Heavy Group 15 Element Compounds of a Sterically Demanding Bis(iminophosphorane)methanide and -methanediide

Complexes of the heavy pnictogen elements Sb and Bi of monoanionic (<i>C</i>,<i>N</i>-chelated: Sb, Bi) and dianionic (<i>N</i>,<i>C</i>,<i>N</i>-pincer type: Bi) bulky substituted bis­(diphenyl­(arylimino)­phosphorano)­methane H₂C­(Ph₂PNR)₂ (R = 2,6-diisopropylphenyl (dipp)) have been prepared via metathetical reactions, and tautomerism within the monoanionic ligand backbone has been observed. The complexes have been characterized by means of X-ray analysis and NMR studies. The dianionic complex was found to feature the rare structural motif of a formal carbon–bismuth­(III) double bond. The molecular structure of the solvate-free potassium salt K­[HC­(Ph₂PNdipp)₂] is reported

Cationic Stannylenes: In Situ Generation and NMR Spectroscopic Characterization

The reaction of ^MeNHC (^MeNHC = 1,3,4,5-tetramethylimidazolylidene, where NHC = N-heterocyclic carbene) adducts to organotin­(II) hydrides Ar*SnH and Ar′SnH [Ar* = 2,6-Trip₂C₆H₃, where Trip = 2,4,6-triisopropylphenyl; Ar′ = 2,6-Mes₂C₆H₃, where Mes = 2,4,6-trimethylphenyl)] with Lewis acids such as B­(C₆F₅)₃ or [CPh₃]⁺ allows the abstraction of hydride and thus the generation of cationic, dicoordinate bis­(σ-C)-substituted stannylenes [ArSn­(NHC)]⁺. The supposedly dicoordinate constitution of this cationic stannylene was investigated by NMR spectroscopy and further supported by density functional theory computations. For Ar′SnH­(^MeNHC), the generated cation was found to be inadequately sterically encumbered, allowing the formation of an adduct, [Ar′(NHC)­Sn–Sn­(H)­(NHC)­Ar′]⁺, which can be described as the protonated bis­(NHC) adduct to the formal 1,2-distannyne

Heavy Group 15 Element Compounds of a Sterically Demanding Bis(iminophosphorane)methanide and -methanediide

Complexes of the heavy pnictogen elements Sb and Bi of monoanionic (<i>C</i>,<i>N</i>-chelated: Sb, Bi) and dianionic (<i>N</i>,<i>C</i>,<i>N</i>-pincer type: Bi) bulky substituted bis­(diphenyl­(arylimino)­phosphorano)­methane H₂C­(Ph₂PNR)₂ (R = 2,6-diisopropylphenyl (dipp)) have been prepared via metathetical reactions, and tautomerism within the monoanionic ligand backbone has been observed. The complexes have been characterized by means of X-ray analysis and NMR studies. The dianionic complex was found to feature the rare structural motif of a formal carbon–bismuth­(III) double bond. The molecular structure of the solvate-free potassium salt K­[HC­(Ph₂PNdipp)₂] is reported

Germa- and Stanna-<i>closo</i>-dodecaborate in Reaction with [PdCl₂(Xantphos)]: P–C and B–H Bond Activation

The two nucleophilic heteroborates germa-<i>closo</i>-dodecaborate and stanna-<i>clos</i>o-dodecaborate show different reactivity toward the electrophile [PdCl₂(Xantphos)]: In the case of the germanium ligand we found straightforward substitution of one chloride ligand and formation of a Ge–Pd bond. The tin ligand also reacts to give the substitution products [PdCl­(SnB₁₁H₁₁)­(Xantphos)]⁻ and [Pd­(SnB₁₁H₁₁)­(Xantphos)], but the complexes exhibit a subsequent reaction under activation of a B–H and P–C bond. A dinuclear Pd­(I)–Pd­(I) complex featuring a P–B bond was characterized, and during its formation the evolution of benzene was detected. The respective germanium derivative does not show an activation reaction even at elevated temperature

Germa- and Stanna-<i>closo</i>-dodecaborate in Reaction with [PdCl₂(Xantphos)]: P–C and B–H Bond Activation

