First structurally characterized silver(I) derivatives with nonfluorinated beta-diketones

Synthetic, spectroscopic, and single-crystal X-ray structural studies of diverse complexes of silver(I) acylpyrazolonate salts AgQ(R') (QH = 1-phenyl-3-methyl-4-R'(C=O)-pyrazol-5-one; Q(1), R = Ph; Q(2), R' = CF(3); Q(3), R' = Me) with neutral ligands L = unidentate PR(3) (R = Ph, o-tolyl, cyclohexyl) and Hmimt (1-methyl-2-mercaptoimidazole) and bidentate dppe (Ph(2)P(CH(2))(2)PPh(2)) and trimen (N,N,N'-trimethylethylenediamine) define the donor capability of the anionic Q(R') ligand in a variety of roles. In the free ligand Q(3)H (which crystallizes in the monoclinic space group C2/c (no. 15), Z = 8, unit cell parameters a = 17.981(6) A, b = 5.0641(4) A, c = 24.271(6) A, and beta = 99.67(2)), the acidic OH group hydrogen-bonds intramolecularly to the adjacent pyrazolone oxygen, i.e., the two oxygen atoms are cis, true of the other Q(R') species structurally characterized here in their anionic complexed forms, in which they chelate the silver in the usual beta-diketonate manner, but not of the free anion, found in the array [Ag(Ph(3)P)(Hmimt)(2)](Q(1)) (triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 11.553(1) A, b = 11.943(1) A, c = 15.479(2) A, alpha = 74.829(2), beta = 76.094(2), and gamma = 78.185(2)), or [Ag(trimen)Q(1)] (monoclinic space group P2(1)/c (no. 14), Z = 4, unit cell parameters a = 7.982(1) A, b = 12.299(2) A, c = 21.507(3) A, and beta = 95.119(3)), which forms an infinite one-dimensional polymer string, Q(1) linking successive silver(I) atoms by coordination by way of the unsubstituted nitrogen and the pyrazolonate oxygen. In all [Ag(R(3)P)(2)(chelate-Q(1))] (R = Ph, Cy) complexes, P(2)Ag(O,O') arrays are found (R = Ph, monoclinic space group C2/c (no. 15), Z = 8, unit cell parameters a = 16.193(8) A, b = 13.859(7) A, c = 39.306(7) A, and beta = 100.02(3); R = Cy, triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 10.4655(9) A, b = 12.079(1) A, c = 22.804(2) A, alpha = 104.872(2), beta = 95.180(2), and gamma = 104.144(2)), also true of [Ag(Ph(3)P)(2)(O,O'-Q(2))] (triclinic space group P(-)1(no. 2), Z = 2, unit cell parameters a = 10.672(2) A, b = 10.710(2) A, c = 18.713(3) A, alpha = 87.573(2), beta = 80.972(2), and gamma = 81.734(2)), whereas [Ag(o-tol(3)P)Q(1)] (monoclinic space group P2(1)/c (no. 14), Z = 2 dimers, unit cell parameters a = 11.8221(6) A, b = 13.2601(6) A, c = 20.5141(10) A, and beta = 91.758(1)) exists as a dinuclear species containing two AgO(2)NP units where the acylpyrazolonate is coordinated in a bridging O,O'-Q-Nfashion. Silver atoms are four-coordinate in all except the Hmimt complex.     

A structurally characterized nitrous oxide complex of vanadium

Nitrous oxide (N(2)O), a widespread greenhouse gas, is a thermodynamically potent and environmentally green oxidant that is an attractive target for activation by metal centers. However, N(2)O remains underutilized owing to its high kinetic stability, and the poor ligand properties of this molecule have made well-characterized metal-N(2)O complexes a rarity. We now report a vanadium-pyrrolide system that reversibly binds N(2)O at room temperature and provide the first single-crystal X-ray structure of such a complex. Further characterization by vibrational spectroscopy and DFT calculations strongly favor assignment as a linear, N-bound metal-N(2)O complex.     

