Alkali‐Metal Pyrazolate Complexes with Unusual Pyrazolate Coordination Modes and Pseudocubane Motifs

The dimeric complex [Li(Ph₂pz)(OEt₂)]₂ ( 1 ) and tetrameric cluster [Na(Ph₂pz)(thf)]₄ ( 2 ) were prepared by treatment of alkali‐metal reagents (nBuLi and Na{N(SiMe₃)₂}, respectively) with 3,5‐diphenylpyrazole (Ph₂pzH) in Et₂O ( 1 ) or THF ( 2 ). The polymer [Na(tBu₂pz)]_n ( 3 ) was obtained from reaction at elevated temperature in a sealed tube between Na metal and 3,5‐di‐tert‐butylpyrazole (tBu₂pzH). The complex [Na₄(tBu₂pz)₂(thf)₃(obds)]₂ ( 4 ; obds=(OSiMe₂)₂O) was obtained as a minor product from prolonged treatment of tBu₂pzH with elemental sodium in a silicone‐greased flask. All four alkali‐metal pyrazolato complexes were characterized by IR and ¹H NMR spectroscopy and X‐ray crystallography.The Li dimer 1 displays μ‐η²:η¹ lithium–pyrazolato binding, in which both lithium atoms are four‐coordinate. Room‐ and variable‐temperature NMR studies (¹H, ¹³C, and ⁷Li) of 1 suggest similar behavior in solution, with peaks coalescing at low temperatures. Complexes 2 and 4 display distorted cubane structures. In 2 , all the sodium atoms are five‐coordinate, whereas 4 contains two sodium/pyrazolate/thf clusters (4:2:3 ratio) bridged by two obds^2? units, as well as two four‐coordinate and two five‐coordinate sodium atoms. Compound 3 is composed of two independent chains with the unusual coordination modes μ₃‐η⁵:η²:η², μ₃‐η⁵:η²:η¹, and μ₃‐η⁴:η²:η¹, with five‐, six‐, and seven‐coordinate sodium atoms. Two oxo‐centered M₈ cage complexes [(tBu₂pz)₆Li₈O] ( 5 ) and [(tBu₂pz)₆Na₈O] ( 6 ) were obtained as by‐products from attempted preparation of [Li(tBu₂pz)] and [Na(tBu₂pz)], respectively, and their structures were determined.     

New Homoleptic Rare Earth 3,5‐Diphenylpyrazolates and 3,5‐Di‐tert‐butylpyrazolates and a Noteworthy Structural Discontinuity

Direct thermally induced reactions between rare earth metals (Ln = Y,Ce, Dy, Ho, and Er) activated by Hg metal and 3,5‐diphenylpyrazole (Ph₂pzH) or 3,5‐di‐tert‐butylpyrazole (tBu₂pzH) yielded either homoleptic complexes [Ln_n(R₂pz)_3n] or a heteroleptic complex [Ln(Ph₂pz)₃(Ph₂pzH)₂] From Ph₂pzH, [Ce₃(Ph₂pz)₉], [Dy₂(Ph₂pz)₆], [Ho₂(Ph₂pz)₆], and [Y(Ph₂pz)₃(Ph₂pzH)₂] were isolated. The first has a bowed trinuclear Ce₃ backbone with two η² pyrazolate ligands on the terminal metal atoms and one on the middle, and bridging by both μ‐η²:η² and μ‐η²:η⁵ ligands between the terminal and the central Ce atoms. Although both the Dy and Ho complexes are dinuclear, the former has the rare μ‐η²:η¹ bridging whilst the latter has μ‐η²:η² bridging. Thus the dysprosium complex is seven‐coordinate and the holmium is eight‐coordinate, in contrast to any correlation with Ln³⁺ ionic radii, and the series has a remarkable structural discontinuity. The heteroleptic Y complex is eight coordinate with three chelating Ph₂pz and two transoid unidentate Ph₂pzH ligands. From tBu₂pzH, dimeric [Ln₂(tBu₂pz)₄] (Ln = Ce, Er) were isolated and are isomorphous with eight coordinate Ln atoms ligated by two chelating terminal tBu₂pz and two μ‐η²:η² tBu₂pz donor groups. They are also isomorphous with previously reported La, Nd, Yb, and Lu complexes.     