The two nucleophilic heteroborates germa-<i>closo</i>-dodecaborate and stanna-<i>clos</i>o-dodecaborate show different reactivity toward the electrophile [PdCl₂(Xantphos)]: In the case of the germanium ligand we found straightforward substitution of one chloride ligand and formation of a Ge–Pd bond. The tin ligand also reacts to give the substitution products [PdCl­(SnB₁₁H₁₁)­(Xantphos)]⁻ and [Pd­(SnB₁₁H₁₁)­(Xantphos)], but the complexes exhibit a subsequent reaction under activation of a B–H and P–C bond. A dinuclear Pd­(I)–Pd­(I) complex featuring a P–B bond was characterized, and during its formation the evolution of benzene was detected. The respective germanium derivative does not show an activation reaction even at elevated temperature

Different Coordination Modes of the Ph₂PC_sp³PPh₂ Pincer Ligand in Rhodium Complexes as a Consequence of C_sp³–H Metal Interaction

Starting from commercially available 4,4′-di-<i>tert</i>-butyldiphenylmethane the pincer ligand bis­(4-<i>tert</i>-butyl-2-(diphenylphosphino)­phenyl)­methane (<b>PCP</b>) was prepared in two steps in moderate yield. Treatment of a solution of RhCl₃·3H₂O in a mixture of isopropyl alcohol and toluene with equimolar amounts of <b>PCP</b> gave the dimeric rhodium complex <b>1</b>. In an electrophilic metalation a facially coordinated pincer complex is formed. When <b>PCP</b> is treated with [CODRhCl]₂ in a solution of pyridine, the square-pyramidal complex <b>2</b> is generated where the bis-phosphine <b>PCP</b> acts as bidentate ligand that coordinates in a cis fashion. SnCl₂ inserts into the Rh–Cl bond of <b>2</b>, which results in an oxidative addition of one of the methylene C–H bonds to form the Rh­(III) complex <b>3</b>, where the <b>PCP</b> ligand coordinates in a meridional way. A 2 equiv portion of <b>PCP</b> reacts with 1 equiv of [CODRhCl]₂ in the presence of the electron-donating ligands HPhPC₆H₄NMe₂, PPh₂Py, and PPh₃, respectively, as well as with stanna- and germa-<i>closo</i>-dodecaborate to give the octahedral Rh­(III) complexes <b>4</b>–<b>8</b>. Attempts to remove the HCl with KO^tBu from complexes <b>4</b>–<b>6</b> produces the planar Rh­(I) compounds <b>9</b> and <b>10</b>. No carbene formation has been observed

Structural and Spectroscopic Characterization of Tin–Tin Double Bonds in Cyclic Distannenes

Three cyclic distannenes, <b>1</b>, <b>3</b>, and <b>4</b>, and one spacer-bridged bis­(stannylene), <b>2</b>, were prepared and thoroughly investigated by single-crystal X-ray diffraction in the solid state, by variable-temperature (VT) ¹¹⁹Sn NMR, VT ¹H NMR, ¹³C NMR, and UV–vis spectroscopy in solution, and by quantum chemical calculations. The tin­(II) compounds feature rigid 9,9-dimethylxanthene or naphthalene backbones and very bulky <i>m</i>-terphenyl substituents Ar^R [=C₆H₃-2,6-{C₆H₂-2,4,6-R₃}₂; R = Me (<b>1</b>, <b>3</b>), <i>i</i>-Pr (<b>2</b>, <b>4</b>)]. For distannenes <b>3</b> and <b>4</b>, the strain of the naphthalene backbone results in rather short tin–tin distances of 2.7299(3) and 2.7688(2) Å, respectively, whereas the xanthene backbone produces long tin–tin distances of 3.0009(7) Å for distannene <b>1</b> and 4.2779(7) Å for the spacer-bridged bis­(stannylene) <b>2</b>. In comparison to the Ar^iPr substituents, the less bulky Ar^Me substituents give rise to stronger trans-bending of the distannenes; moreover, DFT calculations indicate that, in contrast to Ar^iPr, the Ar^Me substituents allow for asymmetric distortion of the trans-bending in dynamic processes. The oxidation products of distannene <b>1</b> and bis­(stannylene) <b>2</b> reveal rare structural motifs: dihydroxydistannoxane <b>5</b> and bis­(dihydroxystannane) <b>6</b>, respectively, which feature terminal Sn–OH functionalities. The reaction of distannene <b>1</b> with 1 equiv of potassium chloride in the presence of the cryptating agent 222 results in the formation of the unusual stannyl stannide <b>7</b>. A modified synthesis protocol for the preparation of distannene <b>1</b> yields in one step the stannyl stannylene <b>8</b> with a center of chirality at the stannyl tin atom. The series <b>1</b>, <b>7</b>, and <b>8</b> represents a variation of electronic tin–tin interactions

