Molecular structures of tris(2-mercapto-1-tert-butylimidazolyl)hydroborato and tris(2-mercapto-1-adamantylimidazolyl)hydroborato sodium complexes: analysis of [Tm(R)] ligand coordination modes and conformations

Bis- and Tris(2-oxobenzimidazolyl)hydroborato Complexes of Sodium and Thallium: New Classes of Bidentate and Tridentate Oxygen Donor Ligands

A series of bis- and tris(oxobenzimidazolyl)hydroborato compounds, namely, [Bo^RBenz]Na and [To^RBenz]-Na (R = Me, Bu^t, Ad), which feature uncommon sterically demanding LX [O₂] and L₂X [O₃] donor ligands, have been obtained via the reactions of NaBH₄ with 1-R-1,3-dihydro-2H-benzimidazol-2-ones. Evidence that the alkyl substituents are suitably located to have a significant impact on the coordination environment is provided by the observation that the methyl derivative [To^MeBenz]Na(κ³-diglyme) exhibits κ³-coordination of the diglyme, whereas the t-butyl and adamantyl derivatives, [To^ButBenz]Na(κ²-diglyme) and [To^AdBenz]Na(κ²-diglyme), exhibit κ²-coordination. The [Bo^RBenz] and [To^RBenz] ligands also allow for isolation of discrete mononuclear thallium compounds, [Bo^RBenz]Tl and [To^RBenz]Tl, for which the steric demands of the ligands have been quantified in terms of both cone angle and buried volume concepts.

Tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl metal complexes, [TismPriBenz]M: a new class of metallacarbatranes, isomerization to a tris(N-heterocyclic carbene) derivative, and evidence for an inverted ligand field

The tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl ligand, [TismPriBenz], has been employed to form carbatrane compounds of both the main group metals and transition metals, namely [TismPriBenz]Li, [TismPriBenz]MgMe, [TismPriBenz]Cu and [TismPriBenz]NiBr. In addition to the formation of atranes, a zinc compound that exhibits κ3-coordination, namely [κ3-TismPriBenz]ZnMe, has also been obtained. Furthermore, the [TismPriBenz] ligand may undergo a thermally induced rearrangement to afford a novel tripodal tris(N-heterocyclic carbene) variant, as shown by the conversion of [TismPriBenz]Cu to [κ4-C4-TismPriBenz*]Cu. The transannular M-C bond lengths in the atrane compounds are 0.19-0.32 Å longer than the sum of the respective covalent radii, which is consistent with a bonding description that features a formally zwitterionic component. Interestingly, computational studies demonstrate that the Cu-Catrane interactions in [TismPriBenz]Cu and [κ4-C4-TismPriBenz*]Cu are characterized by an "inverted ligand field", in which the occupied antibonding orbitals are localized more on carbon than on copper.

Tris(2-mercaptoimidazolyl)hydroborato Cadmium Thiolate Complexes, [TmBut]CdSAr: Thiolate Exchange at Cadmium in a Sulfur-Rich Coordination Environment

A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [TmBut]CdSAr, have been synthesized by the reactions of [TmBut]CdMe with ArSH (Ar = C6H4-4-F, C6H4-4-But, C6H4-4-OMe, and C6H4-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [TmBut]CdSPy and [TmBut]CdSePy have been obtained via the respective reactions of [TmBut]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [TmBut]CdSAr and [TmBut]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS4] motif is distorted tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [TmBut]CdSPy and [TmBut]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms. The ability of the thiolate ligands to participate in exchange was probed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopic studies of the reactions of [TmBut]CdSC6H4-4-F with ArSH (Ar = C6H4-4-But or C6H4-4-OMe), which demonstrate that (i) exchange is facile and (ii) coordination of thiolate to cadmium is most favored for the p-fluorophenyl derivative. Furthermore, a two-dimensional EXSY experiment involving [TmBut]CdSC6H4-4-F and 4-fluorothiophenol demonstrates that degenerate thiolate ligand exchange is also facile on the NMR time scale.

Dihydrobis(methimazolyl)borato complexes of ruthenium and osmium

The reaction of Na[H₂B(mt)₂] (mt = 2-mercapto, 3-methylimidazol-1-yl, methimazolyl) with [Ru(X)Cl(CO)(PPh₃)_n] (n= 3 X = H;n= 2 BO₂C₆H₄, SiCl₃, SiMe₃) affords the complexes [Ru(X)(CO)(PPh₃){κ²-H,S,S′-H₂B(mt)₂}].