Europium is Different: Solvent and Ligand Effects on Oxidation State Outcomes and C-F Activation in Reactions Between Europium Metal and Pentafluorophenylsilver

Unique outcomes have emerged from the redox transmetallation/ protolysis (RTP) reactions of europium metal with [Ag(C₆F₅)(py)] (py=pyridine) and pyrazoles (RR′pzH). In pyridine, a solvent not normally used for RTP reactions, the products were mainly Eu^II complexes, [Eu(RR′pz)₂(py)₄] (RR′pz=3,5-diphenylpyrazolate (Ph₂pz) 1 ; 3-(2-thienyl)-5-trifluoromethylpyrazolate (ttfpz) 2 ; 3-methyl-5-phenylpyrazolate (PhMepz) 3 ). However, use of 3,5-di-tert-butylpyrazole (tBu₂pzH) gave trivalent [Eu(tBu₂pz)₃(py)₂] 4 , whereas the bulkier N,N′-bis(2,6-difluorophenyl)formamidine (DFFormH) gave divalent [Eu(DFForm)₂(py)₃] 5 . In tetrahydrofuran (thf), the usual solvent for RTP reactions, C−F activation was observed for the first time with [Ag(C₆F₅)(py)] in such reactions. Thus trivalent [{Eu₂(Ph₂pz)₄(py)₄(thf)₂(μ-F)₂}{Eu₂(Ph₂pz)₄(py)₂(thf)₄(μ-F)₂}] ( 6 ), [Eu₂(ttfpz)₄(py)₂(dme)₂(μ-F)₂] ( 7 ), [Eu₂(tBu₂pz)₄(dme)₂(μ-F)₂] ( 8 ) were obtained from the appropriate pyrazoles, the last two after crystallization from 1,2-dimethoxyethane (dme). Surprisingly 3,5-dimethylpyrazole (Me₂pzH) gave the divalent cage [Eu₆(Me₂pz)₁₀(thf)₆(μ-F)₂] ( 9 ). This has a compact ovoid core held together by bridging fluoride, thf, and pyrazolate ligands, the last including the rare μ₄-1η⁵(N₂C₃): 2η²(N,N′): 3κ(N): 4κ(N′) pyrazolate binding mode. With the bulky N,N′-bis(2,6-diisopropylphenyl)formamidine (DippFormH), which often favours C−F activation in RTP reactions, neither oxidation to Eu^III nor C−F activation was observed and [Eu(DippForm)₂(thf)₂] ( 10 ) was isolated. By contrast, Eu reacted with Bi(C₆F₅)₃ and Ph₂pzH or tBu₂pzH in thf without C−F activation, to give [Eu(Ph₂pz)₂(thf)₄] ( 11 ) and [Eu(tBu₂pz)₃(thf)₂] ( 12 ) respectively, the oxidation state outcomes corresponding to that for use of [Ag(C₆F₅)(py)] in pyridine.     

Intramolecular Metal⋅⋅⋅π‐Arene Interactions in Neutral and Cationic Main Group Compounds

The role of intramolecular metal???π‐arene interactions has been investigated in the solid‐state structures of a series of main group compounds supported by the bulky amide ligands, [N(^tBuAr^≠)(SiR₃)]^? (^tBuAr^≠=2,6‐(CHPh₂)₂‐4‐tBuC₆H₂, R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh₃ substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{^tBuAr^≠}{SiPh₃})Cl₂ using AlCl₃ afforded the 1:1 salt [Bi(N{^tBuAr^≠}{SiPh₃})Cl][AlCl₄]. This was accompanied by a significant rearrangement of the stabilizing π‐arene contacts in the solid‐state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl‐transfer and generation of the neutral Bi(N{^tBuAr^≠}{SiPh₃})(Ph)Cl.     

Reactivity of Xantphos-Type Rhodium Complexes Towards SF4: SF3 Versus SF2 Complex Generation