Complete Hydrogen Transfer: Tin Hydride Reactivity toward Adamantylisonitrile and Benzonitrile

Adamantylisonitrile and benzonitrile were reacted with bulky substituted organotin trihydride [Ar*SnH₃] [Ar* = (C₆H₃-2,6-Trip₂), Trip = 2,4,6-triisopropylphenyl]. They do not show any reaction at room temperature as well as at 80 °C. After activation of the organotin trihydride with diethylmethylamine in the isonitrile case three hydrogen atoms were transferred from the tin atom to the isonitrile unit and a carbon tin bond was formed to give an intramolecular adduct between a diorganostannylene and a dialkylamine. Benzonitrile as well as adamantylisonitrile react both with low-valent organotin hydride [Ar*SnH]₂. Benzonitrile shows an insertion reaction with the low-valent organotin hydride to yield a dimeric insertion product, whereas the isonitrile carbon atom of adamantylisonitrile abstracts three hydrogen atoms from the low-valent organotin hydride to give an equimolar mixture between (adamantylmethylamido)­organostannylene and a bis­(isonitrile)­distannyne adduct

Reversibility in Reactions of Linker-Bridged Distannenes with Terminal Alkynes at Ambient Temperature

The linker-bridged distannene [(2,6-Mes₂)­C₆H₃Sn]₂C₁₂H₈ (<b>1</b>) featuring an acenaphthene linker and the sterically demanding terphenyl substituent Ar^Me (= C₆H₃-2,6-Mes₂; Mes = C₆H₂-2,4,6-Me₃) was prepared and characterized by single-crystal analysis, NMR spectroscopy, as well as elemental analysis. Furthermore, the reactivity of distannene <b>1</b> and previously reported distannenes <b>2</b> and <b>3</b>, bearing either a naphthalene or a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar^Me, as well as bis­(stannylene) <b>4</b>, featuring a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar^iPr (= C₆H₃-2,6-Trip₂; Trip = C₆H₂-2,4,6-<i>i</i>-Pr₃), toward terminal alkynes at ambient temperature was investigated, leading to the formal [2 + 2] cycloaddition products <b>5</b>–<b>9</b>. The reactions of distannene <b>1</b> with trimethylsilylacetylene and phenylacetylene, the reaction of distannene <b>2</b> with trimethylsilyl–acetylene, as well as the reaction of bis­(stannylene) <b>4</b> with phenylacetylene show reversibility, while distannenes <b>2</b> and <b>3</b> react irreversibly with phenylacetylene at room temperature. A van’t Hoff analysis of variable-temperature ¹H NMR spectra of the cycloadduct of the reaction of distannene <b>1</b> with trimethylsilylacetylene afforded a dissociation enthalpy (Δ<i>H</i>_diss) of 71.6 kJ·mol^–1, which is in surprisingly good agreement with the results of accompanying DFT calculations (Δ<i>H</i>_diss = 70.9 kJ·mol^–1)

Complete Hydrogen Transfer: Tin Hydride Reactivity toward Adamantylisonitrile and Benzonitrile

Adamantylisonitrile and benzonitrile were reacted with bulky substituted organotin trihydride [Ar*SnH₃] [Ar* = (C₆H₃-2,6-Trip₂), Trip = 2,4,6-triisopropylphenyl]. They do not show any reaction at room temperature as well as at 80 °C. After activation of the organotin trihydride with diethylmethylamine in the isonitrile case three hydrogen atoms were transferred from the tin atom to the isonitrile unit and a carbon tin bond was formed to give an intramolecular adduct between a diorganostannylene and a dialkylamine. Benzonitrile as well as adamantylisonitrile react both with low-valent organotin hydride [Ar*SnH]₂. Benzonitrile shows an insertion reaction with the low-valent organotin hydride to yield a dimeric insertion product, whereas the isonitrile carbon atom of adamantylisonitrile abstracts three hydrogen atoms from the low-valent organotin hydride to give an equimolar mixture between (adamantylmethylamido)­organostannylene and a bis­(isonitrile)­distannyne adduct