Control of Olefin Hydroarylation Catalysis via a Sterically and Electronically Flexible Platinum(II) Catalyst Scaffold

Abstract

Pt II complexes supported by dipyridyl ligands have been demonstrated to catalyze olefin hydroarylation. Herein, studies on the influence of dipyridyl motif variation are reported. Increasing the chelate ring size of dipyridyl-ligated Pt II complexes from fiveto six-membered rings by replacing 4,4′-di-tert-butyl-2,2′-bipyridine with 2,2′-dipyridylmethane has been shown to increase catalytic activity and longevity for catalytic ethylene hydrophenylation. For 2,2′-dipyridyl ligands, the presence of methyl groups in the 6/6′-positions of the pyridyl rings reduces the extent of dialkylation to produce diethylbenzenes but also increases the rate of catalyst decomposition. Substituting the methylene spacer between the pyridyl rings of 2,2′dipyridylmethane with more electron-withdrawing groups also reduces catalytic efficiency. The steric profile of Pt II complexes with increased chelate ring size or substituents in the 6/6′-positions of the pyridyl rings provides a marked change in regioselectivity for ethylene hydroarylation using ethylbenzene as well as the linear to branched selectivity for the hydrophenylation of propylene.

Hydrophenylation of ethylene using a cationic Ru(ii) catalyst: comparison to a neutral Ru(ii) catalyst

“…[6][7][8][9][10][11][12][13][14][15][16] Transition metal catalyzed olen hydroarylation provides a complementary route for the alkylation of aromatic substrates that can proceed by a pathway that is different from acid catalyzed aromatic alkylation. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] For some transition metal mediated olen hydroarylation reactions, olen insertion into a metal-aryl bond is followed by aromatic C-H activation and liberation of alkylated aromatic arene (Scheme 1). 17,18,37 Potential benets of this method include the selective production of linear alkyl arenes when using a-olens, selective synthesis of mono-alkyl arenes, regioselective synthesis of dialkyl arenes, and direct synthesis of vinyl arenes using oxidative hydroarylation.…”

Enhancing the catalytic properties of well-defined electrophilic platinum complexes

“…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). 24 Having in mind that platinum complexes bearing bipyridine ligands with electron-withdrawing groups at the 4,4 0 position increase the amount of styrene in the reaction of benzene with ethylene catalysed by complexes 2, the next step was to evaluate the effect of incorporating in the structure of the catalyst more electron rich ligands such as phosphines or N-heterocyclic carbenes such as those in Fig. 1.…”

Reversible PtII–CH3 deuteration without methane loss: metal–ligand cooperation vs. ligand-assisted PtII-protonation

“…Although widely explored in organometallic chemistry, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] to the best of our knowledge, such involvement has not been investigated in the context of C-H reductive elimination from Pt IV , despite the demonstrated ability of κ 2 -(N,N)-DPKsupported Pt II complexes to activate C-H bonds. [34][35][36] Here, we report that the DPK-supported dimethylplatinum(II) complex (1, Scheme 2), upon dissolution in CD 3 OD, undergoes fast and reversible Pt II -CH 3 deuteration (reductive coupling) at room temperature without methane loss (reductive elimination). Mechanistic insights gained from kinetics, analyses of isotope effects, reactivity of model complexes (2-4, Scheme 2) and DFT calculations suggest that DPK enables nonrate-limiting Pt II -protonation via a novel cooperative mechanism between the metal and the ligand.…”