Reactivity of Silyl-Substituted Iron–Platinum Hydride Complexes toward Unsaturated Molecules: 4. Insertion of Fluorinated Aromatic Alkynes into the Platinum–Hydride Bond. Synthesis and Reactivity of Heterobimetallic Dimetallacylopentenone, Dimetallacyclobutene, μ-Vinylidene, and μ2-σ-Alkenyl Complexes

Mixed valence triiron complexes from the conjugation of [FeIFeI] and [FeII] complexes via intermolecular carbyne/alkyne coupling

We present a new synthetic strategy for obtaining mixed-valence triiron complexes where the metal centers are bridged by a novel, highly functionalized hydrocarbyl ligand. The alkynyl-vinyliminium complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X-CCH)CHCNMe2}]CF3SO3 (X = 4-C6H4, [2a1]CF3SO3; X = (CH2)3, [2a2]CF3SO3) were synthesized in almost quantitative yields from the aminocarbyne precursor [Fe2Cp2(CO)2(μ-CO){μ-CNMe2}]CF3SO3, [1a]CF3SO3, and the di-alkynes HCC-X-CCH. Then, the ferracycle [Fe(Cp)(CO){C(NMe2)CHC(4-C6H4CCH)C(O)}], 4a1, was produced in 47% yield from the cleavage of [2a1]CF3SO3 promoted by pyrrolidine. Subsequent reactions of the acetonitrile adducts [Fe2Cp2(CO)(μ-CO)(NCMe){μ-CNMe(R)}]CF3SO3 (R = Me, [1aACN]CF3SO3; R = Xyl, [1bACN]CF3SO3) ([FeIFeI]) with 4a1 ([FeII]) at room temperature resulted in the formation of [FeIFeIFeII] complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X-CCHC(NMe2)FeCp(CO)CO)CHCNMe(R)}]CF3SO3 (R = Me, [5a1]CF3SO3; R = Xyl, [5b1]CF3SO3) in yields ranging from 56% to 64%. The new products were characterized by IR and multinuclear NMR spectroscopy, and the structures of [2a2]CF3SO3 and 4a1 were confirmed by single crystal X-ray diffraction. Cyclic voltammetry and spectroelectrochemical studies on [5a1]+ have revealed that reduction and oxidation events occur almost independently at the [FeIFeI] and [FeII] units, respectively. This observation underscores a minimal electronic interaction between the two fragments within the triiron complex. Accordingly, DFT studies pointed out that the HOMO and LUMO orbitals are predominantly localized in the two distinct compartments of [5a1]+.

1-(4-Formyl-2,6-dimethoxyphenoxy)-4-chlorobut-2-yne

A reaction of biomass-derived aldehyde synringaldehyde and half an equivalent of 1,4-dichlorobut-2-yne was attempted in order to obtain a bis-aldehyde with an alkyne spacer. The reaction was carried out in a basic media to effect bis O-alkylation, as described in literature for the preparation of structurally similar compounds. Nevertheless, only mono alkylation was observed.

Visible light driven generation and alkyne insertion reactions of stable bis-cyclometalated Pt(iv) hydrides

Hydride complexes resulting from the oxidative addition of C–H bonds are intermediates in hydrocarbon activation and functionalization reactions. The discovery of metal systems that enable their direct formation through photoexcitation with visible light could lead to advantageous synthetic methodologies. In this study, easily accessible dimers [Pt₂(μ-Cl)₂(C^N)₂] (C^N = cyclometalated 2-arylpyridine) are demonstrated as a very convenient source of Pt(C^N) subunits, which promote photooxidative C–H addition reactions with different 2-arylpyridines (N′^C′H) upon irradiation with blue light. The resulting [PtH(Cl)(C^N)(C′^N′)] complexes are the first isolable Pt(iv) hydrides arising from a cyclometalation reaction. A transcyclometalation process involving three photochemical steps is elucidated, which occurs when the C^N ligand is a monocyclometalated 2,6-diarylpyridine, and a detailed analysis of the photoreactivity associated with the Pt(C^N) moiety is provided. Alkyne insertions into the Pt–H bond of a photogenerated Pt(iv) hydride are also reported as a demonstration of the ability of this class of compounds to undergo subsequent organometallic reactions.

The photochemical generation of isolable bis-cyclometalated Pt(iv) hydrides via photooxidative C–H addition reactions is demonstrated from easily accessible Pt(ii) precursors using visible light.

