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The novel tetranuclear Pt(IV)–Re(VII) complex [Pt2Me4(OReO3)2(PMePh2)2(µ-bpy-2H)], 4, is synthesized through the reaction of silver perrhenate with a new rollover cycloplatinated(IV) complex [Pt2Me4I2(PMePh2)2(µ-bpy-2H)], 3. In complex 4, while 2,2′-bipyridine (bpy) acts as a linker between two Pt metal centers, oxygen acts as a mono-bridging atom between Pt and Re centers through an unsupported Pt(IV)–O–Re(VII) bridge. The precursor rollover cycloplatinated(IV) complex 3 is prepared by the MeI oxidative addition reaction of the rollover cycloplatinated(II) complex [Pt2Me2(PMePh2)2(µ-bpy-2H)], 2. Complex 2 shows a metal-to-ligand charge-transfer band in the visible region, which was used to investigate the kinetics and mechanism of its double MeI oxidative addition reaction. Based on the experimental findings, the classical SN2 mechanism was suggested for both steps and supported by computational studies. All complexes are fully characterized using multinuclear NMR spectroscopy and elemental analysis. Attempts to grow crystals of the rollover cycloplatinated(IV) dimer 3 yielded a new dimer rollover cyclometalated complex [Pt2I2(PMePh2)2(µ-bpy-2H)], 5, presumably from the C–C reductive elimination of ethane. The identity of complex 5 was confirmed by single crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

We present a Pt-catalyzed direct coupling of benzene to biphenyl. This catalytic reaction employs a cyclometalated platinum(II) complex [PtMe(bhq)(SMe2)] (bhq = benzo[h]quinolate) with PhI(OAc)2 as an oxidant and does not require an acid, a co-catalyst or a solvent. The reaction kinetics and characterization of potential catalytic species are reported. The reaction is first-order in Pt and second-order in benzene, which implicates the second C–H activation step as rate-determining. A Pt(II)/Pt(IV) catalytic cycle is suggested. The reaction commences by oxidation of the Pt(II) complex to give the platinum(IV) species [Pt(bhq)(SMe2)(OAc)2](OAc) followed by C–H activation of benzene to afford the intermediate [PtPh(bhq)(SMe2)(OAc)](OAc) concurrently with the release of HOAc. A second benzene molecule reacts similarly to give the diphenyl intermediate [PtPh2(bhq)(SMe2)](OAc). C–C bond forming reductive elimination ensues to regenerate Pt(II) and complete the catalytic cycle. The proposed mechanism has been examined by DFT computations, which provide support to experimental findings. [ABSTRACT FROM AUTHOR]

We present a Pt-catalyzed direct coupling of benzene to biphenyl. This catalytic reaction employs a cyclometalated platinum(II) complex [PtMe(bhq)(SMe2)] (bhq = benzo[h]quinolate) with PhI(OAc)2 as an oxidant and does not require an acid, a co-catalyst or a solvent. The reaction kinetics and characterization of potential catalytic species are reported. The reaction is first-order in Pt and second-order in benzene, which implicates the second C–H activation step as rate-determining. A Pt(II)/Pt(IV) catalytic cycle is suggested. The reaction commences by oxidation of the Pt(II) complex to give the platinum(IV) species [Pt(bhq)(SMe2)(OAc)2](OAc) followed by C–H activation of benzene to afford the intermediate [PtPh(bhq)(SMe2)(OAc)](OAc) concurrently with the release of HOAc. A second benzene molecule reacts similarly to give the diphenyl intermediate [PtPh2(bhq)(SMe2)](OAc). C–C bond forming reductive elimination ensues to regenerate Pt(II) and complete the catalytic cycle. The proposed mechanism has been examined by DFT computations, which provide support to experimental findings. [ABSTRACT FROM AUTHOR]

Reaction of [PtR 2 (NN)] (R = Me, p -MeC 6 H 4 or p -MeOC 6 H 4 ; NN = 2,2′−bipyridine, 4,4′−dimethyl−2,2′−bipyridine, 1,10−phenanthroline or 2,9−dimethyl−1,10−phenanthroline) with MeSSMe gives the platinum(IV) complexes cis,trans −[PtR 2 (SMe) 2 (NN)]. They are characterized by NMR spectroscopy and elemental analysis. The geometries and the nature of the frontier molecular orbitals of Pt(IV) complexes containing Pt S bonds are studied by means of the density functional theory. [ABSTRACT FROM AUTHOR]

