Cyclocarbopalladation Involving an Unusual 1,5-Palladium Vinyl to Aryl Shift as Termination Step:  Theoretical Study of the Mechanism

Abstract

A DFT/B3LYP model study has been carried out on the cyclocarbopalladation and on an unusual 1,5 vinyl to aryl palladium shift which are the two first steps of a cyclocarbopalladation-Stille coupling tandem reaction of various gamma-bromopropargylic-1,2 diols with alkenyls or alkynyl stannanes catalyzed by Pd(PPh(3))(4). From the calculations, the active intermediates in the catalytic process appear to bear a single phosphine ligand, the palladium(II) center keeping in all cases a square-planar coordination pattern either through intramolecular binding of the triple bond or via an intramolecular Pd...C(phenyl) interaction. The computation of the various transition states and intermediates for the 1,5 vinyl to aryl palladium shift reveals that the intimate mechanism of this pathway corresponds to a one-step hydrogen transfer between the two negatively charged carbon atoms of the vinyl and phenyl groups. A two-step pathway involving a Pd(IV) intermediate is not likely to occur. This conclusion may apply to other 1,n-palladium shifts which have been experimentally observed in various organometallic transformations.

Computational study of the cyclopalladation mechanism of azobenzene with PdCl2 in N,N-dimethylformamide

“…The fact that many reactions catalyzed by palladium include formation of cyclopalladated intermediates [16], makes this subject more important. The mechanism of cyclopalladation has been experimentally studied by many authors (as reviewed in the next section) and a computational study of the cyclopalladation of N,N-dimethylbenzylamine with Pd acetate appeared recently [17].…”

Solvent/Base Effects in the Selective Domino Synthesis of Phenanthridinones That Involves High‐Valent Palladium Species: Experimental and Theoretical Studies

“…[16] Most commonly, the Pd 0 /Pd II redox pair is preferred to the Pd II /Pd IV one. [9,17,18] Besides, Pd III complexes were recently recognized as putative intermediates in catalysis, particularly in some Pd-catalyzed reactions previously suggested to proceed by means of Pd II /Pd IV redox cycles. [19] In these cases, the addition of an oxidant such as PhIA C H T U N G T R E N N U N G (OAc) 2 proved necessary.…”

Are formal oxidation states above one viable in cyclopentadienylcopper cyanides?

“…In this paper, electron correlation effects were included by employing density functional theory (DFT) methods, which have evolved as a practical and effective computa- tional tool, especially for organometallic compounds [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. Two DFT methods were used in this study.…”