Reactions Of Organometallic Complexes Research Articles

The Curious Case of the Allyl Ligand: A Study in Applying the 18-Electron Rule

The 18-electron rule is an incredibly powerful tool for explaining the properties and reactivities of organometallic complexes. With the rule, however, comes the difficulty of choosing a method of implementing it, i.e. what many popular texts refer to as the “donor-pair” (ionic) method or the “neutral-ligand” method. The choice becomes particularly difficult when ligands can be counted in multiple ways via the donor-pair method, as in the case of the allyl ligand. In this investigation we hope to show that a choice of counting method can be chosen based on experimental intuition, as supported by a density functional theory (DFT) investigation. The natural electronic charge of metals, the η3-π-allyl (or simply the allyl) ligand, and the η3-cyclopropenyl ligand are discussed for a variety of organometallic complexes. A variety of DFT exchange-correlation functionals and basis sets, coupled with the Natural Population Analysis method of Landis and Weinhold, reveal the allyl ligand’s charge in a complex can be traced back to its experimental precursor. These results emphasize that the 18-electron rule is not merely a bookkeeping device and that the donor-pair method in the case of the allyl ligand holds more utility than the neutral-ligand method.

ChemInform Abstract: Reflections on Future Directions in Organometallic Electrochemistry

AbstractReview: 52 refs.

Reflections on Future Directions in Organometallic Electrochemistry

Electrochemistry is employed both as an analytical instrumental technique and as a method of inducing changes in the structure and reactivity of organometallic complexes. It is the primary implement for expanding the applications of organometallic electron-transfer (ET) chemistry and is at its most powerful when blended with the use of spectroscopy, DFT calculations of molecular structure, and chemical redox agents. Examples are given of how electrochemistry has traditionally been employed to probe changes in the structure and reactivity of organometallic complexes. Continued advances are expected for all areas in which organometallic ET processes play a role, including catalysis of small-molecule reactions, energy storage and conversion, bio-organometallic chemistry, redox polymers, and analytical and molecular devices. Particular opportunities for redox-active “hybrid” complexes in which organometallic moieties are fused with noninnocent chelate ligands or tagged onto molecular targets are discussed.

Effects of a vanadate-support on the reactivity of theBis(Methallyl)Rhodium Complex [{(η3-C4H7)2Rh}2(V4O12)]2−. A comparison with the acetylacetonato complex

The methallyl moieties of [{(η3-C4H7)2Rh}2(V4O12)]2− couple to yield 2,5-dimethyl-1,5-hexadiene in a selective manner by the action of P(OEt),3, while the reaction of [(η3-C4H7)2 Rh(acac)] with P(OEt)3 produces a mixture of organic compounds. The result shows that the vanadate support has a significant influence on the reactivity of organometallic complexes.

How to use the vibrational data for a better understanding of bonding structure and reactivity of organometallic complexes

The infrared frequency and intensity values of the main vibrational modes of selected examples of hydrocarbon ligands bonded to metals are reported. Despite the approximations on the vibrational analysis, the data offer fundamental information on structure, bonding, and reactivity of the metal-ligand unit, successfully comparable with those obtained by other sources (structural analysis, nmr spectroscopy, MO calculation). A future extension of this topic to the study of the adsorbate surface interaction is proposed, in light of the well-known cluster-surface analogy.

Reactions of organometallic complexes with singlet oxygen. Photooxidation of Vaska's complex

Reactions of organometallic complexes with singlet oxygen. Photooxidation of Vaska's complex

Volume of activation as mechanistic indicator in substitution reactions of organometallic complexes

Abstract The activation entropies for the reaction: are often so small that no distinction can be made between associative and dissociative mechanisms. A changeover in mechanism from dissociatiove ring-opening with Cr to associative ligand attack with Mo is clearly indicated in the pressure studies. In the reaction the activation volumes confirm that both forward and reverse reactions for Cr are dissociatively activated, whereas for Mo the two parallel reactions are dissociatively and associatively activatedly, respectively.

Synthesis, characterization and some reactions of organometallic complexes containing bridging dithionite ligand.

A novel organometallic dithionite complex, [η 5-C 5H 5Fe(CO) 2SO 2] 2, in which the —S(O) 2S(O) 2—ligand bridges two iron atoms has been synthesized by four methods: treatment of Na[η 5-C 5H 5Fe(CO) 2] with a large excess of SO 2, insertion of SO 2 into [η 5-C 5H 5Fe(CO) 2] 2SO 2, reaction of [η 5-C 5H 5Fe(CO) 2] 2Hg with SO 2 and irradiation of [η 5-C 5H 5Fe(CO) 2] 2 in the presence of SO 2. Of the four preparative routes, photolysis proved to be the most general one and also afforded the analogous complexes [M(CO) 5SO 2] 2 (M = Mn or Re) from [M(CO) 5] 2 and SO 2. However, irradiation of [η 5-C 5H 5M(CO) 3] 2 (M = Mo or W) and SO 2 yielded [η 5-C 5H 5M(O)S] 2 instead. The new dithionite complexes were characterized by elemental analysis and infranred and NMR spectroscopy. Photolysis of each of [η 5-C 5H 5Fe(CO) 2SO 2] 2 and [Mn(CO) 5SO 2] 2 resulted in loss of SO 2 to produce [η 5-C 5H 5Fe(CO) 2] 2SO 2 plus [η 5-C 5H 5Fe(CO) 2] 2 and [Mn(CO) 5] 2, respectively. The complex [η 5C 5H 5Fe(CO) 2SO 2] 2 reacted with alkyl iodides (RI) on heating to give η 5-C 5H 5Fe(CO) 2I and η 5-C 5H 5Fe(CO) 2[S(O) 2R], and underwent alkylation by (C 2H 5) 3OPF 6 to yield η 5-C 5H 5Fe(CO) 2[S(O) 2OC 2H 5], among other products. However, no reductive cleavage of [η 5-C 5H 5Fe(CO) 2SO 2] 2 occured with KH.

