(Organo)thallium (I) and (II) chemistry: Syntheses, structures, properties and applications of subvalent thallium complexes with alkyl, cyclopentadienyl, arene or hydrotris(pyrazolyl)borate ligands

Thallium(I) Complexes of Tris(pyridyl)borates and a Comparison to Their Pyrazolyl Analogues

Thallium(I) complexes of B-methylated and B-phenylated tris(pyridyl)borates featuring trifluoromethyl groups at the pyridyl ring 6-positions have been synthesized by metathesis using the corresponding potassium salts [MeB(6-(CF3)Py)3]K and [PhB(6-(CF3)Py)3]K with thallium(I) acetate. The closely related tris(pyrazolyl)borate analogue [PhB(3-(CF3)Pz)3]Tl has also been prepared, and comparisons of structural and spectroscopic features between the two scorpionate families are presented. [MeB(6-(CF3)Py)3]Tl displays κ3-coordination of the tris(pyridyl)borate similar to that of tris(pyrazolyl)borate in [MeB(3-(CF3)Pz)3]Tl, while [PhB(6-(CF3)Py)3]Tl and [PhB(3-(CF3)Pz)3]Tl feature κ2-N,N ligand coordination modes with the B-phenyl groups flanking the thallium sites. 19F NMR spectroscopy of [MeB(6-(CF3)Py)3]Tl reveals the presence of a remarkably large 1208 Hz four-bond thallium-fluorine coupling constant in chloroform at room temperature, which is considerably larger than 878 Hz observed for the pyrazolyl borate analogue [MeB(3-(CF3)Pz)3]Tl. Although [PhB(6-(CF3)Py)3]Tl is structurally nonrigid at room temperature in chloroform, at lower temperatures, the ligand arm exchange slows down, revealing 4JTl-F = 1110 Hz. Steric demands of these ligands have been quantified using the buried volume concept. In addition, ligand transfer chemistry from [MeB(6-(CF3)Py)3]Tl and [PhB(6-(CF3)Py)3]Tl to copper(I) under ethylene and computational analyses of the various coordination modes of tris(pyrazolyl)borates and tris(pyridyl)borates are reported.

A dianionic C3-symmetric scorpionate: synthesis and coordination chemistry

Introducing charges into ligand systems fine-tunes their electronic properties and influences the solubility of their metal complexes. Herein, we present a synthesis of a dianionic, C3-symmetric ligand combining three anionic N-donors tethered to a positively charged phosphonium center. The tris-skatylmethylphosphonium (TSMP) ligand, isolated in the form of its dipotassium salt TSMPK2, is the first dianionic homoscorpionate capable of metal exchange. The potassium cations in TSMPK2 are exchangeable for other metals, which results in rich coordination chemistry. Thus, the ligand displays a bridging μ2:κ2:κ1 coordination mode with trigonal planar Cu(i) centers in the tetrameric complex [(TSMP)Cu]44-. The κ3 mode is accessed upon addition of 1 equiv. of P(OEt)3 per Cu(i) to yield the tetrahedral monomeric complex [(TSMP)CuP(OEt)3]-. Both Fe(ii) and Ni(ii) in pyridine give octahedral high-spin κ3 complexes with composition (TSMP)M(Py)3 (M = Fe, Ni). Displacement of three pyridine ligands in (TSMP)Fe(Py)3 for a second equivalent of TSMP gives a high-spin pseudotetrahedral 2 : 1 complex [(TSMP)2Fe]2- with the ligands in κ2 coordination mode. The reduction in coordination number is likely due to electrostatic repulsion of the negatively-charged indolides as well as their weaker π-accepting character as compared to pyridine.

Phosphine-functionalised tris(pyrazolyl)methane ligands and their mono- and heterobimetallic complexes

The synthesis, characterisation and reactivity of new phosphine-functionalised tris(pyrazolyl)methane ligands (TpmPR₂, 2a-c, with R = Ph, nBu, iPr) are presented. The reaction of 2a-c with [Rh(CO)₂Cl]₂ furnished N,P-heterochelate carbonyl complexes (3a-c), which were used to quantify the donor abilities of the ligands via IR spectroscopy. The coordination flexibility was demonstrated by treating representative members of this new ligand class with [CpRu(acn)₃][PF₆] (acn = acetonitrile), [(tht)AuCl] (tht = tetrahydrothiophene) and [Pd(allyl)Cl]₂ providing either a N,N,P-heteroscorpionate complex (4) or the P-coordinated complexes (5,6) without any involvement of the pyrazolyl entities. With 2a and [Pd(cod)Cl₂], another P,N-heterochelate complex (7) was obtained, which served as a precursor for a heterobimetallic complex containing palladium and copper (8). Detailed NMR spectroscopic and X-ray crystallographic investigations have been performed on all new complexes.

