Ligands In Organometallic Chemistry Research Articles

ChemInform Abstract: Benzannulated Homologues of Cyclopentadienide as Ligands in Organometallic Chemistry

AbstractReview: 218 refs.

3+2] Cycloaddition of propargylic alcohols and α-oxo ketene dithioacetals: synthesis of functionalized cyclopentadienes and further application in a Diels-Alder reaction.

Cyclopentadienes are valuable intermediates in organic synthesis and also ubiquitous as the Cp ligands in organometallic chemistry. As part of ongoing efforts to develop novel organic reactions that employ functionalized alkynes, a [3+2] cycloaddition of propargylic alcohols and ketene dithioacetals has been developed, which leads to fully substituted 2,5-dialkylthio cyclopentadienes in good to excellent yields. In an unusual dethiolating Diels-Alder reaction, the cyclopentadienes were further reacted with maleimides to afford a family of novel fluorescent polycyclic compounds.

3+2] Cycloaddition of Propargylic Alcohols and α‐Oxo Ketene Dithioacetals: Synthesis of Functionalized Cyclopentadienes and Further Application in a Diels–Alder Reaction

AbstractCyclopentadienes are valuable intermediates in organic synthesis and also ubiquitous as the Cp ligands in organometallic chemistry. As part of ongoing efforts to develop novel organic reactions that employ functionalized alkynes, a [3+2] cycloaddition of propargylic alcohols and ketene dithioacetals has been developed, which leads to fully substituted 2,5‐dialkylthio cyclopentadienes in good to excellent yields. In an unusual dethiolating Diels–Alder reaction, the cyclopentadienes were further reacted with maleimides to afford a family of novel fluorescent polycyclic compounds.

Tailor-made N-heterocyclic carbenes for nanoparticle stabilization

N-heterocyclic carbenes (NHCs) represent a leading class of ligands in organometallic chemistry, but have been rarely exploited as stabilizers for metal nanoparticles (NPs). We report the first example of NHC stabilized Pd-NPs that demonstrate long term stability. These NHC Pd-NPs were synthesized by a facile ligand exchange protocol using rationally designed long chained NHCs (LC-NHCs). Furthermore, we demonstrate that the surface modification of Pd-NPs results in significant chemoselectivity in a model reaction.

Observation of a stable carbene at the active site of a thiamin enzyme

Carbenes are highly reactive chemical compounds that are exploited as ligands in organometallic chemistry and are powerful organic catalysts. They were postulated to occur as transient intermediates in enzymes, yet their existence in a biological system could never be demonstrated directly. We present spectroscopic and structural data of a thiamin enzyme in a noncovalent complex with substrate, which implicate accumulation of a stable carbene as a major resonance contributor to deprotonated thiamin.

Graphical Abstract: Eur. J. Inorg. Chem. 25/2011

AbstractThe cover picture shows the molecular structure of GaCp, a sleeping beauty in organometallic chemistry. An easy synthesis of GaCp, which can be carried out with standard laboratory equipment, opens the way for GaCp to become a useful ligand in organometallic chemistry. Details of the synthesis and first structurally characterized molecular compounds exhibiting GaCp units are discussed in the Short Communication by H. Schnöckel, A. Schnepf et al. on page 3681 ff.

A Convenient Synthesis of Cyclopentadienylgallium – The Awakening of a Sleeping Beauty in Organometallic Chemistry (Eur. J. Inorg. Chem. 25/2011)

AbstractThe cover picture shows the molecular structure of GaCp, a sleeping beauty in organometallic chemistry. An easy synthesis of GaCp, which can be carried out with standard laboratory equipment, opens the way for GaCp to become a useful ligand in organometallic chemistry. Details of the synthesis and first structurally characterized molecular compounds exhibiting GaCp units are discussed in the Short Communication by H. Schnöckel, A. Schnepf et al. on page 3681 ff.

