New κ-PNN′- and κ-PNN′O-polydentate ligands: Synthesis, coordination and structural studies

The three-step synthesis of new mixed P/N/N′/O-donor ligands C₆H₃(OH){2-NHC(O)CH₂NCHC₆H₄PPh₂}(4-CH₃) 3a·HH and C₆H₄(OH){3-NHC(O)CH₂NCHC₆H₄PPh₂} 3b·HH, by Schiff base condensation of the 1° amines C₆H₃(OH){2-NHC(O)CH₂NH₂}(4-CH₃) 2a or C₆H₄(OH){3-NHC(O)CH₂NH₂} 2b with C₆H₄(CHO)(2-PPh₂) in refluxing EtOH, is described. Reaction of 1 equiv. of 3a·HH or 3b·HH with MCl₂(cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the κ²-PN-chelate complexes MCl₂(3a·HH) (M = Pd 4a; M = Pt 4b) and MCl₂(3b·HH) (M = Pt 4c). The dichlorometal(II) complexes 4d and 4e, bearing instead a pendant 4-phenolic group, were similarly prepared (in >90% yield). Chloro-bridge cleavage of [Pd(μ-Cl)(η³-C₃H₅)]₂ with 3a·HH or 3b·HH gave the monocationic κ²-PN-chelate complexes [Pd(η³-C₃H₅)(3a·HH)]Cl 5a or [Pd(η³-C₃H₅)(3b·HH)]Cl 5b, respectively. Elimination of cod, and single CH₃ protonation, from Pt(CH₃)₂(cod) upon reaction with 1 equiv. of 3a·HH or 3b·HH in C₇H₈ at room temperature afforded the neutral complexes C₆H₃(OH){2-NC(O)CH₂NCHC₆H₄PPh₂Pt(CH₃)}(4-CH₃) 6a and C₆H₄(OH){3-NC(O)CH₂NCHC₆H₄PPh₂Pt(CH₃)} 6b, respectively bearing a monoanionic (3a·H⁻ or 3b·H⁻) κ³-PNN′-tridentate ligand. Amide and phenol deprotonation were readily achieved, using KO^tBu as base, to give high yields of the κ⁴-PNN′O-tetradentate complexes C₆H₃(O){2-NC(O)CH₂NCHC₆H₄PPh₂Pd}(4-CH₃) 7a and C₆H₃(O){2-NC(O)CH₂NCHC₆H₄PPh₂Pt}(4-CH₃) 7b bearing the dianionic ligand 3a²⁻. All new compounds have been characterised by multinuclear NMR, FTIR, mass spectroscopy and microanalysis. Single crystal X-ray studies have been performed on compounds 1b·1.5CH₂Cl₂, 3b·HH·0.5Et₂O, 6b·CHCl₃ and 7b·0.5Et₂O.     

New palladacyclopentadiene complexes containing an N,P-donor setting. Crystal structure of [Pd{C4(COOMe)4}(o-Ph2PC6H4CHNPr)]

The synthesis of palladacyclopentadiene derivatives with the mixed-donor bidentate ligands o-Ph₂PC₆H₄CHNR (N^∧P) has been achieved. The new complexes of general formula [Pd{C₄(COOMe)₄}(o-Ph₂PC₆H₄CHNR)] [R=Me (1), Et (2), ⁱPr (3), ^tBu (4), NHMe (5)] have been prepared by reaction between the precursor [Pd{C₄(COOMe)₄}]_n and the corresponding iminophosphine. The polymer complex [Pd{C₄(COOMe)₄}]_n also reacts with pyridazine (C₄H₄N₂) to give the insoluble dinuclear complex [Pd{C₄(COOMe)₄}(μ-C₄H₄N₂)]₂ (6), which has been successfully employed as precursor in the synthesis of pyridazine-based palladacyclopentadiene complexes. The reaction of 6 with tertiary phosphines yielded complexes containing an N,P-donor setting of formula [Pd{C₄(COOMe)₄}(C₄H₄N₂)(L)] (L=PPh₃ (7), PPh₂Me (8), P(p-MeOC₆H₄)₃ (9), P(p-FC₆H₄)₃ (10)). The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, ¹H, ¹⁹F and ³¹P NMR). The molecular structure of complex 3 has been determined by a single-crystal diffraction study, showing that the iminophosphine acts as chelating ligand with coordination around the palladium atom slightly distorted from the square-planar geometry.     