Crystal structure of {μ2-1,2-bis-[(4-methyl-phenyl-sulfan-yl]-3-oxoprop-1-ene-1,3-di-yl-1:2κ2 C 3:C 1}dicarbon-yl-1κ2 C-[μ2-methyl-enebis(di-phenyl-phos-phane)-1:2κ2 P:P'](tri-phenyl-phosphane-2κP)iron-platinum(Fe-Pt), [(OC)2Fe(μ-dppm){μ-C(=O)C(4-MeC6H4SCH2)=CCH2SC6H4Me-4}Pt(PPh3)]

The title compound, [FePt(C19H18OS2)(C18H15P)(C25H22P2)(CO)2], 1, [(OC)2Fe(μ-dppm)(μ-C(=O)C(CH2SC6H4Me-4)=CCH2SC6H4Me-4)Pt(PPh3)], represents the first example of a diphosphane-bridged heterobimetallic Fe-Pt dimetalla-cyclo-pentenone complex resulting from a bimetallic activation of metal-coordinated carbonyl ligand with an inter-nal alkyne, namely 1,4-bis-(p-tolyl-thio)-but-2-yne. The bridging μ2-C(=O)C(CH2SC6H4Me-4)=CCH2SC6H4Me-4 unit (stemming from a carbon-carbon coupling reaction between CO and the triple bond of the alkyne di-thio-ether) forms a five-membered dimetalla-cyclo-pentenone ring, in which the C=C bond is π-coordinated to the Fe center. The latter is connected to the Pt center through a short metal-metal bond of 2.5697 (6) Å.

Double addition of phenylacetylene onto the mixed bridge phosphinito-phosphanido Pt(i) complex [(PHCy2)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(PHCy2)](Pt-Pt)

The reaction of the dinuclear phosphinito bridged complex [(PHCy2)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (1) with phenylacetylene affords the η1-alkenyl-μ,η1:η2-alkynyl complex [(η1-trans-(Ph)HC[double bond, length as m-dash]CH)(PHCy2)Pt(μ-PCy2)(μ,η1:η2-PhC[triple bond, length as m-dash]C)Pt{κP-P(O)Cy2}(PHCy2)] (4) displaying a σ-bonded 2-phenylethenyl ligand and an alkynyl (μ-κCα:η2) bridge between the platinum atoms. Complex 4 was shown to form in two steps: initially, the attack of the first molecule of phenylacetylene gives the σ-acetylide complex [(PHCy2)(η1-PhC[triple bond, length as m-dash]C)Pt1(μ-PCy2)Pt2(PHCy2){κP-P(OH)Cy2}](Pt-Pt) (5) featuring an intramolecular π-type hydrogen bond between the POH and the C[triple bond, length as m-dash]C triple bond; fast reaction of 5 with a second molecule of phenylacetylene results in the oxidative addition of the terminal C-H bond of the second alkyne to Pt1 that, after rearrangements, leads to 4. When left in solution for two weeks, complex 4 spontaneously isomerizes completely to [(PHCy2)(η1-trans-(Ph)HC[double bond, length as m-dash]CH)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(η1-PhC[triple bond, length as m-dash]C)(PHCy2)] (7) displaying a 2-phenylethenyl ligand and a phenylethynyl group both σ-bonded to the metal. Density functional calculations at the B3LYP/LACV3P++**//DFT/LACVP* level were carried out to study the thermodynamics of the formation of all considered complexes and to trace the mechanism of formation of the observed products.

Crystal structure of dicarbon-yl[μ2-methyl-enebis(di-phenyl-phosphane)-κ2 P:P'][μ2-2-(2,4,5-tri-methyl-phen-yl)-3-oxoprop-1-ene-1,3-di-yl](tri-phenyl-phosphane-κP)ironplatinum(Fe-Pt)-di-chloro-methane-toluene (1/1/2), [(OC)2Fe(μ-dppm)(μ-C(=O)C(2,4,5-C6H2Me3)=CH)Pt(PPh3)]

The title compound, [(OC)₂Fe(μ-dppm)(μ-C(=O)C(2,4,5-C₆H₂Me₃)= CH)Pt(PPh₃)], represents an example of a diphosphane-bridged heterobimetallic dimetalla­cyclo­pentenone complex resulting from a bimetallic activation of 1-ethynyl-2,4,5-tri­methyl­benzene and a metal-coordinated carbonyl ligand.

The title compound, [FePt(C₁₂H₁₂O)(C₁₈H₁₅P)(C₂₅H₂₂P₂)(CO)₂]·2C₇H₈·CH₂Cl₂ or [(OC)₂Fe(μ-dppm)(μ-C(=O)C(2,4,5-C₆H₂Me₃)=CH)Pt(PPh₃)], represents an example of a diphosphane-bridged heterobimetallic dimetalla­cyclo­pentenone complex resulting from a bimetallic activation of 1-ethynyl-2,4,5-tri­methyl­benzene and a metal-coordinated carbonyl ligand. The bridging μ₂-C(=O)C(2,4,5-C₆H₂Me₃)=CH unit (stemming from a carbon–carbon coupling reaction between CO and the terminal alkyne) forms a five-membered dimetalla­cyclo­pentenone ring, in which the C=C bond is π-coordinated to the Fe centre. The latter is connected to the Pt centre through a short metal–metal bond of 2.5770 (5) Å. In the crystal, the complex is solvated by one di­chloro­methane and two toluene mol­ecules.

Binuclear platinum–iridium complexes: synthesis, reactivity and luminescence

The reactivity of a Pt–Ir metal–metal bonded complex has been studied as a model for bimetallic Pt–Ir catalysts.