Impact of the Alkyne Substitution Pattern and Metalation on the Photoisomerization of Azobenzene-Based Platinum(II) Diynes and Polyynes

Trimethylsilyl-protected
dialkynes incorporating azobenzene linker groups, Me3SiCCRCCSiMe3 (R = azobenzene-3,3′-diyl, azobenzene-4,4′-diyl,
2,5-dioctylazobenzene-4,4′-diyl), and the corresponding terminal
dialkynes, HCCRCCH, have been synthesized and characterized.
The CuI-catalyzed dehydrohalogenation reaction between trans-[Ph­(Et3P)2PtCl] and the deprotected dialkynes
in a 2:1 ratio in iPr2NH/CH2Cl2 gives the platinum­(II) diynes trans-[Ph­(Et3P)2PtCCRCCPt­(PEt3)2Ph], while the dehydrohalogenation polycondensation reaction
between trans-[(nBu3P)2PtCl2] and the dialkynes in a 1:1 molar ratio under
similar reaction conditions affords the platinum­(II) polyynes, [−Pt­(PnBu3)2–CCRCC−]n. The materials have been characterized spectroscopically,
with the diynes also studied using single-crystal X-ray diffraction.
The platinum­(II) diynes and polyynes are all soluble in common organic
solvents. Optical-absorption measurements show that the compounds
incorporating the para-alkynylazobenzene spacers
have a higher degree of electronic delocalisation than their meta-alkynylazobenzene counterparts. Reversible photoisomerization
in solution was observed spectroscopically for the alkynyl-functionalized
azobenzene ligands and, to a lesser extent, for the platinum­(II) complexes.
Complementary quantum-chemical modeling was also used to analyze the
optical properties and isomerization energetics.

本研究合成了含有偶氮苯连接基团的硅基保护二烯烃，化学式为Me3SiC≡CRC≡SiMe3（R为偶氮苯-3,3'-二基，偶氮苯-4,4'-二基，2,5-二辛基偶氮苯-4,4'-二基）及其相应的末端二烯烃，化学式为HC≡CRC≡CH。通过CuI催化在iPr2NH/CH2Cl2溶液中，以2:1的比例进行脱卤化氢反应，得到铂(II)二烯烃trans-[Ph(Et3P)2PtC≡CRC≡CPt(PEt3)2Ph]。在类似的反应条件下，将trans-[(nBu3P)2PtCl2]与二烯烃按1:1的摩尔比进行脱卤化氢聚合反应，得到铂(II)聚烯烃[−Pt(PnBu3)2−C≡CRC≡C−]n。这些材料已通过光谱学方法进行表征，其中二烯烃还通过单晶X射线衍射技术进行研究。铂(II)二烯烃和聚烯烃均溶于常见的有机溶剂。光学吸收测量表明，含有对位烷基偶氮苯间隔基的化合物比其间位烷基偶氮苯同系物具有更高的电子离域程度。通过光谱学方法观察到偶氮苯配体功能化的乙炔基在溶液中的可逆光异构化现象，以及对铂(II)配合物而言，这一现象相对较弱。此外，还利用互补的量子化学模型分析了光学性质和异构化能学。