Synthesis of organometallic pentalenide complexes

While a number of reports have established the unique structures and electronic properties of mono- and dinuclear pentalenide complexes of s, p, d and f block elements, access to these intriguing compounds is restricted by synthetic challenges. Here we review various strategies for the synthesis, functionalisation and (trans)metalation of pentalenide complexes from a practical point of view, pointing out promising avenues for future research that may allow wider access to novel pentalenide complexes for application in many different areas.

Organometallic Zirconium Compounds in an Oxygen-Rich Coordination Environment: Synthesis and Structural Characterization of Tris(oxoimidazolyl)hydroboratozirconium Compounds

A series of tris(oxoimidazolyl)hydroborato ligands, which serve as L₂X [O₃] donors, have been employed to obtain organometallic zirconium compounds in an uncommon oxygen-rich coordination environment. For example, Cp[To^MeBenz]ZrCl₂ has been synthesized via the reaction of [To^MeBenz]Na with CpZrCl₃ and bears a structural resemblance to the bent metallocene dichloride derivative Cp₂ZrCl₂. In addition, the half-sandwich counterparts [To^MeBenz]ZrCl₃ and [To^But]ZrCl₃ have been obtained by metathesis of ZrCl₄ with [To^MeBenz]Na and [To^But]Na, respectively. The structurally related zirconium benzyl compounds [To^RBenz]Zr(CH₂Ph)₃ (R = Me, Bu^t, 1-Ad) have also been synthesized via the reactions of [To^RBenz]Tl with Zr(CH₂Ph)₄, and X-ray diffraction studies demonstrate that the benzyl ligands in these compounds are conformationally flexible and exhibit a large range of Zr-CH₂-Ph bond angles (94.7-131.7°). Protolytic cleavage of one of the benzyl ligands of [To^RBenz]Zr(CH₂Ph)₃ (R = Bu^t, 1-Ad) may be achieved by treatment with [PhNHMe₂][B(C₆F₅)₄] to generate {[To^RBenz]Zr(CH₂Ph)₂}[B(C₆F₅)₄], which are catalysts for the polymerization of ethylene. The molecular structure of the ether adduct, {[To^ButBenz]Zr(CH₂Ph)₂(OEt₂)}[B(C₆F₅)₄], has been determined by X-ray diffraction. In addition to the use of tris(oxoimidazolyl)hydroborato ligands, bis(oxoimidazolyl)hydroborato ligands have also been used to obtain zirconium benzyl compounds in oxygen-rich environments, namely, [Bo^MeBenz]₂Zr(CH₂Ph)₂ and [Bo^AdBenz]₂Zr(CH₂Ph)₂.

Cooperative metal–ligand influence on the formation of coordination polymers, and conducting and photophysical properties of Tl(i) β-oxodithioester complexes

Eight novel luminescent and semiconducting Tl(i) β-oxodithioester complexes forming 1D/2D coordination polymeric structures were investigated using single crystal X-ray diffraction.

Experimental observation and quantum chemical investigation of thallium(i) (Z)-methanediazotate: synthesis of a long sought and highly reactive species

Thallium(i) (Z)-methanediazotate has been synthesised through TlOPr induced cleavage of ¹⁵N-labelled N-methyl-N-nitrosourea, and confirmed by NMR analysis. CCSD(T)/CBS calculations reveal a kinetic product control.

