Triamidostannates(II) as Sterically Demanding Ligands for Rhodium and Iridium

Trianionic Carbocyclic NCN Pincer Ligand: Coordination Chemistry and Reactivity Studies

(BCHT-NCN)H3 (1) [1,6-bis(methylene(bis-2,6-diisopropylaniline)(benzo)cycloheptatriene)] was synthesized by nucleophilic substitution treating 1,6-bis(methylenebromide)(benzo)cycloheptatriene with 2 equiv of Li[2,6-iPr2C6H3NH], Li[Dipp-NH]. Triple deprotonation of (BCHT-NCN)H3 (1) using n-BuLi yields the deprotonation product [(BCHT-NCN)Li3] (2), which crystallizes as a dimer [{[BCHT-NCN]Li3(Et2O)2}2] (2)2. Coordination compounds of the trianionic pincer ligand were obtained with SnCl2, YCl3(THF)3.5, and HfCl4(THF)2: [(BCHT-NCN)SnLi] (3), [(BCHT-NCN)Y(THF)2] (4), [(BCHT-NCN)HfCl2][Li(THF)4] (5), respectively. A hafnium hydride complex [(BCHT-NCN)HfH(HBEt3)][K(Et2O)2] (6) was isolated after reaction of 5 with K[HBEt3]. A MeNHC substitution product [(BCHT-NCN)HfCl(MeNHC)] (7) was synthesized treating compound 5 with MeNHC at rt. Following an n-BuLi reaction of 7 gives an alkyl complex [(BCHT-NCN)Hf(n-Bu)(MeNHC)] (8). Thermolysis of 7 yields the isomerization product [(BCHT-NCN#)HfCl(MeNHC)] (9), which was transferred into a methyl complex [(BCHT-NCN#)HfMe(MeNHC)] (10) upon treatment with MeMgBr. Hydride abstraction from complex 9 leads to a cationic complex [(BCHT-NCN+)HfCl(MeNHC)][Al(OtBuF)4] (11).

Coordination capabilities of bis-(2-pyridyl)amides in the field of divalent germanium, tin and lead compounds

The reactivity of two lithium amides derived from bis-(2-pyridyl)amine (dpa)H or its methyl-substituted congener bis-(6-methyl-2-pyridyl)amine (Me-dpa)H, i.e. (dpa)Li (1) and (Me-dpa)Li (2), toward ECl2 (where E = Ge (dioxane complex) and Sn) is reported. This study produced both heteroleptic complexes (dpa)GeCl (3), [(dpa)SnCl]2 (4), and (Me-dpa)GeCl (5) and homoleptic complexes (dpa)2E (E = Ge (6) or Sn (7)) and (Me-dpa)2E (E = Ge (8) or Sn (9)). The structures of all complexes were established by single-crystal X-ray diffraction analysis showing significant differences depending on the E atom and ligand used. By contrast, in solution, the majority of compounds showed a fluxional behaviour as demonstrated by the NMR study. Finally, it turned out that the Me-dpa ligand, unlike dpa, is able to form ate complexes [(Me-dpa)3E]Li (E = Ge (10), Sn (11) or Pb (12)), whose structures were determined by single-crystal X-ray diffraction analysis. This study revealed the formation of two isomers for Ge and Sn complexes depending on the coordination preference of the lithium atom being coordinated either by nitrogen donors (10-12) or solely by the Ge or Sn electron lone pair (10a and 11a). Furthermore, the NMR experiments proved that the germanium complex 10 exhibits only limited stability in solution and decomposes to germylene 8 and lithium amide 2.

Synthesis and Hydrogenation of Heavy Homologues of Rhodium Carbynes: [(Me3 P)2 (Ph3 P)Rh≡E-Ar*] (E=Sn, Pb)

Tetrylidynes [(Me3 P)2 (Ph3 P)Rh≡SnAr*] (10) and [(Me3 P)2 (Ph3 P)Rh≡PbAr*] (11) are accessed for the first time via dehydrogenation of dihydrides [(Ph3 P)2 RhH2 SnAr*] (3) and [(Ph3 P)2 RhH2 PbAr*] (7) (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate [Ar*SnH2 ]- with [(Ph3 P)3 RhCl] or via reaction between hydrides [(Ph3 P)3 RhH] and 1 / 2  [(Ar*SnH)2 ]. Homologous lead hydride [(Ph3 P)2 RhH2 PbAr*] (7) was synthesized analogously from [(Ph3 P)3 RhH] and 1 / 2  [(Ar*PbH)2 ]. Abstraction of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119 Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis-dihydride [(Me3 P)2 (Ph3 P)RhH2 PbAr*] (12) and the tetrahydride [(Me3 P)2 (Ph3 P)RhH2 SnH2 Ar*] (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride [(Me3 P)2 (Ph3 P)RhH2 SnAr*] (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.

