Facile Metalation of Hbzq
by [<i>cis</i>-Pt(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>(thf)<sub>2</sub>]: A
Route to a Pentafluorophenyl Benzoquinolate Solvate Complex That Easily
Coordinates Terminal Alkynes. Spectroscopic and Optical Properties
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Abstract
A new neutral cyclometalated platinum(II) solvate complex
[<i>cis</i>-Pt(bzq)(C<sub>6</sub>F<sub>5</sub>)(acetone)]
(<b>1</b>) has been prepared by easy C–H activation of
7,8-benzo[<i>h</i>]quinoline on the coordination sphere
of [<i>cis</i>-Pt(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>(thf)<sub>2</sub>] (thf
= tetrahydrofuran). The study of the reaction pathway has led us to
the preparation of the bis(Hbzq) product [<i>cis</i>-Pt(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>(Hbzq)<sub>2</sub>] (<b>2</b>) and the benzoquinoline–benzoquinolate derivative [Pt(bzq)(C<sub>6</sub>F<sub>5</sub>)(Hbzq)] (<b>3</b>). This latter complex
has been characterized by X-ray diffraction, showing the occurrence
of π···π intermolecular stacking interactions
associated to the deprotonated bzq units. The acetone molecule in
[<i>cis</i>-Pt(bzq)(C<sub>6</sub>F<sub>5</sub>)(acetone)]
can be easily displaced by alkynes, allowing the synthesis of the
first reported η<sup>2</sup>-alkyne-cycloplatinate complexes
[Pt(bzq)(C<sub>6</sub>F<sub>5</sub>)(η<sup>2</sup>-RCCR′)]
(R = H, R′ = Ph <b>4</b>, <sup>t</sup>Bu <b>5</b>, Fc <b>6</b>; R = R′ = Ph <b>7</b>), which have
been fully characterized spectroscopically and by DFT studies. These
alkyne complexes are only moderately stable in solution, and all attempts
to obtain crystals suitable for X-ray diffraction were fruitless.
Nevertheless, in the case of the ferrocenyl derivative, crystals of
complex [Pt(κ<i>N</i>:η<sup>2</sup>-bzq-C≡CFc)(C<sub>6</sub>F<sub>5</sub>)(μ-κ<i>C</i><sup>α</sup>:η<sup>2</sup>-C≡CFc)Pt(bzq)(C<sub>6</sub>F<sub>5</sub>)] (<b>8</b>), containing an unusual alkynyl-functionalized
benzoquinoline chelate ligand, were systematically obtained. All complexes
(except those containing the ferrocenyl fragment) present emissive
properties in solution and solid state (77 K), related, in general,
with intraligand (bzq) excited states with some mixing <sup>3</sup>MLCT character, as supported by theoretical calculations. In solid
state at room temperature, aggregation induced emission (AIE) is observed
likely generated by intermolecular π···π
stacking, as supporting by DFT calculations on <b>3</b><sub><b>2</b></sub>. Interestingly, both types of excited states
(<sup>3</sup>IL/<sup>3</sup>MLCT and AIE) seem to be close in energy
in complexes <b>1</b> and <b>3</b>, which show a significant
luminescent thermochromism (green 77 K to orange 298 K)
