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The synthesis of oxidised water-soluble fullerenes, prepared by chemically-induced aerobic oxidation, yields functionalised carbon cluster structures, which are oxidised by the covalent insertion of different oxygen units. Their strictly pH-dependent behaviour in aqueous solutions appears to be properly ascribed to the existence of directly attached carboxylic moieties. The presence of these groups, which are usually neglected and underestimated, has been thoroughly investigated. Several concurrent spectral (UV–VIS, XPS, solid-state 13C CPMAS NMR, FT-IR, Raman, EDAX, TGA-MS, ESI-MS) and chemical (acid–base behaviour, salt precipitation by metal-complexation, carboxylic functionalisation) methods have provided a definitive set of consistent evidence, indicating for the first time the direct linkage of carboxylic groups on water-soluble fullerenes prepared in this manner.

The nu(CN) vibrational spectra of cyanide groups bridging two metal atoms present a confused picture. Factors relevant to the interpretation of the available data are reviewed. Some mechanisms for frequency change, relative to the corresponding terminal species, are made more quantitative than previously described, and others are highlighted for the first time. The kinematic effect is much less important than previously assumed. It seems that an effect responsible for the major part of the frequency increase upon bridging commonly observed is the cation electric field, together with concomitant relaxation (the IVSE model). However, a contribution may well come from the change in the sigma bonding in the CN unit.

A comparison is made between the vibrational characteristics of the carbonyl and cyanide ligands. There are significant differences; the latter has a smaller dipole moment and a larger quadrupole moment associated with the bond stretch. This quadrupole moment may be linked to the observation that the totally symmetric nu(CN) mode does not lie at the highest frequency for some cyanide complexes. There are problems with the pi-bonding model commonly used to interpret the nu(CN) data. For instance, for the first transition row hexacyanoanions, the spectra are almost independent of t2g occupancy but are very sensitive to the formal charge. It is suggested that the observed nu(CN) frequency shifts on complex formation are in large measure determined by the effective charge on the cation to which the cyanide group is attached, and a new model, the Internal Vibrational Stark Effect, is suggested to account for this. The model is supported by DFT calculations. Raman spectra of some cubic cyano species are reported, along with polarization and intensity data.

The ν(MM) Raman spectra of some twenty doubly bridged Os3 carbonyl clusters are interpreted using a new model in which the mass of all the ligands is incorporated. The frequencies are fitted remarkably well; the average standard deviation is 2.1 cm−1. The data from the model seems to have some physical reality in that when applied to the calculation of some structural parameters (OsOs distance and OsOsOs angle) it gives reasonable results.

When the Fe(CO)4 and M(CO)5 (M=Cr, W) groups are co-ordinated in C3v and C4v fashion, respectively, in transition metal carbonyl cluster species they contain two sets of non-symmetry related carbonyl groups. In the application of the spherical harmonic model (SHM) to the interpretation of the infrared spectra of these compounds it proves necessary first to treat these as for a normal, isolated, M(CO)4 or M(CO)5 group and then apply the SHM. This recognition gives insights into the general application of the SHM.

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 η5-C5H5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.

Co2(CO)8 and Te2O react to form the well known Co4(CO)10Te2, Co4(CO)11Te2 complexes and the two new cluster complexes CCo6(CO)12Te2(1), and CCo6(CO)10Te2(Te3) (2). The structures of 1 and 2 were determined by X-ray analysis, together with the triphenylphosphine derivative of 1, CCo6(CO)11(PPh3)Te2(3), which was analyzed to clarify the disordered structure of the parent compound. Complex 1 is formed by a prismatic cluster of cobalt atoms with a carbon embedded in the cage; two tellurium atoms cap the triangular faces of the prism and each cobalt atom links two terminal carbonyl groups. The complex 2 has a similar prismatic cage CCo6; two μ4-Te atoms cap two rectangular faces of the prism, while other two Te atoms bridge two edges of the triangular faces and are linked each other through a third Te atom. Electron counting gives for complex 2 92 electrons: the presence of two long Co–Co distances suggests that the two excess electrons are located on Co–Co antibonding orbitals. Crystal data for 1, space group C2/c, a = 12.845(2) A, b = 13.449(2) A, c = 13.246(2) A, β = 91.95(2)°, Z = 4, R = 0.097 for 2555 reflections; for 2, space group Pnna, a = 17.219(5) A, b= 14.969(6) A, c = 9.178(4) A, Z = 4,R = 0.037 for 3103 reflections; for 3, space group P21/c, a = 9.288(2) A, b = 14.920(6) A, c = 26.300(9) A, β = 99.99(2)°, Z = 4, R = 0.037 for 4300 reflections. The vibrational analysis of the complex 1 was performed and most of the ν(CO), ν(μ6C–Co), ν(Co–Co) and ν(Co–Co) modes were assigned. The ν(Co–Te) modes were interpreted on the basis of the intermolecular coupling, due to the close contact between neighboring clusters in one distinct direction in the crystal.