S−F-bond activation of sulfur tetrafluoride at [Rh(Cl)(^tBuxanPOP)] ( 1 ; ^tBuxanPOP=9,9-dimethyl-4,5-bis-(di-tert-butylphosphino)-xanthene) led to the formation of the cationic complex [Rh(F)(Cl)(SF₂)(^tBuxanPOP)][SF₅] ( 2 a ) together with trans-[Rh(Cl)(F)₂(^tBuxanPOP)] ( 3 ) and cis-[Rh(Cl)₂(F)(^tBuxanPOP)] ( 4 ) which both could also be obtained by the reaction of SF₅Cl with 1 . In contrast to that, the conversion of SF₄ at the methyl complex [Rh(Me)(^tBuxanPOP)] ( 5 ) gave the isolable and room-temperature stable cationic λ⁴-trifluorosulfanyl complex [Rh(Me)(SF₃)(^tBuxanPOP)][SF₅] ( 6 ). Treatment of 6 with the Lewis acids BF₃ or AsF₅ produced the dicationic difluorosulfanyl complex [Rh(Me)(SF₂)(^tBuxanPOP)][BF₄]₂ ( 8 a ) or [Rh(Me)(SF₂)(^tBuxanPOP)][AsF₆]₂ ( 8 b ), respectively. Refluorination of 8 a was possible with the use of dimethylamine giving [Rh(Me)(SF₃)(^tBuxanPOP)][BF₄] ( 9 ). A reaction of 6 with trichloroisocyanuric acid (TClCA) gave the fluorido complex [Rh(F)(Cl)(SF₂)(^tBuxanPOP)][Cl] ( 2 b ) together with chloromethane and SF₅Cl.     

Die Bildung von [(tBu)2P]2P?P[P(tBu)2]2 aus LiP[P(tBu)2]2 und 1,2-Dibromethan. Die Thermolyse von tBu2P?PP(Br)tBu2

[(tBu)₂P]₂P? P[P(tBu)₂]₂ from LiP[P(tBu)₂]₂ and 1,2-Dibromomethane. Pyrolysis of tBu₂P? P?P(Br)tBu₂ All products of the reaction of [tBu₂P]₂PLi 1 with 1,2-dibromoethane 2 were investigated. Already at ?70°C tBu₂P? P?P(Br)tBu₂ 3 as main product and [tBu₂P]₂PBr 4 are formed. Only with an excess of 1 also [tBu₂P]P? P[P(tBu)₂]₂ 5 is obtained. Warming of a pure solution of 3 in toluene from ?70°C to ?30°C leads to 4 , and at 20°C tBu₂PBr and the cyclophosphanes P₄[P(tBu)₂]₄ and P₃[P(tBu)₂]₃ are observed. 5 does not result from 3 , it's rather a byproduct from the reaction of 1 with 4 . Also the ylide 3 and 1 yields 5 .     

Reaktionen des [η2-{P–PtBu2}Pt(PPh3)2] und [η2-{P–PtBu2}Pt(dppe)] mit Metallcarbonylen. Bildung von [η2-{(CO)5M · PPtBu2}Pt(PPh3)2] (M = Cr,W) und [η2-{(CO)5Cr · PPtBu2}Pt(dppe)]

Coordination Chemistry of P-rich Phosphanes and Silylphosphanes. XVI [1] Reactions of [g²-{P–P^tBu₂}Pt(PPh₃)₂] and [g²-{P–P^tBu₂}Pt(dppe)] with Metal Carbonyls. Formation of [g²-{(CO)₅M · PP^tBu₂}Pt(PPh₃)₂] (M = Cr, W) and [g²-{(CO)₅Cr · PP^tBu₂}Pt(dppe)] [η²-{P–P^tBu₂}Pt(PPh₃)₂] 4 reacts with M(CO)₅ · THF (M = Cr, W) by adding the M(CO)₅ group to the phosphinophosphinidene ligand yielding [η²-{(CO)₅Cr · PP^tBu₂}Pt(PPh₃)₂] 1 , or [η²-{(CO)₅W · PP^tBu₂}Pt(PPh₃)₂] 2 , respectively. Similarly, [η²-{P–P^tBu₂}Pt(dppe)] 5 yields [η²-{(CO)₅Cr · PP^tBu₂}Pt(dppe)] 3 . Compounds 1 , 2 and 3 are characterized by their ¹H- and ³¹P-NMR spectra, for 2 and 3 also crystal structure determinations were performed. 2 crystallizes in the monoclinic space group P2₁/n (no. 14) with a = 1422.7(1) pm, b = 1509.3(1) pm, c = 2262.4(2) pm, β = 103.669(9)°. 3 crystallizes in the triclinic space group P1 (no. 2) with a = 1064.55(9) pm, b = 1149.9(1) pm, c = 1693.2(1) pm, α = 88.020(8)°, β = 72.524(7)°, γ = 85.850(8)°.     

