P. L. Stanghellini

1H and 13C NMR studies of acetylenic complexes of Co2(CO)8

Abstract 1H and 13 Cnmr spectra of the acetylenic complexesCo 2 (CO) 6 (RC 2 R′) show downfield shifts of the ligand resonance upon complexation. The slight dependence of the chemical shift of C from the substitution on C′ is discussed in terms of the metal-alkyne bonding. Upfield shifts are observed for the acetylenic carbons when L (P- or As-ligand) substitutes one CO. Variable temperature 13 Cnmr spectra show that the carbonyl are rapidly interchanging and that the rate of exchange depends on R and R′.

Chalcogen derivatives of iron carbonyls I. Substituted derivatives of Fe3(CO)9X2 Complexes (X=S, Se, Te) with ligands

Abstract Series of mono- and disubstituted derivatives of Fe3(CO)9X2 complexes (X= S, Se, Te) with ligands are prepared. Different reactions are found with the Te compound, which also gives additional derivatives. An explanation is proposed, referred to the difference in electron attracting power of the chalcogen atoms. Also the preparations, the properties and the main infrared absorption frequencies of the new compounds are reported.

Dynamic properties of the trinuclear carbonyl cluster FeCo2(CO)9S and its Derivatives

Abstract 13C.-n.m.r. spectra show that the replacement of CO by a group V ligand in FeCo2(CO)9S is at one cobalt atom in the monosubstituted derivative, at the two cobalt atoms in the bisubstituted derivative and at the two cobalt and at the iron atom in the tri-substituted derivative. The substitution is at an equatorial position in each case. Multistage exchange of the carbonyls is a common feature of these complexes. The activation energies for the localised scrambling at the unique iron atom have been evaluated and shown to be influenced by the nature and the number of the substitents at the cobalt atoms. Localised scrambling of the CO of any M(CO)2L moiety is not observed to take place prior of internuclear scrambling.

Chalcogen derivatives of iron carbonyls. II. Carbon monoxide isotopic exchange and substitution reactions with ligands in Fe3(CO)9X2(X = S, Se, Te,) complexes

Abstract Kinetic results on the CO isotopic exchange and substitution reactions with ligands in Fe 3 (CO) 9 X 2 (X = S, Se, Te) complexes are reported. The reaction rates follow an S N 1 and/or S N 2 mechanism depending upon the electronegativity of X and the nucleophilicity of L. The values of k 1 are in agreement with the ν c-o and are referred to a dissociation mechanism. An explanation in terms of electron distribution within the complex is proposed.

Chalcogen derivatives of iron carbonyls. V. Kinetics and mechanism of CO exchange and of substitution reactions of Fe3(CO)9XY complexes (X and Y=S, Se, Te with X≠Y)

Abstract Fe 3 (CO) 9 XY complexes undergo carbonyl substitution with triphenylarsine and triphenylphosphite to give the mono- and di-substituted derivatives, Fe 3 (CO) 8 LXY and Fe 3 (CO) 7 L 2 XY. The preparation and spectra of these compounds are reported. The substitution reactions and the CO exchange reaction proceed according to the two term rate law: rate = k 1 [complex] + k 2 [complex][ligand], in which the relative values of k 1 and k 2 depend on the nature of X, Y, and L. The results are in agreement with the reactivity of the Fe 3 (CO) 9 X 2 complexes.

Redox reactions of metal carbonyls. I. Kinetics and mechanism of disproportionation of Co2(CO)8 with piperidine

Abstract The disproportionation reaction of Co 2 (CO) 8 by nucleophilic attack of piperidine has been investigated at different temperatures in n-heptane with the stopped-flow technique. The reaction is given by a series of successive and/or competitive pathways with different kinetic dependence on the ligand concentration. The experimental findings suggest that a rapid coordination of the ligand (L) occurs until the Co 2 (CO) 7 L 3 species is formed; then the adduct dissociates into ionic fragments. The mechanism and the kinetic parameters are discussed with reference to available findings on Co 2 (CO) 8 .