On the identification of ionic species of neutral halogen dimers, monomers and pincer type palladacycles in solution by electrospray mass and tandem mass spectrometry

Electrospray (ESI) mass spectra analysis of acetonitrile solutions of a series of neutral chloro dimers, pincer type, and monomeric palladacycles has enabled the detection of several of their derived ionic species. The monometallic cationic complexes Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1a) and [Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (1b) and the bimetallic cationic complex [κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]Pd-Cl-Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1c) were detected from an acetonitrile solution of the pincer palladacycles Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl) 1. For the dimeric compounds {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (2, Y=H and 3, CF₃), highly electronically unsaturated palladacycles [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2d, 3d) and their mono and di-acetonitrile adducts, namely, [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (2e, 3e) and [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)₂]⁺ (2f and 3f) were detected together with the bimetallic complex [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]-Cl-Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N](CH₃)₂]⁺ (2a, 3a) and its acetonitrile adducts [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[ κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2b, 3b) and [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[κ¹-C, κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂(CH₃CN)]⁺ (2c, 3c). The dimeric palladacycle {Pd[κ¹-C,κ¹-N-C(CH₃O-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (4) is unique as it behaves as a pincer type compound with the OCH₃ substituent acting as an intramolecular coordinating group which prevents acetonitrile full coordination, thus forming the cationic complexes [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)Pd]⁺ (4b), [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂- κO,κC,κN)Pd(CH₃CN)]⁺ (4c) and [(C₆H₄ (o-MeO)CC(Cl)CH₂N(CH₃)₂-κO, κC,κN)Pd-Cl-Pd(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)]⁺ (4a). ESI-MS spectra analysis of acetonitrile solutions of the monomeric palladacycles Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl)(Py) (5, Y=H and 6, Y=CF₃) allows the detection of some of the same species observed in the spectra of the dimeric palladacycles, i.e., monometallic cationic 2d-3d, 2e-3e and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Py)}⁺ (5a, 6a) and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)(Py)}⁺ (5b, 6b) and the bimetallic 2a, 3a, 2b, 3b, 2c and 3c. In all cationic complexes detected by ESI-MS, the cyclometallated moiety was intact indicating the high stability of the four or six electron anionic chelate ligands. The anionic (chloride) or neutral (pyridine) ligands are, however, easily replaced by the acetonitrile solvent.     

On the existence of MHn species with M=Al, Ga and n=4, 5, 6. Computational study of structures, stabilities and bonding

Based on second-order perturbation theory (MP2) predictions with large 6-311++G(3df, 3pd) basis set we have reviewed the possible structures and stabilities of a series of neutral MH_n(M=Al, Ga; n=4, 5, 6) species. For AlH₄ and AlH₅, our results confirm the previous theoretical findings, which indicate the dihydrogen C_s complexes (²A′) AlH₂(H₂) and (¹A′) AlH₃(H₂), respectively, as the lowest energy isomers. We found, similarly, C_s (²A′) GaH₂(H₂) and (¹A′) GaH₃(H₂) van der Waals complexes as the most stable species of the gallium analogues GaH₄ and GaH₅. The calculated H₂ dissociation energies (D_e) for AlH₂(H₂) and AlH₃(H₂) are of the order 1.8–2.5 kcalmol¹, whereas this range of values for GaH₂(H₂) and GaH₃(H₂) is 1.4–1.8 kcalmol¹ . Symmetry-adapted perturbation theory (SAPT) was used to analyze the interaction energies of these dihydrogen complexes (for n=5) to determine why the Ga species show a smaller binding energy than the Al species. The SAPT partitioning of the interaction energy showed significant differences between AlH₃(H₂) and GaH₃(H₂), resulting from the much stronger “hydride” character of the aluminum species. The experimental observation of AlH₂(H₂) and AlH₃(H₂), and likely GaH₃(H₂), via low-temperature matrix isolation has been reported recently by Pullumbi et al. and Andrews et al., supporting the theoretical predictions. For n=6, we found the degenerate C₂(²A) and C_s(²A′) MH₂(H₂)₂ “double H₂” type van der Waals complexes as the lowest energy species for both M=Al and Ga.Electronic Supplementary Material Supplementary material is available for this article at     