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.

Co 6 C(CO) 12 Se 2 crystallizes in the monoclinic system, space group Cc with a = 16.365(4) A, b = 9.429(2) A, c = 17.479(5) A, β = 122.75(2)°, Z = 4 and (Mo — K a ) = 0.71070 A. The final reliability indices are R = 0.051 and R W = 0.048 for 2081 observed reflections having F > 4.0σ( F ). The molecule consists of a Co 6 trigonal prism with the triangular faces capped by selenium atoms. Each cobalt is bonded to two terminal CO groups. A carbon atom is embedded at the centre of the Co 6 prism. The Raman spectra of polycrystalline samples of this compound and of the sulphur analogue have been recorded. These, together with the corresponding infrared data, can only be understood in terms of a dominant intermolecular coupling on the ν(Co—E) modes (E = S, Se). The origin of this coupling is the close contact between neighbouring clusters in one distinct direction which gives rise to a chain of molecules in the crystal. The significant effect of these oriented close contacts on the vibrational modes is demonstrated.

The crystal structure of Co4(CO)10S2 has been redetermined and that of Co4(CO)10Se2 obtained by X-ray analysis. The compounds are monoclinic and isomorphous, space groupP21/n,Z=2, with (S compound)a=10.42(2)A,b=6.794(1)A,c=12.421(2)A,β=97.27(1) and (Se compound)a=10.110(2)A,b=6.747(2)A,c=12.592(4)A,β=96.37(2); finalR(S)=0.029,R w =0.032 for 1414 reflections and finalR (Se)=0.052,R w =0.054 for 1264 reflections. The molecules, which lie on a crystallographic center of symmetry, consist of a rectangle with Co atoms at the corners, each face of the rectangle being capped by a chalcogen atom. Each Co atom is bonded to two terminal CO groups; there are two bridging CO groups, one on each member of a pair of opposite sides of the rectangle. The vibrational spectra of the sulfur compound are considered in detail. A study of the crystal structure, and recognition of an approximate spectroscopic space group, are shown to be essential for an understanding of thev(CO) infrared spectrum of polycrystalline Co4(CO)10S2. In this molecule, intramolecular vibrational coupling in the crystal leads to extensive modifications of the infrared-activev(CO) molecular coordinates.

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.

The title complex is the main product of the room-temperature reaction between Co 2 (CO) 8 and sulfur. Its crystals are monoclinic, space group C2/c

The average frequency of the bands belonging to the same type of vibrations and the contribution per C-H bond to the total C-H stretching and bending intensities are evaluated and compared with the relevant values for the free alkyne. Both the frequency and intensity data provide informations on the effect induced in the alkyne (bond strengths and charge distributions) by the metal coordination and are related to the type of the metal-alkyne bond, to the nuclearity, and to the geometry of the cluster

The interstitial metal clusters form a fascinating class of complexes of the transition metals, where a non-metallic atom X is uniquely bonded to the metal atoms of the core. From the structural point of view, two subclasses might be distinguished, the properly called “interstitial” clusters, where the heteroatom is completely surrounded by the metal atoms of the cage in which it is inserted, and the “semi-interstitial” or “exposed” clusters, where the heteroatom is placed on, or nearby, a face or an edge of a metal polihedron. Moreover, even if the carbon atom remains the first reported and the most commonly encountered heteroatom, one example at least has appeared with hydrogen1, nitrogen,2 boron,3 phosphorous,4 sulphur,5 silicium,6 arsenic7 and antimony8 interstitial atoms. Together with these more common systems, there is an increasing number of policarbido and polihydrido complexes, containing several interstitial heteroatoms9; recently, an example of a cluster with carbon and hydrogen toget...