Chalcogen derivatives of iron carbonyls. VIII. Reaction of Fe2(CO)6(μX)2 (X = S, Se) with nucleophiles: CO substitution and Fe3X2 cluster formation

Abstract Phosphine ligands L react with Fe 2 (CO) 6 (μX) 2 (X = S, Se) complexes giving rise, together with the expected mono- and bi-substituted derivatives, Fe 2 (CO) 5 LX 2 and Fe 2 (CO) 4 L 2 X 2 , to more complex polynuclear clusters Fe 3 (CO) 9−x L x X 2 ( x = 0, 1, 2). The yield of the different products is shown to depend on the ligand and the reaction conditions. A mechanism is proposed implying the initial formation of an ‘adduct’ Fe 2 (CO) 6 LX 2 , which leads to the binuclear derivatives by loss of CO and to the trinuclear derivatives by coordination on the parent complex via the chalcogen atoms.

IR frequencies and intensities of the vibrational modes of Cx Hy fragments bonded to metal complexes. Relationship with structure, bonding and reactivity

Abstract The following organometallic complexes were studied as models of the coordination between metal atoms and different C x H y ligands: Co 2 Fe(CO) 9 (CCH 2 ), Co 2 Ru(CO) 9 (CCH 2 ), Os 3 (H) 2 (CO) 9 (CCH 2 ) and Co 2 Fe(CO) 9 (CC(H)CH 3 ) (η 3 -η 2 -vinylidene or μ 3 -η 2 -methylvinylidene group); Fe 2 (C 5 H 5 ) 2 (CO) 3 (CCH 2 ) (μ 2 -η 1 -vinylidene group); Os 3 (μ-H)(CO) 9 (CHCH 2 ) (μ 2 -η 2 -vinyl group); CH 3 Mn(CO) 5 (η 1 -methyl group); Os 3 (μ-H) 2 (Co) 10 (CH 2 ) and Fe 2 (CO) 8 (CH 2 ) (μ 2 -η 1 -methylene group); Co 3 (CO) 9 (CH) (μ 3 -methyne group); CO 3 (CO) 9 (CCH 3 ) (μ 3 -η 1 -ethylidyne group); Os 3 (H)(CO) 9 (C 2 H) (μ 3 -η 2 -acetylide group). The infrared frequencies and intensities associated with the main vibrational modes of the ligands (CC and CH stretchings, CH deformations) were evaluated and compared with those of appropriate model molecules. Both the frequency and intensity data can be usefully correlated with structural parameters (e.g. CC and CH bond distances and HCH bond angles) and provide information on the charge distribution on the ligands. It is therefore possible to discuss the type of metal—ligand interaction and the balance between the σ and π contributions to the bond.

Synthesis of [SCo3(CO)7(S2COMe)] and the structure of its PPh3 derivative

SummaryThe title compound has been prepared in reasonable yield by reaction of a methanolic solution of CoCl2 and MeOCS2K with CO. I.r. spectra have been analyzed both in the C-O stretching region and in the region of the main vibrations of the xanthate ligand: an explanation of the appearance of only 4 out of 7 i.r.-active ν(CO) modes is proposed. The structure of the triphenylphosphine derivative has been solved by x-ray diffraction analysis: [SCo3(CO)6(PPh3)(S2COMe)] crystallizes in the triclinic space group P¯1, witha = 10.710(3),b = 10.199(3) andc = 16.208(4) Å, α = 113.57(2)°, β = 98.14(2)°, γ = 104.32(2)°, Z = 2, λ(MoKα) = 0.7107 Å. The final R value is 0.045 [4461 reflections with F > 6 σ(F)]. The molecule is formed by an SCo3 cluster, in which each Co atom coordinates two CO groups. The chelating xanthate ligand is equatorially bonded to two cobalt atoms forming a nonplanar pentaatomic ring; the phosphine is equatorially bonded to the other cobalt atom.

The charge distribution on metal-bonded cyclopentadienyl rings from infrared intensities

Abstract The IR intensities of the CH vibrational modes of a hydrocarbon fragment bonded to a metal atom are a useful probe to evaluate the charge distribution on the fragment. The values of R , the ratio of the overall CH bending and CH stretching IR intensities of the cyclopentadienyl ligand, are reported for several organometallic complexes containing the η 5 -C 5 H 5 M unit. The parameter R is related to several properties of the complexes, such as the ionic charge, the nature of the metal and of the ancillary ligands, the CH bending force constant and to the solid-state structure.