Comparison of thallium(I) complexes with mesityl-substituted tris(pyrazolyl)hydroborate ligands, [Tl{HB(3-Ms-5-Mepz)3}] and [Tl{HB(3-Ms-5-Mepz)2(3-Me-5-Mspz)}]

Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in contemporary coordination chemistry due to the availability of various steric and electronic substituents at the pyrazolyl rings that allow fine-tuning of the open-coordination site for metal centres. The thallium(I) complexes of anionic tridentate-chelating scorpionate ligands, namely [tris(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN2)hydroborato]thallium(I) monohydrate, [Tl(C39H46BN6)]·H2O, (I), and [bis(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN2)(5-mesityl-3-methyl-1H-pyrazol-1-yl-κN2)hydroborato]thallium(I), [Tl(C39H46BN6)], (II), show a {TlIN3} coordination, with average TlI—N bond lengths of 2.53 and 2.55 Å in (I) and (II), respectively. The overall TlIcoordination geometry is distorted trigonal pyramidal, with the average N—TlI—N angle being approximately 73° for both. The dihedral angle between the planes of the pyrazolyl and benzene rings of the mesityl group is 82° in (I), while the corresponding angles in (II) are in the range 64–104°. The structural differences between the two ligands are expected to contribute to the different reactivities of the transition metal coordination complexes towards activation of small molecules such as dioxygen and ethylene.

Benzannulated tris(2-mercapto-1-imidazolyl)hydroborato ligands: tetradentate κ4-S3H binding and access to monomeric monovalent thallium in an [S3] coordination environment

The benzannulated tris(mercaptoimidazolyl)borohydride sodium complex, [Tm(Bu(t)Benz)]Na, has been synthesized via the reaction of NaBH4 with 1-tert-butyl-1,3-dihydro-2H-benzimidazole-2-thione, while [Tm(MeBenz)]K has been synthesized via the reaction of KBH4 with 1-methyl-1,3-dihydro-2H-benzimidazole-2-thione. The molecular structures of the solvated adducts, {[Tm(Bu(t)Benz)]Na(THF)}2(μ-THF)2 and [Tm(MeBenz)]K(OCMe2)3, have been determined by X-ray diffraction, which demonstrates that the [Tm(R)] ligands in these complexes adopt different coordination modes to that in {[Tm(MeBenz)]Na}2(μ-THF)3. Specifically, while the [Tm(MeBenz)] ligand of the sodium complex {[Tm(MeBenz)]Na}2(μ-THF)3 adopts a κ(3)-S3 coordination mode, the potassium complex [Tm(MeBenz)]K(OCMe2)3 adopts a most uncommon inverted κ(4)-S3H coordination mode in which the potassium binds to all three sulfur donors and the hydrogen of the B-H group in a linear KH-B manner. Furthermore, the [Tm(Bu(t)Benz)] ligand of {[Tm(Bu(t)Benz)]Na(THF)}2(μ-THF)2 adopts a κ(3)-S2H coordination mode, thereby demonstrating the flexibility of this ligand system. The monovalent thallium compounds, [Tm(MeBenz)]Tl and [Tm(Bu(t)Benz)]Tl, have been obtained via the corresponding reactions of [Tm(MeBenz)]Na and [Tm(Bu(t)Benz)]Na with TlOAc. X-ray diffraction demonstrates that the three sulfur donors of the [Tm(RBenz)] ligands of both [Tm(MeBenz)]Tl and [Tm(Bu(t)Benz)]Tl chelate to thallium. This coordination mode is in marked contrast to that in other [Tm(R)]Tl compounds, which exist as dinuclear molecules wherein two of the sulfur donors coordinate to different thallium centers. As such, this observation provides further evidence that benzannulation promotes κ(3)-S3 coordination in this system.

Perfluorinated 1H-indazoles and hydrotris(indazol-1-yl)borates. Supramolecular organization and a new synthetic procedure to form scorpionate ligands

The molecular and supramolecular structures of new perfluorinated indazoles and hydrotris(indazolyl)borates reveal various types of intra- and intermolecular interactions and organizations.

Synthesis and structural characterization of tris(2-pyridonyl)methyl complexes of zinc and thallium: a new class of metallacarbatranes and a monovalent thallium alkyl compound

Tris(2-pyridonyl)methanes may be synthesized via the reactions of the respective 2-pyridone with CHX3 (X = Cl, Br) and K2CO3 in the presence of [Bu(n)4N]Br, followed by acid-catalyzed isomerization with camphorsulfonic acid. These compounds provide access to a new class of alkyl ligands that feature oxygen donors and are capable of forming metallacarbatranes and a monovalent thallium alkyl compound.

