Pt^II-Catalyzed Hydrophenylation of α-Olefins: Variation of Linear/Branched Products as a Function of Ligand Donor Ability

Abstract

The Pt II complexes [( x bpy)Pt(Ph)(THF)] + ( x bpy = 4,4′-X 2 -2,2′bipyridyl; x = OMe (1a), t Bu (1b), H (1c), Br (1d), CO 2 Et (1e) and NO 2 (1f)] catalyze the formation of n-propylbenzene and cumene from benzene and propene. The catalysts are selective for branched products, and the cumene/n-propylbenzene ratio decreases with increasing donor ability of the x bpy ligand. DFT(D) calculations predict more favorable activation barriers for 1,2-insertion into the Pt−Ph bond to give branched products. The calculations indicate that 1,2-insertion of propene should be faster than 2,1-insertion for all Pt(II) catalysts studied, but they also indicate that cumene/n-propylbenzene selectivity is under Curtin−Hammett control.

Beyond Friedel and Crafts: Directed Alkylation of C−H Bonds in Arenes

“…[177] Them echanism proposed by the authors is similar to those reported for the previously described iridium(III) and ruthenium(II) systems and is based on the migratory insertion of ethylene into an arylplatinum(II) species.T he resulting complex can then coordinate asecond arene which, after hydrogen transfer and ligand exchange,y ields the desired alkylated product. [178] Whereas an electron-deficient bipyridine improves the selectivity for the branched isomers, the use of ad ipyridylmethane-based ligand drastically improves the selectivity for the monoethylation of benzene. (2)].…”

“…T hey also reported additional electronically and sterically tuned bipyridine-and dipyridylmethane-based ligands to improve the selectivity of the reaction. [178] Whereas an electron-deficient bipyridine improves the selectivity for the branched isomers, the use of ad ipyridylmethane-based ligand drastically improves the selectivity for the monoethylation of benzene. Finally,G oldberg and co-workers reported that the use of 2pyridinylpyrrole as the ligand greatly improves the linear selectivity.…”

Enhancing the catalytic properties of well-defined electrophilic platinum complexes

“…Bipy ligands with electron-poor substituents at the 4,4 0 position originate mixtures in which the cumene/n-propylbenzene is higher (branched to linear product ratios ranging from 3.8 to 4.6). 22 The stability of the platinum catalyst is an important issue in order to develop more efficient catalytic systems. A further step to improve the longevity of the catalyst was made by changing the bipy-type ligands by dipyridyls, such as 2,2-dipyridylmethane (dpm) (Scheme 6).…”

“…However, the efficacy of the dpm-based platinum complex is lower (TO 11.8 in 4 h) than that of the t Bubipy (TO 33.5 in 4 h) in the hydroarylation of propene and benzene, presumably due to steric effects. 22 With respect to the selectivity of the processes, although styrene is a minor component, diethylbenzenes account for about 20% of the final products. Attempts to modify the dipyridyl ligand by means of different E or R groups (E = CH 2 CH 2 , CQO, NH, O; R = Me) did not lead to improvement of the catalyst activity, due in part to catalyst deactivation, although some benefits in selectivity were observed when Me groups are at the 6,6 0 position of the pyridyl units (R = Me).…”

Phosphine and N-heterocyclic carbene ligands on Pt(II) shift selectivity from ethylene hydrophenylation toward benzene vinylation

“…[13][14][15][16][17][18][19][20][21][22] Our group has been studying Pt(II) complexes of the type [(N~N)Pt(THF)(Ph)][BAr' 4 ] (N~N = bis-chelating dipyridyl ligand, Ar' = 3,5-bis(trifluoromethyl)phenyl), which have been found to be active catalysts for ethylene hydrophenylation to yield ethylbenzene. 4,[23][24][25][26][27][28] In addition to ethylbenzene, the formation of styrene is typically observed when using these Pt(II) complexes as catalysts. For the [(N~N)Pt(THF)(Ph)][BAr' 4 ] catalysts, the formation of styrene is proposed to occur via β-hydride elimination from [(N~N)Pt(CH 2 CH 2 Ph)] + intermediates followed by styrene dissociation.…”