Kinetic Addition of Nucleophiles to η³-Propargyl Rhenium Complexes Occurs at the Central Carbon to Produce Rhenacyclobutenes

Abstract

Kinetic addition of nucleophiles occurs at the center carbon of η3-propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH3)3 with C5Me5(CO)2Re[η3-CH2C⋮CC(CH3)3]+BF4 - (3a) gave the metallacyclobutene C5Me5(CO)2ReCH2C(PMe3)CC(CH3)3 +BF4 - (4a), which was characterized by X-ray crystallography. Malonate and acetylide nucleophiles reacted with C5Me5(CO)2Re[η3-CH2C⋮CCH3]+PF6 - (3b) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low temperature to produce the metastable metallacyclobutene C5Me5(CO)2ReCH2C(NC5H5)CCH3 +PF6 - (14b) which rearranged to the η2-allene complex C5Me5(CO)2Re[η2-H2CCC(NC5H5)CH3]+PF6 - (15K) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted η3-propargyl complex 3a below −38 °C to give the rhenacyclobutene complex C5Me5(CO)2ReCH2C(NC5H4NMe2)CC(CH3)3 +BF4 - (22a) which rearranged to the η2-alkyne complex C5Me5(CO)2Re[η2-(CH3)3CC⋮CCH2NC5H4NMe2]+BF4 - (23) at room temperature. Reaction of water with C5Me5(CO)2Re[η3-CH2C⋮CH]+BF4 - (3c) gave the hydroxyallyl complex C5Me5(CO)2Re[η3-CH2C(OH)CH2]+BF4 - (29) by a process proposed to involve nucleophilic addition of water to the central propargyl carbon of 3c followed by protonation of the metallacyclobutene intermediate.

Quantitative Determination of the Regioselectivity of Nucleophilic Addition to η3-Propargyl Rhenium Complexes and Direct Observation of an Equilibrium between η3-Propargyl Rhenium Complexes and Rhenacyclobutenes

“…We chose to study the exchange and rearrangement kinetics of [C 5 Me 5 (CO) 2 Re(CH 2 C(PMe 3 )=CCMe 3 )][BF 4 ] (7) since this metallacyclobutene is relatively stable and had been fully characterized by X-ray crystallography 10. In addition, 7 had been found to slowly rearrange at room temperature to a single product, the η 2 -alkyne complex [C 5 Me 5 (CO) 2 Re( η 2 -Me 3 PCH 2 C≡CCMe 3 )][BF 4 ] (8) ,10 which was further characterized in the current work by X-ray diffraction (Figure 3).…”

“…We have proposed that these double nucleophilic additions occur by oxidative addition to produce an η 3 -propargyl intermediate, which then undergoes addition of the first nucleophile to the central propargyl carbon to produce a metallacyclobutene; this is followed by protonation of the metallacyclobutene to generate an η 3 -allyl complex that is attacked by a second nucleophile (Scheme 5). 10…”

Palladium‐Catalyzed Intramolecular ipso‐Friedel–Crafts Alkylation of Phenols and Indoles: Rearomatization‐Assisted Oxidative Addition

“…The formation of the palladacycle intermediate B and subsequent reductive elimination, proceeds rapidly to give 2 a as an initial product. A rearomatization-assisted oxidative addition of 2 a to Pd 0 subsequently occurs to afford an equilibrium mixture Intramolecular ipso-Friedel-Crafts alkylation of the phenol proceeds on the central carbon atom of the h 3 -propargylpalladium(II) moiety to affords the palladacyclobutene intermediate E. [10] Subsequent protonation by MeOH generates the p-allylpalladium(II) complex F, which is finally converted into 3 a. 2 a and 3 a could be utilized as versatile intermediates for synthesizing multicyclic molecules (Scheme 5).…”

Polycondensation behavior between propargyl carbonates having a bulky ester group and bisphenols in the presence of Pd(0) catalyst: synthesis of exomethylene-containing polyethers

“…Propargyl carbonate 1 reacts with Pd(0) to generate Z 3 -allenyl/ propargyl intermediate A. [26][27][28] The central carbon of A is attacked by bisphenol 2 to produce intermediate B followed by protonation to yield Z 3 -allylpalladium intermediate C. A second 2 attacks intermediate C to afford 4, which is equivalent to 2 and acts as a nucleophile.…”