Ligand-Mediated C–Br Oxidative Addition to Cycloplatinated(II) Complexes and Benzyl-Me C–C Bond Reductive Elimination from a Cycloplatinated(IV) Complex

Reaction of the Pt(II) complexes [PtMe 2 (pbt)], 1a , (pbt = 2-(2-pyridyl)benzothiazole) and [PtMe(C^N)(PPh 2 Me)] [C^N = deprotonated 2-phenylpyridine (ppy), 1b , or deprotonated benzo[h]quinoline (bhq), 1c ] with benzyl bromide, PhCH 2 Br, is studied. The reaction of 1a with PhCH 2 Br gave the Pt(IV) product complex [PtBr(CH 2 Ph)Me 2 (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) 2 Me 2 (pbt)], 4a , as determined by NMR spectroscopy and single-crystal XRD. The reaction of complexes 1b and 1c with PhCH 2 Br gave the Pt(IV) complexes [PtMeBr(CH 2 Ph)(C^N)(PPh 2 Me)] (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)(PPh 2 Me)], 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 S N 2 mechanism and the first order in both the Pt complex and PhCH 2 Br. 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.