Rhodium(I) and palladium(II) complexes with the Schiff base 2,2-bis((4S)-4-benzyl-2-oxazoline)

The Schiff base 2,2^′-bis((4S)-4-benzyl-2-oxazoline) (I) and its coordination complexes with rhodium(I) and palladium(II) (and with 1,5-cyclo-octadiene and allyl ligands) have been characterised by single-crystal X-ray diffraction, mass spectrometry, ¹³C and ¹H NMR spectroscopy: [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)][Rh₂(C₂₀H₂₀N₂O₂)₂](CF₃SO₃)₃ · (CH₃CH₂O) (II) and [Pd(C₂₀H₂₀N₂O₂)(C₃H₅)]CF₃SO₃ (III). We discuss the reasons for the formation of two complex cations for Rh(I), [Rh(C₂₀H₂₀N₂O₂)(C₈H₁₂)]⁺ (IIa) and [Rh₂(C₂₀H₂₀N₂O₂)₂]²⁺ (IIb), and only one for Pd(II).     

Novel oxorhenium(V) ‘3+1’ mixed ligand complexes with 3-thiapentane-1,5-dithiolate and functional mercaptobenzoyl amino acid ethyl ester

Oxorhenium(V) complexes with ‘3+1’ mixed ligands, [ReO(SSS)L], where SSS is η³-(SCH₂CH₂SCH₂CH₂S), L = η¹-(C₆H₄COOH-4-S), η¹-(C₆H₄CONHCH₂COOEt-4-S), η¹-(C₆H₄CONHCH(CH₃)COOEt-4-S), and η¹-(C₆H₄CONHCH(CH₂Ph)COOEt-4-S), have been synthesized. These L ligands and [ReO(SSS)L] complexes were characterized by IR, ¹H NMR, ¹³C NMR, and MAS spectrometers. Molecular structure of [ReO(SSS){η¹-(C₆H₄COOH-4-S)}] complex was determined to be a distorted square pyramidal by single crystal X-ray analytical method.     

Acetyl-CoA decarbonylase/synthase complex from Archaeoglobus fulgidus

The acetyl-CoA decarbonylase/synthase (ACDS) multienzyme complex catalyzes the reversible cleavage and synthesis of acetyl-CoA in methanogens. This report of the enzyme complex in Archaeoglobus fulgidus demonstrates the existence of a functional ACDS complex in an organism that is not a methanogen. The A. fulgidus enzyme complex contained five subunits of 89, 72, 50, 49.5, and 18.5 kDa, and it catalyzed the overall synthesis of acetyl-CoA according to the following reaction: w CO₂ + 2 Fd_red(Fe²⁺) + 2 H⁺ + CH₃– H₄SPt + CoA ⇌ acetyl-CoA + H₄SPt + 2 Fd_ox(Fe³⁺) + H₂O where Fd is ferredoxin, and CH₃–H₄SPt and H₄SPt denote N ⁵-methyl-tetrahydrosarcinapterin and tetrahydrosarcinapterin, respectively. Received: 27 October 1997 / Accepted: 29 January 1998     

The tri–μ–hydrido–bis[(η5–C5Me5)aluminum(III)] theoretical study, the assets of sandwiched M2H3 (M of 13th group elements) stability

