Reaction of N‐Heterocyclic Silylenes with Thioketone: Formation of Silicon–Sulfur Three (Si‐C‐S)‐ and Five (Si‐C‐C‐C‐S)‐Membered Ring Systems

Three‐ and five‐membered rings that bear the (Si‐C‐S ) and (Si‐C‐C‐C‐S ) unit have been synthesized by the reactions of L SiCl ( 1 ; L =PhC(NtBu)₂) and L′ Si ( 2 ; L′ =CH{(C?CH₂)(CMe)(2,6‐iPr₂C₆H₃N)₂}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with L SiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3 . However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4 . Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si resulted in products 4 and 5 , in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C? S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.     

A Series of Isolable Silanoic Thio‐, Seleno‐, and Telluroesters (LSi(X)OR) with Donor‐Supported SiX Double Bonds (L=β‐Diketiminate; X=S,Se, Te)

The first silicon analogues of carbonic (carboxylic) esters, the silanoic thio‐, seleno‐, and tellurosilylesters 3 (Si?S), 4 (Si?Se), and 5 (Si?Te), were prepared and isolated in crystalline form in high yield. These thermally robust compounds are easily accessible by direct reaction of the stable siloxysilylene L(Si:)OSi(H)L′ 2 (L=HC(CMe)₂[N(aryl)₂], L′=CH[(C?CH₂)‐CMe][N(aryl)]₂; aryl=2,6‐iPr₂C₆H₃) with the respective elemental chalcogen. The novel compounds were fully characterized by methods including multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction analysis. Owing to intramolecular N→Si donor–acceptor support of the Si?X moieties (X=S, Se, Te), these compounds have a classical valence‐bond N⁺–Si–X^? resonance betaine structure. At the same time, they also display a relatively strong nonclassical Si?X π‐bonding interaction between the chalcogen lone‐pair electrons (n_π donor orbitals) and two antibonding Si? N orbitals (σ*_π acceptor orbitals mainly located at silicon), which was shown by IR and UV/Vis spectroscopy. Accordingly, the Si?X bonds in the chalcogenoesters are 7.4 ( 3 ), 6.7 ( 4 ), and 6.9 % ( 5 ) shorter than the corresponding Si? X single bonds and, thus, only a little longer than those in electronically less disturbed Si?X systems (“heavier” ketones).     

A Silyliumylidene Cation Stabilized by an Amidinate Ligand and 4‐Dimethylaminopyridine

The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4‐dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [ L Si:]₂ ( 1 ; L =PhC(NtBu)₂) with one equivalent of N‐trimethylsilyl‐4‐dimethylaminopyridinium triflate [4‐NMe₂C₅H₄NSiMe₃]OTf and two equivalents of DMAP in THF afforded [ L Si(DMAP)]OTf ( 2 ). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [ L′ ₂( L )Si]OTf ( 3 ; L′ = L Si:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)₃}] and elemental sulfur in THF afforded the silylsilylene [ L SiSi(H){(NtBu)₂C(H)Ph}] ( 4 ) and the base‐stabilized silanethionium triflate [ L Si(S)DMAP]OTf ( 5 ), respectively. Compounds 2 , 3 , and 5 have been characterized by X‐ray crystallography.     

Imino‐Bridged Bisphosphaalkenes (2,4‐Diphospha‐3‐azapentadienes)

