Bis(mercaptoimidazolyl)(pyrazolyl)hydroborato complexes of zinc, cadmium, and cobalt: structural evidence for the enhanced tendency of zinc in biological systems to adopt tetrahedral M[S4] coordination

Preparation of a borane-appended Co(III) hydride: evidence for metal-ligand cooperativity in O-H bond activation

Cobalt hydrides are known to mediate a number of important chemical transformations including proton (H+), hydride (H-), and hydrogen-atom (H˙) transfer. Central to the tunability of such frameworks is judicious ligand design, which offers the flexibility to alter fundamental properties relevant to reactivity. Herein, we report the preparation of one such cobalt(iii) hydride: [Cp*CoIII(P2BCy4)(H)]BPh4 (Cp* = C5Me5-, P2BCy4 = 1,2-bis(di(3-dicyclohexylborane)propylphosphino)ethane) that is encircled by a boron-based Lewis-acidic secondary coordination sphere. The structure of this species is supported by synchrotron-radiation crystallography, evidencing a terminal Co(iii) hydride with four sp2-hybridized boranes that invite Lewis base coordination. To this end, electrochemical reactivity studies performed using [Cp*CoIII(P2BCy4)Cl]+ or an "all-akyl" model, [Cp*CoIII(dnppe)Cl]+ (dnppe = 1,2-bis(di-n-propylphosphino)ethane) with benzoic or 4-pyridylbenzoic acid show divergent responses for protonation of electrochemically-generated Co(i) to give a Co(iii) hydride. For [Cp*CoIII(P2BCy4)Cl]+, this process is complex, not only involving protonation, but also engagement of the pendant borane moieties in Lewis acid/base interactions. For protonation by benzoic acid, for example, borane-benzoate contacts are substantiated by variable temperature NMR spectroscopic measurements and theoretical calculations, pointing to a cooperative Co-H/B-O bond forming process. These data are discussed in the context of designing new molecular catalysts for ligand-assisted hydrogen evolution reactivity.

Synthesis, Structure, and Reactivity of a Terminal Cadmium Hydride Compound, [κ3-TismPriBenz]CdH

The terminal cadmium hydride compound, [κ³-Tism^PriBenz]CdH, which features the tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl ligand, may be obtained via the reactions of either [κ³-Tism^PriBenz]CdN(SiMe₃)₂ or [Tism^PriBenz]CdOSiPh₃ with PhSiH₃. The Cd-H bond of [κ³-Tism^PriBenz]CdH undergoes (a) metathesis reactions with MeI, Me₃SiX (X = Cl, Br, I, NCO), and Me₃SnX (X = Cl, Br, I) to afford the corresponding [Tism^PriBenz]CdX derivative, (b) insertion with CO₂ and CS₂ to afford respectively [Tism^PriBenz]Cd(κ¹-O₂CH) and [Tism^PriBenz]Cd(κ¹-S₂CH), and (c) hydride abstraction with B(C₆F₅)₃ to afford {[Tism^PriBenz]Cd}[HB(C₆F₅)₃] that possesses a rare trigonal monopyramidal geometry for cadmium.

Heterobimetallic μ2-carbido complexes of platinum and tungsten

The tungsten–platinum μ-carbido complex [WPt(μ-C)Br(CO)₂(PPh₃)₂(Tp*)] (Tp* = hydrotris(dimethylpyrazol-1-yl)borate) undergoes facile substitution of both bromide and phosphine ligands to afford a diverse library of μ-carbido complexes.

Low Molecular Weight Fluorescent Probes (LMFPs) to Detect the Group 12 Metal Triad

Fluorescence sensing, of d-block elements such as Cu2+, Fe3+, Fe2+, Cd2+, Hg2+, and Zn2+ has significantly increased since the beginning of the 21st century. These particular metal ions play essential roles in biological, industrial, and environmental applications, therefore, there has been a drive to measure, detect, and remediate these metal ions. We have chosen to highlight the low molecular weight fluorescent probes (LMFPs) that undergo an optical response upon coordination with the group 12 triad (Zn2+, Cd2+, and Hg2+), as these metals have similar chemical characteristics but behave differently in the environment.

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}].

Crystal structure of di-bromido-(N,N-di-methyl-formamide-κO){2-(1H-indol-3-yl)-N-[(quinolin-2-yl-κN)methyl-idene]ethanamine-κN}cadmium

In the mononuclear title complex, [CdBr2(C20H17N3)(C3H7NO)], synthesized from the quinoline-derived Schiff base 2-(1H-indol-3-yl)-N-(quinolin-2-yl-methyl-ene)ethan-amine (IQME), the coordination geometry around the Cd(2+) atom is distorted trigonal bipyramidal, the axial positions being occupied by the quinoline N atom [Cd-N = 2.401 (3) Å] and one di-methyl-formamide O-atom donor [Cd-O = 2.399 (2) Å]. The equatorial plane is formed by the imine N atom [Cd-N = 2.293 (3) Å] and two bromides [Cd-Br = 2.5621 (8) and 2.5676 (8) Å], with the deviation of the Cd(II) atom from the equatorial plane being 0.046 (1) Å. An intra-molecular C-H⋯Br inter-action occurs. In the crystal, N-H⋯Br inter-actions generate [101] chains.

Dinuclear copper(i) complexes with N-heterocyclic thione and selone ligands: synthesis, characterization, and electrochemical studies

We report dinuclear copper(i) complexes with a variety of monodentate and bidentate thione- and selone-containing ligands. Cu(ii/i) potentials were tuned in a 470 mV range depending on the chalcogenone ligands.

