Platinum Complexes of Alkynyl-Substituted Dimethyldihydropyrenes

A series of photochromic dimethyldihydropyrenes (DHP)
bearing ethyne substituents in the 4-position (RDHP-CCH;
R = H (4), acetyl (5), benzoyl (6), 1-naphthoyl (7), benzo­[e] (8)) were prepared for use as precursors to ethynyl ligands.
Dehydrohalogenation of the adduct of these ethynes with various PtCl2(L)2 complexes afforded a series of cis and trans
square-planar bis­(DHP-ethynyl) platinum complexes, (RDHP-CC)2Pt­(L)2 (cis, R = H, L2 = PEt3 (9), acetyl, PEt3 (10), benzoyl,
PEt3 (11), 1-naphthoyl, PEt3 (12), benzo­[e], PEt3 (13), benzoyl, PPh3 (14), benzo­[e], PPh3 (15); trans, R = H, L2 = dppe (16), benzo­[e], dppe (17), acetyl, bipy (18), 1-naphthoyl, bipy (19), H, phen (20)). The DHP-ethynes bearing acyl
and benzo­[e] substituents on the DHP (5–8) and their platinum complexes (10–19) are photochromic and undergo ring opening
to the related cyclophanediene (CPD) isomer on irradiation with visible
light (λ >550 nm). In the case of the benzo­[e]­DHP 8, adding a 4-ethynyl substituent increases the
rate of photo-opening 4-fold; however, in the acylDHP series 5–7, addition of a 4-ethynyl group slows
the rate of photo-opening by a factor of about 4. The platinum complexes
generally open more slowly than the corresponding alkyne precursors,
again by a factor of about 4. The rate of photo-opening does not appear
to be affected significantly by the nature of the ancillary ligands
or the metal geometry, suggesting that there is poor electronic communication
between the platinum center and the DHP π system. The thermal
back-reaction from the open CPD to closed DHP form is about 50% faster
for the metal complexes than for the DHP-ethyne precursor. The platinum
complexes and the DHP-ethynes were characterized by NMR and IR spectroscopy
and MS and by X-ray crystallography for metal complexes 10, 11, 14, 15, and 17.

一系列在4位带有乙炔基取代基的光致变色二甲基二氢芘（dimethyldihydropyrenes，DHP）[RDHP-C≡CH；R=H(4)、乙酰基(5)、苯甲酰基(6)、1-萘甲酰基(7)、苯并[e](8)]被合成，用作乙炔基配体的前体。将这些乙炔基化合物与不同PtCl₂(L)₂配合物形成的加合物进行脱卤化氢反应，得到一系列顺式和反式的平面正方形双(DHP-乙炔基)铂配合物(RDHP-C≡C)₂Pt(L)₂：顺式构型包括R=H、L₂=PEt₃(9)，R=乙酰基、L₂=PEt₃(10)，R=苯甲酰基、L₂=PEt₃(11)，R=1-萘甲酰基、L₂=PEt₃(12)，R=苯并[e]、L₂=PEt₃(13)，R=苯甲酰基、L₂=PPh₃(14)，R=苯并[e]、L₂=PPh₃(15)；反式构型包括R=H、L₂=dppe(16)，R=苯并[e]、L₂=dppe(17)，R=乙酰基、L₂=bipy(18)，R=1-萘甲酰基、L₂=bipy(19)，R=H、L₂=phen(20)。带有酰基和苯并[e]取代基的DHP-乙炔基化合物（5~8）及其铂配合物（10~19）均具有光致变色性，在可见光（λ>550 nm）照射下会发生开环反应，转化为对应的环蕃二烯（cyclophanediene，CPD）异构体。以苯并[e]-DHP 8为例，引入4-乙炔基取代基可使光开环速率提升4倍；但在酰基DHP系列（5~7）中，引入4-乙炔基则会使光开环速率降低约4倍。铂配合物的光开环速率通常比对应的炔前体更慢，同样约慢4倍。光开环速率似乎不受辅助配体性质或金属中心几何构型的显著影响，表明铂中心与DHP的π体系之间几乎不存在电子通讯。从开环CPD形式到闭环DHP形式的热逆反应速率，金属配合物比DHP-乙炔基前体快约50%。本研究通过核磁共振波谱（nuclear magnetic resonance spectroscopy, NMR）、红外光谱（infrared spectroscopy, IR）、质谱（mass spectrometry, MS）以及X射线晶体衍射（针对配合物10、11、14、15和17）对铂配合物与DHP-乙炔基化合物进行了表征。