Deprotonation of aminophosphaalkenes (RMe₂Si)₂C?PN(H)(R′) (R=Me, iPr; R′=tBu, 1‐adamantyl (1‐Ada), 2,4,6‐tBu₃C₆H₂ (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe₂Si)₂C?P(M)(R′)] with one equivalent of the corresponding P‐chlorophosphaalkenes (RMe₂Si)₂C?PCl provides bisphosphaalkenes (2,4‐diphospha‐3‐azapentadienes) [(RMe₂Si)₂C?P]₂NR′. The thermally unstable tert‐butyliminobisphosphaalkene [(Me₃Si)₂C?P]₂NtBu ( 4 a ) undergoes isomerisation reactions by Me₃Si‐group migration that lead to mixtures of four‐membered heterocyles, but in the presence of an excess amount of (Me₃Si)₂C?PCl, 4 a furnishes an azatriphosphabicyclohexene C₃(SiMe₃)₅P₃NtBu ( 5 ) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P?C double bond and an exocyclic ylidic P⁽⁺⁾? C^(?)(SiMe₃)₂ unit. Using the bulkier iPrMe₂Si substituents at three‐coordinated carbon leads to slightly enhanced thermal stability of 2,4‐diphospha‐3‐azapentadienes [(iPrMe₂Si)₂C?P]₂NR′ (R′=tBu: 4 b ; R′=1‐Ada: 8 ). According to a low‐temperature crystal‐structure determination, 8 adopts a non‐planar structure with two distinctly differently oriented P?C sites, but ³¹P NMR spectra in solution exhibit singlet signals. ³¹P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6‐tBu₃C₆H₂) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P? N bonds in persistent compounds [(RMe₂Si)₂C?P]₂NMes* ( 11 a , 11 b ). DFT calculations for the parent molecule [(H₃Si)₂C?P]₂NCH₃ suggest that the non‐planar distortion of compound 8 will have steric grounds.     

Crystallographic report: Fluoro‐bis‐iso‐propyl‐(2,4,6‐tris‐iso‐propylphenyl)‐ silane,i‐Pr2(2,4,6‐i‐Pr3C6H2)SiF

Owing to steric congestion in i‐Pr₂(2,4,6‐i‐Pr₃C₆H₂)SiF, the geometry at the Si atom deviates slightly from ideal tetrahedral geometry with an increased C? Si? C angle of 119.02(9)° and elongated Si? C and Si? F bond distances. Copyright © 2005 John Wiley & Sons, Ltd.     

Micron‐granula polyolefin with self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups

Self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArN?C]₂(C₁₀H₆)NiBr₂ [Ar = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₂] ( 1 ), [ArN?C(Me)][Ar′N? C(Me)]C₅H₃NFeCl₂ [Ar = Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃, Ar = 2,6‐(i‐Pr)₂C₆H₃, and Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArN?C]₂C₁₀H₆NiBr₂ (Ar = 2,6‐(i‐Pr)₂C₆H₂)], but also greatly improved the morphology of polymer particles to afford micron‐granula polyolefin. The self‐immobilization of catalysts, the formation mechanism of microspherical polymer, and the influence on the size of the particles are discussed. The molecular structure of self‐immobilized nickel catalyst 1 was also characterized by crystallographic analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1018–1024, 2004     

Influence of the Homopolar Dihydrogen Bonding CH⋅⋅⋅HC on Coordination Geometry: Experimental and Theoretical Studies

The reaction of the N‐thiophosphorylated thiourea (HOCH₂)(Me)₂CNHC(S)NHP(S)(OiPr)₂ (HL), deprotonated by the thiophosphorylamide group, with NiCl₂ leads to green needles of the pseudotetrahedral complex [Ni(L‐1,5‐S,S′)₂] ? 0.5 (n‐C₆H₁₄) or pale green blocks of the trans square‐planar complex trans‐[Ni(L‐1,5‐S,S′)₂]. The former complex is stabilized by homopolar dihydrogen C?H???H?C interactions formed by n‐hexane solvent molecules with the [Ni(L‐1,5‐S,S′)₂] unit. Furthermore, the dispersion‐dominated C?H??? H?C interactions are, together with other noncovalent interactions (C?H???N, C?H???Ni, C?H???S), responsible for pseudotetrahedral coordination around the Ni^II center in [Ni(L ‐1,5‐S,S′)₂] ? 0.5 (n‐C₆H₁₄).     

β‐Diketiminate Stabilized Magnesium Hydroxide,Heterobimetallic, and Halide Complexes: Synthesis and X‐ray Structural Studies

The controlled hydrolysis of heteroleptic magnesium amide, LMgN(SiMe₃)₂ (L = CH[C(Me)N(2,6‐iPr₂C₆H₃)]₂) with water afforded the corresponding hydroxide [LMg(OH)·THF]₂ as air and moisture sensitive compound. The presence of a sterically bulky β‐diketiminate ligand prevents the self‐condensation reaction of this hydroxide complex. Single crystal X‐ray analysis shows that the hydroxide is dimeric in the solid state. Reaction of the magnesium amide or LMg(Me)·OEt₂ with LAlMe(OH) generates the heterobimetallic species containing the Mg–O–Al moiety. Additionally, the reaction of methylmagnesiumchloride with the free ligand leads to complex L′MgCl (L′ = CH[Et₂NCH₂CH₂N(CMe)]₂). As revealed by the crystal structure, L′MgCl is a solvent free monomeric magnesium chloride complex that is analogues to the Grignard reagent.     