The first structurally characterized nitrosyl heme thiolate model complex

The NO ligand in the formally {FeNO}6 compound [Fe(oep)(NO)(thiolate)] is bent, and does not impart a significant structural trans effect to the Fe-S bond.     

Charge-transfer spectra of structurally characterized mixed-valence thiolate-bridged Cu(I)/Cu(II) cluster complexes

A series of Cu(II) and Cu(I)/Cu(II) complexes containing the cis-N(amine)(2)S(thiolate)(2) copper complex rac-2 has been synthesized to provide a basis for understanding the charge-transfer spectra of mixed-valence thiolate-bridged Cu(I)/Cu(II) complexes. In combination with Cu(Me(2)-13-N(4)ane), rac-2 yields a monobridged dinuclear homovalent adduct, rac-5, while reaction with CuCl yields the mixed-valance pentanuclear complex rac-6. In the presence of Cu(II)(acac)(2), chiral R,R-1 reacts to form a mixed-valence pentanuclear cation R,R-7. rac-6 exhibits a relatively short Cu(I). Cu(II) contact [2.8231(9) A] and associated structural features that suggest the presence of a weak Cu(I).Cu(II) interaction in a valence-trapped system. Additional structural features in rac-6 and R,R-7 include singly and doubly bridging thiolates, three- and four-coordinated Cu(I) ions, and varying Cu(I) ligand sets. These features extend the types and complexities of electronic absorptions significantly. Spectra of rac-6 and R,R-7 exhibit multiple overlapping absorptions over the entire visible and ultraviolet spectral regions studied, consonant with these observations. Trends resulting from variations in structure type and oxidation state permit a first approach toward developing a detailed assignment of the individual ligand Rydberg, LF, LMCT, MLCT, and possible MMCT absorptions in these complexes.     

Synthesis, structural and computational investigations of UO2I42-: a structurally characterized U(VI)-I anion

The synthesis and characterization of (Ph(4)P)(2)UO(2)I(4).2NCCH(3) is reported. The UO(2)I(4)(2-) anion is not only the first unambiguously characterized anion containing a uranium(VI)-iodine bond, but is also the last member of the UO(2)X(4)(2-) (X = Cl, Br, I) series to be unambiguously identified and structurally characterized, in contrast to salts of the UO(2)Cl(4)(2-) and UO(2)Br(4)(2-) anions, which have all been thoroughly investigated and structurally characterized. (Ph(4)P)(2)UO(2)I(4).2NCCH(3) was characterized using IR, Raman, (1)H, (13)C, and (31)P NMR spectroscopy as well as X-ray diffraction. In addition, a computational investigation of the UO(2)I(4)(2-) anion was undertaken and compared with the experimentally observed structure.     

Addition of dioxygen to an N4S(thiolate) iron(II) cysteine dioxygenase model gives a structurally characterized sulfinato-iron(II) complex

The non-heme iron enzyme cysteine dioxygenase (CDO) catalyzes the S-oxygenation of cysteine by O(2) to give cysteine sulfinic acid. The synthesis of a new structural and functional model of the cysteine-bound CDO active site, [Fe(II)(N3PyS)(CH(3)CN)]BF(4) (1) is reported. This complex was prepared with a new facially chelating 4N/1S(thiolate) pentadentate ligand. The reaction of 1 with O(2) resulted in oxygenation of the thiolate donor to afford the doubly oxygenated sulfinate product [Fe(II)(N3PySO(2))(NCS)] (2), which was crystallographically characterized. The thiolate donor provided by the new N3PyS ligand has a dramatic influence on the redox potential and O(2) reactivity of this Fe(II) model complex.     

A structurally characterized Ni-Al methyl-bridged complex with catalytic ethylene oligomerization activity

A bimetallic Ni-Al (2.5087(15) A) complex with an agostic alpha-C-H, [eta-C5H4CH=N(C6F5)]Fe[eta-C5H4PPh2]Ni(AlMe3), has been isolated and crystallographically established. The complex is active towards ethylene oligomerization/polymerization under moderate conditions.     

