Π-allyl Ligand Research Articles

ChemInform Abstract: Platinum and Palladium Complex Catalyzed Regioselective Nucleophilic Substitutions with Two Different Nucleophiles at the Central and Terminal Carbon Atoms of the π‐Allyl Ligand.

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A Platinum Complex-Catalyzed Reaction of 3-Chloro-1,3-diene Monoepoxides with Carbon Nucleophiles Involving Nucleophilic Substitution at the Central Carbon Atom of the π-Allyl Ligand in the Intermediate Complex. Dependency of Regioselectivity upon the Added Lewis Acids

The reaction of 3-chloro-1,3-diene monoepoxides with sodium ethyl acetoacetate in the presence of a catalytic amount of platinum(0) complex resulted in the formation of furan derivatives. The key feature of this new platinum-catalyzed reaction is the nucleophilic substitution at the central carbon atom of the (π-allyl) complexes, which are formed as intermediates. Then cyclization follows to give furans. Different regio isomers were obtained by changing the Lewis acid added.

Platinum and Palladium Complex-Catalyzed Regioselective Nucleophilic Substitutions with Two Different Nucleophiles at the Central and Terminal Carbon Atoms of the π-Allyl Ligand

The reaction of 2-chloroallyl acetate with a mixture of sodium diethyl methylmalonate and sodium phenoxide in the presence of a platinum(0) complex as a catalyst gave a product having the carbon nucleophile at the central carbon atom of the π-allyl ligand and the oxygen nucleophile at the terminal carbon atom. The key process of this reaction is the nucleophilic substitution at the central carbon atom of the π-allyl ligand. Further examples of nucleophilic substitution at the central and terminal carbon atoms of a π-allyl ligand were demonstrated for the case of a palladium(0) complex as the catalyst.

A New Platinum Complex Catalyzed Reaction Involving Nucleophilic Substitution at the Central Carbon Atom of the π-Allyl Ligand

The reaction of 2-chloro-allyl acetate with sodium ethyl acetoacetate in the presence of a platinum(0) complex gave furan derivatives. The key feature of this new platinum-catalyzed reaction is the...

Synthesis of Molybdenum Dicarbonyl Complexes Bearing Tethered Homoallylic Amines and Sulfides

A series of organomolybdenum complexes, 8−14, bearing a π-allyl ligand tethered to a chelating heteroatom, have been synthesized from the reaction of allylic acetates 1−4 with the sodium salt of β-dicarbonyl compounds 5−7 and Mo(CO)6 in THF. X-ray structural analysis established the relative configuration at the metal center.

Conformational Restriction of Acyclic π-Allyl Ligands in (3,7-Diphenyl-1,5-dimethylbispidinone)(η3-alkenyl)palladium Complexes

A chelating dinitrogen ligand based on the bispidine skeleton is shown to restrict the conformational freedom of small, acyclic π-allyl ligands in palladium complexes. The π-allyl ligand is locked into one single rotamer by entirely steric interactions. These interactions do not require the presence of bulky substituents on the π-allyl ligand. The geometry of these complexes has been investigated by NMR spectroscopy in combination with semiempirical calculations.

Synthesis and Reactions of (π-Allyl)bromo- [hydrotris(3,5-dimethylpyrazolyl)borato]rhodium(III)

TpMe2Rh(coe)(MeCN) (1) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borato, coe = cyclooctene) has been found to readily undergo oxidative addition of allyl bromide at room temperature to give TpMe2Rh(σ-allyl)Br(MeCN) (4). On prolonged reaction time or heating, complex 4 is converted to the π-allyl complex TpMe2Rh(π-allyl)Br (5) with liberation of MeCN. Complex 5 exhibits high reactivity toward MeMgBr and Li[BHEt3], giving TpMe2Rh(π-allyl)Me (8) and TpMe2Rh(π-allyl)H (9), respectively. Deuterium-labeling experiments using Li[BDEt3] indicate that complex 9 is formed mainly by nucleophilic addition of H- to the central carbon of the π-allyl ligand, followed by β-hydrogen elimination of the resultant rhodacyclobutane intermediate. Complex 9 reacts with a variety of alkyl bromides by a radical process to afford 5 and alkanes.

Molybdenum-mediated synthesis of isoxazole compounds through a nitrosyl insertion into a π-allyl ligand

The syntheses of compounds of the type CpMo(CO)2[η3-anti-1-CH2CH(OH)R-syn-3-R′CH2–C3H3] are described; their reactions with excess nitrosonium tetrafluoroborate produce 3-(1′-R′CH2CHCH)-5-R-isoxazole, which involves a remarkable nitrosyl insertion into the π-allyl ligand as the key step.