Tetraphosphanylsilane – A Mild PH2‐Transfer Reagent and Building Block for the Synthesis of a Rhombododecahedral Li6P6Si2‐Cluster Framework

Reaction of the PH₂‐transfer reagent Si(PH₂)₄ ( 1 ) with SiCl₄ affords a mixture of the Cl_nSi(PH₂)_4–n compounds ( 2 a , n = 1), ( 2 b , n = 2), and ( 2 c , n = 3) which were characterized by ¹H‐³¹P‐COSY NMR spectroscopy. The formation of ( 2 a ) is drastically accelerated by using GeCl₄ instead of SiCl₄ as PH₂ acceptor, but a stable molecular GeCl_4–n(PH₂)_n containing product could not be obtained. In contrast, conversion of (C₆F₅)₃GeCl with Si(PH₂)₄ ( 1 ) furnishes 2 a but also the remarkably stable tris(pentafluorophenyl)phosphaneylgermane ( 3 ). The latter is isolated in the form of colorless crystals in 97% yield and represents the first PH₂‐substituted germane being structurally characterized by single‐crystal X‐ray diffraction. Protolysis of 1 with MeOH and PhOH occurs relatively fast and leads to mixtures of compounds of the type (RO)_nSi(PH₂)_4–n ( 4 , n = 1), ( 5 , n = 2), and ( 6 , n = 3). The sterically congested phenols MesOH and 3,5‐Me₂PhOH react with 1 only to the respective mono‐ and disubstituted silylphosphanes ( 4 c , d ) and ( 5 c , d ), respectively; 4 c and 4 d were isolated by fractional condensation in the form of air‐ and moisture‐sensitive oils. Lithiation of 1 with four molar equiv. of LiNiPr₂ in THF/Et₂O at –80 °C, surprisingly, leads to insoluble Si(PHLi)₄ ( 8 a ) which was tetrasilylated with iPr₃SiOSO₂CF₃, affording the tetrakis(triisopropylsilylphosphaneyl)silane ( 8 b ). However, attempts to achieve the tetralithiation of the P atoms in 8 b through reaction with four molar equiv. BuLi leads to the unexpected cluster formation of butyl‐tris[lithium(triisopropylsilyl)phosphanideyl] silane‐dimer ( 9 ) in 30% yield and LiPHSiiPr₃; compound 9 consists of a Li₆P₆Si₂ cluster framework.     

From As‐Zincoarsasilene (LZn‐As=SiL′) to Arsaethynolato (As≡C−O) and Arsaketenylido (O=C=As) Zinc Complexes

The reactivity of the As‐zincosilaarsene LZn?As=SiL′ A (L=[CH(CMeNDipp)₂]^?, Dipp=2,6‐ⁱPr₂C₆H₃, L′=[{C(H)N(2,6‐ⁱPr₂‐C₆H₃)}₂]^2?) towards small molecules was investigated. Due to the pronounced zwitterionic character of the Si=As bond of A , it undergoes addition reactions with H₂O and NH₃, forming LZnAs(H)SiOH(L′) 1 and LZnAs(H)SiNH₂(L′) 2 . Oxygenation of A with N₂O at ?60 °C furnishes the deep blue 1,2‐disiloxydiarsene, [LZnOSi(L′)As]₂ 4 , presumably via dimerization of the arsinidene intermediate LZnOSi(L′)As 3 . Oxygenation of A with CO₂ leads to the monomeric arsaethynolato siloxido zinc complex LZnOSi(L′)(OC≡As) 5 , essentially trapping the intermediary arsinidene 3 with liberated CO following initial oxidation of the Si=As bond. DFT calculations confirm the ambident coordination mode of the anionic [AsCO] ligand in solution, with the O‐arsaethynolato [As≡C?O]^.? in 5 , and the As‐arsaketenylido ligand mode [O=C=As]^? present in LZnO?Si(L′)(?As=C=O) 5′ akin to the analogous phosphorus system, [PCO]^?.     

