Reduction of [Cp*Sb]4 with Subvalent Main-Group Metal Reductants: Syntheses and Structures of [(L1 Mg)4 (Sb4 )] and [(L2 Ga)2 (Sb4 )] Containing Edge-Missing Sb4 Units

Reactivity of E4 (E4 =P4 , As4 , AsP3 ) towards Low-Valent Al(I) and Ga(I) Compounds

The reactivity of yellow arsenic and the interpnictogen compound AsP₃ towards low-valent group 13 compounds was investigated. The reactions of [LAl] (1, L=[{N(C₆ H₃ ⁱ Pr₂ -2,6)C(Me)}₂ CH]^- ) with As₄ and AsP₃ lead to [(LAl)₂ (μ,η^1:1:1:1 -E₄ )] (E₄ =As₄ (3 b), AsP₃ (3 c)) by insertion of two fragments [LAl] into two of the six E-E edges of the E₄ tetrahedra. Furthermore, the reaction of [LGa] (2) with E₄ afforded [LGa(η^1:1 -E₄ )] (E₄ =As₄ (4 b), AsP₃ (4 c)). In these compounds, only one E-E bond of the E₄ tetrahedra was cleaved. These compounds represent the first examples of the conversion of yellow arsenic and AsP₃ , respectively, with group 13 compounds. Furthermore, the reactivity of the gallium complexes towards unsaturated transition metal units or polypnictogen (E_n ) ligand complexes was investigated. This leads to the heterobimetallic compounds [(LGa)(μ,η^2:1:1 -P₄ )(LNi)] (5 a), [(Cp'''Co)(μ,η^4:1:1 -E₄ )(LGa)] (E=P (6 a), As (6 b), Cp'''=η⁵ -C₅ H₂ ^t Bu₃ ) and [(Cp'''Ni)(η^3:1:1 -E₃ )(LGa)] (E=P (7 a), As (7 b)), which combine two different ligand systems in one complex (nacnac and Cp) as well as two different types of metals (main group and transition metals). The products were characterized by crystallographic and spectroscopic methods.

Modulating the frontier orbitals of L(X)Ga-substituted diphosphenes [L(X)GaP]2 (X = Cl, Br) and their facile oxidation to radical cations

Modulating the electronic structures of main group element compounds is crucial to control their chemical reactivity. Herein we report on the synthesis, frontier orbital modulation, and one-electron oxidation of two L(X)Ga-substituted diphosphenes [L(X)GaP]2 (X = Cl 2a, Br 2b; L = HC[C(Me)N(Ar)]2, Ar = 2,6-i-Pr2C6H3). Photolysis of L(Cl)GaPCO 1 gave [L(Cl)GaP]22a, which reacted with Me3SiBr with halide exchange to [L(Br)GaP]22b. Reactions with MeNHC (MeNHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gave the corresponding carbene-coordinated complexes L(X)GaPP(MeNHC)Ga(X)L (X = Cl 3a, Br 3b). DFT calculations revealed that the carbene coordination modulates the frontier orbitals (i.e. HOMO/LUMO) of diphosphenes 2a and 2b, thereby affecting the reactivity of 3a and 3b. In marked contrast to diphosphenes 2a and 2b, the cyclic voltammograms (CVs) of the carbene-coordinated complexes each show one reversible redox event at E 1/2 = -0.65 V (3a) and -0.36 V (3b), indicating their one-electron oxidation to the corresponding radical cations as was confirmed by reactions of 3a and 3b with the [FeCp2][B(C6F5)4], yielding the radical cations [L(X)GaPP(MeNHC)Ga(X)L]B(C6F5)4 (X = Cl 4a, Br 4b). The unpaired spin in 4a (79%) and 4b (80%) is mainly located at the carbene-uncoordinated phosphorus atoms as was revealed by DFT calculations and furthermore experimentally proven in reactions with n Bu3SnH, yielding the diphosphane cations [L(X)GaPHP(MeNHC)Ga(X)L]B(C6F5)4 (X = Cl 5a, Br 5b). Compounds 2-5 were fully characterized by NMR and IR spectroscopy as well as by single crystal X-ray diffraction (sc-XRD), and compounds 4a and 4b were further studied by EPR spectroscopy, while their bonding nature was investigated by DFT calculations.