Thallophilic interactions and Tl-aryl π-interactions are competitive with cation-cation repulsion: [LTl2L]2+ dications as salts of weakly co-ordinating anions

The synthesis and characterization by single-crystal X-ray diffraction of two thallium salts of the non-co-ordinating anion [B{3,5-(CF3)2C6H3}4] are reported. They possess Tl-Tl contacts supported by Tl-aryl interaction. This cation association overcomes both electrostatic repulsion and cation-anion size and charge matching considerations in the [LTl2L](2+) dications so formed.

Improved syntheses, and structural and electronic characterization of carboxamide-substituted TpCONHPh,Meand TpCONHt-Bu,Meligands

Improvements in the syntheses of the carboxamide-substituted tris(pyrazolyl)borate ligands TpCONHPh,Me[tris(3-anilinocarbonyl-5-methylpyrazol-1-yl)borate] and TpCONHt-Bu,Me[tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl)borate] are reported. Their TlIsalts, namely [tris(3-anilinocarbonyl-5-methylpyrazol-1-yl-κN2)borato]thallium(I), [Tl(C33H31BN9O3)], (II), and [tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl-κN2)borato]thallium(I), [Tl(C27H43BN9O3)], (III), as well as the CuIcarbonyl complexes (TpCONHPh,Me)Cu(CO), namely carbonyl[tris(3-anilinocarbonyl-5-methylpyrazol-1-yl-κN2)borato]copper(I) tetrahydrofuran trisolvate, [Cu(C33H31BN9O3)(CO)]·3C4H8O, (IV), and (TpCONHt-Bu,Me)Cu(CO), namely carbonyl[tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl-κN2)borato]copper(I) tetrahydrofuran hemisolvate, [Cu(C27H43BN9O3)(CO)]·0.5C4H8O, (V), have been prepared. Their spectroscopic properties and structures are compared with those of related compounds. The molecules of (II)–(V) show hydrogen bonding to either solvent molecules or neighboring complex moleculesviaamide groups. The title compounds feature the ability to engage other ligands in hydrogen bonding and they show strong electron-withdrawing character. Compound (V) displays voids ofca800 Å3in the crystal structure.

Anhydrous thallium hydrogen L-glutamate: polymer networks formed by sandwich layers of oxygen-coordinated thallium ions cores shielded by hydrogen L-glutamate counterions

Anhydrous thallium hydrogen L-glutamate [Tl(L-GluH)] crystallizes from water (space group P2(1)) with a layer structure in which the thallium ions are penta- and hexacoordinated exclusively by the oxygen atoms of the γ-carboxylate group of the hydrogen L-glutamate anions to form a two-dimensional coordination polymer. The thallium-oxygen layer is composed of Tl(2)O(2) and TlCO(2) quadrangles and is only 3 Å high. Only one hemisphere of the thallium ions participates in coordination, indicative of the presence of the 6s(2) lone pair of electrons. The thallium-oxygen assemblies are shielded by the hydrogen l-glutamate anions. Only the carbon atom of the α-carboxylate group deviates from the plane spanned by the thallium ions, the γ-carboxylate groups and the proton bearing carbon atoms, which are in trans conformation. Given the abundance of L-glutamic and L-aspartic acid in biological systems on the one hand and the high toxicity of thallium on the other hand, it is worth mentioning that the dominant structural motifs in the crystal structure of [Tl(L-GluH)] strongly resemble their corresponding analogues in the crystalline phase of [K(L-AspH)(H(2)O)(2)].

Synthesis of Pd3Tl and Pd6Tl2 complexes based on a trinuclear aryl-palladium(II) complex acting as a metallaligand toward thallium(I) through Tl-arene and Tl-I bonds

The metallaligand [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] (L(2) = 4,4'-di-tert-butyl-2-2'-bipyridine = tbbpy) reacts with TlOTf to afford the complex [{(PdIL(2))(3)C(6)Me(3)-1,3,5}Tl]OTf, which exists in the solid state as a 2:1 mixture of monomer and dimer, both showing Tl(I)-I and Tl(I)-η(6)-mesitylene bonds. In solution, only the monomer is observed. Heating of toluene solutions of [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] affords the dinuclear complex [(PdIL(2))(2)(C(6)HMe(3)-1,3,5)].