ChemInform Abstract: Molecular Basis of Catalytic Reactions Involving Olefin and Allyl Complexes of Group 10 Metals

Molecular level understanding of a relationship between structure, bonding and reactivity of olefin and allyl complexes of group 10 metals is presented. In addition to three types of olefin complexes previously known, namely 3-coordinated M (O), 4-and 5-coordinated M (II) complexes, a complex containing, π-olefin and, π-allyl ligands simultaneously represents a new type of the group 10 metal-olefin compounds possessing some unique stability, structural and reactivity aspects. Dynamic equilibria and electrophilic substitution of novel σ-allyl-metal complexes are presented. Mechanistic knowledge concerning stoichiometric reactions of π-allyl-metal complexes, namely nucleophilic substitution and reductive elimination, is surveyed and its relevance to actual catalysis is also discussed.

Acyldemetallation of titanium(III) π-allylic complexes

Titanium(III) π-allylic complexes, prepared by the interaction of 1,3-dienes or trienes with Cp 2TiCl 2 and n-PrMgBr, react with carboxylic acid chlorides RCOCl (R = alkyl, aryl, alkenyl) to give β, γ-unsaturated ketones in high yields. The reaction takes place at the most substituted carbon atom of the π-allylic ligand.

2:1-Cocyclization of but-2-yne with the ?-allyl ligand in cationic ?-allyl complexes of ruthenium, osmium, and rhodium

A new reaction was found consisting of 2:l-cocyclization of but-2-yne and the π-allyl ligand in Ru, Os, and Rh complexes with formation of 2-5-η-2,3,4,5-tetramethylcyclohexa-2,4-dien-1-yl-σ-methyl derivatives of these metals.

第１０族元素のオレフィンおよびアリル錯体を含む触媒反応の分子論的基礎

Molecular level understanding of a relationship between structure, bonding and reactivity of olefin and allyl complexes of group 10 metals is presented. In addition to three types of olefin complexes previously known, namely 3-coordinated M (O), 4-and 5-coordinated M (II) complexes, a complex containing, π-olefin and, π-allyl ligands simultaneously represents a new type of the group 10 metal-olefin compounds possessing some unique stability, structural and reactivity aspects. Dynamic equilibria and electrophilic substitution of novel σ-allyl-metal complexes are presented. Mechanistic knowledge concerning stoichiometric reactions of π-allyl-metal complexes, namely nucleophilic substitution and reductive elimination, is surveyed and its relevance to actual catalysis is also discussed.

Bimetallic transition metal carbene complexes—some novel aspects and developments

Readily available (butadiene)zirconocene and -hafnocene complexes react with various metal carbonyls to form metallacyclic metal oxycarbene complexes. The π-allyl species Cpa 2 MOC[M′L n ]C 4 H 6 ) (M = Zr, Hf) can often be obtained crystalline. The bimetallic carbene complexes exhibit a rather short OC(carbene) bond distance indicating a pronounced metal acyl complex character. Carbene complex formation between (s- trans -η 4 -butadiene)zirconocene and CpCO(CO) 2 or CPV(CO) 4 , respectively is reversible. The equilibrium can be shifted towards the carbene complex side by reducing the electron density at the carbene ligand bearing metal or by using the hafnium instead of the zirconium containing butadiene metallocene reagent. Five-membered benzannelated zirconium oxycarbene complexes CP 2 ZrOC[W(CO) 5 ](C 6 H 4 ) were obtained by CC-coupling from thermally generated (1,2-didehydrobenzene)zirconocene and W(CO) 6 . This carbene complex is an oligomer in the solid state as revealed by X-ray diffraction. Monomeric units are linked together via intermolecular ZrOCW bonds. This zirconium oxycarbene complex acts as an organometallic Lewis acid in solution. It reversibly coordinates organic carbonyl compounds. Zirconium oxycarbene complexes CP 2 Zr(OR)C(Ph)W(CO) 5 react readily with several non-stabilized phosphorus ylides to produce zirconium enolates CP 2 Zr(OR)C(Ph)CHR which can be used as carbon nucleophiles in syn -selective aldol condensation reactions. The (butadiene)zirconocene derived metallacyclic zirconium oxycarbene complexes CP 2 ZrOC[M(CO) 5 ](C 4 H 6 ) (M = Cr, Mo, W) act as carbon nucleophiles at the Zr-bound substituted π-allyl ligand. Ketones or aldehydes are CC-coupled regioselectively to the allyl-CH 2 terminus to form chiral nine-membered metallacyclic products.

La{(Ph2P)2CH}3]—a Homoleptic Lanthanum Complex with π‐Allyl‐like Coordinated Diphosphinomethanide Ligands

In the complex 1, diphosphinomethanide ligands are arranged spoke-like like π-allyl ligands about the central atom, whereas in the previously known complexes of these ligands, coordination takes place via the lone pairs of the P atoms. Thus, 1 is an example for the analogy between phosphorus and carbon chemistry, also in unsaturated systems.

