Vinylic Deprotonation in the Coordination Sphere of Platinum(II): Regioselective Formation of Alkenyl Complexes

Abstract

Reaction of [PtCl(η2‐CH2=CHAr)(tmeda)](ClO4) (1) [Ar = C6H5 (1a), 4‐CH3OC6H4 (1b), 3‐NO2C6H4 (1c); tmeda = N,N,N′,N′‐tetramethylethylenediamine) with triethylamine, or even with inorganic carbonate, leads to the abstraction of a vinylic proton and formation of the (alkenyl)platinum species [PtCl{(E)‐CH=CHAr}(tmeda)] (2) in high yield. The initially formed (E) isomer, in solution of chlorinated solvents, partly isomerizes into the (Z) form [equilibrium ratio (E)/(Z) ≈︁ 4:1]; the isomerization reaction is rather slow and is catalyzed by visible light. The nature of the phenyl substituent (electron donor OMe or electron‐withdrawing NO2 group) does not appear to affect the rate of deprotonation. The nature and stereochemistry of the formed (alkenyl)platinum species has been elucidated through 1D and 2D 1H and 13C NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Aiding Factors in the Formation of Azaplatinacyclobutane Rings – X‐ray and Crystal Structure of [Pt{CH(Ph)CH2NEt2‐κC,κN}(N,N,N′,N′‐tetramethylethylenediamine)]+ and of Its Open‐Chain Precursor

“…C 6 H 5 , 1b) were prepared by ethene exchange on the cationic complex [PtCl(η 2 -C 2 H 4 )(tmeda)](ClO 4 ) (1c) by following a reported procedure. [17] Amine addition compounds 2xy were prepared by reaction of the alkene complex 1 (0.4 mmol), suspended in dichloromethane (8 mL), with a slight excess of the amine (NHMe 2 , m; NHEt 2 , n; 1.2-fold the stoichiometric amount). After stirring for 3 h at room temperature, complete dissolution of the solid was observed.…”

Insertion of alkynes into Pt–X bonds of square planar [PtX2(N^N)] (X = Cl, Br, I) complexes

“…This is a clear indication that the two hydrogen atoms are in trans positions with respect to the double bond. 28,29 Moreover, the coupling constants between β-proton and 195 Pt (42 and 62 Hz for complexes 5 and 6, respectively) are smaller than corresponding coupling constants in complexes in which the β-proton and 195 Pt are trans to one another (≈ 100-200 Hz 30 ), thus confirming the relative cis position of Pt and β-proton.…”

“…43 Interestingly, the nucleophilic attack of X − on the π-bonded alkyne extends to halides the possibility of acting as nucleophiles toward unsaturated molecules π bonded to cationic complexes of platinum(II). [8][9][10][11]13,15,23,25,28,29,41,42 13 C} NMR data (δ, CDCl 3 ) for [PtX(η 1 -E-CHvCHX)(η 2 -CH 2 vCH 2 )(Me 2 phen)], X = Br, (7) and I, (12); syn and anti-[PtBr(η 1 -E-CHvCHBr)(η 2 -propene)(Me 2 phen)] (10); syn and anti-[PtBr(η 1 -E-CHvCHBr)(η 2 -cis-2-butene)(Me 2 phen)] (11); [PtBr(η 1 -E-CHvCHBr)(CuO)-(Me 2 phen)] ( evolve to square planar alkenyl complexes of the type [PtX(η 1 -E-CHvCHX)(Me 2 phen)] (X = Br, I). In the presence of excess acetylene, the square planar alkenyl complexes are in equilibrium with the pentacoordinate alkyne-alkenyl species [PtX-(η 1 -E-CHvCHX)(η 2 -CHuCH)(Me 2 phen)] (X = Br, I).…”

Photo-isomerisation of alkenyl complexes of platinum(ii): structural, spectroscopic, kinetic and computational investigations

“…The observed selectivity appears to have a kinetic origin since in the cationic precursor the abstracted proton (the one trans to the aromatic ring) is the most exposed to the solvent and, hence, the most easily accessed by the attacking base. 19 In chlorinated solvents, the E isomer partially isomerises into the corresponding Z form. Thus we decided to investigate the mechanism of the isomerisation process to see if the presence of a metal atom ( platinum in the present case) directly bound to an olefinic carbon would influence a transformation very much alike to the classic cis-trans isomerisation of a stilbene molecule.…”

“…The alkenyl complexes [PtCl(η 1 -C α H-C β HAr)(tmeda)], 2, (Ar = C 6 H 5 , (E)-2a; 4-CH 3 O-C 6 H 4 , (E)-2b; 3-NO 2 -C 6 H 4 , (E)-2c; and 3-CH 3 O-C 6 H 4 , (E)-2d) were prepared according to the procedure described in ref 19…”