The ν (CO) spectra of 31 M 5 transition metal carbonyl clusters are interpreted in terms of the spherical harmonic and tensor harmonic models. It seems that the former is that which is generally applicable but that the splittings of the (spherical) P mode are larger than had previously been considered indicative of this model. An explanation in terms of the cluster asymmetry is suggested.

The ν(CO) spectra of a series of transition metal cluster compounds are compared with their structures. Despite considerable structural differences, the spectra in the terminal region are surprisingly invariant. Rather more variation is shown in the bridging region spectra; it proves possible to understand these variations in terms of a qualitative model. A generalisation concerning bridging region spectra is presented.

Vibrational frequencies of the methoxy groups in the cluster compounds [Re2(μ2-OCH3)3(CO)6] [P(C6H5)4] and [Re3(μ2-H)3(μ3-OCH3)(CO)9][N{P(C6H5)3}2] are assigned using selective deuterium substitution. The νs(CH3) and ρ(CH3) modes were found to be the most sensitive to the state of coordination of the methoxy group. A comparison of the cluster data with RAIRS data for methanol adsorbed on Cu(100) and Cu(111) single crystal faces provides a unifying model for the surface methoxy species. This consists of μ2-coordinated methoxy groups tilted to the surface normal on both surfaces at low coverage, but with the tilt angle decreasing with higher surface coverage.

The reaction of [Fe3(CO)12] with RNO2(R = Et or PrI) gives, among complexes of well known structures, many other iron–nitrogen–carbonyl complexes which are indicative of novel reaction paths, such as reduction of a nitro-to a nitroso-group, hydrogen abstraction, and N–C bond breakage. The complexes have been fully characterized by means of i.r., mass, and 1H and 13C n.m.r. spectroscopy. The crystal structure of the title complex has been determined by X-ray diffractometry from 2 446 reflections (R 0.037). Crystals are triclinic, space group P, with Z= 2 in a unit cell of dimensions a= 12.008(5), b= 9.827(4), c= 8.580(4), A, α= 120.53(4), β= 99.29(1), and γ= 96.80(1)°. The structure consists of two Fe(CO)3 units linked by an Fe–Fe bond and doubly bridged by the nitrogen of the isopropylamido-ligand and the nitrogen and oxygen of the oximato-ligand. The n.m.r. study shows the presence of a substantial torsional barrier about the N–Fe and N–O bonds and localized carbonyl interchange.

The paper reports the synthesis, spectroscopic properties and structural characterization of a new di-iron carbonyl compound Fe 2 (CO) 6 (μ-OCCH 2 C 6 H 5 )(μ-NC(CH 3 ) 2 ), obtained in the reaction between Fe 3 (CO) 12 and 2-nitropropane in toluene solution. The complex crystallizes in the monoclinic P2 1 /n space group with a = 19.70(5), b = 11.62(4), c = 16.78(4) A and β = 95.19(2)°, Z = 8 and shows the presence of two independent molecules in the unit cell. The mlecular structure consists basically of two Fe(CO) 3 unites, joined by a FeFe bond and bridged by the benzylcarboxy and isopropylene amido ligands. The presence of the former ligand represents a proof of activation of the solvent, which probably occurs via an unstable hydrido alkyl iron intermediate.

13C-n.m.r. spectra of (μ-SR)2Fe2(CO)6, (μ-SR)2Fe2(CO)5P(n-Bu)3 and (μ-X)2Fe2(CO)6 (X=S or Se) show that the solid state structure is maintained in solution. N.m.r. evidence indicates that two isomeric species, not separable by means of the usual physicochemical methods, are present for (μ-SPh)2Fe2(CO)6 with an overwhelming predominance of theanti form. The phosphine substitutes a COtrans to the iron-iron bond. For any of the iron chalcogen derivatives examined, variable temperature13C-n.m.r. spectra show that carbonyl exchange occur in one step. The energy barrier for the exchange of carbon monoxide in the phosphine derivative is lower than that in the unsubstituted complex.