A Zwitterionic Silylene as Reactive Intermediate and Its Unusual Dimerization to an N‐Heterobicyclic Disilane

A way to synthesize the transient zwitterionic silylene L′Si : 8 {L’=CH[(C=CH₂)CMe(N(tBu))₂]} and achieve its facile dimerization to the remarkable N‐heterobicyclic disilane 8 ₂ is described. At first, employing the β‐diketiminate ligand L [L=CH(CMeN(tBu))₂], both starting materials LH ( 2 ) and its N‐lithium salt LLi ( 3 ) can react with SiBr₄ to yield the silylene precursor L′SiBr₂ ( 4 ) by silicon‐induced C? H activation at an exocyclic methyl group on the backbone of the ligand. Compound 4 reacts with SiBr₄ above room temperature to afford the unexpected terminal CH(SiBr₃)‐substituted dibromosilane 6 along with the unique tricyclic trisilane 7 . Reduction of 4 with KC₈ at 0 °C furnishes the novel N‐heterobicyclic disilane 8 ₂, which is a formal dimer of the desired zwitterionic silylene L′Si : ( 8 ). It has been reasoned that compound 8 ₂ may results from [4+1] cycloaddition of two molecules of 8 to give the transient dimer 8 ₂ ′ , which subsequently undergoes hydrogen transfer from a terminal methyl group on the backbone of the C₃N₂Si ligand to the low‐coordinate Si atom. The latter dimerization can be rationalized by the intrinsic zwitterionic character of 8 and insufficient steric protection through the tBu groups at the nitrogen atoms. The novel compounds 3 , 4 , 6 , 7 , and 8 ₂ have been characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, mass spectrometry, and elemental analysis. Additionally, the structures of 3 , 6 , 7 , and 8 ₂ were also established by single‐crystal X‐ray diffraction analyses.     

Transition‐Metal‐Mediated Cleavage of a SiSi Double Bond

Reaction of carbene‐stabilized disilicon ( 1 ) with Fe(CO)₅ gives the 1:1 adduct L:Si?Si[Fe(CO)₄]:L (L:=C{N(2,6‐Prⁱ₂C₆H₃)CH}₂) ( 2 ) at room temperature. At raised temperature, however, 2 may react with another equivalent of Fe(CO)₅ to give L:Si[μ‐Fe₂(CO)₆](μ‐CO)Si:L ( 3 ) through insertion of both CO and Fe₂(CO)₆ into the Si₂ core, which represents the first experimental realization of transition metal‐carbonyl‐mediated cleavage of a Si?Si double bond. The structures and bonding of both 2 and 3 have been investigated by spectroscopic, crystallographic, and computational methods.     

Synthesis, structure, and reactivity of a pyridine-stabilized germanone

The first isolable pyridine‐stabilized germanone has been prepared and its reactivity toward trimethylaluminum has been investigated. The germanone adduct results from a stepwise conversion that starts from 4‐dimethylaminopyridine (DMAP) and the ylide‐like N‐heterocyclic germylene LGe: (L=CH{(C?CH₂)(CMe)[N(aryl)]₂}, aryl=2,6‐iPr₂C₆H₃) ( 1 ) at room temperature, and gives the corresponding germylene–pyridine adduct L(DMAP)Ge: ( 2 ) in 91 % yield. The latter reacts with N₂O at room temperature to form the desired germanone complex L(DMAP)Ge?O ( 3 ) in 73 % yield. The Ge? O distance of 1.646(2) Å in 3 is the shortest hitherto reported for a Ge?O species. The reaction of 3 with trimethylaluminum leads solely to the addition product LGe(Me)O[Al(DMAP)Me₂] ( 4 ). The latter results from insertion of the Ge?O subunit into an Al? Me bond of AlMe₃ and concomitant migration of the DMAP ligand from germanium to the aluminum atom. Compounds 2 – 4 have been fully characterized by analytical and spectroscopic methods. Their molecular structures have been established by single‐crystal X‐ray crystallographic analysis.     