Bis‐Phosphaketenes LM(PCO) 2 (M=Ga, In): A New Class of Reactive Group 13 Metal‐Phosphorus Compounds

Phosphaketenes are versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel bis‐phosphaketenes, LM(PCO)₂ (M=Ga 2 a, In 2 b; L=HC[C(Me)N(Ar)]₂; Ar=2,6‐i‐Pr₂C₆H₃) by salt metathesis reactions and their reactions with LGa to metallaphosphenes LGa(OCP)PML (M=Ga 3 a, In 3 b). 3 b represents the first compound with significant In−P π‐bonding contribution as was confirmed by DFT calculations. Compounds 3 a and 3 b selectively activate the N−H and O−H bonds of aniline and phenol at the Ga−P bond and both reactions proceed with a rearrangement of the phosphaethynolate group from Ga−OCP to M−PCO bonding. Compounds 2–5 are fully characterized by heteronuclear (¹H, ¹³C{¹H}, ³¹P{¹H}) NMR and IR spectroscopy, elemental analysis, and single crystal X‐ray diffraction (sc‐XRD).

Synthesis of polyantimony ligand complexes starting from Cp*4Sb4

The reactivity of Cp*₄Sb₄ (1) towards ionic compounds and transition metal complexes with labile ligands was investigated in order to synthesize polyantimony ligand complexes. The silver salts [Ag][X] and the metalate Na[Cp*Mo(CO)₃] were primarily used, leading in the raction with Cp*₄Sb₄ to the formation of [Cp*₂Sb][X] (X = TEF (2a), FAL (2b)), [(Cp*Mo(CO)₃)₃(μ₃-Sb₃)] (3) and [Cp*Mo(CO)₂(η³-Sb₃)] (4), respectively. The reaction of 1 with the transition metal complexes [(Cp'''M)₂(tol)] leads to a degradation of the original Sb₄ unit and to the formation of [(Cp'''M)₄(μ₃-Sb)₄] (M = Ni (5); Co (6)). Towards [Cp^RFe(CO)₂]₂, substitutions on the antimony atoms were observed to give [{Cp^RFe(CO)₂}₄(μ₄-Sb₄)] (Cp^R = Cp'' (7a), Cp''' (7b)). All complexes were characterized by XRD and spectroscopic methods.

Selective 1,2 addition of polar X-H bonds to the Ga-P double bond of gallaphosphene L(Cl)GaPGaL

Gallaphosphene L(Cl)GaPGaL 1 (L = HC[C(Me)N(2,6-i-Pr₂-C₆H₃)]₂) reacts at ambient temperature with a series of polar X-H bonds, i.e. ammonia, primary amines, water, phenol, thiophenol, and selenophenol, selectively with 1,2 addition at the polar Ga-P double bond. The gallium atom serves as electrophile and the phosphorous atom is protonated in all reactions. The resulting complexes L(Cl)GaP(H)Ga(X)L (X = NH₂2, NHi-Pr 3, NHPh 4, OH 5, OXyl 6, SPh 7, SePh 8) were characterized by IR and heteronuclear (¹H, ¹³C{¹H}, ³¹P{¹H}) NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Reversible and Irreversible [2+2] Cycloaddition Reactions of Heteroallenes to a Gallaphosphene

[2+2] Cycloaddition reactions of gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(2,6-i-Pr2 C6 H3 )]2 ) with carbodiimides [C(NR)2 ; R=i-Pr, Cy] and isocyanates [RNCO; R=Et, i-Pr, Cy] yielded four-membered metallaheterocycles LGa(Cl)P[μ-C(X)NR]GaL (X=NR, R=i-Pr 2, Cy 3; X=O, R=Et 4, i-Pr 5, Cy 6). Compounds 4-6 reversibly react with CO2 via [2+2] cycloaddition at ambient temperature to the six-membered metallaheterocycles LGa(Cl)P[μ-C(O)O]-μ-C(O)N(R)GaL (R=Et 7, i-Pr 8, Cy 9). Compounds 2-9 were characterized by IR and heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR spectroscopy and elemental analysis, while quantum chemical calculations provided a deeper understanding on the energetics of the reactions.

Transfer of polyantimony units

Transfer reagents are useful tools in chemistry to access metastable compounds. The reaction of [Cp′′₂ZrCl₂] with KSb(SiMe₃)₂ leads to the formation of the novel polyantimony triple decker complex [(Cp′′Zr)₂(μ,η^1:1:1:1:1:1-Sb₆)] (1, Cp′′ = 1,3-di-tertbutyl-cyclopentadienyl), containing a chair-like Sb₆⁶⁻ ligand. Compound 1 represents a valuable transfer reagent to form novel antimony ligand complexes. Thus, the reaction of 1 with Cp^R-substituted transition metal halides of nickel, cobalt and iron leads to the formation of a variety of novel Sb_n ligand complexes, such as the cubane-like compounds [(Cp′′′Ni)₄(μ₃-Sb)₄] (2) and [(Cp′′′Co)₄(μ₃-Sb₄)] (3a) or the complexes [(Cp^BnCo)₃(μ₃-Sb)₂] (4) and [(Cp′′′Fe)₃(μ₃-Sb)₂] (5), representing a trigonal bipyramidal structure. Moreover, beside the transfer of Sb₁ units, also the complete entity can be transferred as seen in the iron complex [(Cp′′′Fe)₃(μ_3,η^4:4:4-Sb₆)] (6). DFT calculations shed light on the bonding situation of the products.