Quantum-chemical study of Ni complexes active in reactions of oligomerization of olefins and polymerization of allenes

Based on EHM calculations of complexes of ethylene, allene, and dimethylallene with π-allylnickel bromide, it was shown that the activity of the corresponding monomers in the oligomerization reaction is determined by the elevated charge density on the terminal C atom of the π-allyl ligand in the trans position to the halogen. Addition of alienes to the C atom of π-allyl takes place on the central C atom in allene, characterized by a reduced charge density, the activity of the complexes in substitution of the halogen increases in the order Cl < Br< I, and the activity of the monomers increases in the order ethylene < allene < 1,1-dimethylallene.

Synthesis of substituted π-cyclopentadienyl complexes of ruthenium, rhodium and iridium by a novel reaction of intramolecular condensation of π-allyl ligand and alkyne. X-ray structure of [η-C 6H 6Ru(η-C 5H 3Ph 2-1,2)]BF 4

The five-membered carbon ring-forming reaction between π-allyl-π-arene complexes of Ru and π-allyl-π-cyclopentadienyl complexes of Rh and Ir with a series of aryl- and alkyl-substituted alkynes was used to prepare [η-C 6H 6Ru(η-C 5H 5- m-n R m 1R n 2)] + and [η-C 5R 5M(η-C 5H 5- m-n R m 1R n 2)] + cations (R 1,2=alkyl, aryl; m = 1,2; n = 1,2; M = Rh, Ir; R = H, Me), which were obtained as their BF 4 − or PF 6 − salts in good yields. The scope of the reaction and the mechanism are discussed. [η-C 6H 6Ru(η-C 5H 3Ph 2-1,2)]BF 4 was characterized by X-ray crystallography.

X-ray crystal structure of (η 5-pentamethylcyclopentadienyl) (η 3-1,3-dimethylallyl)chlororhodium: localized “Di-π-olefin-σ” bonding of cyclopentadienyl

The crystal structure of (η 5-C 5Me 5)(η 3-MeHCCHCHMe)RhCl at −120°C was determined ( R = 0.041 for 1790 reflections). The molecule has approximate mirror symmetry. The cyclopentadienyl ring is bent by 6.8°, acquiring an envelope-like conformation, and its bonding with Rh is of a partially-localized η 4:η 1 type with RhC(“π-diolefin”) of 2.206–2.235 Å and RhC(“σ-bonded”) of 2.151 Å. The syn-arrangement of the Me groups in the π-allyl ligand, assigned by NMR spectra, is confirmed.

IR Spectroscopic study of matrix-isolated free allyl radicals and analysis of vibrational spectra and structure of ?-allyl organometallic compounds

1. By the technique of matrix isolation of products from the vacuum pyrolysis of 1,5-hexadiene-d10, the IR spectrum of the free allyl radical C3D5 has been obtained for the first time. 2. On the basis of the IR spectra of the C3H5 and C3D5 radicals, vibrational frequencies of the allyl radical have been calculated, and the bands have been assigned to the normal vibrations. 3. A systematic comparison has been made of the vibrational frequencies of the allyl radical and the Π-allyl ligand in the composition of organometallic compounds. It has been established that the frequencies of out-of-plane vibrations ρw(CH2), ρt(CH2), and ρ(CH) are substantially higher for the Π-allyl ligand; the frequencies of vibrations taking place in the plane of the allyl fragment are little different for the two cases. A new assignment has been proposed for a number of frequencies in the spectra of Π-allyl complexes. 4. The system of bonds for the allyl radical is characterized by relatively low frequencies of stretching vibrations and the force constant 5. 8 mdyne/A. The values of νs(CCC) and νas(CCC) show that upon formation of a Π-allyl complex, there is no loosening of the carbon-carbon bonds of the ligand, in contrast to Π-complexes of unsaturated compounds.

Stereochemistry of the reaction of an optically active π-allylpalladium complex with nucleophiles

The stereochemistry of the reaction of π-allylpalladium complexes with nucleophiles has been elucidated using optically active (–)-(1S,2R,3R)-di-µ-chloro-bis(1-methyl-3-phenyl-π-allyl)dipalladium(II); dimethyl sodiomalonate and dimethylamine attack a carbon atom of the π-allyl ligand from the side opposite to the palladium (inversion), and phenyl and allyl Grignard reagents attack the π-allyl carbon atom from the same side as the palladium (retention).

Stereochemistry in the palladium-catalyzed rearrangement of some cyclohex-2-enyl acetoacetates

The palladium-catalyzed decarboxylation and rearrangement of cis -5-substituted-cyclohex-2-enyl acetoacetates to give the corresponding methyl ketone proceed mostly with retention of configuration, indicative of an enolate addition to the π-allylic ligand trans to the palladium. The reaction from the trans-isomer is not stereoselective.