic 6, again containing a linear P4-unit. Besides spectroscopic characterization, the structural details of compounds 1, 4, 6, and 8 could be determined by SC-XRD. Moreover, DFT calculations were used to rationalize the reactivity of 1, derived compounds and intermediates. As a key feature, 1 undergoes ring opening polymerization to a linear polyphosphane 9.

An Air-Stable Storage Compound for White Phosphorus: Reversible Addition to a Stannylene and Chemical Release of P4

Controlled insertion into a single P-P bond of white phosphorus (P4) was achieved by employing a diaryl stabilized stannylene, Ar*2Sn (Ar*=2,6-bis(benzhydryl)-4-iPr-phenyl). Conversions of the stannylene with P4 gave a non-pyrophoric, air-stable storage compound, which releases P4 quantitively upon irradiation with light (354 or 455 nm). Alternatively, the phosphorus cage is detached by reacting the storage compound with PhChChPh (Ch=Se, Te). Despite the recent advances in the directed conversion of P4 using main group element compounds, Ar*2Sn constitutes only the second structurally characterized example of a stannylene capable of performing controlled, reversible addition and release of white phosphorus.

Activation of non-polar bonds by an electron-rich gallagermylene

The electron-rich germylene LGa(μ-Cl)GeArMes (1) (L = CH[C(Me)N(Dipp)]2, Dipp = 2,6-iPr2C6H3, ArMes = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2) shows promising potential in the σ-bond activation of unpolar molecules as is shown in oxidative addition reactions with H2 and P4, yielding L(Cl)GaGe(H)2ArMes (2) and L(Cl)Ga(P4)GeArMes (3). Compounds 2 and 3 were characterised spectroscopically (1H, 13C{1H}, (31P{1H}), IR) and by single-crystal X-ray diffraction (sc-XRD).

Synthesis and reactivity of N-heterocyclic carbene (NHC)-supported heavier nitrile ylides

The synthesis and isolation of stable heavier analogues of nitrile ylide as N-heterocyclic carbene (NHC) adducts of phosphasilenyl-tetrylene [(NHC)(TerAr)Si(H)PE14(TerAr)] (E14 = Ge 1, Sn 2; TerAr = 2,6-Mes2C6H3, NHC = IMe4) are reported. The delocalized Si-P-E14 π-conjugation was examined experimentally and computationally. Interestingly, the germanium derivative 1 exhibits a 1,3-dipolar nature, leading to an unprecedented [3 + 2] cycloaddition with benzaldehyde, resulting in unique heterocycles containing four heteroatoms from group 14, 15, and 16. Further exploiting the nucleophilicity of germanium, activation of the P-P bond of P4 was achieved, leading to a [(NHC)(phosphasilenyl germapolyphide)] complex. Moreover, the [3 + 2] cycloaddition and the σ-bond activation by 1 resemble the characteristics of the classic nitrile ylide.

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 the GaI Cation for Bond Activation: from Oxidative Additions into C-Cl and H-P Bonds to Reversible Insertion into P4

Although the discovery of the GaI complex salt [Ga(PhF)2-3 ][Al(ORF )4 ] (RF =C(CF3 )3 , PhF=C6 H5 F) invoked the preparation of a diverse library of cationic Ga(I) coordination complexes and clusters, studies on small molecule activation with low-valent GaI cations are scarce. Herein, a first experimental study on the reactivity of a monomeric Ga(I) cation activated with a pyridine-diimine pincer ligand (in [Ga(PDIdipp )][Al(ORF )4 ]) towards small-molecules is reported. First controlled oxidative additions of the GaI cation into C-Cl, H-P and P-P bonds are presented. Moreover, the [4+1]cycloaddition to butadienes was achieved. Intriguingly, the isolated, blue insertion product into the P-P bond of P4 allows for the quantitative release of the P4 molecule upon reaction with AlEt3 and butadienes. Reversible P4 insertion of main-group metals has previously been reported for Ge and Sn, respectively. The experimental study is supported by high-level computational analysis of the in-part reversible oxidative additions at the DLPNO-CCSD(T)/def2-TZVPP//PBEh-3c/def2-mSVP level of theory with COSMO-RS solvation in 1,2-difluorobenzene.