The stability of the tri–μ–hydrido–bis[(η⁵–C₅Me₅)aluminum], Cp*₂Al₂H₃, 1 is studied at B3LYP/6–311+G(d,p), CCSD(T)//B3LYP/6–311+G(d,p) and MP4//B3LYP/6–311+G(d,p) levels. The coordination between Al₂H₃ entity and both C₅(CH₃)₅ groups is ensured by strong electrostatic and orbital interactions. The orbital analysis of the interacting fragments shows that Al₂H₃ acceptor, which keeps its tribridged structure, implies the vacant ( \texta₁￠ ) \left( {{\text{a}}_1^\prime } \right) and five antibonding (a₂^￠￠ a_2^{\prime \prime } , e′ and e″) molecular orbitals to interact with two orbitals mixtures, b₁ and e" of the donors (C₅Me₅). When we take into account the solvent effect, the computation shows that 1 seems to be stable in condensed phase with a tribridged bond between the Al atoms [Cp*Al(μ-H)₃AlCp*], whereas in the gas phase, the monobridged Cp*AlH(μ-H)AlHCp* 4 is slightly favored (4 kcal mol⁻¹). We propose that 1 could be prepared thanks to Cp*Al (2) and Cp*AlH₂ (3) reaction in acidic medium. The experimental treatment of this type of metallocenes would contribute to the development of the organometallic chemistry of 13th group elements.      

Thermodynamic stability and energetics of DNA duplexes containing major intrastrand cross-links of second-generation antitumor dinuclear PtII complexes

The effects of major DNA intrastrand cross-links of antitumor dinuclear Pt^II complexes [{trans-PtCl(NH₃)₂}₂-μ-{trans-(H₂N(CH₂)₆NH₂(CH₂)₂NH₂(CH₂)₆NH₂)}]⁴⁺ (1) and [{PtCl(DACH)}₂-μ-{H₂N(CH₂)₆NH₂(CH₂)₂NH₂(CH₂)₆NH₂)}]⁴⁺ (2) (DACH is 1,2-diaminocyclohexane) on DNA stability were studied with emphasis on thermodynamic origins of that stability. Oligodeoxyribonucleotide duplexes containing the single 1,2, 1,3, or 1,5 intrastrand cross-links at guanine residues in the central TGGT, TGTGT, or TGTTTGT sequences, respectively, were prepared and analyzed by differential scanning calorimetry. The unfolding of the platinated duplexes was accompanied by unfavorable free energy terms. The efficiency of the cross-links to thermodynamically destabilize the duplex depended on the number of base pairs separating the platinated bases. The trend was 1,5→1,2→1,3 cross-link of 1 and 1,5→1,3→1,2 cross-link of 2. Interestingly, the results showed that the capability of the cross-links to reduce the thermodynamic stability of DNA (ΔG ₂₉₈⁰) correlated with the extent of conformational distortions induced in DNA by various types of intrastrand cross-links of 1 or 2 determined by chemical probes of DNA conformation. We also examined the efficiency of the mammalian nucleotide excision repair systems to remove from DNA the intrastrand cross-links of 1 or 2. The efficiency of the excinucleases to remove the cross-links from DNA depended on the length of the cross-link; the trend was identical to that observed for the efficiency of the intrastrand cross-links to thermodynamically destabilize the duplex. Thus, the results are consistent with the thesis that an important factor that determines the susceptibility of the intrastrand cross-links of dinuclear platinum complexes 1 and 2 to be removed from DNA by nucleotide excision repair is the efficiency of these lesions to thermodynamically destabilize DNA.     

Complexation associated rearrangement of iminobiphosphines to diphosphinoamines

The reaction of the iminobiphosphines RNPPh₂-PPh₂, where R = C₆H₄(p-CN), C₆H₄(m-CN), C₆H₄(o-C₆H₅), C₆F₅ or C₆H₄(o-CF₃), with one molecular equivalent of M(cod)Cl₂ (M = Pd or Pt) results in a rearrangement of the NPP unit to the more commonly encountered P-N-P unit, forming mono-chelating complexes of general formula M{RN(PPh₂)₂}Cl₂. The related reaction of the same range of iminobiphosphines with Pt(cod)Cl₂ (but not Pd(cod)Cl₂) in 2:1 ratio affords complexes of general formula [Pt{RN(PPh₂)₂}₂]2Cl. All 15 complexes are isolated in moderate to high yield and they have been fully characterised by spectroscopic methods. Six complexes, viz. [M{C₆H₄(p-CN)N(PPh₂)₂}Cl₂], [M{C₆H₄(m-CN)N(PPh₂)₂}Cl₂] and [M{C₆H₄(o-C₆H₅)N(PPh₂)₂}Cl₂] (M = Pd and Pt), have been characterised in the solid state by single crystal X-ray diffraction analysis.     