Abstract: Three d8 square-planar complexes of the type [PtMe2(LL)], [LL=2,2′-bipyridine (NN), 2-(2-pyridyl)phosphinine (PN) and 2,2′-biphosphinine (PP)], with a systematic variation in the chelating ligands, have been chosen for investigating their SN2-type oxidative addition reactions with MeI by means of DFT calculations with the B3LYP functional. The oxidative addition proceeded via a transition state with a nearly linear arrangement of the I–CH3–Pt moiety. It was found that the addition of MeI is exothermic for all three chelate rings, and [PtMe2(NN)] is predicted to react with a much lower barrier than either [PtMe2(PN)] or [PtMe2(PP)]. In agreement with the available experimental data, the DFT results suggest that the MeI oxidative addition is more favorable with the complex bearing the 2,2′-bipyridine ligand as compared to the other chelate rings, 2-(2-pyridyl)phosphinine (PN) or 2,2′-biphosphinine (PP). [Copyright &y& Elsevier]

The organoplatinum complexes cis -[PtAr 2 (SMe 2 ) 2 ] (Ar = p– MeC 6 H 4 and p– MeOC 6 H 4 ) and cis,cis -[Me 2 Pt(μ-SMe 2 ) 2 PtMe 2 ] react very easily - in acetone at room temperature - with 1 or 2 equiv 1,1′–bis(diphenylphosphino)acetylene (= dppac), to give the diplatinum(II) complexes [Pt 2 R 4 (μ–dppac) 2 ], ( 1 , R = Me; 2 , R = p– MeC 6 H 4 ; 3 , R = p– MeOC 6 H 4 ) in which two square-planar R 2 Pt units are held together by two bridging dppac ligands. All the complexes were characterized using multinuclear ( 1 H, 31 P and 195 Pt) NMR spectroscopy and single crystal X-ray structure determination. Investigation of electronic structures and related DFT and TD-DFT calculations supported a mixed 1 IL (intraligand charge transfer)/ 1 MLCT (metal-to-ligand charge transfer) for R = Me and L'LCT (ligand-to-ligand charge transfer) for R = p– MeC 6 H 4 and p– MeOC 6 H 4 . [ABSTRACT FROM AUTHOR]

Abstract: The binuclear complex [Pt2Me2(bhq)2(μ-dppf)], 1a, in which bhqH = benzo{h}quinoline and dppf = 1,1′-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(bhq)] with 0.5 equiv of dppf at room temperature. The reaction of Pt(II)–Pt(II) complex 1a with excess MeI gave the Pt(IV)–Pt(IV) complex [Pt2I2Me4(bhq)2(μ-dppf)], 2a. The complexes were fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and elemental analysis. The kinetic and mechanism of the reaction of complex 1a with MeI was investigated in CHCl3 and based on the data, obtained from UV–vis and low temperature 31P NMR spectroscopies, a mechanism involving stepwise oxidative addition of MeI to the two Pt(II) centers is suggested. Reaction rates concerning the complex 1a, having bhq ligand, are almost 1.4 times slower than those involving the ppy complex [Pt2Me2(ppy)2(μ-dppf)], ppyH = 2-phenylpyridine, reported previously (Inorg. Chem. 2008, 47, 5441). This is attributed to the stronger donor ability of the ppy ligand as compared to that of the bhq ligand as is further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes. A comparative kinetic study of reaction of the dimeric platinum(II) complex [Pt2Me2(bhq)2(μ-dppm)], 1b, where dppm = bis(diphenylphosphino)methane, with MeI was also performed to investigate the effect of bridging biphosphine ligand on the kinetic and mechanism of the dimeric complexes with MeI. A double MeI oxidative addition was observed for which the classical SN2 mechanism for both steps, as well as the possible intermediates, is suggested. [Copyright &y& Elsevier]