Synthesis,Interionic Structure,and Reactivity toward CO and p‐Methylstyrene of Palladacyclic Compounds Bearing α‐Diimine Ligands

Palladacyclic compounds [Pd(C₆H₄(C₆H₅C?O)C?N? R)(N? N)] [X] (R = Et, ⁱPr, 2,6‐ⁱPr₂C₆H₃; N? N = bpy = 2,2′‐bipyridine, or 1,4‐(o,o′‐dialkylaryl)‐1,4‐diazabuta‐1,3‐dienes; [X]^? = [BF₄]^? or [PF₆]^?) were synthesized from the dimers [{Pd(C₆H₄(C₆H₅C?O)C?N? R)(μ‐Cl)}₂] and N? N ligands. Their interionic structure in CD₂Cl₂ was determined by means of ¹⁹F,¹H‐HOESY experiments and compared with that in the solid state derived from X‐ray single‐crystal studies. [Pd(C₆H₄(C₆H₅C?O)C?N? R)(N? N)] [X] complexes were found to copolymerize CO and p‐methylstyrene affording syndiotactic or isotactic copolymers when bpy or 1,4‐(o,o′‐dimethylaryl)‐1,4‐diazabuta‐1,3‐dienes were used, respectively. The reactions with CO and p‐methylstyrene of the bpy derivatives were investigated. Two intermediates derived from a single and a double insertion of CO into the Pd? C bonds were isolated and completely characterized in solution.     

N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons

Stable N‐heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C₆H₄)(IPr)] and [(IPr)(C₆H₄)₂(IPr)] ( 4 and 5 , respectively; IPr=C{N(2,6‐iPr₂C₆H₃)}₂CHCH), are reported. In a nickel‐catalyzed double carbenylation of 1,4‐Br₂C₆H₄ and 4,4′‐Br₂(C₆H₄)₂ with IPr ( 1 ), [(IPr)(C₆H₄)(IPr)](Br)₂ ( 2 ) and [(IPr)(C₆H₄)₂(IPr)](Br)₂ ( 3 ) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC₈. Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet?triplet energy gap ΔE_S?T of 10.7 kcal mol^?1, whereas 4 features more quinoidal character with a rather large ΔE_S?T of 25.6 kcal mol^?1. In view of the low ΔE_S?T, 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character.     

Transition‐Metal‐Mediated Cleavage of Fluoro‐Silanes under Mild Conditions

Si?F bond cleavage of fluoro‐silanes was achieved by transition‐metal complexes under mild and neutral conditions. The Iridium‐hydride complex [Ir(H)(CO)(PPh₃)₃] was found to readily break the Si?F bond of the diphosphine‐ difluorosilane {(o‐Ph₂P)C₆H₄}₂Si(F)₂ to afford a silyl complex [{[o‐(iPh₂P)C₆H₄]₂(F)Si}Ir(CO)(PPh₃)] and HF. Density functional theory calculations disclose a reaction mechanism in which a hypervalent silicon species with a dative Ir→Si interaction plays a crucial role. The Ir→Si interaction changes the character of the H on the Ir from hydridic to protic, and makes the F on Si more anionic, leading to the formation of H^δ+???F^δ? interaction. Then the Si?F and Ir?H bonds are readily broken to afford the silyl complex and HF through σ‐bond metathesis. Furthermore, the analogous rhodium complex [Rh(H)(CO)(PPh₃)₃] was found to promote the cleavage of the Si?F bond of the triphosphine‐monofluorosilane {(o‐Ph₂P)C₆H₄}₃Si(F) even at ambient temperature.     

Preparation of Stable Low‐Oxidation‐State Group 14 Element Amidohydrides and Hydride‐Mediated Ring‐Expansion Chemistry of N‐Heterocyclic Carbenes

Various low oxidation state (+2) group 14 element amidohydride adducts, IPr ? EH(BH₃)NHDipp (E=Si or Ge; IPr=[(HCNDipp)₂C:], Dipp=2,6‐iPr₂C₆H₃), were synthesized. Thermolysis of the reported adducts was investigated as a potential route to Si‐ and Ge‐based clusters; however, unexpected transmetallation chemistry occurred to yield the carbene–borane adduct, IPr ? BH₂NHDipp. When a solution of IPr ? BH₂NHDipp in toluene was heated to 100 °C, a rare C? N bond‐activation/ring‐expansion reaction involving the bound N‐heterocyclic carbene donor (IPr) transpired.     