Lanthanide(II) Complexes of the Dihydrotriazinido Ligand [N{C(Ph)=N}2C(tBu)Ph]−

The potassium dihydrotriazinide K(L^Ph,tBu) ( 1 ) was obtained by a metal exchange route from [Li(L^Ph,tBu)(THF)₃] and KOtBu (L^Ph,tBu = [N{C(Ph)=N}₂C(tBu)Ph]). Reaction of 1 with 1 or 0.5 equivalents of SmI₂(thf)₂ yielded the monosubstituted Sm^II complex [Sm(L^Ph,tBu)I(THF)₄] ( 2 ) or the disubstituted [Sm(L^Ph,tBu)₂(THF)₂] ( 3 ), respectively. Attempted synthesis of a heteroleptic Sm^II amido‐alkyl complex by the reaction of 2 with KCH₂Ph produced compound 3 due to ligand redistribution. The Yb^II bis(dihydrotriazinide) [Yb(L^Ph,tBu)₂(THF)₂] ( 4 ) was isolated from the 1:1 reaction of YbI₂(THF)₂ and 1 . Molecular structures of the crystalline compounds 2 , 3· 2C₆H₆ and 4· PhMe were determined by X‐ray crystallography.     

Isolation of a Cationic Platinum(II) σ‐Silane Complex

The platinum complex [Pt(I^tBuⁱPr′)(I^tBuⁱPr)][BAr^F] interacts with tertiary silanes to form stable (<0 °C) mononuclear Pt^II σ‐SiH complexes [Pt(I^tBuⁱPr′)(I^tBuⁱPr)(η¹‐HSiR₃)][BAr^F]. These compounds have been fully characterized, including X‐ray diffraction methods, as the first examples for platinum. DFT calculations (including electronic topological analysis) support the interpretation of the coordination as an unusual η¹‐SiH. However, the energies required for achieving a η²‐SiH mode are rather low, and is consistent with the propensity of these derivatives to undergo Si?H cleavage leading to the more stable silyl species [Pt(SiR₃)(I^tBuⁱPr)₂][BAr^F] at room temperature.     

Alkali Blues: Blue-Emissive Alkali Metal Pyrrolates

2-Iminopyrroles [H^tBuL, 4-tert-butyl phenyl(pyrrol-2-ylmethylene)amine] are non-fluorescent π systems. However, they display blue fluorescence after deprotonation with alkali metal bases in the solid state and in solution at room temperature. In the solid state, the alkali metal 2-imino pyrrolates, M(^tBuL), aggregate to dimers, [M(^tBuL)(NCR)]₂ (M=Li, R=CH₃, CH(CH₃)CNH₂), or polymers, [M(^tBuL)]_n (M=Na, K). In solution (solv=CH₃CN, DMSO, THF, and toluene), solvated, uncharged monomeric species M(^tBuL)(solv)_m with N,N′-chelated alkali metal ions are present. Due to the electron-rich pyrrolate and the electron-poor arylimino moiety, the M(^tBuL) chromophore possesses a low-energy intraligand charge-transfer (ILCT) excited state. The chelated alkali cations rigidify the chromophore, restricting intramolecular motions (RIM) by the chelation-enhanced fluorescence (CHEF) effect in solution and, consequently, switch-on a blue fluorescence emission.     

Synthesis and Characterization of Methylzinc Tri(tert‐butyl)silylphosphanide as well as Related Sodium and Potassium Phosphanylzincates

The reaction of dimethylzinc and tri(tert‐butyl)silylphosphane in toluene yielded dimeric methylzinc tri(tert‐butyl)silylphosphanide ( 1 ) which crystallized tetrameric. Compound 1 was deprotonated with sodium in DME and the solvent‐separated dimeric ion pair [(dme)₃Na]⁺ [(dme)Na(MeZn)₂(μ‐PSitBu₃)₂]^? ( 2 ) was isolated. The reaction of 1 in THF with two equivalents of potassium and one equivalent of tri(tert‐butyl)silylphosphane gave dimeric [{tBu₃Si(H)P}{(thf)₂K}₂(MeZn)(PSitBu₃)]₂ ( 3 ). Both of these phosphanylzincates contain Zn₂P₂ cycles with Zn‐P bond lengths of approximately 237 pm, whereas in 1 larger Zn‐P bond lengths of 248.5 pm were found due to the larger coordination numbers of the phosphorus and zinc atoms.     