Abstract: New cyclometalated platinum(II) complexes [PtMe(C^N)L], 1, in which C^N=deprotonated 2-phenylpyridine (ppy), benzo[h]quinoline (bhq) or 2-(p-tolyl)pyridine (tpy) and L=PPh3 or PMePh2, were synthesized by the reaction of [PtMe(C^N)(SMe2)] with 1equiv of L. The reaction of complexes 1 with MeI gave the cyclometalated Pt(IV) complexes [PtMe2I(C^N)L], 3. On the basis of kinetic studies, using Uv–visible spectroscopy, it was suggested that the latter oxidative addition reactions were proceeded by an SN2 mechanism. The rates of the reactions at different temperatures were measured and consistent with the proposed mechanism, large negative ΔS ‡ values were found for each reaction. Besides, rate of reactions (in CHCl3) involving the PPh3 complexes [PtMe(C^N)(PPh3)], were almost 3–5 times slower than those involving the PMePh2 complexes [PtMe(C^N)(PMePh2)]. This was attributed to the electronic and steric effects of PPh3 ligand as compared with that of PMePh2 ligand which was further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes. [Copyright &y& Elsevier]

Kinetic and mechanism of addition of alkyl halides (RI = MeI and EtI) to [PtMe 2 (pbt)], in which pbt = 2-(2-pyridyl)benzothiazole, to give the Pt(IV) complexes [PtIRMe 2 (pbt)] were investigated. • The organoplatinum(II) and (IV) complexes of 2-(2-pyridyl)benzothiazole are synthesized. • New platinum complexes are characterized by NMR spectroscopy and X-ray crystallography. • The kinetics of oxidation of Pt(II) complex to Pt(IV) complex by alkyl halides are studied. The alkyl halides, RI (MeI and EtI), were oxidatively added to a Pt(II) complex [PtMe 2 (pbt)], 1 , in which pbt = 2-(2-pyridyl)benzothiazole, to give the Pt(IV) complexes [PtIRMe 2 (pbt)] (R = Me; 2 and R = Et; 3). Kinetics of the reactions in toluene and acetone were studied using UV–vis spectroscopy between 5 and 40 °C and an S N 2 mechanism was suggested. The reaction of MeI with complex 1 was considerably faster than EtI. The reactions followed second-order kinetics, rate = k 2 [ 1 ][RI], and the rates in the polar solvent acetone were faster than those in the nonpolar solvent toluene. Activation parameters have been determined and large negative values for Δ S ‡ were obtained. The results were also confirmed using DFT calculations. The computational investigations were used to determine the geometry of the species involved in the suggested mechanism and energy barriers. [ABSTRACT FROM AUTHOR]

Mono- and di-nuclear cycloplatinated(II) compounds are synthesized and characterized. For this purpose, chelating 2-(2′-pyridyl)-benzimidazolate ligand and non-chelating ancillary phosphine ligands (as terminal or bridging ligand) were employed to construct the structures. The photophysical properties of the complexes are also described and compared to similar cycloplatinated(II) complexes including C^N ligands. • Mono- and di-nuclear Pt(II) complexes are synthesized. • New complexes are characterized by NMR spectroscopy, X-ray crystallography and mass spectrometry. • The photophysical properties of the complexes are investigated under different conditions. • The photophysical results are interpreted and supported by TD-DFT calculations. The starting complex [Pt(Me)(DMSO)(pbz)] (1 , pbz = 2-(2-pyridyl)benzimidazolate) was prepared by a known method using the reaction of [Pt(Me) 2 (DMSO) 2 with Hpbz at room temperature. Reaction of 1 with an equivalent of a phosphine ligand gave the neutral mononuclear complexes [Pt(Me)(L)(pbz)] (2 , L = PPh 3 and 3 , L = PPh 2 Me). Reaction of 1 with 0.5 equivalent of the linear diphosphine 1,1′–bis(diphenylphosphino)acetylene (dppac) gave the binuclear complex [Pt 2 (Me) 2 (μ-dppac)(pbz) 2. Each complex was fully characterized by NMR spectroscopy, X-ray single-crystal crystallography and mass spectrometry. The photophysical properties of the complexes were investigated under different conditions and interpretation was supported by TD-DFT calculations. The low-lying transitions in the absorption and emission spectra were assigned as having LLCT/MLCT (ligand to ligand charge transfer/metal to ligand charge transfer) character. We also describe the luminescence properties of [Pt(Me)(PPh 3)(ppy)] and [Pt(Me)(PPh 2 Me)(ppy)] (ppy is 2-phenylpyridinate), the (N^C−) analogues of 2 and 3. [ABSTRACT FROM AUTHOR]