The first structurally characterized nonorganometallic titanium(III) alkoxo-bridged dinuclear complexes

The reaction of [Ti4(OMe)14Cl2] (1) with an excess of AlMe3 gave the cocrystallite [Ti2(mu-OMe)2(mu-Cl)Cl3(thf)3].[Ti2(mu-OMe)3Cl3(thf)3] (2.3) species in a 1:1 ratio. Similar to 2, [Ti2(mu-OEt)2(mu-Cl)Cl3-(thf)3] (4) was obtained in the reaction of an equimolar mixture of TiCl4 and Ti(OEt)4 with Al/AlMe3. The short distance [2.543(1)av A in 2.3 and 2.599(1) A in 4] between "Ti(+3)" atoms, their diamagnetism, and ELF analysis indicate the presence of a Ti-Ti bond.     

A novel organometallic columnar complex containing endohedral silver(I)-ethynediyl binding and exterior silver(I)-aromatic interaction

Unprecedented eta 3 pi-donor behavior of the benzyltrimethy-lammonium ion is observed in the polymeric silver(I) complex [(PhCH2NMe3)Ag7(C2)(CF3CO2)6]n that comprises a columnar backbone constructed from the fusion of Ag8 square antiprisms each enclosing an acetylide dianion.     

Solution study of a structurally characterized monoalkoxo-bound monooxo-vanadium(V) complex: spontaneous generation of the corresponding oxobridged divanadium(V,V) complex and its electroreduction to a mixed-valence species in solution

An interesting transformation of a structurally characterized monooxoalkoxovanadium(V) complex [VO(OEt)L] (LH 2 = a dibasic tridentate ONO donor ligand) in solution leading to the formation of the corresponding monooxobridged divanadium(V,V) complex (VOL) 2O is reported. This binuclear species in solution is adequately characterized by elemental analysis, measurement of conductance (in solution), various spectroscopic (UV-vis, IR, NMR, and mass spectrometry) techiniques and by cyclic voltammetry. The corresponding mixed-valence vanadium(IV,V) species has been generated in CH 3CN solution by controlled potential electrolysis of (VOL) 2O. This mixed-valence species is identified and studied by EPR technique (at room temperature and at liquid nitrogen temperature) and also by UV-vis spectroscopy. This study may be regarded as a general method of obtaining monooxo-bridged binuclear vanadium(V,V) species from the corresponding mononuclear monooxoalkoxovanadium(V) complexes of some selected dibasic tridentate ONO chelating ligands, which can be utilized as the precursor of monooxobridged divanadium(IV,V) mixed-valence species in solution obtainable by controlled potential electrolysis.     

The first structurally characterized N-heterocyclic carbene complex with a ligand derived from pyrimidine

Oxidative addition of N-alkyl-2-halopyrimidinium cations to [Pd(PPh₃)₄] gives straightforward access to the cationic complexes [(PPh₃)₂(NHC)PdX]BF₄ (3a,b) with pyrimidine-derived NHC-ligands. The new complexes were fully characterized including X-ray crystallography.     

Tricarbonylmanganese(I) derivatives of [Di(pyrazolyl)(2-pyridyl)methyl]aryl scorpionates

The cobalt(II) chloride catalyzed Peterson rearrangement reactions between sulfinyldi-(pyrazolyl) and aryl(pyridyl)methanone derivatives yield di(pyrazolyl)(pyridyl)hetero-scorpionate ligands. Reaction of these ligands with Mn(CO)₅Br in the presence of a silver salt produces the monometallic complexes {[κ³-PhC(pz)₂(2-py)]Mn(CO)₃}(O₃SCF₃) (1a), {[κ³-PhC(pz)₂(2-py)]Mn(CO)₃}(PF₆) (1b), {[κ³-PhC(^4-Mepz)₂(2-py)]Mn(CO)₃}(PF₆) (2), {[κ³-p-BrC₆H₄C(pz)₂(2-py)]Mn(CO)₃}(PF₆) (3), and the bimetallic complexes [(CO)₃Mn{m-C₆H₄[C(pz)₂(2-py)]₂}Mn(CO)₃](BF₄)₂ (5a) and {m-C₆H₄[C(pz)₂(2-py)Mn(CO)₃]₂}(PF₆)₂ (5b) (pz = pyrazolyl ring, py = pyridyl ring). These octahedral manganese complexes show interesting structural diversity, with the complexes being organized in the solid state into complex supramolecular structures by an array of non-covalent forces.     

