N-Coordinated Tin(II) Trifluoromethanesulfonates and Their Reactions with Transition Metal Carbonyls

Accessing Homo- and Heterobimetallic Complexes with a Dianionic Pentadentate Ligand

The tetrapyrazolylpyridyl diborate (B2Pz4Py) ligand provides a suitable platform for the isolation of heterobimetallic main-group element compounds as well as homotetrametallic copper complexes. The heterobimetallic tin(II)-lithium(I) (1) and tin(II)-thallium(I) (2) complexes have been synthesized, isolated, and fully characterized including single-crystal X-ray diffraction analysis. When reacted with copper(I) sources, complex 2 grants access to a homotetrametallic copper(I) complex (4). Upon subsequent oxidation, 4 gives rise to the bimetallic copper(II) complex 5, in which the two copper(II) centers are connected via a bridging bromido ligand (CuII-μ-Br-CuII).

Intramolecularly O,N,O-Coordinated Tin(II) Salts: Syntheses, Structures, Cyclization, and Transition Metal Complexation

We report the syntheses of tin(II) salts of the types [L1SnX]SnX3 [L1=2,6-{(i-PrO)2(O)P}2C5H3N: 1, X=Cl; 2, X=Br], [L2SnCl]SnCl3 [L2=2-{(i-PrO)Ph(O)P}-6-{(i-PrO)2(O)P}C5H3N: 3], [L3SnX]SnX3 [L3=2,6-{MeO(O)C}2C5H3N: 4, X=Cl; 5, X=Br], [L4SnX]SnX3 [L4=2,6-{Et2N(O)C}2C5H3N: 6, X=Cl; 7, X=Br]. These compounds were obtained by addition of SnX2 to the corresponding ligand inducing autoionization of the respective tin(II) halide. The thermal stability of 1, 3, and 4 was elucidated, giving, under ester cleavage and cyclisation, the tin(II) derivatives 8-12. The reaction of [L1SnCl]SnCl3 (1) with W(CO)4(thf)2 afforded the tungsten tetracarbonyl complex [{L1SnCl}{SnCl3}W(CO)4] (13), representing the first example in which a tin(II) stannate anion and a tin(II) stannylium cation simultaneously coordinate to a transition metal centre. The compounds were characterized by single crystal X-ray diffraction analyses and in part by elemental analyses, IR and NMR spectroscopy, electrospray ionization mass spectrometry. DFT calculations accompany the experimental work.

Tin(II) cations stabilized by non-symmetric N,N',O-chelating ligands: synthesis and stability

A series of novel non-symmetric neutral N,N',O-chelating ligands derived from the α-iminopyridine 2-(C(R¹)N(C₆H₃-2,6-iPr₂))-6-(R²R³PO)C₅H₃N (L1: R¹ = H, R² = R³ = Ph; L2: R¹ = Me, R² = R³ = Ph; L3: R¹ = H; R² = Ph, R³ = EtO; L4: R¹ = Me, R² = Ph, R³ = EtO; L5: R¹ = H, R² = R³ = iPrO; L6: R1 = Me, R² = R³ = iPrO) were synthesized. Ligands L1-6 were reacted with SnCl₂ and Sn(OTf)₂ with the aim of studying the influence of different R²R³PO functional groups on the Lewis base mediated ionization of SnCl₂ and Sn(OTf)₂. While all ligands L1-6 provided the corresponding ionic tin(II) complexes [L1-6 → SnCl]⁺[SnCl₃]^- (1-6), only ligands L1, L4 and L6 were able to stabilize tin(II) dications [L1,4,6 → Sn(H₂O)][OTf]₂ (7-9). The auto-ionized compounds [L3-6 → SnCl]⁺[SnCl₃]^- possessing ethylphenyl phosphinate and diisopropylphosphite substituents undergo elimination of EtCl and iPrCl, respectively, yielding compounds 10-13. These can either be interpreted as neutral tin(II)phosphinate chloride (10, 11) and tin(II)phosphonate chloride (12, 13), respectively, containing Sn-O and Sn-Cl bonds, and a PO → SnCl₂ interaction, or as zwitterionic compounds, where the positive charge of the central tin atom is compensated by an [OSnCl₂]^- anion. Finally, DFT studies were performed to better understand the steric and electronic properties of the ligands L1-6 as well as the nature of the bonds in the resulting products, with a particular focus on complexes 10-13.