Snapshots of sequential polyphosphide rearrangement upon metallatetrylene addition

Insertion and functionalization of gallasilylenes [LPhSi-Ga(Cl)LBDI] (LPh = PhC(NtBu)2; LBDI = [{2,6-iPr2C6H3NCMe}2CH]) into the cyclo-E5 rings of [Cp*Fe(η5-E5)] (Cp* = η5-C5Me5; E = P, As) are reported. Reactions of [Cp*Fe(η5-E5)] with gallasilylene result in E-E/Si-Ga bond cleavage and the insertion of the silylene in the cyclo-E5 rings. [(LPhSi-Ga(Cl)LBDI){(η4-P5)FeCp*}], in which the Si atom binds to the bent cyclo-P5 ring, was identified as a reaction intermediate. The ring-expansion products are stable at room temperature, while isomerization occurred at higher temperature, and the silylene moiety further migrates to the Fe atom, forming the corresponding ring-construction isomers. Furthermore, reaction of [Cp*Fe(η5-As5)] with the heavier gallagermylene [LPhGe-Ga(Cl)LBDI] was also investigated. All the isolated complexes represent rare examples of mixed group 13/14 iron polypnictogenides, which could only be synthesized by taking advantage of the cooperativity of the gallatetrylenes featuring low-valent Si(ii) or Ge(ii) and Lewis acidic Ga(iii) units/entities.

Gradual Donor Stabilization of a Transient Ferrocene Bridged Bisphosphanyl Phosphenium Cation

A transient phosphenium cation embedded into a [3]ferrocenophane scaffold was formed via chloride abstraction. The cation has been trapped with phosphane, carbene, and silylene donors resulting in stable adducts or bond activation of the ferrocenophane bridge. In the absence of donors, dimerization of the phosphenium cation to the corresponding dication is observed or P-C bond activation with migration of a substituent leading to a putative phosphoniodiphosphene. Using 1,3-di-tert-butylimidazol-2-silylene as the donor, further reaction of the initially formed chlorosilane leads to activation of a P-P bond of the ferrocenophane scaffold with ring expansion of the ansa-bridge. The donor formation and bonding situation are investigated by density functional theory calculations as well as experimental methods (e.g., NMR spectroscopy and X-ray crystallography).

An Isolable 2,5‐Disila‐3,4‐Diphosphapyrrole and a Conjugated Si=P−Si=P−Si=N Chain Through Degradation of White Phosphorus with a N,N ‐Bis(Silylenyl)Aniline

White phosphorus (P₄) undergoes degradation to P₂ moieties if exposed to the new N,N‐bis(silylenyl)aniline PhNSi₂1 (Si=Si[N(tBu)]₂CPh), furnishing the first isolable 2,5‐disila‐3,4‐diphosphapyrrole 2 and the two novel functionalized Si=P doubly bonded compounds 3 and 4. The pathways for the transformation of the non‐aromatic 2,5‐disila‐3,4‐diphosphapyrrole PhNSi₂P₂2 into 3 and 4 could be uncovered. It became evident that 2 reacts readily with both reactants P₄ and 1 to afford either the polycyclic Si=P‐containing product [PhNSi₂P₂]₂P₂3 or the unprecedented conjugated Si=P−Si=P−Si=NPh chain‐containing compound 4, depending on the employed molar ratio of 1 and P₄ as well as the reaction conditions. Compounds 3 and 4 can be converted into each other by reactions with 1 and P₄, respectively. All new compounds 1–4 were unequivocally characterized including by single‐crystal X‐ray diffraction analysis. In addition, the electronic structures of 2–4 were established by Density Functional Theory (DFT) calculations.

Selective [2+1+1] Fragmentation of P 4 by heteroleptic Metallasilylenes

Small‐molecule activation by low‐valent main‐group element compounds is of general interest. We here report the synthesis and characterization (¹H, ¹³C, ²⁹Si NMR, IR, sc‐XRD) of heteroleptic metallasilylenes L¹(Cl)MSiL² (M=Al 1, Ga 2, L¹=HC[C(Me)NDipp]₂, Dipp=2,6‐ⁱPr₂C₆H₃; L²=PhC(N^tBu)₂). Their electronic nature was analyzed by quantum chemical computations, while their promising potential in small‐molecule activation was demonstrated in reactions with P₄, which occurred with unprecedented [2+1+1] fragmentation of the P₄ tetrahedron and formation of L¹(Cl)MPSi(L²)PPSi(L²)PM(Cl)L¹ (M=Al 3, Ga 4).

