Kloning Manusia

In the last few years, very rapid progress in the cloning technology and its development towards human cloning has become a hotly-debated issue. Cloning, which is the process of formation of a number of individuals with the same genetic structure, can be done by means of embryo-splitting method and nuclear transfer. Human cloning through the nuclear transfer method is directed towards two purposes, i.e. reproduction and therapy. The relatively new transgenic technology can be combined with the cloning technique to produce clones with new genes. However, pros and cons arise concerning the development of research on human cloning, particularly cloning for reproductive purposes. Therefore, there is need for a moratorium period before human cloning can be performed in order that solutions for all kinds of problems related to safety and ethics can be found

Strong Solvent-Dependent Preference of Δ and Λ Stereoisomers of a Tris(diamine)nickel(II) Complex Revealed by Vibrational Circular Dichroism Spectroscopy

In the present study, we use vibrational circular dichroism (VCD) spectroscopy to investigate the metal-centered Δ and Λ chirality of a tris­(diamine)­nickel­(II) complex. Chiral diphenylethylenediamine is chosen as the ligand, which puts the Δ and Λ isomers of the complex in a diastereomeric relationship. X-ray crystallography indicates an equal preference of both stereoisomers in the solid state. This equal preference is also supported by the related density functional theory calculations. A comparison between the experimental and calculated VCD spectra also proves the existence of both isomers in an acetonitrile solution. However, a significant shift of the equilibrium toward the Λ diastereomer is found for the complex in dimethyl sulfoxide. This solvent-induced preference for a particular absolute configuration is hypothesized to arise from a stronger and more effective solvation of the Λ isomer. The observation that the solvent can significantly influence and shift an equilibrium between two diastereomeric forms is expected to have important implications on structural analysis and on how reaction mechanisms are rationalized

Stoichiometric Reactivity Relevant to the Mor-DalPhos/Pd-Catalyzed Cross-Coupling of Ammonia and 1-Bromo-2-(phenylethynyl)benzene

While Mor-DalPhos/Pd precatalyst mixtures have in general proven to be highly effective for the monoarylation of ammonia employing a range of (hetero)­aryl (pseudo)­halide cross-coupling partners, we have observed previously that 1-bromo-2-(phenylethynyl)­benzene (Ar*Br) is a challenging substrate for this catalyst system. We report herein on our efforts to examine some possible modes of catalyst inhibition by this substrate. Treatment of [CpPd­(allyl)] with Mor-DalPhos in the presence of Ar*Br afforded [(κ²-<i>P</i>,<i>N</i>-Mor-DalPhos)­Pd­(Br)­(Ar*)] (<b>1</b>; 85%), which was transformed into [(κ³-<i>P</i>,<i>N,O</i>-Mor-DalPhos)­Pd­(Ar*)]⁺OTf^– (<b>3</b>; 83%) upon treatment with AgOTf. The characterization of <b>3</b> establishes the ability of the Mor-DalPhos ligand to adopt a κ³-P,N,O structure, which may influence the course of some Pd-catalyzed amination processes. While treatment of <b>1</b> with AgOTf in the presence of ammonia, or alternatively treatment of <b>3</b> with ammonia, resulted in the clean formation of [(κ²-<i>P</i>,<i>N</i>-Mor-DalPhos)­Pd­(NH₃)­(Ar*)]⁺OTf^– (<b>2</b>), our efforts to isolate this compound were thwarted by the facile loss of ammonia from <b>2</b> to give <b>3</b>. Neither NMR spectroscopic nor X-ray crystallographic data obtained for <b>1</b> and <b>3</b> support the existence of significant Pd···alkyne interactions in these complexes. Treatment of the Pd(0) species [L₂Pd­(diphenylacetylene)] (L₂ = Mor-DalPhos, <b>4</b>; L₂ = CyPF<i>t</i>Bu-JosiPhos, <b>5</b>) with Ar*Br resulted in divergent behavior: while multiple phosphorus-containing products were observed in the case of <b>4</b>, under analogous conditions <b>5</b> was transformed cleanly into [(κ²-<i>P</i>,<i>P</i>-JosiPhos)­Pd­(Br)­(Ar*)] (<b>6</b>). The identification of <b>6</b> was facilitated via independent synthesis from Ar*Br, JosiPhos, and [CpPd­(allyl)] (90%). These observations suggest that the inferior performance of Mor-DalPhos relative to JosiPhos in the arylation of ammonia using Ar*Br may be attributable in part to the inefficiency with which putative [(Mor-DalPhos)­Pd­(alkyne)] species re-enter the catalytic cycle via C–Br oxidative addition

