Selective Alkene Insertion into Inert Hydrogen–Metal Bonds Catalyzed by Mono(phosphorus ligand)palladium(0) Complexes

Abstract

Isolated mono(phosphorus ligand)palladium(0) complexes catalyzed alkene insertions into hydrogen−tungsten bonds. These insertions using WHCp(CO) 3 with ethyl acrylate and dimethyl fumarate smoothly gave the corresponding alkyltungsten complexes. Kinetic studies involving the stoichiometric reactions and DFT calculations suggest the following steps: (i) formation of a mono(phosphorus ligand)mono(alkene)palladium(0) species, (ii) subsequent reaction of a metal hydride with the palladium(0), (iii) insertion of the coordinated alkene into the resulting palladium hydride, and (iv) reductive elimination between the alkyl and metal on the palladium center to release the alkylmetal species with regeneration of a palladium(0) by a reaction with alkene.

Ligand-Controlled Regiodivergent Hydrosilylation of Conjugated Dienes Catalyzed by Mono(phosphine)palladium(0) Complexes

“…The KIE value ( k H / k D ) estimated by using these initial rates based on these independent reactions was 4.51. The KIE is primary and indicates the rate-determining step (rds) in this catalysis to involve the Si–H or Pd–H cleavage step. − No dependence of the reaction rate on substrate concentrations suggests that the rds is an intramolecular step such as the migratory insertion of the Pd–H bond to the CC bond. …”

“…HSiPh 3 , HSiPh 2 Me, HSiPhMe 2 , HSiBnMe 2 , HSi­(OEt) 3 , HSiEt 3 , diallyl ether, and dienes 3a , 3b , 3m , 3n , 3o , and 3p were purchased from TCI or Aldrich. The mono­(phosphine)­palladium(0) complexes Pd­{η 2 :η 2 -(CH 2 CHCH 2 ) 2 O}­(PR 3 ) (R = Me ( 1a ), Et ( 1b ), Cy ( 1c ), OEt ( 1d ), O i Pr ( 1e ), Ph ( 1f ), OPh ( 1g )), , DSiPh 3 ( 2a - d ), HSiAr 3 (Ar = C 6 H 4 OMe-4 ( 2b ), C 6 H 4 Me-4 ( 2c ), C 6 H 4 Cl-4 ( 2d ), C 6 H 4 CF 3 -4 ( 2e )), and dienes 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , and 3q were prepared by literature procedures with modification. 1 H, 2 H, and 13 C­{ 1 H} NMR spectra were measured on a 400 MHz (for 1 H) NMR spectrometer.…”

NHO to aNHC Isomerization at a Pd0‐Center

“…Two different protocols were utilized for this purpose. In situ generation of [CpPd(allyl)] from [(µ‐Cl)Pd(allyl)] 2 and NaCp followed by the addition of an excess of dvds and one molar equivalent IPrCH 2 in THF . After stirring the deep red mixture for 24 h at room temperature, removal of the volatiles and extraction of the residue with n ‐hexane afforded a reddish material from which colorless X‐ray quality crystals were grown by placing a saturated toluene solution layered with n ‐hexane at –30 °C over a period of 72 h. These crystals were determined to be an unexpected aNHC–Pd 0 complex [(aIPrCH 3 )Pd(dvds)] ( 1 ) (Figure , left).…”

Mechanism and Stereoselectivity of the Elementometalation Process of Activated Alkyne RCCR(RCO2Me) by Cp2TaH3

“…However, the addition of 1 equiv of alkynes into several polyhydride complexes leads to the displacement of H 2 from the metal center, rather than the insertion into the MH bond, unless the alkenes or alkynes contain strong electron‐withdrawing groups, such as CO 2 Me, CO 2 t Bu, CO 2 TMS, and so on . Komine and coworkers also reported the insertion of selective alkenes into inert MH bonds of molybdenum and tungsten hydrides MHCp(CO) 3 (MMo, W) catalyzed by palladium(0) complexes, and showed that ( Z )‐ and ( E )‐alkenes (MeO 2 CCCCO 2 Me) can be easily inserted into the Mo/WH bonds and have a high reaction rate and yield …”

“…[12][13][14][15] Komine and coworkers also reported the insertion of selective alkenes into inert M H bonds of molybdenum and tungsten hydrides MHCp(CO) 3 (M Mo, W) catalyzed by palladium(0) complexes, and showed that (Z)-and (E)-alkenes (MeO 2 CC CCO 2 Me) can be easily inserted into the Mo/W H bonds and have a high reaction rate and yield. [16,17] Recently, the synthesis and characterization of metal alkyne complexes have been reported by some groups. [18][19][20][21][22][23] The reactivity, [24][25][26] stereochemistry, [27][28][29] and mechanism [23,30] of alkyne or alkene insertion into M E bonds have also received increasingly more attention.…”