Generation of a π-Bonded Isomer of [P4 ]4- by Aluminyl Reduction of White Phosphorus and its Ammonolysis to PH3

By employing the highly reducing aluminyl complex [K{(NON)Al}]₂ (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), we demonstrate the controlled formation of P₄ ^2- and P₄ ^4- complexes from white phosphorus, and chemically reversible inter-conversion between them. The tetra-anion features a unique planar π-bonded structure, with the incorporation of the K⁺ cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P₄ ^4- fragment. This complex is extremely reactive, acting as a source of P^3- : exposure to ammonia leads to the release of phosphine (PH₃ ) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P₄ and NH₃ (>5 kbar and >250 °C).

Imino(silyl)disilenes: application in versatile bond activation, reversible oxidation and thermal isomerization

Two novel disilenes of type ABSi[double bond, length as m-dash]SiAB bearing N-heterocyclic imino (A = NItBu) and trialkylsilyl (B = SitBu31, B = SitBu2Me 2) groups are reported. The reduced steric demand in 2 results in a highly stable, nonetheless flexible system, wherefore (E/Z) isomerization is observed from room temperature up to 90 °C. The proposed isomerization mechanism proceeds via monomeric silylenes in line with experimental results. Despite enhanced stability, disilene 2 retains high reactivity in the activation of small molecules, including H2. The rare example of a disilene radical cation 7 is isolated and shows reversible redox behavior. White phosphorous (P4) selectively reacts with 2 to give the unique cage-compound 8. Selective thermal rearrangement of 2 at higher temperatures yields the A2Si[double bond, length as m-dash]SiB2-type disilene 9 (A = NItBu, B = SitBu2Me), which bears characteristics of a zwitterionic and a dative central Si-Si bond. The proposed mechanism proceeds via an initial NHI migration followed by silyl migration.

Bicyclic and tricyclic phosphanes with p-block substituents

This review summarises the experimental and structural knowledge on polycyclic phosphanes, with a focus on bicyclic and tricyclic phosphanes, as they have not only been the most studied in the last 25 years, but also show the greatest diversity in terms of constitutional isomerism and structural motifs. Moreover, only polycyclic phosphanes that have p-block substituents at all free valences are discussed.

Reversible Activation and Transfer of White Phosphorus by Silyl-Stannylene

Use of a silyl supported stannylene (Mes TerSn(Sit Bu3 ) [Mes Ter=2,6-(2,4,6-Me3 C6 H2 )2 C6 H3 ] enables activation of white phosphorus under mild conditions, which is reversible under UV light. The reaction of a silylene chloride with the activated P4 complex results in facile P-atom transfer. The computational analysis rationalizes the electronic features and high reactivity of the heteroleptic silyl-substituted stannylene in contrast to the previously reported bis(aryl)stannylene.

Small Molecule Activation by Two-Coordinate Acyclic Silylenes

In recent decades, the chemistry of stable silylenes (R2Si:) has evolved significantly. The first major development in this chemistry was the isolation of a silicocene which is stabilized by the Cp* (Cp* = η5-C5Me5) ligand in 1986 and subsequently the isolation of a first N-heterocyclic silylene (NHSi:) in 1994. Since the groundbreaking discoveries, a large number of isolable cyclic silylenes and higher coordinated silylenes, i.e. Si(II) compounds with coordination number greater than two, have been prepared and the properties investigated. However, the first isolable two-coordinate acyclic silylene was finally reported in 2012. The achievements in the synthesis of acyclic silylenes have allowed for the utilization of silylenes in small molecule activation including inert H2 activation, a process previously exclusive to transition metals. This minireview highlights the developments in silylene chemistry, specifically two-coordinate acyclic silylenes, including experimental and computational studies which investigate the extremely high reactivity of the acyclic silylenes.

