Transformationen von Acetylenliganden an Triethylphosphan‐substituierten Eisencarbonyl‐Fragmenten

Abstract

Der Stickstoffkomplex [(OC)2(Et3P)2Fe]2N2 (1) reagiert mit Acetylenen R'C = CR' (R', R2 = H, Ph) unter Bildung von q2-Acetylcnverbindungen (OC)z(Et3P)2FeR'C=CR* (R' = R2 = H, 2a; R' = H, R2 = Ph, Zb; R' = R' = Ph, 2c). 2a und 2b unterliegen in Lasung einer reversiblen oxidativen Addition, wobei (0C)z-(Et3PhFe(H)CrCR2-Komplexe (R2 = H, 3a; R2 = Ph, 3b) entstehen. Belichtet man (OC)4FePEt3 in Gegenwart von Stickstoff und setzt dann rnit Acetylen urn, so erhiilt man ein Pentacarbonylmethylenketenbis(triethylphosphan)dieisen-System 4. UberschuD an Acetylen fiihrt neben 4 zu einer (OC)2PEt3Fe-Troponverbindung. Die Strukturen von 2b und 4 wurden durch eine Rentgenbeugungsanalyse bestimmt.d8-ML4-Teilchen eignen sich grundsatzlich fur die feste Anbindung von 2e-n-Acceptorliganden". Stabile AcetylenKornplexe konnten allerdings mit Fe(CO),-Einheiten nur selten erhalten werden". Im allgerneinen beobachtet man in der Acetylenchernie rnit Eisencarbonylfragrncnten die bevorzugte Bildung von Clu~ter-Gerusten~'. In diesem Zusamrnenhang schien die Frage von Bedeutung, ob durch die Blockierung von einer oder zwei Ligandpositionen rnit festhaftenden Phosphordonatoren im Fe(CO),-Fragment die Clusterbildung unterdruckt wird. Daruber hinaus sollte untersucht werden, ob die an Clustern bekannten Elementarschritte wie C-H-Aktivierung und C-C-Verknupfungsreaktionen eventuell auch an Eisen-Teilchen niederer Nuclearitat beobachtet werden konnen. The dinitrogen complex [(OCMEt3P)2Fe]2N2 (1) reacts with acetylenes R1C=CR2 (RI, R2 = H, Ph) to yield q2-acetylene compounds (OC)z(Et3P2)FeR'C=CR2 (R' = R2 = H, 2a; R' = H, R7 = Ph, 2b; R1 = R2 = Ph, 2c). 20 and Zb undergo a reversible oxidative addition in solution to form (OC)2(Et3P)2Fe(H)C r CR2 complexes (R2 = H, 3% R2 = Ph, 3b). Irradiation of (OC).,FePEt, in the presence of nitrogen and subsequent purging with acetylene produces a pentacarbonylmethyleneketenebis(triethy1phospha-ne)diiron system 4. In addition to 4, excess of acetylene also leads to an (OC),(PEt,)Fe tropone compound. The structures of 2 b and 4 were determined by X-ray diffraction analyses.

Use of the MnCC system in organometallic and organic synthesis

“…A similar dynamic process (38) was described for 74, whose crystal structure corresponds to the "TMM type", but which in solution is in equilibrium with the -vinylidene isomer 74a [109]. In contrast, the substitution of CO by PPh 3 in 78 (reaction (40)) resulted in C 3 O migration from Pt to the vinylidene C 1 atom, the Pt Pt bond splitting and formation of the unusual complex 79 [110].…”

Unusual Formation and Reactivity of a Diplatinum μ-Phenylethenylidene Complex: Synthesis and Structures of cis,cis-[(PPh3)(C6F5)2Pt(μ-η1:η3-CHPhCCO)Pt(PPh3)2] and cis,cis-[(PPh3)2Pt{μ-η2(C,S):η1(C)-C(SPh)(CH2Ph)}Pt(C6F5)2(CO)] Dinuclear Compounds

“…There are many examples of carbonylation (or insertion) of terminal carbene and carbyne ligands affording ketene and ketenyl complexes, in many cases promoted by strongly nucleophilic phosphines. , This well-known process has utility in organic synthesis and has also been pointed out to be a key step of C−C bond formation in the hydrogenation of carbon monoxide to oxygenated compounds. 23b, However, the insertion of CO into a carbene bridging ligand is a rare process and the cases reported involve carbonylation or insertion of CO into a μ-methylene (μ-CH 2 ) group. , As far as we know, there is only one report in the literature of insertion of CO into a μ-vinylidene bridging ligand . However, in this case, both the μ-CCH 2 derivative and the methyleneketene μ-CH 2 CCO complex exist in solution as a mixture of two isomers in equilibrium . On the other hand, ketene , and vinylidene 4 ligands have been suggested as potential intermediates in CO reduction processes; therefore, their interconversion is relevant.…”

Combined Photoredox and Iron Catalysis for the Cyclotrimerization of Alkynes

“…IR spectroscopic studies with FeCl 2 (MeCN) 1.4 showed no band shifting on addition of DIPEA or phenylacetylene individually, whereas complete consumption of FeCl 2 (MeCN) 1.4 occurred in the presence of both DIPEA (2 equiv) and phenylacetylene (2 equiv). The resultant IR spectrum of the light‐brown mixture exhibited no ν C≡C bands of hypothetical σ‐alkynyliron species . We cannot exclude the formation of (π‐alkyne)iron complexes that would exhibit a bathochromic shift (and lower intensity bands) owing to strong back‐bonding or the presence of polynuclear alkyne complexes .…”

“…The resultant IR spectrum of the light-brown mixture exhibited no n CC bands of hypothetical s-alkynyliron species. [29,30] We cannot exclude the formation of (p-alkyne)iron complexes that would exhibit a bathochromic shift (and lower intensity bands) owing to strong backbonding or the presence of polynuclear alkyne complexes. [30,1] The potential formation of [FeCl 2 L x (p-PhCCH) y ] n [32] complexes is in accordance with the observed full conversion of FeCl 2 (MeCN) 1.4 in the presence of amine and alkyne (no alkyne deprotonation) and the slight shift of the 1 H NMR signal of CH upon addition of DIPEA to FeCl 2 (MeCN) 1.4 and phenylacetylene.…”