Molecular structures of tris(1-tert-butyl-2-mercaptoimidazolyl)hydroborate complexes of titanium, zirconium and hafnium

Cyclopentadienyl and tris(pyrazolyl)hydroborate have found much use as supporting ligands in the chemistry of titanium, zirconium and hafnium, especially with respect to applications involving olefin polymerization catalysis. In contrast, closely related tris(1-alkyl-2-mercaptoimidazolyl)hydroborate, [Tm^R], ligands have so far found little application to the chemistry of these elements, despite the fact that such ligands are currently used extensively in coordination chemistry. In view of the fact that a substituent in the 2-position exerts a direct influence on the steric environment of the metal center, we report here the application of the sterically demanding tris(1-tert-butyl-2-mercaptoimidazolyl)hydroborate [Tm^t-Bu] ligand to these metals. Dichlorido(η⁵-cyclopentadienyl)[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κ³S,S',H]zirconium(IV) benzene hemisolvate, [Zr(C₂₁H₃₄BN₆S₃)(C₅H₅)Cl₂]·0.5C₆H₆, (I), dichlorido(η⁵-cyclopentadienyl)[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κ³S,S',H]titanium(IV) benzene hemisolvate, [Ti(C₂₁H₃₄BN₆S₃)(C₅H₅)Cl₂]·0.5C₆H₆, (II), [bis(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κ³S,S',H]dichlorido(η⁵-cyclopentadienyl)zirconium(IV), [Zr(C₁₄H₂₄BN₄S₂)(C₅H₅)Cl₂], (III), (1-tert-butyl-2,3-dihydro-1H-imidazole-2-thione-κS)(1-tert-butyl-2-sulfanylidene-1H-imidazol-3-ido-κ²N³,S)dichlorido(η⁵-cyclopentadienyl)zirconium(IV) benzene monosolvate, [Zr(C₇H₁₁N₂S)(C₇H₁₂N₂S)(C₅H₅)Cl₂]·C₆H₆, (IV), and tribenzyl[tris(1-tert-butyl-2-sulfanylidene-2,3-dihydro-1H-imidazol-3-yl)borato-κ³S,S',S'']hafnium(IV) benzene tetrasolvate, [Hf(C₇H₇)₃(C₂₁H₃₄BN₆S₃)]·4C₆H₆, (V), have been structurally characterized by X-ray diffraction. The [Tm^t-Bu] ligand coordinates to Ti and Zr in Cp[κ³S₂,H-Tm^t-Bu]MCl₂ [M = Zr, (I), and Ti, (II)] in a κ³S₂,H mode, while the benzyl compounds [Tm^t-Bu]M(CH₂Ph)₃ [M = Zr and Hf, (V)] exhibit κ³S₃ coordination.

Synthesis, structure and reactivity of [TmBut]ZnH, a monomeric terminal zinc hydride compound in a sulfur-rich coordination environment: access to a heterobimetallic compound

The zinc hydride complex, [Tm^But]ZnH, undergoes insertion of CO₂ and facile protolytic cleavage, of which the latter provides access to heterobimetallic [Tm^But]ZnMo(CO)₃Cp.

Exchange of Alkyl and Tris(2-mercapto-1-t-butylimidazolyl)hydroborato Ligands Between Zinc, Cadmium and Mercury

The tris(2-mercaptoimidazolyl)hydroborato ligand, [Tm^But ], has been used to investigate the exchange of alkyl and sulfur donor ligands between the Group 12 metals, Zn, Cd and Hg. For example, [Tm^But ]₂Zn reacts with Me₂Zn to yield [Tm^But ]ZnMe, while [Tm^But ]CdMe is obtained readily upon reaction of [Tm^But ]₂Cd with Me₂Cd. Ligand exchange is also observed between different metal centers. For example, [Tm^But ]CdMe reacts with Me₂Zn to afford [Tm^But ]ZnMe and Me₂Cd. Likewise, [Tm^But ]HgMe reacts with Me₂Zn to afford [Tm^But ]ZnMe and Me₂Hg. However, whereas the [Tm^But ] ligand transfers from mercury to zinc in the methyl system, [Tm^But ]HgMe/Me₂Zn, transfer of the [Tm^But ] ligand from zinc to mercury is observed upon treatment of [Tm^But ]₂Zn with HgI₂ to afford [Tm^But ]HgI and [Tm^But ]ZnI. These observations demonstrate that the phenomenological preference for the [Tm^But ] ligand to bind one metal rather than another is strongly influenced by the nature of the co-ligands.

