Bis(diphenylphosphino)acetylene as bifunctional ligand in cycloplatinated complexes: Synthesis, characterization, crystal structures and mechanism of MeI oxidative addition

Abstract

Binuclear cycloplatinated(II) complexes with general formula of [Pt 2 Me 2 (C^N) 2 (m-dppac)], (1, ĈN ¼ deprotonated 2-phenylpyridine (ppy); 2, ĈN ¼ deprotonated benzo{h}quinoline (bhq)) in which dppac ¼ 1,1 0-bis(diphenylphosphino)acetylene, are synthesized by the reaction of [PtMe(SMe 2)(C^N)] with 0.5 equiv of dppac at room temperature. The complexes are fully characterized using multinuclear (1 H, 31 P and 195 Pt) NMR spectroscopy and complex 2 is further identified by single crystal X-ray structure determination. Kinetics of the reaction of complexes 1 and 2 with MeI are investigated in CHCl 3 and based on the UVevis and 31 P NMR data, a mechanism involving a double MeI oxidative addition is suggested. The classical S N 2 mechanism is proposed for both steps and the involved intermediates are suggested. Although MeI in each step was trans oxidatively added to one of the platinum(II) centers, further trans to cis isomerizations of methyl and iodide ligands were also identified. The rates are almost four times slower in the second step as compared to the first step due to the electronic effects transmitted through the dppac ligand. Reaction rates concerning complex 2, having bhq ligand, are almost 1.3 times slower than those involving the related ppy complex 1. This is attributed to the stronger donor ability of the ppy ligand, as compared to that bhq ligand and is in agreement with the values of 1 J PtP observed in the 31 P NMR spectra of the complexes 1 and 2. The structure of the Pt(IV)ePt(IV) dimeric complex [Pt 2 I 2 Me 4 (ppy) 2 (m-dppac)], 3, produced by oxidative addition of complex 1 to MeI, is also determined using X-ray diffraction which is the first X-ray structural determination of a diplatinum complex containing two Pt(IV) centers bridged by one dppac ligand.

Oxidation of a rollover cycloplatinated(ii) dimer by MeI: a kinetic study

“…1-3 2-Phenylpyridine is a typical compound, and its reaction with a transition metal complex forms an orthometalated intermediate with the help of nitrogen coordination to the metal. [8][9][10] Electron density on the Pt (II) center of a [PtR 2 (LL)] complex can be manipulated by selecting R ligand, which has either electron-withdrawing or electron-donating ability. 4 In this type of cyclometalation, the two nitrogen atoms of bpy at first coordinate to metal and then the coordination of one nitrogen to the metal is switched to carbon-metal bond by rotation of the pyridine ring (Scheme 1).…”

Reactivity comparison of five-and six-membered cyclometalated platinum(ii) complexes in oxidative addition reactions

“…2 Although the most well-studied examples of these compounds are five-membered ring complexes containing N−Pt−C(phenyl) moiety, [3][4][5] six-membered cyclometalated complexes are relatively rare. [12][13][14][15][16][17][18][19][20][21] For example, the trans or cis oxidative additions of an alkyl halide to cyclometalated platinum(II) complexes give the corresponding alkyl-cyclometalated platinum(IV) complex. [12][13][14][15][16][17][18][19][20][21] For example, the trans or cis oxidative additions of an alkyl halide to cyclometalated platinum(II) complexes give the corresponding alkyl-cyclometalated platinum(IV) complex.…”

Theoretical studies of methyl iodide oxidative addition to adjacent metal centers in diplatinum(II) complexes

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 In a two-step oxidative addition reaction of this type of complexes with no metal-metal bond, it is suggested that the first addition occurs faster than the second. [23][24][25]27 In the present study, we…”

“…The oxidative additions of alkyl halides to bridged binuclear platinum complexes have been briefly investigated and can yield products formed by single or double oxidative addition. [22][23][24][25][26][27] Also in recent years there has been a great interest in investigating the application of binuclear platinum(II) complexes in the field of platinum chemotherapy. 28 Therefore, it is interesting to extend the theoretical studies of monoplatinum complexes by studying binuclear complexes containing two platinum centers.…”