Theoretical mechanistic study of the reaction of the methylidyne radical with methylacetylene

A detailed doublet potential energy surface for the reaction of CH with CH₃CCH is investigated at the B3LYP/6-311G(d,p) and G3B3 (single-point) levels. Various possible reaction pathways are probed. It is shown that the reaction is initiated by the addition of CH to the terminal C atom of CH₃CCH, forming CH₃CCHCH 1 (1a,1b). Starting from 1 (1a,1b), the most feasible pathway is the ring closure of 1a to CH₃–cCCHCH 2 followed by dissociation to P ₃ (CH₃–cCCCH+H), or a 2,3 H shift in 1a to form CH₃CHCCH 3 followed by C–H bond cleavage to form P ₅ (CH₂CHCCH+H), or a 1,2 H-shift in 1 (1a, 1b) to form CH₃CCCH₂ 4 followed by C–H bond fission to form P ₆ (CH₂CCCH₂+H). Much less competitively, 1 (1a,1b) can undergo 3,4 H shift to form CH₂CHCHCH 5. Subsequently, 5 can undergo either C–H bond cleavage to form P ₅ (CH₂CHCCH+H) or C–C bond cleavage to generate P ₇ (C₂H₂+C₂H₃). Our calculated results may represent the first mechanistic study of the CH + CH₃CCH reaction, and may thus lead to a deeper understanding of the title reaction.     

Synthesis and characterization of some oxovanadium(V) complexes with internally functionalized oximes: Crystal and molecular structures of heptacoordinated [VO{ONC(CH3)(C4H3O-2)}3] and [VO{ONC(CH3)(C4H3S-2)}3] · 0.5C6H6

New oxovanadium(V) complexes with internally functionalized oximes of the type VO{OPrⁱ}_3−n{ONC(CH₃)(Ar)}_n] (where Ar = C₄H₃O-2, C₄H₃S-2 and C₅H₄N-2 and n = 1-3) have been prepared in quantitative yields by the reaction of VO(OPrⁱ)₃ with the corresponding oximes in various stoichiometric ratios in refluxing anhydrous benzene. The products have been characterized by elemental analyses and spectroscopic (FT IR, ¹H, ¹³C{¹H} and ⁵¹V NMR) studies. FAB mass spectral analysis of [VO{OPrⁱ}{ONC(CH₃)C₄H₃S}₂] indicates the monomeric nature of the complex. ⁵¹V NMR values for these complexes suggest the formation of tetra-coordinate species in solution. However, the single crystal X-ray diffraction studies of [VO{ONC(CH₃)(C₄H₃O-2)}₃] and [VO{ONC(CH₃)(C₄H₃S-2)}₃] · 0.5C₆H₆ exhibit the presence of vanadium(V) atoms in a unique hepta-coordination state with distorted pentagonal bipyramidal geometry in the solid state. The oxo- atom occupies the axial position while the oximato ligands are bonded in a dihapto (η²-N,O) manner with the formation of three membered rings.     

Characteristics and nature of the intermolecular interactions in boron-bonded complexes with carbene as electron donor: an <Emphasis Type="Italic">ab initio</Emphasis>, SAPT and QTAIM study

We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene–BX₃ complexes, where X = H, OH, NH₂, CH₃, CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B–C_carbene interaction due to the short B–C_carbene distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH₂ > OH > CH₃ > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with ∇² ρ _BCP >0, the B–C_carbene bond critical points (BCPs) are characterized by a reasonably large value of the electron density (ρ _BCP) and H_BCP <0, indicating that the potential energy overcomes the kinetic energy density at BCP and the B–C_carbene bond is a polar covalent bond.     

