Dihydroguaiazulenide Complexes and Catalysts of Group 8-12 Transition Metals: Ligands from Renewable Feedstock Replace, even Outmatch Petrochemical Based Cyclopentadienyl Chemistry

We present an in-depth study of the sterically demanding Cp-synthon (8-H-GuaH)Li isolated from natural product guaiazulene (Gua) as a ligand transfer reagent towards late transition metal complex precursors. The synthesis and full characterization of selected, essentially unexplored homo- and heteroleptic 8-H-guaiazulenide complexes of iron, ruthenium, cobalt, rhodium, platinum, copper and zinc are discussed in detail. In order to demonstrate their potential in catalytic applications, [(GuaH)PtMe3 ] was selected. The latter proved an even higher catalytic activity in light induced olefin hydrosilylation at catalyst loads as low as 5 ppm than classical [CpPtMe3 ] in a typical test reaction of silicone elastomer fabrication. Our results demonstrate that traditional petrochemical based Cp metal chemistry and catalysis can be replaced, sometimes even outmatched by superior catalysts based on cheap building blocks from renewable feedstock.

Primary Alcohols via Nickel Pentacarboxycyclopentadienyl Diamide Catalyzed Hydrosilylation of Terminal Epoxides

The efficient and regioselective hydrosilylation of epoxides co-catalyzed by a pentacarboxycyclopentadienyl (PCCP) diamide nickel complex and Lewis acid is reported. This method allows for the reductive opening of terminal, monosubstituted epoxides to form unbranched, primary alcohols. A range of substrates including both terminal and nonterminal epoxides are shown to work, and a mechanistic rationale is provided. This work represents the first use of a PCCP derivative as a ligand for transition-metal catalysis.

Metallacyclopentadienes: synthesis, structure and reactivity

Metallacyclopentadienes, which possess two M-C(sp²) bonds and feature the structure of M(C[upper bond 1 start]R¹[double bond, length as m-dash]CR²-CR³[double bond, length as m-dash]C[upper bond 1 end]R⁴), are an important class of five-membered metallacycles. They are considered as both reactive intermediates in the stoichiometric and catalytic transformations of organic molecules and useful precursors to main group element compounds, and have received considerable attention in organometallic chemistry, coordination chemistry and synthetic organic chemistry over the past six decades because of their unique metallacyclic structure. This review comprehensively presents the synthesis, structure and reactivity of the s-, p-, d- and f-block metallacyclopentadienes distributed in the whole periodic table. In addition, their application in synthetic organic chemistry and polymer chemistry is summarized. This review aims to be beneficial for the design and synthesis of novel metallacyclopentadienes, and for promoting the rapid development of metallacyclic chemistry.

Formation of a spiro compound via coupling of a cyclopentadienyl ligand with a diene moiety of titanacyclopentadiene

The treatment of titanacyclopentadienes with bismuth(iii) chloride gave spiro compounds in moderate yields. Two carbon atoms of the diene moiety of the titanacyclopentadiene were connected to one carbon atom of the Cp ligand. This is in sharp contrast to the formation of dihydroindene derivatives, where two carbon-carbon bonds were formed between the diene moiety and the adjacent two carbon atoms of the Cp ligand.

C-C and C-N Couplings Following Hydride Addition on Isocyanide Cyclopolyenyl Dimolybdenum Complexes to Give Tethered Aldimine and Aminocarbene Derivatives

Reaction of [Mo₂ Cp₂ (μ-κ¹ :κ¹ ,η⁶ -PMes*)(CO)₂ ] with S or Se followed by protonation with [H(OEt₂ )₂ ](BAr'₄ ) gave the cationic derivatives [Mo₂ Cp₂ {μ-κ²_P,E :κ¹_P ,η⁵ -EP(C₆ H₃ tBu₃ )}(CNR)(CO)₂ ](BAr'₄ ) (E=S; R=tBu, iPr, Ph, 4-C₆ H₄ OMe, Xyl; or E=Se; R=tBu; Ar'=3,5-C₆ H₃ (CF₃ )₂ ). Reaction of the latter with K[BHsBu₃ ] yielded the aldimine complexes [Mo₂ Cp₂ {μ-κ²_P,E :κ²_P,N ,η⁴ -SP(C₆ H₃ tBu₃ (CHNR))}(CO)₂ ] and their aminocarbene isomers [Mo₂ Cp₂ {μ-κ²_P,E :κ²_P,C ,η⁴ -SP(C₆ H₃ tBu₃ (NRCH))}(CO)₂ ] (R ≠ Xyl), following C-C and C-N couplings, respectively. Monitoring of these reactions revealed that the initial H^- attack takes place at a Cp ligand to give cyclopentadiene intermediates [Mo₂ Cp{μ-κ²_P,S :κ¹_P ,η⁵ -SP(C₆ H₃ tBu₃ )}(η⁴ -C₅ H₆ )(CNR)(CO)₂ ], which then undergo C-H oxidative addition to give the hydride isomers [Mo₂ Cp₂ {μ-κ²_P,S :κ¹_P ,η³ -SP(C₆ H₃ tBu₃ )}(H)(CNR)(CO)₂ ]. In turn, the latter rearrange to give the aldimine and aminocarbene complexes. DFT calculations revealed that the hydride intermediates first undergo migratory insertion of the isocyanide ligand into the Mo-H bond to give unobservable formimidoyl intermediates, which then evolve either by nucleophilic attack of the N atom on the C₆ ring (C-N coupling) or by migratory insertion of the formimidoyl ligand into the C₆ ring (C-C coupling). Our data suggest that increasing the size of the substituent R at the isocyanide ligand destabilizes the aldimine isomer to a greater extent, thus favoring formation of the aminocarbene complex.