Insertion Products from Photolysis of Tp‘(CO)₃WH and Alkynes

Abstract

Irradation of Tp′(CO) 3 WH in the presence of alkynes produces a diverse array of products, including η 2 -vinyl, η 2 -acyl, metallafuran, and carbyne complexes. A common mechanistic feature consistent with the observed distribution of products is cis insertion of alkynes into a photogenerated "Tp′(CO) 2 WH" species. Initial cis 2,1-insertion of the alkynes leads to η 2vinyl and η 3 -allyl products, while cis 1,2-insertion ultimately produces η 2 -acyl, metallafuran, and carbyne products. An X-ray structure of a metallafuran product, Tp′(CO) 2 W(η 2 (C,O)-C(Bu n )CHC(dO)CHdCHBu n ), shows trans stereochemistry for the double bond of the pendant 1-hexenyl group, which indicates that cis 1,2-insertion of the first equivalent of alkyne forms an intermediate η 1 -vinyl complex. Additional support for η 1 -vinyl intermediates is present in the η 2 -acyl product Tp′(CO) 2 W(η 2 (C,O)-C(dO)CHdCHC(CH 3 ) 3 ), which evinces a trans double bond as assayed via 1 H NMR. Irradiation of Tp′(CO) 3 WH in the presence of Me 3 SiCtCCH 3 produces two isomers of Tp′(CO) 2 W(η 3 -syn-CH 2 CHCHSiMe 3 ) which differ in the orientation of the allyl fragment relative to the metal center. Heating of the allyl complex results in an unusual η 3 -allyl to carbyne rearrangement.

Interaction of alkynes with palladium POCOP-pincer hydride complexes and its unexpected relation to palladium-catalyzed hydrogenation of alkynes

“…In addition to an (E)-, (Z)-, or α-substituted-alkenyl complex stemmed from cis-1,2-, 2 trans-1,2-, 3 or 2,1-insertion, 2d,f,3,4 an alkylidyne complex may be produced via the rearrangement of an η 2 -alkenyl intermediate. 5 Moreover, facile alkyne-to-vinylidene isomerization 6 makes it possible to incorporate 2 equiv. of alkyne for the synthesis of a butadienyl complex.…”

Novel Substitutions of 1-Alkoxy- and 1-Arylsulfonyloxy-η3-allylmolybdenum Complexes. A Case for η1-Alkenyl Carbene Complexes as Intermediates

“…Support for this mechanistic assumption comes from the published structures of known TpM(CO)(Z)(carbene) complexes (M = Mo, W; Z = CO, NO, other L:), which, in each case, depict the MoCR 2 plane bisecting the plane defined by the Mo and the two basal plane pyrazole ligands (Figure ). If the substitution reactions investigated here pass through a carbene complex that possesses the same geometry ( D , Figure ), then full racemization must ensue when these achiral cationic complexes are attacked by the incoming nucleophile from either equivalent π-face.…”

“…It is suggested that useful stereocontrol emanating from enantiomerically enriched complexes could result either (1) by using an internally tethered nucleophile that is attached to the π-complex via a preexisting stereocenter (cf., earlier studies of the stereocontrolled functionalization of η 3 -pyranyl- and η 3 -pyridinylmolybdenum complexes) or (2) by exploring reaction variables that can inhibit the partitioning of the substitution reaction pathway through an achiral η 1 -vinylcarbene. Finally, the chemistry described within, when extended from molybdenum to tungsten, is likely to provide a useful procedure to generate stable vinylcarbene complexes …”

Untitled

“…99 105 The irradiation of [WH(CO) 3 TpA] in the presence of a series of alkynes gives a wide range of products, namely with h 2 -vinyl, h 2 -acyl, metallafuran and carbyne groups attached to the tungsten; the variety of products is compatible with the photochemically promoted loss of carbon monoxide, followed by either cis-1,2-or cis-2,1-alkyne insertion to give h 1 -vinyl intermediates. 106 A one-pot tri-substitution on a series of [Cr(CO) 3 (h 6 -arene)] complexes has been reported, and evidence is given for the formation of a rare tri-anionic species. 107 It has been shown that the PhCr(CO) 3 substituent efficiently stabilises both propargyl cations and anions; in subsequent trapping reactions of the anions which can spectroscopically be investigated the regioselectivity depends upon the hardness of the attacking electrophile.…”