Monohalide Complexes Research Articles

One Electron Changes Everything: Synthesis, Characterization, and Reactivity Studies of [Re(NCCH3)6]3.

Oxidation of [Re(NCCH3)6]2+ with the thianthrene radical cation results in the formation of [Re(NCCH3)6]3+, one of the very rare cases of a fully solvated +3 complex. It was fully characterized by spectroscopy and X-ray structure analysis. In contrast to its reduced analogue, [Re(NCCH3)6]3+ exhibits a much faster CH3CN exchange. Hence, substitution reactions proceed at 20 °C within minutes. Its potential as a versatile precursor for ReIII chemistry was examined with a series of substitution reactions. The more lipophilic analogue [Re(NCPh)6]3+ was synthesized by nitrile exchange in benzonitrile (NCPh). The Re(II) analogue of [Re(NCPh)6]3+, [Re(NCPh)6]2+, forms by AgI-mediated oxidation of in situ formed [Re(η6-C6H6)(NCPh3)3]+ in NCPh. The same synthetic strategy is feasible for the synthesis of [Re(NCCH3)6]2+ as well. [Re(NCCH3)6]3+ reacts with 1,4,7-trithiacyclononane (C6H12S3) to yield sevenfold-coordinated [Re(κ3-C6H12S3)2(NCCH3)]3+. The reaction of [Re(NCCH3)6]3+ with 1 equiv of (NBu4)X produces the ReIII monohalide complexes [ReX(NCCH3)5]2+ (X = Cl, Br, I). Mixed ReIII dihalides (trans-[ReXY(NCCH3)4]+) were obtained by treating [ReX(NCCH3)5]2+ with a second equivalent of (NBu4)Y (if X = Cl, Y = Br, I; if X = Br, Y = I). Because of this fast CH3CN exchange, [Re(NCCH3)6]3+ is a very suitable precursor for new ReIII complexes.

Synthesis and electronic structure of a series of first-row transition-metal pyrazine(diimine) complexes in two oxidation states

The synthesis, molecular and electronic structures, and redox properties of pyrazine(diimine) (PzDI) metal dihalide complexes (DiPPPZDI)MX2 (DiPP = 2,6-diisopropylphenyl; M = Mn, Fe, Co, Ni; X = Cl, Br) are presented and compared. The dihalide complexes are reduced to (DiPPPZDI)MX monohalide complexes, and the role of ligand redox non-innocence in the electronic structure of the reduced compounds is examined and compared to related pyridine(diimine) (PDI) compounds. The compounds were characterized by NMR spectroscopy, UV-VIS spectroscopy, cyclic voltammetry, X-ray crystallography, and Evans method magnetometry. Similar to previously reported PDI compounds, the reduced monohalide complexes are best described as divalent metal centers coupled to a reduced radical anion ligand. Structural and computational analyses show that the ligand in (DiPPPZDI)MX is reduced by one electron and bears significant spin density. Comparison across the series of first-row transition metals shows increasing metal-ligand covalency for the later metals. These results may be useful in the design of modified heteroarene(diimine) ligands for first-row transition-metal catalysis in the future.

Aminotroponiminatogermaacid Halides with a Ge(E)X Moiety (E = S, Se; X = F, Cl)

Fluorination of aminotroponiminate (ATI) ligand-stabilized germylene monochloride [(t-Bu)(2)ATI]GeCl (1) with CsF gave the aminotroponiminatogermylene monofluoride [(t-Bu)(2)ATI]GeF (2). Oxidative addition reaction of compound 2 with elemental sulfur and selenium led to isolation of the corresponding germathioacid fluoride [(t-Bu)(2)ATI]Ge(S)F (3) and germaselenoacid fluoride [(t-Bu)(2)ATI]Ge(Se)F (4), respectively. Similarly, reaction of aminotroponiminatogermylene monochloride [(i-Bu)(2)ATI]GeCl (9) with elemental sulfur and selenium gave the aminotroponiminatogermathioacid chloride [(i-Bu)(2)ATI]Ge(S)Cl (11) and aminotroponiminatogermaselenoacid chloride [(i-Bu)(2)ATI]Ge(Se)Cl (12), respectively. Compound 9 has been prepared through a multistep synthetic route starting from 2-(tosyloxy)tropone 5. All compounds (2-4 and 6-12) were characterized through the multinuclear NMR spectroscopy, and single-crystal X-ray diffraction studies were performed on compounds 2, 4, and 8-12. The germaselenoacid halide complexes 4 and 12 showed doublet (-142.37 ppm) and singlet (-213.13 ppm) resonances in their (77)Se NMR spectra, respectively. Germylene monohalide complexes 2 and 9 have a germanium center in distorted trigonal pyramidal geometry, whereas a distorted tetrahedral geometry is seen around the germanium center in germaacid halide complexes 4, 11, and 12. The length of the Ge═E bond in germathioacid chloride (11) and germaselenoacid halide (4 and 12) complexes is 2.065(1) and 2.194(av) Å, respectively. Theoretical studies (based on the DFT methods) on complexes 4, 11, and 12 reveal the nature of the Ge═E multiple bond in these germaacid halide complexes with computed Wiberg bond indices (WBI) being 1.480, 1.508, and 1.541, respectively.