Reactions of tBu2P–PLi–PtBu2 with [(Et3P)2MCl2] (M = Ni,Pd, Pt). Synthesis and Properties of [(1,2‐η‐tBu2P=P–PtBu2)M(PEt3)Cl] (M=Ni,Pd)

^tBu₂P–PLi–P^tBu₂·2THF reacts with [cis‐(Et₃P)₂MCl₂] (M = Ni, Pd) yielding [(1,2‐η‐^tBu₂P=P–P^tBu₂)Ni(PEt₃)Cl] and [(1,2‐η‐^tBu₂P=P–P^tBu2)Pd(PEt₃)Cl], respectively. ^tBu₂P– PLi–P^tBu₂ undergoes an oxidation process and the ^tBu₂P–P–P^tBu₂ ligand adopts in the products the structure of a side‐on bonded 1,1‐di‐tert‐butyl‐2‐(di‐tert‐butylphosphino)diphosphenium cation with a short P–P bond. Surprisingly, the reaction of ^tBu₂P–PLi–P^tBu₂·2THF with [cis‐(Et₃P)₂PtCl₂] does not yield [(1,2‐η‐^tBu₂P=P–P^tBu₂)Pt(PEt₃)Cl].     

Heterodinukleare Komplexe: Synthese und Kristallstrukturen von [RuRh(μ‐CO)(CO)4(μ‐PtBu2)(tBu2PH)], [RuRh(μ‐CO)(CO)3(μ‐PtBu2)(μ‐Ph2PCH2PPh2)] und [CoRh(CO)4(μ‐H)(μ‐PtBu2)(tBu2PH)]

Heterobinuclear Complexes: Synthesis and X‐ray Crystal Structures of [RuRh(μ‐CO)(CO)₄(μ‐P^tBu₂)(^tBu₂PH)], [RuRh(μ‐CO)(CO)₃(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)], and [CoRh(CO)₄(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] [Ru₃Rh(CO)₇(μ₃‐H)(μ‐P^tBu₂)₂(^tBu₂PH)(μ‐Cl)₂] ( 2 ) yields by cluster degradation under CO pressure as main product the heterobinuclear complex [RuRh(μ‐CO)(CO)₄(μ‐P^tBu₂)(^tBu₂PH)] ( 4 ). The compound crystallizes in the orthorhombic space group Pcab with a = 15.6802(15), b = 28.953(3), c = 11.8419(19) Å and V = 5376.2(11) ų. The reaction of 4 with dppm (Ph₂PCH₂PPh₂) in THF at room temperature affords in good yields [RuRh(μ‐CO)(CO)₃(μ‐P^tBu₂)(μ‐dppm)] ( 7 ). 7 crystallizes in the triclinic space group P 1 with a = 9.7503(19), b = 13.399(3), c = 15.823(3) Å and V = 1854.6 ų. Moreover single crystals of [CoRh(CO)₄(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] ( 9 ) could be obtained and the single‐crystal X‐ray structure analysis revealed that 9 crystallizes in the monoclinic space group P2₁/a with a = 11.611(2), b = 13.333(2), c = 18.186(3) Å and V = 2693.0(8) ų.     

Koordinativ ungesättigte Dirutheniumkomplexe: Synthese und Kristallstrukturen von [Ru2(CO)3L(μ‐η1 : η2‐C≡CPh)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)] (L = CO,PnBu3)

Coordinatively Unsaturated Diruthenium Complexes: Synthesis and X‐ray Crystal Structures of [Ru₂(CO)₃L(μ‐η¹ : η²‐C≡CPh)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)] (L = CO, PⁿBu₃) [Ru₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 1 ) reacts with several phosphines (L) in refluxing toluene under substitution of one carbonyl ligand and yields the compounds [Ru₂(CO)₃L(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] (L = PⁿBu₃, 2 a ; L = PCy₂H, 2 b ; L = dppm‐P, 2 c ; dppm = Ph₂PCH₂PPh₂). The reactivity of 1 as well as the activated complexes 2 a – c towards phenylethyne was studied. Thus 1 , 2 a and 2 b , respectively, react with PhC≡CH in refluxing toluene with elimination of dihydrogen to the acetylide‐bridged complexes [Ru₂(CO)₄(μ‐η¹ : η²‐C≡CPh)(μ‐P^tBu₂)(μ‐dppm)] ( 3 ) and [Ru₂(CO)₃L(μ‐η¹ : η²‐C≡CPh)(μ‐P^tBu₂)(μ‐dppm)] ( 4 a and 4 b ). The molecular structures of 3 and 4 a were determined by crystal structure analyses.     