Tuning the metal-ligand bond in the σ-complexes of stannylenes and azabenzenes

The metal-ligand bond in a set of 60 σ-complexes has been investigated by electronic structure computations. These σ-complexes originate from the unique combination of 12 stannylenes (SnX₂ ) with five azabenzene ligands (pyridine, pyrazine, pyrimidine, pyridazine, and s-triazine), where the nitrogen center of the ligand acts as σ-donor and the tin(II) center as σ-acceptor in a 1:1 fashion. The Sn ← N bond and the total interaction between the stannylene and azabenzene moieties of the σ-complexes are characterized in depth to relate the Sn ← N strength to the substitution pattern at SnX₂ and to the number and the positioning of N atoms in the azabenzenes. Such X substituents as (iso)cyano and trifluoromethyl groups enhance the interaction strength, while the presence of alkyl, phenyl, and silyl substituents in SnX₂ diminishes the stability of σ-complexes. A gradual weakening of the total interaction is associated with the growing number of N atoms in the azabenzenes, while the N-atom positioning in pyridazine is particularly effective in strengthening the interaction with stannylenes. Variations in the Sn ← N bond strength usually follow those in the total interaction between the moieties but the interacting quantum atoms picture of Sn ← N reveals certain intriguing exceptions.

Pseudo-One-Coordinate Tetrylenium Salts Bearing a Bulky Carbazolyl Substituent

Syntheses of a bulky carbazole-based substituent, the parent 1,8-bis(3,5-di-tert-butylphenyl)-3,6-di-tert-butyl-carbazole (R-H) and a series of chlorotetrylenes, RECl (E=Ge, Sn, Pb), are described. Detailed analysis of the properties of the carbazole-based substituent revealed that it features flexible high bulkiness and electronic non-innocence, which may make it suitable for many applications in both main-group and transition-metal chemistry. To further showcase the employability of the novel substituent, the chlorotetrylenes were subjected to halide abstraction reactions, affording the corresponding tetrylenium salts [RE][Al(OC₄ F₉ )₄ ] (E=Ge, Sn, Pb) as strongly coloured compounds.

Iminopyridine ligand complexes of group 14 dihalides and ditriflates – neutral chelates and ion pair formation

Reaction of the chelating imino-pyridine ligand SIMPY, (SIMPY=2-(DippN=CH)-C5H4N), Dipp=2,6- i Pr2-C6H3, with germanium(II) and tin(II) halides provides the respective neutral complexes [SIMPY·EX2] (EX2: E=Ge, X=Cl, Br; E=Sn, X=Cl, Br, I). The method is readily extendable to give the tin(II) triflate complex [SIMPY·Sn(OTf)2] (OTf, triflate=CF3SO3 −). In the solid state, the neutral compounds [SIMPY·EX2] exist as monomers, in which the four-coordinate tetrel atoms feature a slightly distorted disphenoidal geometry around germanium and tin. Reaction of the tridentate imino-pyridine ligand DIMPY, (DIMPY=2,6-(DippN=CH)2-C5H3N) with Sn(OTf)2 provided access to a neutral tin(II) complex. Similar to the previously reported reactions leading to the germanium and tin chloride complexes [DIMPY·SnCl]+[SnCl3]−, and [Me2DIMPY·EX]+[EX3]− (Me2DIMPY=2,6-(DippN=C(Me))2-C5H3N, E=Ge, Sn; X=Cl), the reactions of DIMPY with GeX2·dioxane (X=Cl, Br) and SnX2 (X=Br, I) yielded Ge(II) and Sn(II) based ion pairs [DIMPY·EX]+[EX3]− (E=Ge, X=Cl, Br; E=Sn, X=Br, I) as a consequence of spontaneous dissociation of the group 14 dihalides. The tetrel atoms in the cationic parts in [DIMPY·EX]+[EX3]− are four-coordinate as one halide substituent is replaced by the coordination of a second imino donor group from the ligand. The anionic fragments adopt a pyramidally, tri-coordinate geometry. In contrast, the DIMPY tin(II) ditriflate complex crystallizes with two independent, neutral molecules per asymmetric unit, in which one of the tin centers is five- coordinate by interaction with three donor sites of the chelating bis(imino)pyridine ligand and two additional contacts towards the oxygen atoms of the triflate counter-anions. In the second crystallographically independent complex the tin atom is six-coordinate with a slightly distorted octahedral geometry via interaction with THF as an additional donor molecule. All compounds reported were studied by means of multinuclear NMR spectroscopy. In addition, the solid state structures of the complexes [SIMPY·EX2] (EX2: E=Ge, X=Cl, Br; E=Sn, X=Cl, Br, I), the ion pairs [DIMPY·EX]+[EX3]− (E=Ge, X=Cl; E=Sn, X=Br) and the tin(II) ditriflate [DIMPY·Sn(OTf)2] were authenticated by means of single-crystal X-ray diffraction analyses. Moreover, [DIMPY·Sn(OTf)2] was investigated by 119Sn Mössbauer spectroscopy.