Reactivity of phosphonodithioato-dppt NiII mixed ligand complexes with halogens: first example of a metal-coordinating tribromide anion

The first example of a metal complex containing a tribromide anion is presented and characterised by X-ray diffraction. Hybrid DFT calculations were used to investigate the nature of the bond in coordinating trihalides and the differences with the corresponding mono-halide complexes.

Intramolecular C–H Bond Activation by Lanthanoid Complexes Bearing a Bulky Aminopyridinato Ligand

AbstractThe present work is aimed towards the synthesis of C–H activation products of various group 3 and lanthanoid metals bearing a bulky aminopyridinato ligand, (2,6‐diisopropylphenyl)[6‐(2,6‐dimethylphenyl)pyridin‐2‐yl]amine (1, Ap′H). Deprotonation of1using KH leads to polymeric [Ap′K]n(2), which undergoes clean salt metathesis reaction with MX3[M = Sc, Nd and Sm, and X = Cl or M = La and X = Br] forming mono thf adducts [Ap′2ScCl(thf)] (3), [Ap′2LaBr(thf)] (4), [Ap′2NdCl(thf)] (5), and [Ap′2SmCl(thf)] (6). However, reacting2with LuCl3leads to mono‐ as well as bis(aminopyridinato)lutetium complexes [Ap′LuCl2(thf)2] (7) and [Ap′2LuCl(thf)] (8), respectively, while the analogous reaction with LaCl3at 50 °C produces the tris(aminopyridinato)lanthanum complex [Ap′3La] (9). For the selective synthesis of8in good yield amine elimination route was adopted. X‐ray diffraction studies revealed a distorted octahedral coordination for the bis(aminopyridinato) complexes3,4and6, despite the differences in their ionic radii. Alkylation of the bis(aminopyridinato) monohalide complexes with equimolar amounts of LiCH2SiMe3in hexane allowed the isolation of the corresponding alkyl derivatives. For the smaller metals like Sc and Lu affording [Ap′2ScCH2SiMe3(thf)] (10) and [Ap′2LuCH2SiMe3(thf)] (11), respectively. However, lanthanoids with large ionic radii such as La and Nd resulted in the formation of methyl group C–H bond activation products [Ap′(Ap′–H)La(thf)2] (12) and [Ap′(Ap′–H)Nd(thf)] (13), respectively. Most likely an alkyl species was formed which then undergoes intramolecular C–H activation and C–H activation runs fast with regard to the rate of alkyl complex formation. The alkylation of6(Sm) with LiCH2SiMe3did not give a clear product. The reaction of11with PhSiH3(Ph = phenyl) led via intramolecular C–H bond activation to [Ap′(Ap′–H)Lu(thf)] (14). In this case most likely a hydride species was formed which then undergoes rapid C–H activation. The alkyl complex10(Sc) did not react with PhSiH3. The molecular structures of11,12and13have been confirmed by X‐ray crystal structure analysis.

Chelation-Assisted Carbon-Halogen Bond Activation by a Rhodium(I) Complex

Chelation-assisted activation of C-X bonds (X = Cl, Br, and I) took place in the reaction of [Rh(PPh(3))(2)(acetone)(2)](+) and 2-(2-halophenyl)pyridine or 10-halobenzo[h]quinoline. A series of 16-electron five-coordinate cationic rhodium(III) monohalide complexes was synthesized at room temperature. Neutral octahedral rhodium(III) dihalide complexes were obtained when the corresponding cationic monohalide complexes were further heated in acetone. Rhodium and iridium diiodides with these cyclometalation motifs could be alternatively synthesized from the reaction of the corresponding cyclometalated hydride complexes and I(2). X-ray crystal structures of representative monohalide and dihalide complexes are reported. Octahedral rhodium(III) dihalide complexes are active catalysts for the dimerization of terminal alkynes, while 16-electron cationic rhodium(III) monohalides are inactive.