A readily-prepared and efficient solid-supported scavenger for molybdenum alkoxides and a structurally characterized model complex

A very effective solid support for the removal of molybdenum-based metathesis catalysts can be prepared by placing a salicylimine on a polystyrene support. The resin is produced by treating Merrifield’s resin with H₂NBuⁿ, 4-chloromethylsalicylaldehyde, and p-toluidine in succession. The final resin had an identifiable CN stretch in the IR and a resonance assigned to the HCN hydrogen was found by MAS ¹H NMR of the swelled resin. Solutions of Mo[C(H)CMe₂Ph](NAr)(OBu^t_F6)₂ (Mo_F6) and Mo[C(H)CMe₂Ph](NAr)(OAd)₂ (Mo_Ad), where Ar = 2,6-diisopropylphenyl and Ad = 1-adamantyl, were treated with the scavenger, which reduced the remaining molybdenum concentration as examined by ICP-MS to 30-50 ppb. Catalyst was also scavenged from ring-closing metathesis of diethyl diallylmalonate by Mo_F6; the decrease in molybdenum concentration on addition of scavenger followed first order kinetics with initial and final concentrations of 54 000 and 15 ppb, respectively. We also prepared a model system where a soluble salicylimine (H-DIB) was reacted with Mo[C(H)CMe₂Ph](NAr)(OAd)₂ to produce Mo[C(H)CMe₂Ph](NAr)(DIB)₂, which was structurally characterized.     

Photocontrolled DNA binding of a receptor-targeted organometallic ruthenium(II) complex

A photoactivated ruthenium(II) arene complex has been conjugated to two receptor-binding peptides, a dicarba analogue of octreotide and the Arg-Gly-Asp (RGD) tripeptide. These peptides can act as "tumor-targeting devices" since their receptors are overexpressed on the membranes of tumor cells. Both ruthenium-peptide conjugates are stable in aqueous solution in the dark, but upon irradiation with visible light, the pyridyl-derivatized peptides were selectively photodissociated from the ruthenium complex, as inferred by UV-vis and NMR spectroscopy. Importantly, the reactive aqua species generated from the conjugates, [(η(6)-p-cym)Ru(bpm)(H(2)O)](2+), reacted with the model DNA nucleobase 9-ethylguanine as well as with guanines of two DNA sequences, (5')dCATGGCT and (5')dAGCCATG. Interestingly, when irradiation was performed in the presence of the oligonucleotides, a new ruthenium adduct involving both guanines was formed as a consequence of the photodriven loss of p-cymene from the two monofunctional adducts. The release of the arene ligand and the formation of a ruthenated product with a multidentate binding mode might have important implications for the biological activity of such photoactivated ruthenium(II) arene complexes. Finally, photoreactions with the peptide-oligonucleotide hybrid, Phac-His-Gly-Met-linker-p(5')dCATGGCT, also led to arene release and to guanine adducts, including a GG chelate. The lack of interaction with the peptide fragment confirms the preference of such organometallic ruthenium(II) complexes for guanine over other potential biological ligands, such as histidine or methionine amino acids.     

Insertion of Ga(DDP) into the Au-Cl bond of (PPh3)AuCl: a first structurally characterized Au-Ga bond

The reaction of (PPh(3))AuCl with the low valent gallium compound Ga(DDP) (DDP = 2-((2,6-diisopropylphenyl)amino-4-((2,6-diiso-propylphenyl)imino)-2-pentene) yields the insertion products [{Ga(DDP)}Au{Ga(DDP)Cl}] (1) and [(PPh(3))Au{Ga(DDP)Cl}] (2), the first examples of molecular compounds with Au-Ga bonds.