Synthesis and Characterization of Heterobimetallic (Pd/B) Nindigo Complexes and Comparisons to Their Homobimetallic (Pd₂, B₂) Analogues

Reactions of Nindigo-BF₂ complexes with Pd­(hfac)₂ produced mixed complexes with Nindigo binding to both a BF₂ and a Pd­(hfac) unit. These complexes are the first in which the Nindigo ligand binds two different substrates, and provide a conceptual link between previously reported bis­(BF₂) and bis­(Pd­(hfac)) complexes. The new Pd/B complexes have intense near IR absorption near 820 nm, and they undergo multiple reversible oxidations and reductions as probed by cyclic voltammetry experiments. The spectral, redox, and structural properties of these complexes are compared against those of the corresponding B₂ and Pd₂ complexes with the aid of time-dependent density functional calculations. In all cases the low-energy electronic transitions are ligand-centered π–π* transitions, but the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energiesand hence the absorption wavelength as well as the oxidation and reduction potentialsare significantly modulated by the moieties bound to the Nindigo ligand

Exploring the Variable Hapticity of the Arylamide Ligand: Access to σ‑Amidophenyl and π‑Cyclohexadienylimine Structures

A study of the preference for σ vs π coordination of the arylamido ligand to a late transition metal shows that LiNPh₂ reacts with RuHCl­(PPh₃)₃ (<b>1</b>) to yield the bent-seat piano-stool complex RuH­[(η⁵-C₆H₅)­NPh]­(PPh₃)₂ (<b>2a</b>) but with RuHCl­(CO)­(PPh₃)₃ (<b>3</b>) to yield the σ-amide RuH­(η¹-NPh₂)­(CO)­(PPh₃)₂ (<b>4</b>). The stability of the σ-bound NPh₂ ligand in <b>4</b> reflects the π acidity of the CO ligand, which inhibits PPh₃ loss. Carbonylation of <b>2a</b> at 50 °C affords Ru­(CO)₃(PPh₃)₂ (<b>8</b>) and HNPh₂, suggesting sequential π → σ isomerization and reductive elimination. The phenoxide ligand behaves similarly: RuH­(η⁵-C₆H₅O)­(PPh₃)₂ (<b>2b</b>) is formed from <b>1</b> but RuH­(η¹-OPh)­(CO)­(PPh₃)₃ (<b>5</b>) is formed from <b>3</b>, and carbonylation of <b>2b</b> gives <b>8</b> and phenol, although more forcing conditions are required (90 °C). The crystal structure of <b>2a</b> is reported

Unsymmetrical Dicarbenes Based on <i>N</i>-Heterocyclic/Mesoionic Carbene Frameworks: A Stepwise Metalation Strategy for the Generation of a Dicarbene-Bridged Mixed-Metal Pd/Rh Complex

A pair of linked imidazolium/triazolium salts have been prepared using copper-catalyzed azide–alkyne cycloaddition (CuAAC or “click” chemistry) and methylation protocols, producing a precursor for bidentate <i>N</i>-heterocyclic carbene (NHC)/mesoionic carbene (MIC) ligands, representing a rare example of an NHC/MIC hybrid. Metalation of one-half of this dicationic species using the basic ligand-containing [Pd­(OAc)₂] in the presence of potassium iodide or half an equivalent of [Rh­(μ-OMe)­(COD)]₂ yields NHC-anchored/pendent triazolium species of Pd or Rh, respectively. The pendent Pd species can be further functionalized through iodide substitution by various monophosphines, which preferentially adopt a cis or trans arrangement depending on the bulk of the anchored NHC substituent. Combining these “internal-base” and “pendent” strategies, the pendent MIC­(H)⁺ arm of the <i>trans</i>-triethylphosphine-functionalized Pd species can be metalated by [Rh­(μ-OMe)­(COD)]₂, resulting in the generation of a hybrid NHC/MIC-bridged mixed-metal Pd/Rh species. This complex represents the first example of a hybrid unsymmetrical dicarbene bridging two different metals

Tandem C–F and C–H Bond Activation in Fluoroolefins Promoted by a Bis(diethylphosphino)methane-Bridged Diiridium Complex: Role of Water in the Activation Processes