Syntheses and Structural Characterizations of Vanada- and Niobatricarbadecaboranyl Monohalide Complexes

The syntheses and structural characterizations of the vanadium and niobium monohalide tricarbadecaboranyl complexes 1-(η5-C5H5)-1-Br-2-Ph-1,2,3,4-VC3B7H9 (1), [1-(η5-C5H5)-1,1‘-μ-Cl-2-Ph-closo-1,2,3,4-NbC3B7H9]2 (2), [1-(η5-C5H5)-1,1‘-μ-Cl-2-Me-closo-1,2,3,4-NbC3B7H9]2 (3), and commo-Nb-1-Cl-(4-Me-1,2,3,4-NbC3B7H9)2 (4) are described. X-ray crystallographic studies of 1, 3, and 4 confirmed that they are monohalide complexes in which the V3+ and Nb3+ ions are sandwiched between cyclopentadienyl and/or tricarbadecaboranyl monoanions. These compounds are analogues of (η5-C5H5)2VX and (η5-C5H5)2NbX but, unlike their metallocene counterparts, are air- and water-stable, further illustrating the unique ability of the tricarbadecaboranyl ligand to stabilize complexes with the metals in lower oxidation states.

Cytotoxicity and mode of action of vanada- and niobatricarbadecaboranyl monohalide complexes in human HL-60 promyelocytic leukemia cells

Vanada- and niobatricarbadecaboranyl monohalide complexes proved to be potent cytotoxic agents against murine and human leukemia and lymphoma growth as well as HeLa suspended uterine carcinoma. The vanada complex reduced the growth of KB nasopharynx, Hepe liver, HCT-8 ileum and 1-A9 ovary solid carcinomas. A mode of action study in human HL-60 promyelocytic leukemia cells showed that DNA and purine de novo syntheses were significantly inhibited with suppression of the regulatory enzymes activities of DNA polymerase α and PRPP-amido transferase. There was moderate inhibition of RNA synthesis and m-RNA polymerase activity. These complexes did not inhibit human topoisomerase I or II activity, although the niobium complex nicked the DNA. The complexes did activate caspases 3, 6 and 9 which are linked to apoptosis programmed cell death. These vanada- and niobatricarbadecaboranyl monohalide complexes appear to be more specific in their effects on leukemia cell metabolism than other sandwich complexes which have broad effects on multiple enzymes.

Formation and reactivity of paramagnetic organometallic nickel complexes of 21-oxa- and 21-selenaporphyrins— 1H NMR and EPR investigations

Addition of aryl Grignard reagents to a toluene solution of nickel(II) monohalide complexes of 5.20-bis( p-tolyl)-10.15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5.20-diphenyl-10.15-bis( p-tolyl)-21-selenaporphyrin (SeDPDTPH) at 203 K resulted in formation of paramagnetic σ-aryl nickel(II) derivatives which were identified and characterized by means of 1H NMR. The coordination of the aryl ligand has been unambiguously proven by the unique downfield pattern of the corresponding resonances. The ( σ-aryl)nickel(II) derivatives are in the high-spin electronic state: (d xv ) 2(d vz ) 2(d vz ) 2(d z 2 ) 2(d z 2 ) 1(d x 2 y 2 ) 1. A homolytic cleavage of the Ni 11-C bond has been determined for (ODTDPP)Ni II(Ar) and (SeDPDTP)Ni II(Ar) in toluene with formation of low-valent nickel species: (ODTDPP)Ni and (SeDPDTP)Ni. One-electron reduction of (SeDPDTP)Ni IICl to generate (SeDPDTP)Ni has been investigated by means of EPR, involving 61Ni isotope enrichment and spectral simulations. A considerable increase in metal d-orbital contribution to the singly occupied molecular orbital has been observed upon coordination of 1-methylimidazole to (SeDPDTP)Ni.

New Syntheses of Cp*2Th(Ph)2 and Cp*2Th(Me)(aryl) Derivatives

The complex Cp*{sub 2}ThPh{sub 2} (1) is known to be a useful precursor in elimination reactions to yield transient benzyne adduct. This complex may be prepared in improved yield from the reaction of PhMgBr with Cp*{sub 2}ThCl{sub 2} in the presence of p-dioxane. Ortho-substituted precursors Cp*{sub 2}Th(Me)(o-MeOC{sub 6}H{sub 4}) (2), Cp*{sub 2}TH(Me)(o-MeC{sub 6}H{sub -4}) (3), and Cp*{sub 2} Th(Me)(2,5-Me{sub 2}C{sub 6}H{sub 3}) (4) are reported for the first time, having been prepared in one-pot procedures using a similar method. The respective intermediate monohalide complexes have also been prepared at room temperature. The tolyl and xylyl derivatives exist as pairs of rotamers in solution, demonstrating the significant steric constraints imposed on this type of complex by ortho substituents. Halide exchange is observed in the preparation of the aryl-halide complexes when arylmagnesium bromides are employed. The extent of this exchange is influenced by the addition of p-dioxane to reaction mixtures. 22 refs.