ChemInform Abstract: Phosphorus-Nitrogen Heterocycles as Ligands in Organometallic Chemistry.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ethynyl[2.2]paracyclophanes and 4-isocyano[2.2]paracyclophane as ligands in organometallic chemistry

An alternative synthesis of (±)-4-ethynyl[2.2]paracyclophane (PCP C CH) ( 5) and 4,16-diethynyl[2.2]paracyclophane ( 6) via the Corey–Fuchs reaction has been developed. The olefinic intermediate 4-dibromovinyl[2.2]paracyclophane ( 3) has been isolated and structurally characterized. The racemic terminal alkyne 5 was employed as starting material for assembling of a luminescent extended π-conjugated system containing a thiophene unit and for a catalytic bis-silylation reaction yielding the olefinic dithioether Z-PhSCH 2Me 2SiC(H) C(PCP)SiMe 2CH 2SPh ( 9). The dimetallatetrahedran [Co 2(CO) 6(μ-η 2–PCP–CCH)] (10) has been prepared and its crystal structure determined by an X-ray diffraction analysis. Alkyne 5 has also been used for the preparation of the Pt(0) complex [Pt(PPh 3) 2(PCP C CH)] ( 11) and the heterodinuclear dimetallacyclopentenone [(OC) 2Fe{μ C( O)C(PCP) C(H)}(μ-dppm)Pt(PPh 3)] ( 12). The synthesis and reactivity of 4-isocyano[2.2]paracyclophane ( 15) towards heterobimetallic iron–platinum and palladium–platinum complexes is also presented. Opening of the dative iron → platinum bond of [(OC) 4Fe(μ-dppm)PtCl 2] ( 16) occurred upon addition of 15 to a CH 2Cl 2 solution of 16 leading to [(OC) 4Fe{μ-dppm}PtCl 2(C N PCP)] ( 17). Treatment of [ClPd(μ-dppm) 2PtCl] ( 18) with isocyanide 15 in a 1:1 ratio affords the A-frame compound [ClPd(μ-dppm) 2(μ-C N PCP)PtCl] ( 19), resulting from formal insertion of 15 into the Pd–Pt bond. Addition of 2 equiv. of 15– 18 leads to the ionic A-frame compound [ClPd(μ-dppm) 2(μ-C N PCP)Pt(C N PCP)]Cl ( 20).

Cyclopenta[b]thienyl Ligand in Organometallic Chemistry. Synthesis of Cyclopenta[b]thiophene 5-Complexes with Metal Coordination at the Thiophene Ring

Unlike isoelectronic η6-indenyl ruthenium, manganese, and chromium complexes, heating of Mn(CO)5OTf, [Ru(Cp*)Cl4], and Cr(C10H8)(CO)3 with isomeric 2-ethyl-5-methylcyclopenta[b]thiophenes leads to the corresponding η5-complexes where the metal is coordinated at the C5-carbocycle. The structure of the complex Mn(Th)(CO)3 (Th = 2-ethyl-5-methylcyclopenta[b]thienyl) was proved by X-ray analysis.

1,2-azaborolyls, isoelectronic analogues of the ubiquitous cyclopentadienyl ligand: synthesis of B-heteroatom-substituted 1,2-azaborolyl complexes and an assessment of their electronic features.

The substituent on boron allows the electronic nature of the heterocycle of B-heteroatom-substituted (R=H, O, S, N, P, and F) 1,2-azaborolyl complexes to be modulated. Given that 1,2-azaborolyl is isoelectronic with cyclopentadienyl (see scheme), one of the most widely used ligands in organometallic chemistry, it seems likely that the diverse array of compounds synthesized in this study will stimulate the development of applications of η5-(1,2-azaborolyl) ligands in metal-catalyzed processes. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2002/z17871_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Cyclopenta[b]thienyl Ligand in Organometallic Chemistry. Studies of the Regioselectivity of the Synthesis of New σ‐Element‐Substituted Cyclopenta[b]thiophene Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cyclopenta[b]thienyl ligand in organometallic chemistry. Studies of the regioselectivity of the synthesis of new σ-element-substituted cyclopenta[b]thiophene derivatives