Oxidation reactions of a versatile, two-coordinate, acyclic iminosiloxysilylene

Due to their outstanding reactivity, acyclic silylenes have emerged as attractive organosilicon alternatives for transition metal complexes on the way to metal-free catalysis. However, exploration of their reactivity is still in its infancy, as only a few derivatives of this unique compound class have been isolated so far. Here, we present the results of an extensive reactivity investigation of the previously reported acyclic iminosiloxysilylene 1. Divalent silylene 1 proved to be a versatile building block for a plethora of novel organosilicon compounds. Thus, not only the activation of the rather challenging targets NH₃ and P₄ could be achieved, but also the conversion into a reactive donor-free silaimine, which itself turned out to be a useful reagent for small molecule activation. In addition, 1 served as an excellent precursor for gaining access to donor-stabilized heavier carbonyl compounds. Our results thus provide further insights into the chemistry of low-valent silicon at the interface between carbon and transition metals.

Where silylene–silicon centres matter in the activation of small molecules

Small molecules such as H₂, N₂, CO, NH₃, O₂ are ubiquitous stable species and their activation and role in the formation of value-added products are of fundamental importance in nature and industry.

An unusual Ni2Si2P8 cluster formed by complexation and thermolysis

A ternary Ni₂Si₂P₈ cluster compound is formed selectively by thermolysis of a well-defined nickel complex. This reaction illustrates a potentially useful strategy for the preparation of heteroatom-doped transition metal-phosphide clusters.

A bis(germylene) functionalized metal-coordinated polyphosphide and its isomerization

Pentaphosphaferrocene, [Cp*Fe(η⁵-P₅)], was used as an air-stable source of polyphosphorus units to synthesize a novel bis(germylene)-functionalized transition metal polyphosphide complex, which further undergoes a unique constitutional isomerization.

A vinyl silylsilylene and its activation of strong homo- and heteroatomic bonds

A facile route to an two-coordinate acyclic silylene that can activate strong homo- and heteroatomic bonds is reported.

The facile synthesis of a rare two-coordinate acyclic silylene (R₂Si:) that is stabilized using a bulky vinylic N-heterocyclic olefin ligand and the strongly σ-donating hypersilyl group [Si(SiMe₃)₃]^– is reported. This vinyl-substituted silylene exhibits an excellent combination of prolonged thermal stability along with high reactivity towards small molecules. Despite being stable for months in solution, the reactivity of this new silylene is manifest in its ambient temperature activation of strong B–H, Si–Cl, C–O, P–P and C–H bonds.

Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO)₅ }₂ ] (1 a) (Cp*=C₅ Me₅ ) with the anionic cyclo-P_n ligand complex [(η³ -P₃ )Nb(ODipp)₃ ]^- (2, Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)₅ }₂ {μ₃ ,η^3:1:1 -P₄ Cp*}Nb(ODipp)₃ ]^- (3), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)₅ }₂ ] (E=P: 1 a, As: 1 b) with the neutral complex [Cp'''Co(η⁴ -P₄ )] (Cp'''=1,2,4-tBu₃ C₅ H₂ ) led to a cyclo-P₄ E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P₄ ligand. Starting from 1 a, the two isomers [Cp'''Co(μ₃ ,η^4:1:1 -P₅ Cp*){W(CO)₅ }₂ ] (5 a,b), and from 1 b, the three isomers [Cp'''Co(μ₃ ,η^4:1:1 -AsP₄ Cp*){W(CO)₅ }₂ ] (6 a-c) with unprecedented cyclo-P₄ E ligands (E=P, As) were isolated. The complexes 6 a-c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P₄ As ligands. The possible reaction pathways for the formation of 5 a,b and 6 a-c were investigated by a combination of temperature-dependent ³¹ P{¹ H} NMR studies and DFT calculations.

The Chemistry of Yellow Arsenic

The generation and handling of the light-sensitive and metastable yellow arsenic (As₄) is extremely challenging. In view of recent breakthroughs in synthesizing As₄ storage materials and transfer reagents, the more intensive use of yellow arsenic as a source for further reactions can be expected. Given these aspects, the current stage of knowledge of the direct use of As₄ is comprehensively summarized in the present review, which lists the activation of As₄ by main group elements as well as transition metal compounds (including the f-block elements). Moreover, it also partly compares the reaction outcomes in relation to the corresponding reactions of P₄. The possibility of using alternative sources for generating arsenic moieties and compounds is also discussed. The release of As₄ molecules from precursor compounds and the use of transfer reagents for polyarsenic entities open up new synthetic pathways to avoid the direct generation of yellow arsenic solutions and to ensure its smooth usage for subsequent reactions.