The synthesis and characterization of the unique polyantimony complex [(Cp′′Zr)₂(μ,η^1:1:1:1:1:1-Sb₆)] (1) is described. Compound 1 was used as antimony source to transfer Sb_n units to late transition metal fragments [Cp^RM] (M = Fe, Co, Ni).

Multi-Talented Gallaphosphene for Ga-P-Ga Heteroallyl Cation Generation, CO2 Storage, and C(sp3 )-H Bond Activation

Gallaphosphene L(Cl)GaPGaL (2; L=HC[C(Me)N(2,6-i-Pr2 C6 H3 )]2 ), which is synthesized by reaction of LGa(Cl)PCO (1) with LGa, reacts with [Na(OCP)(dioxane)2.5 ] to LGa(OCP)PGaL (3), whereas chloride abstraction with LiBArF 4 yields [LGaPGaL][BArF 4 ] (4; BArF 4 =B(C6 F5 )4 ). 4 represents a heteronuclear analog of the allyl cation according to quantum chemical calculations. Remarkably, 2 reversibly reacts with CO2 to yield L(Cl)Ga-P[μ-C(O)O]2 GaL (5), while reactions with acetophenone and acetone selectively give compounds 6 and 7 by C(sp3 )-H bond activation.

Synthesis of Unprecedented 4d/4f-Polypnictogens

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cpt Mo(CO)2 }2 (μ,η2:2 -E2 )] (E=As, Sb; Cpt =tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2 Sm] and [(CpMe4nPr )2 Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As2 2- anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

A Mechanistic Study on Reactions of Group 13 Diyls LM with Cp*SbX2 : From Stibanyl Radicals to Antimony Hydrides

Oxidative addition of Cp*SbX₂ (X=Cl, Br, I; Cp*=C₅Me₅) to group 13 diyls LM (M=Al, Ga, In; L=HC[C(Me)N (Dip)]₂, Dip=2,6‐iPr₂C₆H₃) yields elemental antimony (M=Al) or the corresponding stibanylgallanes [L(X)Ga]Sb(X)Cp* (X=Br 1, I 2) and ‐indanes [L(X)In]Sb(X)Cp* (X=Cl 5, Br 6, I 7). 1 and 2 react with a second equivalent of LGa to eliminate decamethyl‐1,1’‐dihydrofulvalene (Cp*₂) and form stibanyl radicals [L(X)Ga]₂Sb^. (X=Br 3, I 4), whereas analogous reactions of 5 and 6 with LIn selectively yield stibanes [L(X)In]₂SbH (X=Cl 8, Br 9) by elimination of 1,2,3,4‐tetramethylfulvene. The reactions are proposed to proceed via formation of [L(X)M]₂SbCp* as reaction intermediate, which is supported by the isolation of [L(Cl)Ga]₂SbCp (11, Cp=C₅H₅). The reaction mechanism was further studied by computational calculations using two different models. The energy values for the Ga‐ and the In‐substituted model systems showing methyl groups instead of the very bulky Dip units are very similar, and in both cases the same products are expected. Homolytic Sb−C bond cleavage yields van der Waals complexes from the as‐formed radicals ([L(Cl)M]₂Sb^. and Cp*^.), which can be stabilized by hydrogen atom abstraction to give the corresponding hydrides, whereas the direct formation of Sb hydrides starting from [L(Cl)M]₂SbCp* via concerted β‐H elimination is unlikely. The consideration of the bulky Dip units reveals that the amount of the steric overload in the intermediate I determines the product formation (radical vs. hydride).

Frontiers in the solution-phase chemistry of homoatomic group 15 Zintl clusters

Recent developments in the solution-phase chemistry of polypnictogen Zintl cluster are discussed, including the preparation of new clusters, wet synthetic methods, and their subsequent small molecule activations.