Reactions of 2-ethyl-5-methylcyclopenta[b]thienyllithium (thiopentalenyllithium) (2) with various electrophilic reagents afford σ-element-substituted thiopentalenes. However, the reaction with Ph3SnCl yields only one of two possible isomers,viz, triphenyl(4H-cyclopenta[b] thiophen-4-yl)stannane (4c), whereas the reactions with Me3SiCl, Me3SiCl, or Ph2PCl give both possible isomers,viz., trimethyl(6H-cyclopenta[b]thiophen-6-yl)silane (3a) and trimethyl(4H-cyclopental[b]thiophen-4-yl)silane (4a), trimethyl(6H-cyclopenta[b]thiophen-6-yl)stannane (3b) and trimethyl(4H-cyclopental[b]thiophen-4-yl)stannane (4b), or diphenyl(6H-cyclopenta[b]thiophen-6-yl)phosphine (3d) and diphenyl(4H-cyclopenta[b]thiophen-4-yl)phosphine (4d) in ratios of 1∶2, 1∶2, or 1∶1, respectively. The structure of compound4c was established by X-ray diffraction analysis. The observed regioselectivity of formation of compound4c is attributed to the specific precoordination of the tin atom by the sulfur atom of the thiopentalenyl ligand and to the steric overcrowding of the Sn atom in organotin electrophiles.

The use of macrocyclic and polydentate ligands in ruthenium organometallic chemistry

This report deals with two stereochemically different tridentate N 3-ligands suitable as ancillary ligands in the organometallic chemistry of ruthenium. [{Ru( p-cymene)(Cl)} 2(μ-Cl) 2] assisted the template synthesis of a tridentate N 3-macrocycle derived from 2-aminobenzaldehyde, thus forming [Ru(η 3-C 21H 15N 3)Ru( p-cymene)] 2+2Cl −, 1. The ligand 2, PyrPic·H, derived from the condensation of pyrrole-2-aldehyde and 2-picolylamine, functions as a monoanionic tridentate ligand in the reaction with [{Ru(COD)(Cl)} 2(μ-Cl) 2] leading to [Ru(COD)(Cl)(PyrPicH 2)], 4, which undergoes the ionization of the RuCl bond both in pyridine or in THF in the presence of AgTf, leading to [Ru(PyrPicH)Py 3] +Cl −, 5 and [Ru(COD)(PyrPicH)Tf], 6, respectively. The alkylation of 4 using LiMe led to [(RuMe)(PyrPicH)(COD)], 7, which undergoes a methane elimination to yield [Ru 2(μ-PyrPic) 2(COD) 2], 8. The reaction of potassiumpyren [pyren= N, N′-ethylenebis(2-pyrrolyliminato)dianion], 10, with [{Ru(COD)(Cl)} 2(μ-Cl) 2] led to the Ru-macrocyclic derivative [Ru(Pyren)(COD)], 11, where COD fills two cis-positions around ruthenium. Extended Hückel calculations have been carried out on the two stereochemically different RuN 3 fragments having a facial (see complex 1) and a meridional ( 4, 5, 6, 7 and 8) arrangements in order to identify the difference in the frontier orbitals for the metal reactivity.

Is CO a Special Ligand in Organometallic Chemistry? Theoretical Investigation of AB, Fe(CO)4AB, and Fe(AB)5 (AB = N2, CO, BF, SiO)

