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The heterobinuclear isomers [η⁶-(2-ferrocenyl)indene]-Cr(CO)3 (1) and [η⁶-(3-ferrocenyl)indene-Cr(CO)3 (2) have been prepared and the crystal structure determination showed that the Fe(C5H5) and Cr(CO)3 groups in the two molecules are disposed in different conformations with respect to the Cp-indene bridging ligand, cisoid in 1 and transoid in 2. Preliminary electrochemical (CV) and spectroscopic (IR and near-IR) results obtained for the corresponding monooxidized 1⁺ and 2⁺ demonstrate the existence of stronger electronic coupling in 1⁺ than in 2⁺.

The new η²-formamidinyl Zr complex Zr(NMeCyc)2[C(NAr)NMeCyc]2 (1) (Ar = 2,6-dimethylphenyl, Cyc = cyclohexyl) was prepared upon double insertion of 2,6-dimethyl phenyl isocyanide in the Zr−N bond of Zr(NMeCyc)4. 1 was then converted into Zr(OC6F5)2[C(NAr)NMeCyc]2 (2) and ZrCl2[C(NAr)NMeCyc]2 (3) by reacting it with C6F5OH and [NHMe3]Cl, respectively. The crystal structure of 1 was established by X-ray analysis. All the complexes have been tested as catalysts for the polymerization of ethylene and 1-hexene in the presence of [NHMe2Ph][B(C6F5)4] as cocatalyst.

The heterobimetallic CpFe(μ-η⁵: η⁵-as-indacenediide)RhL2 complexes (L2 = COD (2), NBD (3), (ethylene)2 (4)) have been obtained from metalation of the mononuclear lithium CpFe(η⁵-as-indacenediide) with [Rh(μ-Cl)L2]2. Mixtures of syn and anti heterobimetallic complexes were formed and fully characterized by 2D NMR spectroscopy. The reactivity at the rhodium center is greatly influenced by the presence of the ferrocenyl moiety. The voltammetric behavior and the optical spectra are in favor of the existence of significant electronic interactions between the two metals.

The binuclear [η⁵-(1-ferrocenyl)indenyl]Rh(NBD) (1), [η⁵-(1-ferrocenyl)indenyl]Rh(COD) (1a), and [η⁵-(1-ferrocenyl)indenyl]Rh(CO)2 (2) complexes have been synthesized (NBD = norbornadiene; COD = cycloocta-1,5-diene). The crystal structure determination showed that the iron and rhodium nuclei are disposed in a transoid configuration in 1 probably to avoid steric repulsions. On the contrary, in 2 the metals are in a cisoid configuration due to the presence of stabilizing π-hydrogen bonds between the CO's and the hydrogens of the unsubstituted cyclopentadienyl ring. The results of the chemical and electrochemical oxidation of 2 are in favor of the existence of an effective interaction between the two metals.

The solution behavior of the cationic complexes [Pd(η³-allyl)(P−N)]⁺ (P−N = o-(PPh2)C6H4CH&dbd;NR (R = C6H4OMe-4, Me, CMe3, (R)-bornyl); allyl = propenyl (1a−4a) and 3-methyl-2-butenyl (1b−4b)) consists essentially of three dynamic processes:  (i) a very fast conformational change of the P−N chelate ring, which moves above and below the P−Pd−N coordination plane, (ii) a relatively fast η³−η¹−η³ interconversion which brings about a syn−anti exchange only for the allylic protons cis to phosphorus; (iii) a slower apparent rotation of the η³-allyl ligand around its bond axis. For 1b−3b, two geometrical isomers are observed, the predominant one having the allyl CMe2 group trans to phosphorus. The complexes 4a and 4b, containing the chiral (R)-bornyl group, are present in solution with two and four diastereomeric species, respectively. The X-ray structural analysis of 4b(ClO4) shows the presence of two diastereomeric molecules in the unit cell, both having distorted-square-planar coordination geometries, characterized by rather elongated Pd−CMe2 bonds trans to phosphorus and by a marked distortion of the allyl ligand, which is rotated away from the PPh2 group. The complexes [Pd(η³-allyl)(P−N)]⁺ react with secondary amines HY in the presence of fumaronitrile, yielding [Pd(η²-fn)(P−N)] and allylamines. Under pseudo-first-order conditions the amination rates obey the laws kobs = k2[HY] + k3[HY]² for 1a−4a and kobs = k2[HY] for 1b, 3b, and 4b. The k2 term is related to direct bimolecular attack on a terminal allyl carbon of the substrate, whereas the k3 term is ascribed to parallel attack by a further amine molecule on the intermediate [Pd(allyl)(P−N)(HY)]⁺. The k2 values increase with increasing basicity and decreasing steric hindrance of the amine, and with increasing electron-withdrawing ability and increasing bulkiness of the P−N nitrogen substituent. The higher amination rates for [Pd(η³-allyl)(P−N)]⁺, compared to [Pd(η³-allyl)(α-diimine)]⁺, are essentially due to lack of displacement equilibria of the P−N ligand by amines.

The complexes [Pd(η³-allyl)(N-N‘)]ClO4 [allyl = 2-butenyl or 3-methyl-2-butenyl, N-N‘ = C5H3(6-R)N-2-CH&dbd;NR‘ (R = H, R‘ = Me, CMe3, C6H4OMe-4; R = Me, R‘ = C6H4OMe-4) and C5H4N-2-CH2NMe2] are present in solution with different isomers, the structures of which may be assigned by an ¹H NMR criterion based on chemical shift changes of the pyridine H(6) and/or of the allylic methyl protons, as confirmed also by 2D ¹H NMR spectra. The isomer distribution depends mainly on the steric requirements of both the allyl and N-N‘ ligands:  for [Pd(η³-3-methyl-2-butenyl)(N-N‘)]ClO4 the predominant isomer (ca. 100%) has a structure with the allylic methyl groups cis to the coordinated pyridine nitrogen when N-N‘ = C5H4N-2-CH&dbd;NCMe3 and cis to the coordinated imino nitrogen when N-N‘ = C5H3(6-Me)N-2-CH&dbd;NC6H4OMe-4. In chlorinated solvents (dichloromethane-d2 or 1,1,2,2-tetrachloroethane-d2) the isomers undergo mutual interconversion through a mechanism involving an apparent rotation of the η³-allyl ligand around its bond axis to the metal. The interconversion rates depend on the nature of allyl and N-N‘ ligands and increase considerably when the compounds are dissolved in dimethyl-d6 sulfoxide. The apparent allyl rotation also occurs for the analogous (η³-2-methyl-2-propenyl)palladium(II) derivatives. For [Pd(η³-2-methyl-2-propenyl)(N-N‘)]ClO4 [N-N‘ = C5H3(6-Me)N-2-CH&dbd;NC6H4OMe-4] the allyl rotation rate increases with increasing concentration up to a limiting constant value. This behavior is interpreted on the basis of a mechanism involving a fast and reversible association of the cationic complex with the perchlorate anion to form a loose ion pair which undergoes a rate-determining molecular geometry rearrangement upon coordination of ClO4^-. For a solution of [Pd(η³-3-methyl-2-butenyl)(N-N‘)]ClO4 (N-N‘ = C5H4N-2-CH2NMe2) in 1,1,2,2-tetrachloroethane-d2, the 2-D ROESY spectrum suggests that the apparent allyl rotation at 28 °C does not involve Pd−NMe2 bond breaking. The rupture of this bond takes place when the temperature is raised to ca. 90 °C or when the complex is dissolved in dimethyl-d6 sulfoxide at ambient temperature.