The Influence of β-diiminato Ligands on As4 Activation by Cobalt Complexes

In a systematic study of the activation of As₄, three [LCo(tol)] (L=β‐diiminato) complexes have revealed different steric and electronic influences. 2,6‐Diisopropylphenyl (Dipp) and 2,6‐dimethylphenyl (dmp) flanking groups were used, one of the ligands with H backbone substituents (β‐dialdiminate L⁰) and two with Me substituents (β‐diketiminates L³ and L¹). In the reaction with As₄, different dinuclear products [(LCo)₂As₄] (LM=L⁰ (1), L¹ (2), L³ (3)) were isolated, with all showing differently shaped [Co₂As₄] cores in the solid state: octahedral in 1, prismatic in 2, and asterane‐like in 3. Thermal treatment of 3 leads to the abstraction of one arsenic atom to yield [(L³Co)₂As₃] (4). All products were comprehensively characterized by single‐crystal X‐ray diffraction, FD‐MS, and ¹H NMR spectroscopy. A rational explanation for the different reactivity is also proposed and DFT calculations shed light on the nature of the highly flexible [Co₂As₄] cores.

Samarium Polystibides Derived from Highly Activated Nanoscale Antimony

Zintl ions in molecular compounds are of fundamental interest for basic research and application. Two reactive antimony sources are presented that allow direct access to molecular polystibide compounds. These are Sb amalgam (Sb/Hg) and ultrasmall Sb⁰ nanoparticles (d=6.6±0.8 nm), which were used independently as precursors for the synthesis of the largest f-element polystibide, [(Cp*₂ Sm)₄ Sb₈ ]. Whereas the reaction of the nanoparticles with [Cp*₂ Sm] directly led to [(Cp*₂ Sm)₄ Sb₈ ], Sm/Sb/Hg intermediates were isolated when using Sb/Hg as the precursor. These Sm/Sb/Hg intermediates [{(Cp*₂ Sm)₂ Sb}₂ (μ-Hg)] and [{(Cp*₂ Sm)₃ (μ⁴ ,η^1:2:2:2 -Sb₄ )}₂ Hg] were synthetically trapped and structurally characterized, giving insight in the formation mechanism of polystibide compounds.

A General Route to Metal-Substituted Dipnictenes of the Type [L(X)M]2 E2

Two equivalents of LGa (L=HC[C(Me)N(2,6-iPr₂ C₆ H₃ )]₂ ) reacted with PX₃ (X=Cl, Br) with insertion into two P-X bonds and formation of [L(X)Ga]₂ PX (X=Cl 1, Br 2), whereas the analogous reaction with AsCl₃ occurred with twofold insertion and subsequent elimination of LGaCl₂ and formation of the Ga-substituted diarsene [L(Cl)Ga]₂ As₂ (3). Analogous findings were observed in the reactions with Me₂ NAsCl₂ , yielding the unsymmetrically-substituted diarsene [L(Cl)Ga]As=As[Ga(NMe₂ )L] (4). The reaction of As(NMe₂ )₃ with LGa gave [L(Me₂ N)Ga]₂ As₂ (5) after heating at 165 °C for five days, whereas the reaction with LAl gave [L(Me₂ N)Al]₂ As₂ (6) after heating at only 80 °C for one day. Finally, two equivalents of LGa reacted with Bi(NEt₂ )₃ to give [L(Et₂ N)Ga]₂ Bi₂ (7). Complexes 1-7 were characterized by NMR spectroscopy (¹ H, ¹³ C, ³¹ P), elemental analysis, and single-crystal X-ray diffraction (except for 1 and 5). The bonding situations in 4, 6, and 7 were analyzed by quantum chemical calculations.

From stable Sb- and Bi-centered radicals to a compound with a Ga=Sb double bond

Neutral stibinyl and bismuthinyl radicals are typically short-lived, reactive species. Here we show the synthesis and solid-state structures of two stable stibinyl [L(Cl)Ga]₂Sb· 1 and bismuthinyl radicals [L(I)Ga]₂Bi· 4, which are stabilized by electropositive metal centers. Their description as predominantly metal-centered radicals is consistent with the results of NMR, EPR, SQUID, and DFT studies. The Lewis-acidic character of the Ga ligands allow for significant electron delocalization of the Sb- and Bi- unpaired radical onto the ligand. Single-electron reduction of [L(Cl)Ga]₂Sb· gave LGaSbGa(Cl)L 5, the first compound containing a Ga=Sb double bond. The π-bonding contribution is estimated to 9.56 kcal mol⁻¹ by NMR spectroscopy. The bonding situation and electronic structure is analyzed by quantum mechanical computations, revealing significant π backdonation from the Sb to the Ga atom. The formation of 5 illustrates the high-synthetic potential of 1 for the formation of new compounds with unusual electronic structures.

Radicals of heavy main-group elements represent important intermediates in chemical synthesis, yet few have been isolated. Here the authors stabilize neutral stibinyl and bismuthinyl radicals using gallium-based ligands, and reduce the former to afford a Ga=Sb double bond-containing complex.