The First Class of Square-Planar Platinum(II) Complexes Containing Electron-Poor Alkenes. Rare Insertion of an Alkene into a Pt−Alkyl Bond^†

The first class of square-planar Pt(II) complexes bearing electron-poor alkenes, i.e., [PtMe(N,N-chelate)(η2-CH2CHCOR)]BF4 (R = H, NMe2, Me, OMe), is described. By using N,N ligands with suitable steric properties, it was possible to inhibit olefin dynamic processes in solution, thus allowing a thorough characterization of the complexes. Insertion of methyl acrylate into the Pt−Me bond provides a rare example of migratory insertion of an alkene into a Pt−alkyl bond

Preparation of Benzylstannanes by Zinc-Mediated Coupling of Benzyl Bromides with Organotin Derivatives. Physicochemical Characterization and Crystal Structures

Benzyltrialkyl- (1−13) and benzyltriphenylstannanes (16−22) have been easily prepared in a one-pot synthesis via coupling reaction of benzyl bromide derivatives (C6H5CH2Br and XYC6H3CH2Br, X = H, Y = o-, m-, p-CH3, o-, m-, p-F, o-, m-Cl, and p-Br; X = o-F, Y = p-Br) with R3SnCl compounds (R = Et, Pr, Bu, and Ph) in THF/H2O (NH4Cl) medium mediated by zinc powder. Such coupling also occurs with (Bu3Sn)2O. Dibenzyldibutylstannane (15) is prepared by reaction of benzyl bromide with Bu2SnCl2 or (Bu2SnCl)2O, and (2-naphthylmethyl)tributylstannane (14) by reaction of 2-(bromomethyl)naphthalene with Bu3SnCl. 13C- and 119Sn-NMR data are reported for all compounds, and Mössbauer data for benzyltributylstannanes 10 and 11 and benzyltriphenylstannanes 16−18 and 20−22. The crystal structures of Ph3SnBn, with Bn = o- (17) and m-ClC6H4CH2 (18) and o- (20) and m-FC6H4CH2 (21) have been determined

Heterobimetallic Indenyl Complexes. Mechanism of Cyclotrimerization of Dimethyl Acetylenedicarboxylate (DMAD) Catalyzed by <i>trans</i>-[Cr(CO)₃(Heptamethylindenyl)Rh(CO)₂ ]^†

The complex trans-[Cr(CO)3(heptamethylindenyl)Rh(CO)2] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the “true” catalyst, likely to be the complex trans-[Cr(CO)3−Ind*−Rh(DMAD)2], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)3−Ind*−Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C−H bond activation of the solvent cyclohexane

Preparation of Benzylstannanes by Zinc-Mediated Coupling of Benzyl Bromides with Organotin Derivatives. Physicochemical Characterization and Crystal Structures

Benzyltrialkyl- (1−13) and benzyltriphenylstannanes (16−22) have been easily prepared in a one-pot synthesis via coupling reaction of benzyl bromide derivatives (C6H5CH2Br and XYC6H3CH2Br, X = H, Y = o-, m-, p-CH3, o-, m-, p-F, o-, m-Cl, and p-Br; X = o-F, Y = p-Br) with R3SnCl compounds (R = Et, Pr, Bu, and Ph) in THF/H2O (NH4Cl) medium mediated by zinc powder. Such coupling also occurs with (Bu3Sn)2O. Dibenzyldibutylstannane (15) is prepared by reaction of benzyl bromide with Bu2SnCl2 or (Bu2SnCl)2O, and (2-naphthylmethyl)tributylstannane (14) by reaction of 2-(bromomethyl)naphthalene with Bu3SnCl. 13C- and 119Sn-NMR data are reported for all compounds, and Mössbauer data for benzyltributylstannanes 10 and 11 and benzyltriphenylstannanes 16−18 and 20−22. The crystal structures of Ph3SnBn, with Bn = o- (17) and m-ClC6H4CH2 (18) and o- (20) and m-FC6H4CH2 (21) have been determined

Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)−Rh(I)−Cr(0) Triads of the Polyaromatic Cyclopentadienyl−Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of η6-Cr(CO)3{η5-[(2-ferrocenyl)indenyl]Rh(CO)2} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal−metal (Fe−Cr) interaction with respect to the structurally correlated binuclear system

Designing Molecules for Metal−Metal Electronic Communication: Synthesis and Molecular Structure of the Couple of Heterobimetallic Isomers [η⁶-(2-Ferrocenyl)indene]-Cr(CO)₃ and [η⁶-(3-Ferrocenyl)indene]-Cr(CO)₃

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+

Heterobimetallic Indenyl Complexes. Synthesis and Carbonylation Reaction of <i>anti</i>-[Cr(CO)₃-μ,η:η-indenyl-Ir(COD)]

The reaction of the anti-[Cr(CO)3-μ,η:η-indenyl-Ir(COD)] (I) complex with an excess of CO in CH2Cl2 at 203 K produces quantitatively the η1-[η6-Cr(CO)3-indenyl]-Ir(COD)(CO)2 intermediate which above 273 K converts into the fully carbonylated complex η1-[η6-Cr(CO)3-indenyl]Ir(CO)4; this in turn is stable up to 313 K. Carbonylation of the anti-[Cr(CO)3-μ,η:η-indenyl-Ir(COE)2] analogue (II) gives the η1-[η6-Cr(CO)3-indenyl]-Ir(CO)4 (VII) species in a single fast step. In contrast to the behavior of the corresponding rhodium complexes, for which η1 intermediates have never been observed and the aromatized substitution product is the stable product, the rearomatization of the cyclopentadienyl ring in iridium complexes to give the “normal” substitution product, viz., anti-[Cr(CO)3-μ,η:η-indenyl-Ir(CO)2] (III) is a difficult process which takes place only on bubbling argon through the solution. The final product III is barely stable in solution. If the carbonylation is carried out using a blanket of CO over the solution of complexes I and II, viz., failing CO, the scarcely soluble iridium dimer [η6-Cr(CO)3-indenyl-η3-Ir(CO)3]2 (IX) stable in the solid state is obtained, probably by dimerization of the unstable intermediate anti-[η6-Cr(CO)3-indenyl-η3-Ir(CO)3] (X)

Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)−Rh(I)−Cr(0) Triads of the Polyaromatic Cyclopentadienyl−Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of η6-Cr(CO)3{η5-[(2-ferrocenyl)indenyl]Rh(CO)2} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal−metal (Fe−Cr) interaction with respect to the structurally correlated binuclear system

Organometallic Chemistry of Ph₃PCCO. Synthesis, Characterization, X-ray Structure Determination, and Density Functional Study of the First Stable Bis-<i>η</i>¹-ketenyl Complex, <i>trans</i>-[PtCl₂{<i>η</i>¹-C(PPh₃)CO}₂]

Mono- and bis-η1-ketenyl Pt(II) complexes have been synthesized by reacting Zeise's salt or the related dimeric compound, [{PtCl2(C2H4)}2], with the oxocumulenic ylide ketenylidenetriphenylphosphorane, Ph3PCCO, 1, in suitable ratios. In particular, the η1-ketenyl derivative, trans-[PtCl2(C2H4){η1-C(PPh3)CO}], 2, has been isolated and characterized. The reaction of 2 with one more equivalent of 1 displaces the coordinated ethylene giving the first stable bis-η1-ketenyl derivative, trans-[PtCl2{η1-C(PPh3)CO}2], 6. The X-ray crystal structure of 6 shows a trans centrosymmetric geometry around Pt, with the PCCO moiety and the metal lying in a plane that forms an angle of ∼65° with the Pt(II) coordination plane. Density functional calculations indicate that steric effects play a leading role in determining such an arrangement. Data on the reactivity of 2 and 6 are also reported

Heterobimetallic (Ferrocenyl)indenyl Rhodium Complexes. Synthesis, Crystal Structure, and Oxidative Activation of [η⁵-(1-Ferrocenyl)indenyl]RhL₂ [L₂ = COD, NBD, (CO)₂]^‖

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