Chemistry without solvents: properties and reactions of organometallic complexes in the gas phase

The application of ion cyclotron resonance spectroscopy to the study of organometallic reactions is described. Methodology is outlined for the determination of metal-hydrogen, metal-carbon and metal-ligand bond dissociation energies and representative results are given. These data are of fundamental importance in understanding the reactions of organic molecules at transition metal centers. Decarbonylation of aldehydes and dehydrogenation of alkanes are treated as examples of oxidative addition processes. Elimination of methane from hydrido methyl complexes exemplifies the study of reductive elimination reactions. Additional examples include studies of the acylation and alkylation of metal complexes, and the reactions of molecular hydrogen with several coordinatively unsaturated species.

Reactivity of organometallic complexes containing tin-metal bonds. Activation or deactivation of tin-carbon bond towards electrophilic substitution?

As numerous experiments with electrophilic reagents have shown, organotin-transition metal complexes may be formally considered as pseudohalides. Hence there is an activation of aromatic and a deactivation of aliphatic tin-carbon bonds.

Reactions of organometallic complexes with carbon monoxide. Part III. Carbonylation of neopentyl and other alkyl complexes of mercury(II)

The reactions of carbon monoxide with nitrato(alkyl)mercury complexes HgRNO3(R = Bun, Me3C·CH2, and MeO·CH2·CH2) have been investigated in methanol. At low pressures (25 atm.) the main products were the esters RCO2Me and the nitro-compounds, RNO2. At higher pressures (200–300 atm.)α-oxo-esters, RCO·CO2Me, are also found. Nitrato(neopentyl)mercury was studied to allow a search to be made for rearranged products derived from the t-pentyl (1,1-dimethylpropyl) group. None was found and it is concluded that the mechanism of carbonylation does not involve carbonium ion formation as does the solvolysis of these complexes. The formation of an intermediate carbonyl complex is suggested. Nitrato-(n-butyl)mercury reacts with carbon monoxide in water, yielding n-pentanoic acid while in benzene solution nitroalkanes and alkyl nitrates are formed together with alcohols, acids, and esters (ROH, RCO2H, and RCO2R) that probably arise from traces of water.

Reactions of organometallic complexes with carbon monoxide. Part II. Reactions of phenyl compounds of iodine(III), lead(IV), and thallium(III)

The reactions of PhPb(OAc)3 and of compounds of the type lPh2X and TlPhX2(X = Cl, NO3, or RCO2) with carbon monoxide have been studied. Methyl benzoate and benzoic acid are formed in methanol solution, and also some methyl benzoylformate was obtained from lPh2OAc. Only the thallium compounds react in benzene solution, the main product being thallium(I) benzoate. For lPh2NO3 and TlPhCl2, a comparison between the reactivity towards carbon monoxide and triphenylphosphine has been made, and the complexes TlPhCl2(PPh3) has been characterised.

Reactions of organometallic complexes with carbon monoxide. Part I. Carbonylation and reduction of arylmercury(II) complexes and some related reactions of ethylene

The reactions of phenylmercury(II) complexes with carbon monoxide have been investigated to establish whether ‘carbonylation’ reactions take place. The basic nitrate, (HgPh)2(OH,NO3), is the only complex that yields useful amounts of benzoic acid derivatives. The pattern of reactivity of the complexes, HgPhX is reminiscent of that of mercury(II) salts and follows the ‘hardness’ of X. In aqueous solution, oxyanion complexes are reduced either to diphenylmercury and mercury or to mercury alone; this is consistent with attack of HgPh+ or H+ on a mercurated formic acid derivative. Similar reactions occur in benzene but the reduction of nitric acid by carbon monoxide as it is formed has a buffer effect which prevents reductive cleavage of (HgPh)2(OH,NO3). Benzoato(phenyl)-mercury is formed together with decomposition products from the reaction intermediate, benzoyl nitrate. This decomposition is very pressure sensitive, yielding benzoic anhydride at high pressure and biphenyl derivatives at low pressure. Carbonylation of (HgPh)2(OH,ClO4) also gives a small yield of benzoic acid. In methanol solution HgPh(CO·OMe) is formed by addition reactions of carbon monoxide when X = OH– or AcO–. The basic nitrate yields, also, some diphenylmercury but mainly methyl benzoate and methyl benzoylformate. Phenylmercury(II) complexes also add ethylene forming HgPh(CH2CH2OMe).