Synthesis and characterization of the homologous M-M bonded series Ar'MMAr' (M = Zn, Cd, or Hg; Ar' = C6H3-2,6-(C6H3-2,6-Pr(i)2)2) and related arylmetal halides and hydride species

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are reported. The compounds Ar'MMAr' (M = Zn, Cd, or Hg; Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) were synthesized by reduction of the corresponding arylmetal halides by alkali metal/graphite (Zn or Hg) or sodium hydride (Cd). These compounds possess almost linear C-M-M-C core structures with two-coordinate metals. The observed M-M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) A for the zinc, cadmium, and mercury species, respectively. The shorter Hg-Hg bond in comparison to that of Cd-Cd is consistent with DFT calculations which show that the strength of the Hg-Hg bond is greater. The arylmetal halides precursors (Ar'MI)(1 or 2), and the highly reactive hydrides (Ar'MH)(1 or 2), were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar'HgI, is monomeric. The arylzinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) mu-H-bridged structures. The Ar'HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar'HgH by Ar'H. It was also shown that the decomposition of Ar'Cd(mu-H)(2)CdAr' at room temperature leads to the M-M bonded Ar'CdCdAr', thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate.

Applications of Tripodal [S(3)] and [Se(3)] L(2)X Donor Ligands to Zinc, Cadmium and Mercury Chemistry: Organometallic and Bioinorganic Perspectives

The tripodal tris(2-mercapto-1-R-imidazolyl)hydroborato ligand system, [Tm(R)], and its selenium counterpart, [Tse(R)], provide useful platforms for investigating organometallic and bioinorganic aspects of the chemistry of zinc, cadmium and mercury in sulfur-rich and selenium-rich coordination environments. For example, the tridentate [Tm(R)] ligand provides an [S(3)] donor array that is of use for mimicking aspects of zinc enzymes and proteins that have sulfur-rich active sites, such as the Ada DNA repair protein. With respect to mercury, an interesting application of the [Tm(Bu(t) )] ligand is the synthesis of the mercury alkyl compounds [Tm(Bu(t) )]HgR (R = Me, Et) that react with PhSH to yield [Tm(Bu(t) )]HgSPh and RH, a reaction that emulates mercury detoxification by the organomercurial lyase, MerB. In addition to the tridentate [Tm(R)] and [Tse(R)] ligands, applications of the bidentate counterparts, [Bm(R)] and [Bse(R)] are also described.

Synthesis and structural characterization of tris(2-seleno-1-mesitylimidazolyl) hydroborato complexes: a new type of strongly electron donating tripodal selenium ligand

A new tripodal ligand that features three selenium donors, namely the tris(2-seleno-1-mesitylimidazolyl)hydroborato ligand, [Tse(Mes)], has been constructed via the reaction of KBH(4) with 1-mesitylimidazole-2-selone; comparison of the IR spectroscopic data of [Tse(Mes)]Re(CO)(3) with those of a variety of related LRe(CO)(3) complexes demonstrates that the [Tse(Mes)] ligand is more strongly electron donating than Cp, Cp*, [Tp], [Tp(Me(2))] and [Tm(Mes)] ligands.

Zn−OH2 and Zn−OH Complexes with Hydroborate-Derived Tripod Ligands: A Comprehensive Study

The complete array of those hydrotris(pyrazolyl/thioimidazolyl)borate ligands that were developed and used in the author's laboratories, with N3, N2S, NS2, and S3 donor sets, was scanned for their ability to form Zn-OH2 and Zn-OH complexes. The coordination motifs found were Zn-OH2, Zn-OH, Zn-OH-Zn, and Zn-O2H3-Zn. Of these, the well-established Zn-OH motif was complemented with novel species bearing N3, NS2, and S3 tripods. The Zn-OH2 motif was observed only with pyrazolylborate ligands and only in unusual situations with coordination numbers higher than 4 for zinc. The new Zn-OH-Zn motif was realized for three different pyrazolylborates, for one NS2 tripod, and for two S3 tripods. Finally, it was verified that the Zn-O2H3-Zn motif again occurs only with pyrazolylborate ligands. The new complexes were identified by a total of 11 structure determinations.

Thiolate exchange in [TmR]ZnSR' complexes and relevance to the mechanisms of thiolate alkylation reactions involving zinc enzymes and proteins

The zinc and cadmium thiolate complexes [TmBut]MSCH2C(O)N(H)Ph (M = Zn, Cd) may be obtained via treatment of the respective methyl complex [TmBut]MMe with PhN(H)C(O)CH2SH. The molecular structure of [TmBut]ZnSCH2C(O)N(H)Ph has been determined by X-ray diffraction, thereby demonstrating the presence of an intramolecular N-H S hydrogen bond between the amide N-H group and thiolate sulfur atom. [TmBut]ZnSCH2C(O)N(H)Ph mimics the function of the Ada DNA repair protein by undergoing alkylation with MeI to give [TmBut]ZnI and MeSCH2C(O)N(H)Ph. A series of crossover experiments and 1H NMR magnetization transfer studies establish that thiolate exchange between [TmR]ZnSR' derivatives is facile in this system, an observation that supports the previous suggestion that the alkylation of [TmPh]ZnSCH2C(O)N(H)Ph by MeI may proceed via a sequence that involves dissociation of [PhN(H)C(O)CH2S]-.

Bis(pyrazolyl)(thioimidazolyl)borate Ligands: The Missing Member in the N3···S3 Scorpionate Series

The anionic bis(pyrazolyl)(thioimidazolyl)borate ligands BpMt(R) with R = tert-butyl and isopropyl were obtained as their potassium salts by reacting potassium tris(pyrazolyl)borate with the corresponding thioimidazoles in the melt at 150 degrees C. They were applied to form some tetrahedral zinc complexes and identified by the crystal structures of (BpMt(t-Bu))ZnCl and (BpMt(i-Pr))Zn-SC(6)H(4)-p-Cl.