The cyclometalated complexes [Pt(ppy)Ar(SMe 2 )] or [Pt(bhq)Ar(SMe 2 )], where ppyH = 2-phenylpyridine, bhqH = benzo[h]quinoline, and Ar = 4-tolyl or 4-anisyl, react with bis(diphenylphosphino)methane, dppm, in a 1:1 ratio to give the corresponding complexes [Pt(ppy)Ar(κ 1 -dppm)] and [Pt(bhq)Ar(κ 1 -dppm)], in which the dppm ligands are monodentate, or in a 2:1 ratio to give the symmetrical binuclear complexes [{Pt(ppy)Ar} 2 (μ-dppm)] and [{Pt(bhq)Ar} 2 (μ-dppm)], in which the dppm ligands are bridging bidentate. Most remarkably, the reaction of [Pt(ppy)Ar(SMe 2 )] with [Pt(bhq)Ar 0 (κ 1 -dppm)] or of [Pt(bhq)Ar 0 (SMe 2 )] with [Pt(ppy)Ar(κ 1 -dppm)] occurs selectively to give the unsymmetrical bridged complexes [(ppy)ArPt(μ-dppm)PtAr 0 (bhq)]. An example of each structural type has been characterized crystallographically, and it is shown that some of the bhq complexes undergo supramolecular self-assembly through π-stacking. † Part of the Dietmar Seyferth Festschrift. Dedicated to Professor Dietmar Seyferth for his pioneering research in organometallic chemistry and his outstanding service to Organometallics.

Reaction of the Pt­(II) complexes [PtMe2(pbt)], 1a, (pbt = 2-(2-pyridyl)­benzothiazole) and [PtMe­(C^N)­(PPh2Me)] [C^N = deprotonated 2-phenylpyridine (ppy), 1b, or deprotonated benzo­[h]­quinoline (bhq), 1c] with benzyl bromide, PhCH2Br, is studied. The reaction of 1a with PhCH2Br gave the Pt­(IV) product complex [PtBr­(CH2Ph)­Me2(pbt)]. The major trans isomer is formed in a trans oxidative addition (2a), while the minor cis products (2a′ and 2a″) resulted from an isomerization process. A solution of Pt­(II) complex 1a in the presence of benzyl bromide in toluene at 70 °C after 7 days gradually gave the dibromo Pt­(IV) complex [Pt­(Br)2Me2(pbt)], 4a, as determined by NMR spectroscopy and single-crystal XRD. The reaction of complexes 1b and 1c with PhCH2Br gave the Pt­(IV) complexes [PtMeBr­(CH2Ph)­(C^N)­(PPh2Me)] (C^N = ppy; 2b; C^N = bhq, 2c), in which the phosphine and benzyl ligands are trans. Multinuclear NMR spectroscopy ruled out other isomers. Attempts to grow crystals of the cycloplatinated­(IV) complex 2b yielded a previously reported Pt­(II) complex [PtBr­(ppy)­(PPh2Me)], 3b, presumably from reductive elimination of ethylbenzene. UV–vis spectroscopy was used to study the kinetics of reaction of Pt­(II) complexes 1a–1c with benzyl bromide. The data are consistent with a second-order SN2 mechanism and the first order in both the Pt complex and PhCH2Br. The rate of reaction decreases along the series 1a ≫ 1c > 1b. Density functional theory calculations were carried out to support experimental findings and understand the formation of isomers.