A Three-Membered Cyclic Phosphasilene

Small unsaturated phosphacycles are versatile reagents owing to their strain and the added functionality of the double bond and the phosphorus lone pair. Herein we report the synthesis and isolation of the smallest possible cyclic phosphasilene as a stable adduct with an N-heterocyclic carbene (NHC). First reactivity studies show a) that the PSi₂ ring is a competent ligand to the Fe(CO)₄ fragment via the phosphorus lone pair and b) that the abstraction of the NHC by BPh₃ results in the rapid head-to-head or head-to-tail dimerization of the PSi₂ unit. The relatively facile NHC cleavage indicates that the P=Si double bond is available for further manipulation.

Cyclometallation of a germylene ligand by concerted metalation-deprotonation of a methyl group

The reaction of [CH{(CMe)(2,6-iPr2C6H3N)}2]GeCl with LiN(SiMe3)2 was previously reported, which led to the formation of a hetero-fulvene type germylene, [CH{(CMe)(C[double bond, length as m-dash]CH2)(2,6-iPr2C6H3N)}2]Ge through the deprotonation of the C-H bond from the methyl substituents. In this paper, we attempted the analogous reaction with (Dipp)NCMeCHCOMeGeCl using LiN(SiMe3)2 which gave rise to a metathesis product, (Dipp)NCMeCHCOMeGeN(SiMe3)2 (2). However, the reactions of 2 with [M2Cl2(μ-Cl)2(η5-Cp*)2] (M = Rh and Ir) resulted in cyclometallated Rh and Ir complexes through the activation of the C-H bond from the germylene ligand. The complexes were characterized by single crystal X-ray analysis, which authenticated the presence of Ge-Rh and Ge-Ir bonds. DFT studies have been performed to understand the mechanism.

Selective Derivatization of a Hexaphosphane from Functionalization of White Phosphorus

The reaction of LGa (L = Dipp(4-(Dipp-imino)pent-2-en-2-yl)amide; Dipp: 2,6-diisopropylphenyl) and white phosphorus was revisited. A plethora of unprecedented polyphosphanes in addition to the known monoinserted product LGaP₄ (1) are observed. An optimized synthesis of the hitherto unknown hexaphosphane (LGa)₂P₆ (3) is presented, and its subsequent selective derivatization with Brønsted acids, MeOTf, Ph₂ECl (E = P, As), and NaOCP provides access to a wealth of functionalized hexa- and heptaphosphanes.

The Unusual Role of Aromatic Solvent in Single-Site AluminumI Chemistry: Insights from Theory

The single-site activation of strong σ bonds (such as that of H-H, P-H, and N-H) remains a significant challenge in main-group chemistry, with only a few cases reported to date. In this regard, recent exciting experiments performed with aluminum^I complexes hold significance because they have been seen to activate a variety of strong σ bonds. Such chemistry is generally seen to occur in aromatic solvents. Current computational studies with DFT reveal the interesting reason for this: an explicit aromatic solvent molecule acts as a catalyst by converting the aluminum^I complex into aluminum^III during the process. Different cases of σ-bond activation by aluminum^I complexes have been investigated and the efficiency of H-X (X=H, NHtBu, PPh₂ ) bond activation in the presence of an explicit benzene solvent molecule is orders of magnitude higher than that in its absence. The current work therefore reveals the chemistry of aluminum^I complexes to be richer and more complex than that previously realized, and shows it to be dependent on metal-solvent cooperativity; the first known example of its kind in main-group chemistry.

A Tetracyclic Octaphosphane by Successive Addition, Inversion, and Condensation Reactions

An example of an octaphosphane of type R₂ P₈ (R=(DDP)Ga) was isolated by treatment of cage compound (DDP)GaP₄ (2, DDP=(2,6-diisopropylphenyl)(4-((2,6-diisopropylphenyl)imino)pent-2-en-2-yl)amide) with (C₆ F₅ )₂ PBr. The initially formed endo-exo butterfly shaped pentaphosphane 7 rapidly rearranges to the more stable exo-exo isomer 8, which undergoes dimerization to decaphosphane 11. Compound 11 unexpectedly eliminates tetraaryldiphosphane 13 to give tetracyclo[3.3.0.0^2,7 .0^4,6 ]octaphosphane [(DDP)GaBr]₂ P₈ (12). The reaction steps were confirmed by crystal structure analysis of the key intermediates and supported by kinetic studies using NMR techniques.