The compound [Co8(CO)21(µ5-CS2)(µ5-C2S)], a minor product of the reaction between [Co2(CO)8] and CS2, has been characterized by X-ray diffraction analysis. The crystals are monoclinic, space group Cc, with a= 9.208(4), b= 15.864(6), c= 25.36(1), β= 96.39(3)°, and Z= 4. The Co atoms were located by the Patterson method, the S, C, and O atoms by Fourier difference maps. The final R was 0.0899 for 3 206 reflections with F > 6σ(F). The structure consists of an assembly of three cobalt clusters, the central one being the most interesting part of the complex, as it shows an unprecedented Co2(µ-SC) fragment. The compound is formally derived from a previously reported one by isolobal substitution of a Co(CO)3 group by a C–R group [R = CCo3(CO)9].

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.

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 .

Co6C(CO)12S2 (I) has been isolated in crystalline form from the mixture of more than a dozen of carbonyl products formed when Co2(CO)8 reacts at room temperature with CS2. Crystals of I are monoclinic with space group Cc, and lattice constants a  16.250(5), b  9.413(4), c  16.036(5) A, β  116.77(4)°. Structure refinement gave R  0.034 for 1974 reflections. The CCo6S2 core of the molecule possesses idealized D3h geometry. It is composed of a Co6 trigonal prism, enclosing a C atom in the centre, and the triangular faces are capped symmetrically by the two S atoms. The core contains two sorts od CoCo distances: short one (2.432 A) along the triangular edges, and long ones (2.669 A) along the lateral edges. The average CoC distance is 1.94 A, and the average CoS distance 2.192 A. 13CO-enriched samples were prepared photochemically and their IR spectra used in the assignment of the CO stretching frequencies. The CO stretching force constant was calculated to be 1670(2) Nm-1. By the use of 13CS2, I has also been obtained in a selectively carbido-13C-labelled form. The vibrational frequencies of the carbide atom were observed, and that at 819 cm-1 (13C: 790 cm-1) assigned to the species , and that at 548 cm-1 (13C: 535.5 cm-1) to species E′. For the Co-C(carbide) force constant a value of 155 Nm-1 was calculated. The cobalt—sulphur stretching frequencies were found at 309 cm-1 ( ) and 239 cm-1 (E′). The CoS stretching force constant, 78 Nm-1, is considerably lower than that obtained for SCo3-(CO)9, viz. 112 Nm-1.

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.

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′.

Cristallisation dans le groupe P2 1 2 1 2 1 (Affinement jusqu'a R=0,045). Les six Co sont disposes en forme de bateau. Les quatre Co de la base forment un carre regulier, avec des liaisons Co-Co des 4 cotes. Les deux Co situes au sommet sont lies de la facon suivante: Co-C-C-Co. Les 6 Co portent des CO. Un pont sulfuro est etabli entre les 4 Co de base

The reaction of the title complexes with phosphine-like ligands proceeds by two competing path, one, first order in [complex] and (L), the other first order in [complex] and second order in (L). The mechanism can be explained by a rate-determining formation of an intermediate Fe2(CO)6L(μX)2, which can lose CO or react further with another L prior to decomposition. The effect of both X and L on the rate of the two paths is discussed. The values of the rate constants show a large discriminating ability of the substrate versus the ligand, and this is tentatively explained by a facile coordination of the ligand on the complex via a low-energy empty M.O.

The title reaction at CO pressures up to 1 atm. gives rise quantitatively to Ru3(CO)12 and Ru(CO)5. A kinetic study shows complicated dependence of the rate of the reaction on the concentration of the complex, of CO and H2. The isotopic effect, when the reactivity of the hydride and of the deuteride complexes are compared, suggests the contemporary breaking or weakening of RuRu and RuH bonds as the rate-determining step. The proposed reaction mechanism points out the importance of a ‘butterfly-shaped’ Ru4 intermediate, as a probable active form in many catalytic reactions involving tetranuclear ruthenium carbonyls.