Paramagnetic .sigma.-bonded phenylnickel(II) macrocyclic systems. Nuclear magnetic resonance identification of (.sigma.-phenyl)nickel(II) 5,20-diphenyl-10,15-bis(p-tolyl)-21-thiaporphyrin and (.sigma.-phenyl)nickel(II) N-methyltetraphenylporphyrin

Addition of the phenyl Grignard reagent to toluene or dichloromethane solutions of nickel(II) monohalide complexes of 5,20-diphenyl-10,15-bis(p-tolyl)-21-thiaporphyrin (SDPDTPH) and N-methyltetraphenylporphyrin (NCH 3 TPPH) at -10 o C resulted in formation of paramagnetic (σ-phenyl)nickel(II) derivatives which were characterized by means of 1 H NMR and 2 H NMR.

Nuclear magnetic resonance study of the molecular and electronic structure of nickel(II) tetraphenyl-21-thiaporphyrins

The proton NMR spectra or high-spin (S=1) nickel(II) monohalide complexes or tetraphenyl-21-thiaporphyrin have been recorded and assigned by means or specific deuteration, methyl substitution, and line width consideration. The characteristic pattern of pyrrole (downfield) and thiophene resonances (upfield) has been estahlished. The specific assignment of pyrrole resonances has been achieved by NOE measurements. Replacement of chloride by perchlorate results in formation of low-spin diamagnetic complex Ni II (STPP)ClO 4 in chlorororm

Variation in stability of monohalide complexes and some properties of the solvated cations within the Mn 2+-Zn 2+ series

The stability of the monohalide complexes of the divalent first-row transition metal cations in water as well as in other donor solvents follows the sequence: MnX + > FeX + > CoX + > NiX + < CuX + > ZnX +. Moreover, some of the properties of the M(solvent) 6 2+ solvo-cations may be rationalized in terms of the same series. The observed sequence is opposite to that known as the Irving—Williams series.

ChemInform Abstract: Stability Sequences of Cadmium(II) and Zinc(II) Monohalide Complexes in Alcohols and Binary Solvent Mixtures Containing Methanol, Dimethylsulfoxide, Acetonitrile, and Water.

Abstract Classification schemes, such as Ahrland's ‘a’-‘b’ organization of ligand acceptors, are important to the systemization of coordination chemistry. Aside from Ahrland's extensive studies in dimethylsulfoxide, little is known about the effects of solvent choice upon acceptor classification. Furthermore, there is a dearth of information about the behavior of fluoride complexes under non-aqueous conditions due to the lack of a suitable measurement technique for such studies. This renders previous halide studies incomplete, since the hardest ligand has been systematically excluded. We report the results of potentiometric studies of the stabilities of monohalide complexes (F−, Cl−, Br−) of cadmium(II) and zinc(II) in methanol, ethanol and binary solvent mixtures such as methanol/water, dimethylsulfoxide/ methanol, dimethylsulfoxide/water and acetonitrile/ water. This data provides important new information related to non-aqueous behavior of these d10 acceptors, particularly with respect to solvent-related stability sequence changes previously reported for cadmium(II).

Stability sequences of cadmium(II) and zinc(II) monohalide complexes in alcohols and binary solvent mixtures containing methanol, dimethylsulfoxide, acetonitrile and water

Classification schemes, such as Ahrland's ‘a’-‘b’ organization of ligand acceptors, are important to the systemization of coordination chemistry. Aside from Ahrland's extensive studies in dimethylsulfoxide, little is known about the effects of solvent choice upon acceptor classification. Furthermore, there is a dearth of information about the behavior of fluoride complexes under non-aqueous conditions due to the lack of a suitable measurement technique for such studies. This renders previous halide studies incomplete, since the hardest ligand has been systematically excluded. We report the results of potentiometric studies of the stabilities of monohalide complexes (F −, Cl −, Br −) of cadmium(II) and zinc(II) in methanol, ethanol and binary solvent mixtures such as methanol/water, dimethylsulfoxide/ methanol, dimethylsulfoxide/water and acetonitrile/ water. This data provides important new information related to non-aqueous behavior of these d 10 acceptors, particularly with respect to solvent-related stability sequence changes previously reported for cadmium(II).

Raman spectra of monohalide complexes of mercury (II) in aqueous solution

Raman spectra of monohalide complexes of mercury (II) in aqueous solution