A supramolecular hydrogen‐bonded complex between 1,3,5‐tris(diisobutylhydroxysilyl)benzene and trans‐bis(4‐pyridyl)ethylene

The trisilanol 1,3,5‐(HOi‐Bu₂Si)₃C₆H₃ ( 7 ), prepared in three steps from 1,3,5‐tribromobenzene via the intermediates 1,3,5‐(Hi‐Bu₂Si)₃C₆H₃ ( 8 ) and 1,3,5‐(Cli‐Bu₂Si)₃C₆H₃ ( 9 ) forms an equimolar complex with trans‐bis(4‐pyridyl)ethylene (bpe), 7 ·bpe, whose structure was investigated by X‐ray crystallography. The hydrogen‐bonded network features a number of SiO? H(H)Si and SiO? H hydrogen bridges. Evidence was found for cooperative strengthening within the sequential hydrogen bonds. Copyright © 2007 John Wiley & Sons, Ltd.     

Triamidoamine–Uranium(IV)‐Stabilized Terminal Parent Phosphide and Phosphinidene Complexes

Reaction of [U(Tren^TIPS)(THF)][BPh₄] ( 1 ; Tren^TIPS=N{CH₂CH₂NSi(iPr)₃}₃) with NaPH₂ afforded the novel f‐block terminal parent phosphide complex [U(Tren^TIPS)(PH₂)] ( 2 ; U–P=2.883(2) Å). Treatment of 2 with one equivalent of KCH₂C₆H₅ and two equivalents of benzo‐15‐crown‐5 ether (B15C5) afforded the unprecedented metal‐stabilized terminal parent phosphinidene complex [U(Tren^TIPS)(PH)][K(B15C5)₂] ( 4 ; U?P=2.613(2) Å). DFT calculations reveal a polarized‐covalent U?P bond with a Mayer bond order of 1.92.     

From Dibismuthenes to Three‐ and Two‐Coordinated Bismuthinidenes by Fine Ligand Tuning: Evidence for Aromatic BiC3N Rings through a Combined Experimental and Theoretical Study

The reduction of N,C,N‐chelated bismuth chlorides [C₆H₃‐2,6‐(CH?NR)₂]BiCl₂ [where R=tBu ( 1 ), 2′,6′‐Me₂C₆H₃ ( 2 ), or 4′‐Me₂NC₆H₄ ( 3 )] or N,C‐chelated analogues [C₆H₂‐2‐(CH?N‐2′,6′‐iPr₂C₆H₃)‐4,6‐(tBu)₂]BiCl₂ ( 4 ) and [C₆H₂‐2‐(CH₂NEt₂)‐4,6‐(tBu)₂]BiCl₂ ( 5 ) is reported. Reduction of compounds 1 – 3 gave monomeric N,C,N‐chelated bismuthinidenes [C₆H₃‐2,6‐(CH?NR)₂]Bi [where R=tBu ( 6 ), 2′,6′‐Me₂C₆H₃ ( 7 ) or 4′‐Me₂NC₆H₄ ( 8 )]. Similarly, the reduction of 4 led to the isolation of the compound [C₆H₂‐2‐(CH?N‐2′,6′‐iPr₂C₆H₃)‐4,6‐(tBu)₂]Bi ( 9 ) as an unprecedented two‐coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene {[C₆H₂‐2‐(CH₂NEt₂)‐4,6‐(tBu)₂]Bi}₂ ( 10 ) was obtained by the reduction of 5 . Compounds 6 – 10 were characterized by using ¹H and ¹³C NMR spectroscopy and their structures, except for 7 , were determined with the help of single‐crystal X‐ray diffraction analysis. It is clear that the structure of the reduced products (bismuthinidene versus dibismuthene) is ligand‐dependent and particularly influenced by the strength of the N→Bi intramolecular interaction(s). Therefore, a theoretical survey describing the bonding situation in the studied compounds and related bismuth(I) systems is included. Importantly, we found that the C₃NBi chelating ring in the two‐coordinated bismuthinidene 9 exhibits significant aromatic character by delocalization of the bismuth lone pair.