Exohedral functionalization vs. core expansion of siliconoids with Group 9 metals: catalytic activity in alkene isomerization

Taking advantage of pendant tetrylene side-arms, stable unsaturated Si₆ silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)₂Cl]₂ inserts into an endohedral Si–Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si₆ benzpolarene motif. In the case of [Ir(cod)Cl]₂ (cod = 1,5-cyclooctadiene) a similar Si–Si insertion leads to the contraction of the Si₆ cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes.

Unprecedented metallasiliconoids are accessible from a silylene-substituted Si₆ siliconoid and Group 9 metal fragments. The isomerization of terminal alkenes to 2-alkenes is competitively catalyzed by these species ( = silicon).

Synthesis and Complexation of a Free Germanide Bearing a Tridentate N-Heterocyclic Substituent

The tris-N-heterocycle germanide (tmim)Ge^- (1) (tmimH₃ = tris(3-methylindol-2-yl)methane) was synthesized by nucleophilic substitution for the tmim^3- trianion on GeCl₂·dioxane. In combination with the previously reported (tmim)Si^- and (tmim)P analogues, it provides a convenient model for investigating the influence of the central atom on the properties of isoelectronic ligands. Complexation of the germanide (tmim)Ge^- to CuCl resulted in the dimeric chloro cuprate [(tmim)GeCu(μ-Cl)]₂ ^2-, which is prone to dissociation in MeCN to form the neutral, solvated germylcopper (tmim)GeCu(NCMe)₃. The reaction of 1 with Fe₂(CO)₉ afforded the germyl iron tetracarbonyl [(tmim)GeFe(CO)₄]^-. Analysis of the ν̃(CO) infrared absorption bands in this complex indicates that the combined electron donating and accepting properties of 1 are found in between those of (tmim)P and (tmim)Si^-. In contrast to (tmim)Si^-, (tmim)Ge^- is reluctant to coordinate to FeCl₂, likely because of its softer Lewis base character. Key structural features of the ligands and complexes reflect changes in their electronic properties. In particular, the N-Ge-N angles increase upon coordination to a metal fragment, suggesting increasing hybridization of the Ge s- and p-orbitals. These findings will be useful in further understanding low-valent heavier group 14 complexes in organometallic chemistry.

Coordination chemistry of stannylene-based Lewis pairs – insertion into M–Cl and M–C bonds. From base stabilized stannylenes to bidentate ligands

The coordination chemistry of intramolecular stannylene phosphorus Lewis pairs incorporated into four or three membered ring molecules is presented.

{[Ir3(cod)3(μ3-S)2](μ3-S)SnCl}2 – a ternary Ir–Sn–S cluster with the iridium atoms in three different chemical environments

The cluster {[Ir₃(cod)₃(μ₃-S)₂](μ₃-S)SnCl}₂ with an unprecedented topology of Sn, Ir, and S atoms was obtained by reactions of organo-functionalized tinsulfide clusters with [IrCl(cod)]₂.

Dinuclear copper complexes: coordination of Group 14 heteroborates

The dinuclear copper(i) complex [Cu₂(μ-dmapm)(CH₃CN)₂][BF₄]₂ was reacted with Group 14 heteroborates. Four different coordination motives have been characterized.

Step-by-step synthesis of the endohedral stannaspherene [Ir@Sn12]3- via the capped cluster anion [Sn9Ir(cod)]3-

The endohedral stannaspherene cluster anion [Ir@Sn(12)](3-) was synthesized in two steps. The reaction of K(4)Sn(9) with [IrCl(cod)](2) (cod: 1,5-cyclooctadienyl) in ethylenediamine (en) solution first yielded the [K(2,2,2-crypt)](+) salt (2,2,2-crypt: 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) of the capped cluster anion [Sn(9)Ir(cod)](3-). Subsequently, crystals of this compound were dissolved in en, followed by the addition of triphenylphosphine or 1,2-bis(diphenylphosphino)ethane and treatment at elevated temperatures. [Ir@Sn(12)](3-) was obtained and characterized as the [K(2,2,2-crypt)](+) salt. The isolation of [Sn(9)Ir(cod)](3-) as an intermediate product establishes that the formation of the stannaspherene [Ir@Sn(12)](3-) occurs through the oxidation of [Sn(9)Ir(cod)](3-). Among the structurally characterized tetrel cluster anions, [Ir@Sn(12)](3-) is a unique example of a stannaspherene, and one of the rare spherical clusters encapsulating a metal atom that is not a member of Group 10. Single-crystal structure determination shows that the novel Zintl ion cluster has nearly perfect icosahedral I(h) point symmetry.