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH₃)₂}₂-μ-H₂N(CH₂)₆NH₂](NO₃)₂ (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH₃)₂}₂-μ-{H₂N(CH₂)₆NH₂}]Cl₂ (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37°C by a combination of multinuclear (¹⁹⁵Pt, {¹H-¹⁵N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH₃)₂]⁺ (III) and trans-[Pt(AcMet)₂(NH₃)₂]²⁺ (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{cis-Pt(AcMet)(NH₃)₂}] (V); [{cis-Pt(AcMet)(NH₃)₂}₂-μ-NH₂(CH₂)₆NH₂] (VI); [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)NH₃] (VII); [{PtCl(AcMet)(NH₃)}₂-μ-NH₂(CH₂)₆NH₂] (VIII); [{trans-Pt(AcMet)₂(NH₃)}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)(NH₃)] (IX) and the fully substituted [{trans-Pt(AcMet)₂(NH₃)}₂-μ-{NH₂(CH₂)₆NH₂] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498–5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.     

Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

 The reaction of the macrocycles 1,4,7-tris (3,5-di-tert-butyl-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L¹H₃, or 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L²H₃, with Cu(ClO₄)₂·6H₂O in methanol (in the presence of Et₃N) affords the green complexes [Cu^II(L¹H)] (1), [Cu^II(L²H)]·CH₃OH (2) and (in the presence of HClO₄) [Cu^II(L¹H₂)](ClO₄) (3) and [Cu^II(L²H₂)] (ClO₄) (4). The Cu^II ions in these complexes are five-coordinate (square-base pyramidal), and each contains a dangling, uncoordinated pendent arm (phenol). Complexes 1 and 2 contain two equatorially coordinated phenolato ligands, whereas in 3 and 4 one of these is protonated, affording a coordinated phenol. Electrochemically, these complexes can be oxidized by one electron, generating the phenoxyl-copper(II) species [Cu^II(L¹H)]^+ ·, [Cu(L²H)]^+ ·, [Cu^II(L¹H₂)]^2+ ·, and [Cu^II(L²H₂)]^2+ ·, all of which are EPR-silent. These species are excellent models for the active form of the enzyme galactose oxidase (GO). Their spectroscopic features (UV-VIS, resonance Raman) are very similar to those reported for GO and unambiguously show that the complexes are phenoxyl-copper(II) rather than phenolato-copper(III) species. Received: 10 February 1997 / Accepted: 7 April 1997     

Aggregation of imino-phosphonate monoester complexes

The aggregates {[Zn(L¹)]H₂O}_∞ and {[Y(L²)]₄Na₃(H₂O)₂(MeOH)_1.2}(NO₃)₃·2H₂O·5.6MeOH have been assembled from complexes of imino-phosphonate monoester ligands [L¹]²⁻ {CH₂[CH₂NC(CH₃)PO₂(OMe)]₂}²⁻ and [L²]³⁻ {N[CH₂CH₂NC(CH₃)PO₂(OMe)]₃}³⁻, the topology of these materials differing from that of their imino-carboxylate analogues.     

Complexes of binucleating ligands. XVI. Some diazotate-bridged palladium(II) complexes

The acetate-bridged complex, LPd₂(CH₃CO₂), in which L^3? is a binucleating ligand containing a bridging thiophenoxide unit, reacts with the syn-phenyldiazotate ion to yield the syn-diazotate-bridged complex LPd₂(syn-C₆H₅NNO) and with the anti-phenyldiazotate ion to yield LPd₂ (anti-C₆H₅NNO). The anti-complex isomerises to syn in boiling benzene, in contrast to the isomerisation of the free diazotate ions which proceeds spontaneously in the opposite direction. A para-nitro substituent has a pronounced labilising effect upon the isomerisation and LPd₂(CH₃CO₂) reacts with sodium anti-p-nitrophenyldiazotate at room temperature to yield the syn complex, LPd₂(syn-p-NO₂·C₆H₄·NNO). Nitrosourethane, C₂H₅OOC·NH·NO, reacts with LPd₂(CH₃CO₂) to generate LPd₂(C₂H₅OOC·NNO).     