The known rollover cycloplatinated(II) complex [Pt 2 Me 2 (PPh 3 ) 2 (µ-bpy-2H)], 1, in which bpy-2H acts as a bridging rollover ligand, was reacted with MeI to give a new binuclear rollover cycloplatinated(IV) complex [Pt 2 Me 4 I 2 (PPh 3 ) 2 (µ-bpy-2H)], 2. Stereochemistry of 2 was fully identified by NMR spectroscopy ( 1 H and 31 P) and confirmed by DFT calculations.To the best of our knowledge, 2 is the first example of a diplatinum(IV) complex having a bridging rollover bipyridine ligand. 1 has a 5d π (Pt)→π*(bpy) MLCT band in the visible region which was used to easily follow the kinetic of its reaction with MeI; a double MeI oxidative addition was observed and classical S N 2 mechanism was suggested for the both steps of reaction. The large negative entropy of activation (∆S ‡ ), found in each step, complies with an associative process. The rates are almost 3-5 times slower in the second step as compared to the first step, due the electronic effects transmitted through the rollover bpy ligand. The rates were also compared with that reported for the corresponding monomeric cyclometalated complex [PtMe(bpy-H)(PPh 3 )] and found to be higher (in step 1) and usually lower (in step 2). Theoretical computations of geometry of the possible reaction transition 2 sates and intermediates revealed that each step of the reaction take places via a transition state with a nearly linear arrangement of the I-CH 3 -Pt moiety. The computational results are in a good agreement with the experimental findings, confirming the proposed mechanism.16 easily reacted with MeI to give A which is followed by a slower reaction to give 2.Calculated energies of the transition states TS1 (+45.5 kJmol -1 ) and TS2 (+48.2 kJmol -1 ) are in excellent agreement with the observed values of ∆H ≠ = 40.9 and 51.7 kJmol -1 for the first and second steps, respectively. Fig. 6. The B3LYP/(LANL2DZ, 6-31G(d))/chloroform optimized structures involved during oxidative addition reaction of [Pt 2 Me 2 (PPh 3 ) 2 (µ-bpy-2H)], 1, with CH 3 I. The H atoms are removed for clarity (except for the methyl group of the CH 3 I). Selected bond angles (°) and bond lengths (Å) are also shown.

The compound [PtMe(bzpy)(DMSO)] (1; bzpy = 2-benzylpyridinate) was synthesized by reaction of cis-[PtMe 2 (DMSO) 2 ] with 1 equiv of bzpyH under reflux conditions in toluene through C-H activation of the carbon-hydrogen bond in 2-benzylpyridine. Then, the complex [PtMe(bzpy)(PPh 3 )], 2, was prepared by addition of PPh 3 to complex 1. Complex 2 undergoes oxidative addition with methyl iodide to give [PtMe 2 I(bzpy)(PPh 3 )], 3. NMR spectroscopy ( 1 H and 31 P), and X-ray crystallography (supported by DFT calculations) clearly showed that the thermodynamic isomer product 3, with iodide trans to C of bzpy rather than the related kinetic isomer, 3, in which iodide is trans to methyl, is obtained. Mechanistic studies using UV-vis spectroscopy and DFT calculations indicate that the reaction occurs by a S N 2 mechanism. The kinetic study of the oxidative addition of methyl iodide to the non-planar, six-membered cyclometalated complex with that of the five-membered cyclometalated [PtMe(ppy)(PPh 3 )], in which ppy = 2-phenylpyridinate, shows that the ring size of the chelating unit has a significant impact on the rate of the reaction.

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The diorganoplatinum(II) complexes [PtR 2 (triphos-P,P′)] (1; R = Me, p-MeC 6 H 4 and triphos = bis(2-(diphenylphosphino)ethyl)phenylphosphine), containing one free phosphine atom, react with cyclometalated platinum complexes [PtR′(C ∧ N)(SMe 2 )] (2; R′ = Me, p-MeC 6 H 4 and C ∧ N is deprotonated 2-phenylpyridine (ppy) or deprotonated benzo[h]quinoline (bhq)) to give the cyclometalated diplatinum(II) complexes [Pt 2 R 2 R′(C ∧ N)(triphos)] (3). In these binuclear platinum(II) compounds, triphos acts as both a chelating and bridging ligand to stabilize the produced diplatinum complexes. The complexes 3 were readily characterized by multinuclear NMR spectroscopy and elemental microanalysis. The crystal structure of complex 3f (R = Me, R′ = p-MeC 6 H 4 , and C ∧ N = bhq) was further determined by X-ray crystallography, giving the first example of an X-ray structural determination of a diplatinum complex with a triphos ligand acting simultaneously as both a chelating and bridging ligand.