Carbon monoxide, CO, is a ubiquitous ligand in organometallic and coordination chemistry. In the present paper we investigate the neutral isoelectronic molecules AB = N2, CO, BF, and SiO and their coordination in the model complexes Fe(CO)4AB and Fe(AB)5, using nonlocal density functional theory and a large, polarized STO basis set of triple-ζ quality (NL-SCF/TZ(2P)). Our aim is to get more insight into the ligating properties of SiO and BF in comparison to CO and N2. The computed 298 K Fe(CO)4−AB bond dissociation enthalpies of C3v-symmetric Fe(CO)4AB are 18.1, 42.3, 67.9, and 35.6 kcal/mol for N2, CO, BF, and SiO, respectively; the corresponding values for C2v-symmetric Fe(CO)4AB are comparable: 19.0, 42.3, 66.7, and 39.7 kcal/mol. Good, balanced σ donation (through 5σ) and π acceptance (through 2π) are what makes CO a good donor, of course. The gap between these frontier orbitals (5σ and 2π) becomes even smaller in SiO and BF. The analysis of the bonding mechanism of the Fe−AB bond shows that SiO is a better σ donor but a worse π acceptor ligand than CO and that BF should be superior to CO in terms of both σ donor and π acceptor properties. However, these polar ligands are therefore also more reactive; and more sensitive, e.g. to nucleophilic attack, because of a low-energy 2π LUMO. Our results suggest that BF and SiO should, in principle, be excellent ligands. We also find interesting side-on and O-bound local minima, not very unstable, for SiO bound to an Fe(CO)4 fragment.

Might BF and BNR2 be alternatives to CO? A theoretical quest for new ligands in organometallic chemistry

Might BF and BNR2 be alternatives to CO? A theoretical quest for new ligands in organometallic chemistry

2,6-Bis(2,4,6-triisopropylphenyl)phenyl as an extraordinarily bulky ligand in organometallic chemistry. Synthesis and molecular structure of [(Mes*2C6H3)MCl2]2 (M = Ga, In; Mes* = C6H2Pri3-2,4,6)

Gallium chloride or indium chloride interacts with 2,6-bis(2,4,6-triisopropylphenyl)phenyllithium, (Mes*2C6- H3)Li (Mes* = C6H2Pri3-2,4,6), affording [(Mes*2C6H3)MCl2]2 (M = Ga 1, In 2), interesting group 13 organometallic crystalline dimers, characterized by elemental analyses, 1H and 13C NMR spectroscopy, and single-crystal X-ray diffraction.

Solid angles III. The role of conformers in solid angle calculations

The values of the solid angles Ω for a range of commonly encountered ligands in organometallic chemistry (phosphines, phosphites, amines, arsines and cyclopentadienyl rings) have been determined. The solid angles were derived from a single energy conformer in a geometry constrained in a prototypical metal environment, i.e. with the ligand attached to Cr(CO) 5. This choice permits comparison with recent ligand repulsive energies E R reported by Brown. Correlations between Ω, ER and θ for the range of ligands studied typically gave correlation coefficients greater than 0.8. The values of the weighted average solid angle Ω , using an extension of the methodology by Brown and Mosbo, have also been determined. The minimum conformer solid angle values are correlated with the weighted average solid angle ( r = 0.96), suggesting that the minimum-energy conformation is a good approximate measure of steric size.

ChemInform Abstract: Rigid Bidentate Nitrogen Ligands in Organometallic Chemistry and Homogeneous Catalysis. Part 4. Palladium Complexes Containing Rigid Bidentate Nitrogen Ligands as Catalysts for Carbon‐Carbon Bond Formation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Rigid bidentate nitrogen ligands in organometallic chemistry and homogeneous catalysis. 8. On the Mechanism of Formation of Homocoupled Products in the Carbon-Carbon Cross-Coupling Reaction Catalyzed by Palladium Complexes Containing Rigid Bidentate Nitrogen Ligands: Evidence for the Exchange of Organic Groups between Palladium and the Transmetalating Reagent

SOURCE (OR PART OF THE FOLLOWING SOURCE): Type article Title On the mechanism of formation of homocoupled products in the carboncarbon crosscoupling reaction catalyzed by palladium complexes containing rigid bidentate nitrogen ligands: evidence for the exchange of organic groups between palladium and the transmet Author(s) R. van Asselt, C.J. Elsevier Faculty FNWI: Van 't Hoff Institute for Molecular Sciences (HIMS), FNWI Year 1994