N-substituted ethylcarbamate complexes of thorium(IV) and lanthanum(III) nitrates

N-substituted ethylcarbamates form with thorium nitrate the complexes Th(NO₃)₄·3RHNC(O)OC₂H₅ (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH) and with lanthanum nitrate the complexes La(NO₃)₃· 2RR′NC(O)OC₂H₅·3H₂O (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH; R′ = H and R = CH₃, C₆H₅; R′ = C₂H₅ or R = R′ = CH₃). In addition the anhydrous La(NO₃)₃·3(C₂H₅)₂NC(O)OC₂H₅ has been isolated. From the IR spectra it is deduced that the carbamates coordinate the metal through the carbonyl oxygen atom and that the nitrato groups act as chelated ligands. ¹H nmr spectral data of the complexes are reported and discussed.     

Heteroligand copper(I) complexes of N-thiophosphorylated thioureas and phosphanes: Versatile structures and luminescence

Reaction of the potassium salts of (EtO)₂P(O)CH₂C₆H₄-4-(NHC(S)NHP(S)(OiPr)₂) (HL^I), (CH₂NHC(S)NHP(S)(OiPr)₂)₂ (H₂L^II) or cyclam(C(S)NHP(S)(OiPr)₂)₄ (H₄L^III) with [Cu(PPh₃)₃I] or a mixture of CuI and Ph₂P(CH₂)_1-3PPh₂ or Ph₂P(C₅H₄FeC₅H₄)PPh₂ in aqueous EtOH/CH₂Cl₂ leads to [Cu(PPh₃)L^I] (1), [Cu₂(Ph₂PCH₂PPh₂)₂L^II] (2), [Cu{Ph₂P(CH₂)₂PPh₂}L^I] (3), [Cu{Ph₂P(CH₂)₃PPh₂}L^I] (4), [Cu{Ph₂P(C₅H₄FeC₅H₄)PPh₂}L^I] (5), [Cu₂(PPh₃)₂L^II] (6), [Cu₂(Ph₂PCH₂PPh₂)L^II] (7), [Cu₂{Ph₂P(CH₂)₂PPh₂}₂L^II] (8), [Cu₂{Ph₂P(CH₂)₃PPh₂}₂L^II] (9), [Cu₂{Ph₂P(C₅H₄FeC₅H₄)PPh₂}₂L^II] (10), [Cu₈(Ph₂PCH₂PPh₂)₈L^IIII₄] (11), [Cu₄{Ph₂P(CH₂)₂PPh₂}₄L^III] (12), [Cu₄{Ph₂P(CH₂)₃PPh₂}₄L^III] (13) or [Cu₄{Ph₂P(C₅H₄FeC₅H₄)PPh₂}₄L^III] (14) complexes. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy; their compositions were examined by microanalysis. The luminescent properties of the complexes 1-14 in the solid state are reported.     

Synthesis and characterization of η-cyclopentadienyl-silylallyl niobium and tantalum complexes

Reaction of the disilylcyclopentadiene 1,1-[SiMe₂(CH₂CHCH₂)]₂C₅H₄ with NbCl₅ gave the new allylsilyl-substituted monocyclopentadienyl niobium complex [Nb{η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}Cl₄]. This compound was reacted with LiNHtBu or NH₂tBu to give the imido derivative [Nb{η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}(NtBu)Cl₂], which was further alkylated to the imido alkyl complexes [Nb{η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}(NtBu)R₂] (R = Me, CH₂Ph) and [Nb{η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}(NtBu)Cl (CH₂Ph)]. Reaction of the imido complexes with the corresponding lithium cyclopentadienides gave the dicyclopentadienyl-imido complexes [M(η⁵-C₅R₅){η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}(NtBu)Cl] (M = Nb, Ta; R = H, Me). Metallocene dichlorides [M(η⁵-C₅R₅){η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}Cl₂] (M = Nb, Ta; R = H, Me) were easily prepared by reduction with Na/Hg and simultaneous transmetallation of [Ta(η⁵-C₅R₅)Cl₄] with Li[C₅H₄SiMe₂(CH₂CHCH₂)] and of [Nb{η⁵-C₅H₄SiMe₂(CH₂CHCH₂)}Cl₄] with Li(C₅R₅). All of the new compounds have been characterized by elemental analysis, and IR and NMR spectroscopy.