Cyclization of N-alkyldithiocarbamates in alkaline media,a counter example of well-known chemistry – an experimental and theoretical study

In strong alkaline media, the reaction of 2-(tert-butylamino)ethanol (3: R?=?Bu^t) with CS₂ at 0°C produced a cyclic dithiocarbamate, 3-tert-butylthiazolidine-2-thione (1: R?=?Bu^t), rather than alkaline metal or ammonium salts of [S₂CN(Bu^t)CH₂CH₂OH]^?. This is in contrast to isolation of stable alkaline metal or ammonium salts of [S₂CN(R)CH₂CH₂OH]^? (R?=?Me, Et, Pr, or CH₂CH₂OH) obtained in analogous reactions. The use of Ni(OAc)₂, both as a source of Ni(II) and a weaker base, in a one-pot reaction with (3: R?=?Bu^t) and CS₂, successfully gave the first reported metal complex of [S₂CN(Bu^t)CH₂CH₂OH]^?, namely [Ni{S₂CN(Bu^t)CH₂CH₂OH}₂] (2: R?=?Bu^t). Compounds 1 and 2 have been fully characterized by infrared and NMR spectroscopies, and by X-ray crystallography. DFT calculations on the cyclization and stabilities of [S₂CN(R)CH₂CH₂OH]^? (R?=?Pr and Bu^t) have been carried out.     

A Comparative Study on the Thermodynamics of Halogen Bonding of Group 10 Pincer Fluoride Complexes

The thermodynamics of halogen bonding of a series of isostructural Group 10 metal pincer fluoride complexes of the type [(3,5-R₂-^tBuPOCOP^tBu)MF] (3,5-R₂-^tBuPOCOP^tBu=κ³-C₆HR₂-2,6-(OPtBu₂)₂ with R=H, tBu, COOMe; M=Ni, Pd, Pt) and iodopentafluorobenzene was investigated. Based on NMR experiments at different temperatures, all complexes 1-tBu (R=tBu, M=Ni), 2-H (R=H, M=Pd), 2-tBu (R=tBu, M=Pd), 2-COOMe (R=COOMe, M=Pd) and 3-tBu (R=tBu, M=Pt) form strong halogen bonds with Pd complexes showing significantly stronger binding to iodopentafluorobenzene. Structural and computational analysis of a model adduct of complex 2-tBu with 1,4-diiodotetrafluorobenzene as well as of structures of iodopentafluorobenzene in toluene solution shows that formation of a type I contact occurs.     

Synthese eines hexanuklearen Calcium–Phosphor‐Käfigs über heteroleptische Calcium‐amid‐phosphanid‐Vorstufen

Synthesis of a Hexanuclear Calcium–Phosphorus‐Cage The metalation of tri(tert‐butyl)silylphosphane with calcium bis[bis(trimethylsilyl)amide] yields the dimer {(Me₃Si)₂N–Ca(THF)[μ‐P(H)Si^tBu₃]}₂ ( 1 ). In THF monomerization occurs and dismutation reactions lead to the homoleptic compounds, namely (THF)₂Ca[N(SiMe₃)₂]₂ and (THF)₄Ca[P(H)Si^tBu₃]₂. In toluene, 1 undergoes dismutation reactions, bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] is regained and [(Me₃Si)₂N–Ca(THF)]₂Ca[P(H)Si^tBu₃]₄ ( 2 ) precipitates. At raised temperatures, 2 undergoes a homometallic metalation with the loss of two equivalents of HN(SiMe₃)₂ and dimerizes. The thus formed cage compound (THF)₂Ca₆[PSi^tBu₃]₄[P(H)Si^tBu₃]₄ ( 3 ) with a central Ca₄P₄ heterocubane moiety crystallizes upon cooling of the toluene solution. The molecular structures of 2 and 3 were determined.     

