Frustrated Lewis pair-like splitting of aromatic C–H bonds and abstraction of halogen atoms by a cationic [( F PNP)Pt] + species
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This manuscript explores new chemistry that can be related to the unobserved 14-electron [(FPNP)Pt]+ transient ( FPNP = (4-F-2-(iPr2P)C6H 3)2N). Its reactivity can be accessed via abstraction of triflate from (FPNP)PtOTf (1) with K[B(C6F 5)4] in various solvents serving as substrates. With benzene, toluene and fluorobenzene, net heterolytic splitting of an aromatic C-H bond across the N-Pt bond is observed, without any detectable intermediates, leading to the [(FPN(H)P)Pt-Ar]+ products (Ar = Ph, 3a; Ar = C6H4Me, 3b (ortho), 3c (meta), 3d (para); Ar = o-C 6H4F, 3e). The latter can be alternatively prepared by protonation of the neutral (FPNP)Pt-Ar compounds. Compounds 3a-3e do not release free arene under thermolysis at 80 °C, and compounds 3b/c/d do not interconvert under ambient temperature. With chlorobenzene and bromobenzene, the kinetic product is the κ1-Cl or κ1-Br adduct [(FPNP)Pt-Cl-Ph]+ (4) or [(FPNP)Pt-Br- Ph]+ (10). Compound 4 rearranges into a C-H splitting product [( FPN(H)P)Pt-C6H4Cl]+ (3f), while 10 slowly reacts by formal transfer of Br atom to Pt. An analogous Cl atom transfer to Pt is observed upon the reaction of 1 with K[B(C6F 5)4] in dichloromethane, producing [(FPNP)PtCl] [B(C6F5)4] (9a) which features an oxidized FPNP ligand framework. X-Ray diffractometry established structures of [(FPN(H)P)Pt-C6H4F-o][B(C6F 5)4] (3e, disordered rotamers), [(FPN(H)P)Pt- C6H4Me][B(C6F5)4] (disordered meta- and para-isomers 3c/d), and [(FPNP)PtCl][HCB 11Cl11] (9b). DFT calculations at the PBE0 and M06-L levels on the free [(FPNP)Pt]+ cation predict a relatively small (10-12 kcal mol-1) separation between the singlet and the triplet states. The relatively low triplet energy is probably related to the viability of the unexpected halogen atom abstraction reactions. © The Royal Society of Chemistry 2013.
author list (cited authors)
DeMott, J. C., Bhuvanesh, N., & Ozerov, O. V.