The title compound, obtained from the reaction of [Co2(CO)8] with CS2, has been fully characterized by X-ray diffraction analysis. The incorrectness of the previously reported formulation, [{Co3(CO)9(CS)}2], is ascribed to the disordered –S–C(O)– chain joining the two CCo3(CO)9 entities. The compound is triclinic, space group P, with a= 8.794(4), b= 12.576(4), c= 8.113(4)A, α= 105.14(3), β= 113.32(4), γ= 95.61(1)°, and Z= 1. The cobalt atoms were located by the conventional Patterson method and the C, O, and S atoms by subsequent Fourier-difference maps. The final R value was 0.046 for 2 021 reflections with I > 3σ(I). The central part of the molecule, C–S–C(O)–C, is planar, with large π-electron delocalization and with different orientations with respect to the two Co3 triangles. Its vibrational modes correspond to the i.r. bands at 1 642 [ν(C–O)], 1 137 [ν(C–C)], and 924 and 768 cm–1[ν(S–C)].

The mass spectra of several bis(nickel cyclopentadienyl)acetylene complexes (Cp2Ni2RC2R′) are discussed. The major processes of decomposition of the parent ions can be satisfactorily described in terms of: a) loss of the alkyne ligand; b) loss of a cyclopentadiene molecule; c) loss of a NiCp fragment; d) fragmentation of the R groups. The effect of the R and R′ groups is taken into account to explain the different breakdown pathways.

sym-(CO)9Co3C(CS2)Co3(CO)7S has been isolated from the mixture formed in the reaction of Co2(CO)8 with CS2. This is the fifth member of the CmSnCop(CO)q family identified by X-ray diffraction studies. The molecular structure of the title compound is discussed and briefly compared with that of the asymmetric isomer and related compounds.

Some new complexes in the series Cp 2 Ni 2 RC 2 R′ (Cp = π-cyclopentadienyl; R = H, R′ = CH 3 ; R = CH 3 , R′ = C 6 H 5 ; R = R′ = COOCH 3 ) have been synthesized and the effect of the R and R′ groups in teh displacement Cp 2 Ni 2 - RC 2 R′ + R′'C 2 R‴ + RC 2 R′ has been investigated. Spectroscopic properties (IR, 1 H and 13 C NMR) are described, the nature of the bond between acetyle and nickel is discussed and it is suggested that the triple bond of the coordinated acetylene has virtually total olefinic character.

In this work the substitution reactions were studied, of one acetylenic derivative, by another, in the complexes Co 2 (CO) 6 C 2 RR′ in which R and R′CF 3 , COOCH 3 , C 6 H 5 , CH 2 Cl, CH 3 , CH 2 N(C 2 H 5 ) 2 and H. On the basis of such reactions, relative stabilities of the various acetylenic derivatives were determined and discussed in terms of the acceptor character of the different acetylenes. Also reported are the preparations and properties of some new compounds of this series.

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.

Different solvents exercise two effects, electrostatic and nucleophilic, in CO exchange reaction rates on the Fe 3 (CO) 9 Te 2 complex. These effects are discussed and a kinetic mechanism is proposed. A comparison is also made between the electron attracting power of Te atoms and the diphenylacetylenic group in the similar complexes, Fe 3 (CO) 9 Te 2 and Fe 3 (CO) 9 C 2 (C 6 H 5 ) 2 .

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.

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.

A re-examination of the kinetic of reaction between Cp2Ni2(CO)2 and diphenylacetylene shows that a second-order mechanism is significant at very high concentration of the ligand, whereas at low concentration a two-stage mechanism is more important. It is noted also that the side-reactions, as the complete decomposition or the reaction of Cp2Ni2(CO)2 with CO, do not change significantly the value of the specific rate constant of the main reaction.

The kinetics of 14CO exchange and CO replacement in [FeCo2(CO)9S] have been studied with a variety of ligands. The rate equation is Kobs.=k1+k2[L], in which the ligand-independent path is often negligible, except with very poor nucleophiles such as CO or AsPh3. The ligand-dependent path indicates the very high electrophilicity and great discriminating power among the ligands of the co-ordination site, suggesting that bond making plays an important role in the transition state. The probable mechanism is discussed in terms of steric accessibility of the co-ordination site and in terms of a bonding model for the cluster complex. The rates of the successive CO substitutions with PBu3 indicate that the ligand already bonded to the cluster affects the reactivity of the adjacent metal atom, i.e. CO dissociation is practically unaffected, whereas ligand co-ordination is greatly decreased.