Ring-Functionalized Molybdenocene Complexes

Propene complexes of molybdenum and tungsten stabilized by intramolecular coordination of the 1-(quinol-8-yl)indenyl ligand

Synthesis, reactivity and properties of unusually stable propene complexes of molybdenum and tungsten are reported.

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.

Stabilization of η3-indenyl compounds by sterically demanding N,N-chelating ligands in the molybdenum coordination sphere

A series of η³-indenyl molybdenum compounds, isostructural with the well-known η³-allyl compounds, was synthesized from the recently established synthon [{(η⁵-4,7-Me₂C₉H₅)Mo(CO)₂(μ-Cl)}₂].