The diiridium complex [Ir₂(CO)₃(μ-H)­(depm)₂]⁺ (<b>1</b>) reacts with vinyl fluoride, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene, undergoing C–F bond activation in all cases, in addition to C–H activation in the incompletely substituted fluoroolefins. Reaction of <b>1</b> with vinyl fluoride readily undergoes geminal C–F/C–H activation, resulting in the bridging vinylidene product, [Ir₂(H)­(CO)₃(μ-CCH₂)­(depm)₂]⁺ (<b>2</b>). Compound <b>1</b> reacts with 1,1-difluoroethylene at subambient temperature to give minor amounts of [Ir₂(CO)₃(κ¹:η²-CCH)­(depm)₂]⁺ (<b>4</b>), resulting from the loss of 2 equiv of HF from the fluoroolefin complex, along with a mixture of two isomers of [Ir₂(C­(F)CH₂)­(CO)₃(μ-CF₂CH₂)­(depm)₂]⁺ (<b>5a</b>/<b>5b</b>), in which 2 equiv of the olefin has been incorporated. Compound <b>1</b> also reacts with trifluoroethylene at −30 °C, giving a 1:1 mix of isomers of the trifluoroethylene-bridged species [Ir₂(H)­(CO)₃(μ-CFHCF₂)­(depm)₂]⁺ (<b>7a</b>/<b>7b</b>), and warming this mixture above −15 °C converts both isomers to two products, [Ir₂(H)­(CO)₃(μ-CCF₂)­(depm)₂]⁺ (<b>8</b>), in which the geminal C–F and C–H bonds in the fluoroolefin have been activated, and [Ir₂(H)­(CO)₃(μ-CHCF₃)­(depm)₂]⁺ (<b>9</b>), the result of a [1,2]-fluoride shift to give the bridging 2,2,2-trifluoroethylidene moiety. Compound <b>9</b> reacts further with a second equivalent of trifluoroethylene over 12 h to produce the 2,2,2-trifluoroethylidene/<i>cis</i>-difluorovinyl complex, [Ir₂(C­(F)CFH)­(CO)₃(μ-CHCF₃)­(depm)₂]⁺ (<b>10</b>). Finally, tetrafluoroethylene reacts with <b>1</b> to produce the bridged adduct, [Ir₂(H)­(CO)₃(μ-CF₂CF₂)­(depm)₂]⁺ (<b>11</b>), followed by a single C–F activation to give [Ir₂(C­(F)CF₂)­(CO)₃(depm)₂]⁺ (<b>12</b>). The roles of the hydride ligand and exogenous water in the C–F activation processes are discussed

Diverse Coordination Modes and Transformations of Allenes at Adjacent Iridium/Osmium Centers

The methylene-bridged complex, [IrOs­(CO)₃(μ-CH₂)­(dppm)₂]­[BF₄] (dppm = μ-Ph₂PCH₂PPh₂) (<b>2</b>), reacts with allene, resulting in C–C bond formation, to yield an equilibrium mix of two isomers of [IrOs­(CO)₃(μ-η³:κ¹-C­(CH₂)₃)­(dppm)₂]­[BF₄] (<b>3</b>/<b>3a</b>), in which the hapticity of the trimethylenemethane ligand with respect to the two metals, as well as the carbonyl ligand arrangement, is different in each isomer. Reaction of <b>2</b>, as the triflate salt (<b>2-CF</b>_<b>3</b><b>SO</b>_<b>3</b>), with methylallene also yields two isomers, [IrOs­(CO)₃(μ-η³:κ¹-C­(CHCH₃)­(CH₂)₂)­(dppm)₂]­[CF₃SO₃] (<b>4</b>/<b>4a</b>); however, in this case, the binding mode of the substituted trimethylenemethane moiety is the same in each isomer and differs only in the position of the methyl group on the allylic moiety. The addition of 1,1-dimethylallene to <b>2-CF</b>_<b>3</b><b>SO</b>_<b>3</b> results in loss of 4-methyl-1,3-pentadiene and subsequent reaction of the remaining “[IrOs­(CO)₃(dppm)₂]⁺” species with excess 1,1-dimethylallene to give [IrOs­(CO)₃(μ-η³:κ¹-CH₂CCMe₂)­(dppm)₂]­[CF₃SO₃] (<b>5</b>), in which the dimethylallene moiety is κ¹-bound to Os through the central carbon and η³-bound to Ir. Both allene and methylallene react with the tetracarbonyl complex, [IrOs­(CO)₄(dppm)₂]­[BF₄] (<b>6</b>), to generate analogous products, [IrOs­(CO)₃(μ-η³:κ¹-CH₂CCHR)­(dppm)₂]­[BF₄] (R = H (<b>7</b>), CH₃ (<b>8</b>), respectively). Reaction of <b>6-CF</b>_<b>3</b><b>SO</b>_<b>3</b> with 1,1-dimethylallene yields [IrOs­(CO)₄(μ-CC­(H)­C­(CH₃)CH₂)­(dppm)₂]­[CF₃SO₃] (<b>9</b>), the result of activation of the geminal C–H bonds of the unsubstituted end of the allene, and additional activation of a methyl C–H bond. The addition of 1,1-difluoroallene to <b>6-CF</b>_<b>3</b><b>SO</b>_<b>3</b> yields [IrOs­(CO)₄(μ-κ¹:κ¹-F₂C<i>C</i><i>C</i>H₂)­(dppm)₂][CF₃SO₃] (<b>10</b>), in which this cumulene bridges both metal centers through the central carbon and the CH₂ end of the substrate. These reactivities are compared to those of related Ir₂, Rh/Ru, Rh/Os, and Ir/Ru complexes