The “Metallo”-Diels–Alder Reactions: Examining the Metalloid Behavior of Germanimines

Addition of MesN₃ (Mes=2,4,6-Me₃C₆H₂) to germylene [(NON^tBu)Ge] (NON^tBu=O(SiMe₂NtBu)₂) ( 1 ) gives germanimine, [(NON^tBu)Ge=NMes] ( 2 ). Compound 2 behaves as a metalloid, showing reactivity reminiscent of both transition metal-imido complexes, undergoing [2+2] addition with heterocumulenes and protic sources, as well as an activated diene, undergoing a [4+2] cycloaddition, or “metallo”-Diels–Alder, reaction. In the latter case, the diene includes the Ge=N bond and π-system of the Mes substituent, which is reactive towards dienophiles including benzaldehyde, benzophenone, styrene, and phenylacetylene.     

1,3-Diphosphacyclobutene Cobalt Complexes

The synthesis and characterization of rare 1,3-diphosphacyclobutene transition-metal complexes is described. Reactions of the cobalt-hydride complex [Co(P₂C₂tBu₂)₂H] ( G ) with nBuLi, tBuLi, or PhLi afforded [Li(solv)_x{Co(η³-P₂C₂tBu₂HR)(η⁴-P₂C₂tBu₂)}] ( 1 : R=nBu, (solv)_x=(Et₂O)₂; 2 : R=tBu, (solv)_x=(thf)₂; 3 : R=Ph, (solv)_x=(Et₂O)(thf)₂), with an η³-coordinated 1,3-diphosphacyclobutene ligand as a result of organyl-anion attack at one of the phosphorus atoms of the bis(1,3-diphosphacyclobutadiene) backbone. In contrast to the reactions with PhLi, the aryl-magnesium compounds p-tolyl magnesium chloride and p-fluorophenyl magnesium bromide deprotonate [Co(P₂C₂tBu₂)₂H] to give the magnesium salt [Mg(MeCN)₆][Co(η⁴-P₂C₂tBu₂)₂]₂ ( 4 ), which contains a bis(1,3-diphosphacyclobutadiene)-cobaltate anion. The [Co(η⁴-P₂C₂tBu₂)₂]⁻ anions are well separated from the octahedral [Mg(MeCN)₆]²⁺ cation in the molecular structure of 4 . Compound 1 reacts with Me₃SiCl to give neutral [Co(η³-P₂C₂tBu₂HnBu)(η⁴-P₂C₂tBu₂SiMe₃)] ( 5 , 52 % yield) with an SiMe₃ group attached to one of the P atoms of the previously unfunctionalized backbone.     

Koordinativ ungesättigte Dieisenkomplexe: Synthese und Kristallstrukturen von [Fe2(CO)4(μ‐H)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)] und [Fe2(CO)4(μ‐CH2)(μ‐H)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)]

Coordinatively Unsaturated Diiron Complexes: Synthesis and Crystal Structures of [Fe₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)] and [Fe₂(CO)₄(μ‐CH₂)(μ‐H)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)] [Fe₂(μ‐CO)(CO)₆(μ‐H)(μ‐P^tBu₂)] ( 1 ) reacts spontaneously with dppm (dppm = Ph₂PCH₂PPh₂) to give [Fe₂(μ‐CO)(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 2 c ). By thermolysis or photolysis, 2 c loses very easily one carbonyl ligand and yields the corresponding electronically and coordinatively unsaturated complex [Fe₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 3 ). 3 exhibits a Fe–Fe double bond which could be confirmed by the addition of methylene to the corresponding dimetallacyclopropane [Fe₂(CO)₄(μ‐CH₂)(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 4 ). The reaction of 1 with dppe (Ph₂PC₂H₄PPh₂) affords [Fe₂(μ‐CO)(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppe)] ( 5 ). In contrast to the thermolysis of 2 c , yielding 3 , the heating of 5 in toluene leads rapidly to complete decomposition. The reaction of 1 with PPh₃ yields [Fe₂(CO)₆(H)(μ‐P^tBu₂)(PPh₃)] ( 6 a ), while with ^tBu₂PH the compound [Fe₂(μ‐CO)(CO)₅(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] ( 6 b ) is formed. The thermolysis of 6 b affords [Fe₂(CO)₅(μ‐P^tBu₂)₂] and the degradation products [Fe(CO)₃(^tBu₂PH)₂] and [Fe(CO)₄(^tBu₂PH)]. The molecular structures of 3 , 4 and 6 b were determined by X‐ray crystal structure analyses.