Thermal and Photochemical Ring-Bromination in Naphthyl‑, Naphthdiyl‑, and Dicarboximideperyl-Platinum Complexes

Brominated
polycyclic aromatic compounds are important synthons, but their synthesis
can be difficult. Herein, we report that Pt­(IV) centers σ-bonded
to naphthalene and a dicarboximideperylene activate the ring systems
to selective thermal and photochemical bromination. Thus, trans-Pt­(PEt3)2(Br)3­(4-bromo-1-naphthyl)
and Br2 give trans-Pt­(PEt3)2(Br)3­(7,4-dibromo-1-naphthyl). Introduction
of a second Pt­(IV) center is achieved by double oxidative addition
of 1,4-dibromonaphthalene to 2Pt­(PEt3)4. Bromination
of [trans-Pt­(PEt3)2Br]2­(1,4-naphthdiyl) yields [trans-Pt­(PEt3)2(Br)3]2­(1,4-naphthdiyl),
which further brominates on the ring to give [trans-Pt­(PEt3)2(Br)3]2­(6,7-dibromo-1,4-naphthdiyl).
Photoreduction of the Pt­(IV) centers with 1-hexene gives first mixed-valent
[trans-Pt­(PEt3)2(Br)3]­[trans-Pt­(PEt3)2(Br)]­(6,7-dibromo-1,4-naphthdiyl)
and then [trans-Pt­(PEt3)2Br]2­(6,7-dibromo-1,4-naphthdiyl). Photoreduction of trans-Pt­(PEt3)2(Br)3(PMI)
(PMI = N-(2,5-di-tert-butylphenyl)­perylen-3-yl-9,10-dicarboximide)
without 1-hexene slowly gives ring-bromination at the PMI 12-position.
HOTf treatment cleaves the Pt–PMI bond to give 12-bromo-N-(2,5-di-tert-butylphenyl)­perylene-9,10-dicarboximide.
The reaction chemistry indicates that the Pt­(IV) center is equivalent
to a bulky, electron-donating group for the naphthalene and PMI ring
systems.