Rational and Predictable Chemoselective Synthesis of Oligoamines via Buchwald–Hartwig Amination of (Hetero)Aryl Chlorides Employing Mor-DalPhos

We report a diverse demonstration of synthetically useful chemoselectivity in the synthesis of di-, tri-, and tetraamines (62 examples) by use of Buchwald–Hartwig amination employing a single catalyst system ([Pd­(cinnamyl)­Cl]₂/<b>L1</b>; <b>L1</b> = <i>N</i>-(2-(di­(1-adamantyl)­phosphino)­phenyl)­morpholine, Mor-DalPhos). Competition reactions established the following relative preference of this catalyst system for amine coupling partners: linear primary alkylamines and imines > unhindered electron-rich primary anilines, primary hydrazones, <i>N</i>,<i>N</i>-dialkylhydrazines, and cyclic primary alkylamines > unhindered electron-deficient primary anilines, α-branched acyclic primary alkylamines, hindered electron-rich primary anilines ≫ cyclic and acyclic secondary dialkylamines, secondary alkyl/aryl and diarylamines, α,α-branched primary alkylamines, and primary amides. The new isomeric ligand <i>N</i>-(4-(di­(1-adamantyl)­phosphino)­phenyl)­morpholine (<i>p</i>-Mor-DalPhos, <b>L2</b>) was prepared in 63% yield and was crystallographically characterized; the [Pd­(cinnamyl)­Cl]₂/<b>L2</b> catalyst system exhibited divergent reactivity. Application of the reactivity trends established for [Pd­(cinnamyl)­Cl]₂/<b>L1</b> toward the chemoselective synthesis of di-, tri-, and tetraamines was achieved. Preferential arylation was observed at the primary alkylamine position within 2-(4-aminophenyl)­ethylamine with [Pd­(cinnamyl)­Cl]₂/<b>L1</b> and 4-chlorotoluene (affording <b>5a</b>); the alternative regioisomer (<b>5a′</b>) was obtained when using [Pd­(cinnamyl)­Cl]₂/<b>L2</b>. These observations are in keeping with coordination chemistry studies, whereby binding of 2-(4-aminophenyl)­ethylamine to the in situ generated [(<b>L1</b>)­Pd­(<i>p</i>-tolyl)]⁺ fragment occurred via the primary amine moiety, affording the crystallographically characterized adduct [(<b>L1</b>)­Pd­(<i>p</i>-tolyl)­(<i>N</i>H₂CH₂CH₂(4-C₆H₄NH₂)]⁺OTf^– (<b>7</b>) in 72% yield

Prototypical Phosphine Complexes of Antimony(III)

Complexes of the generic formula [Cl_<i>n</i>(PR₃)_<i>m</i>Sb]^{(3–<i>n</i>)+} (<i>n</i> = 1, 2, 3, or 4 and <i>m</i> = 1 or 2) have been prepared featuring [ClSb]²⁺, [Cl₂Sb]¹⁺, Cl₃Sb, or [Cl₄Sb]¹⁻ as acceptors with one or two phosphine ligands {PMe₃, PPh₃, PCy₃ (Cy = C₆H₁₁)}. The solid-state structures of the complexes reveal foundational features that define the coordination chemistry of a lone pair bearing stibine acceptor site. The experimental observations are interpreted with dispersion-corrected density functional theory calculations to develop an understanding of the bonding and structural diversity