Synthesis and structures of cadmium carboxylate and thiocarboxylate compounds with a sulfur-rich coordination environment: carboxylate exchange kinetics involving tris(2-mercapto-1-t-butylimidazolyl)hydroborato cadmium complexes, [Tm(Bu(t))]Cd(O2CR)

A series of cadmium carboxylate compounds in a sulfur-rich environment provided by the tris(2-tert-butylmercaptoimidazolyl)hydroborato ligand, namely, [Tm(Bu(t))]CdO2CR, has been synthesized via the reactions of the cadmium methyl derivative [Tm(Bu(t))]CdMe with RCO2H. Such compounds mimic aspects of cadmium-substituted zinc enzymes and also the surface atoms of cadmium chalcogenide crystals, and have therefore been employed to model relevant ligand exchange processes. Significantly, both (1)H and (19)F NMR spectroscopy demonstrate that the exchange of carboxylate groups between [Tm(Bu(t))]Cd(κ(2)-O2CR) and the carboxylic acid RCO2H is facile on the NMR time scale, even at low temperature. Analysis of the rate of exchange as a function of concentration of RCO2H indicates that reaction occurs via an associative rather than dissociative pathway. In addition to carboxylate compounds, the thiocarboxylate derivative [Tm(Bu(t))]Cd[κ(1)-SC(O)Ph] has also been synthesized via the reaction of [Tm(Bu(t))]CdMe with thiobenzoic acid. The molecular structure of [Tm(Bu(t))]Cd[κ(1)-SC(O)Ph] has been determined by X-ray diffraction, and an interesting feature is that, in contrast to the carboxylate derivatives [Tm(Bu(t))]Cd(κ(2)-O2CR), the thiocarboxylate ligand binds in a κ(1) manner via only the sulfur atom.

Influence of Benzannulation on Metal Coordination Geometries: Synthesis and Structural Characterization of Tris(2-mercapto-1-methylbenzimidazolyl)hydroborato Cadmium Bromide, {[TmMeBenz]Cd(μ-Br)}2

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complex, {[TmMeBenz]Cd(μ-Br)}2, may be synthesized via the reaction of [TmMeBenz]K with CdBr2. X-ray diffraction demonstrates that {[TmMeBenz]Cd(μ-Br)}2 exists as a dimer, which is in marked contrast to the monomeric structure of the non-benzannulated counterpart, [TmMe]CdBr, and thereby demonstrates that benzannulation of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato ligands can have a distinct impact on the molecular structure of their metal complexes. In accord with this observation, density functional theory calculations indicate that the benzannulated dimers, {[TmMeBenz]Cd(μ-X)}2 (X = Cl, Br, I), are more stable with respect to dissociation than are their non-benzannulated counterparts, {[TmMe]Cd(μ-X)}2. Furthermore, the calculations also indicate that the stability of the dimer depends on the nature of X, such that the dimer becomes more stable in the sequence I < Br < Cl.

Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium halide complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI: a rare example of cadmium in a trigonal bipyramidal sulfur-rich coordination environment

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complexes, {[Tm(MeBenz)]Cd(μ-Cl)}2 and [Tm(MeBenz)]CdI, have been synthesized via the reactions of [Tm(MeBenz)]K with CdCl2 and CdI2, respectively. While X-ray diffraction studies demonstrate that the iodide derivative, [Tm(MeBenz)]CdI, is a monomer, the chloride derivative, {[Tm(MeBenz)]Cd(μ-Cl)}2, exists as a dimer, which is unprecedented for Group 12 [Tm(R)]MX (X = Cl, Br, I) compounds. Furthermore, the cadmium centers of {[Tm(MeBenz)]Cd(μ-Cl)}2 are trigonal bipyramidal, which is an uncommon motif for cadmium complexes with a [S3Cl2] coordination sphere.