Probing Ruthenium−Acetylide Bonding Interactions: Synthesis, Electrochemistry, and Spectroscopic Studies of Acetylide−Ruthenium Complexes Supported by Tetradentate Macrocyclic Amine and Diphosphine Ligands

The synthesis and spectroscopic properties of trans-[RuL4(C⋮CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations
into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the
[-C⋮C(C6H4C⋮C)n-1Ph] and [-C⋮C(C6H4)n-1Ph] (n = 1−3) series upon the electronic and electrochemical
characteristics of trans-[RuL4(C⋮CAr)2]0/+ are presented. DFT and TD-DFT calculations have been
performed on trans-[Ru(L‘)4(C⋮CAr)2]0/+ (L‘ = PH3 and NH3) to examine the metal−acetylide π-interaction
and the nature of the associated electronic transition(s). It was observed that (1) the relationship between
the transition energy and 1/n for trans-[Ru(dmpe)2{C⋮C(C6H4C⋮C)n-1Ph}2] (n = 1−3) is linear, and (2)
the sum of the dπ(RuII) → π*(C⋮CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C⋮CAr)2] and the π(C⋮CAr) → dπ(RuIII) LMCT energy for trans-[Ru(16-TMC or N2O2)(C⋮CAr)2]+ corresponds to the intraligand
ππ* absorption energy for trans-[Ru(16-TMC or N2O2)(C⋮CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C⋮C(C6H4C⋮C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 Å. The
electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying
L4 and Ar to give E1/2 values for oxidation of trans-[RuL4(C⋮CAr)2] that span over 870 mV and λmax values
of trans-[RuL4(C⋮CAr)2] that range from 19 230 to 31 750 cm-1. The overall experimental findings suggest
that the π-back-bonding interaction in trans-[RuL4(C⋮CAr)2] is weak and the [RuL4] moiety in these molecules
may be considered to be playing a “dopant” role in a linear rigid π-conjugated rod.

本文详述了反式-[RuL₄(C≡CAr)₂]（其中L₄可为1,2-双(二甲基膦基)乙烷二聚体((dmpe)₂)、1,5,9,13-四甲基-1,5,9,13-四氮杂环十六烷(16-TMC)或1,12-二甲基-3,4:9,10-二苯并-1,12-二氮杂-5,8-二氧杂环戊十五烷(N₂O₂)）的合成过程与光谱性质。本文还系统研究了两类炔基配体系列——[-C≡C(C₆H₄C≡C)_{n-1}Ph]与[-C≡C(C₆H₄)_{n-1}Ph]（n=1~3）——中[RuL₄]中心、炔基配体以及炔碳链长的变化，对反式-[RuL₄(C≡CAr)₂]^(0/+)的电子与电化学特性所产生的影响。针对反式-[Ru(L')₄(C≡CAr)₂]^(0/+)（其中L'为PH₃与NH₃）开展了密度泛函理论(Density Functional Theory, DFT)与含时密度泛函理论(Time-Dependent Density Functional Theory, TD-DFT)计算，以探究金属-炔基的π相互作用及相关电子跃迁的本质。研究结果表明：(1) 对于反式-[Ru((dmpe)₂){C≡C(C₆H₄C≡C)_{n-1}Ph}₂]（n=1~3），其跃迁能与1/n呈线性关系；(2) 反式-[Ru(16-TMC或N₂O₂)(C≡CAr)₂]的dπ(Ru(II))→π*(C≡CAr)金属到配体电荷转移(Metal-to-Ligand Charge Transfer, MLCT)能量，与反式-[Ru(16-TMC或N₂O₂)(C≡CAr)₂]^+的π(C≡CAr)→dπ(Ru(III))配体到金属电荷转移(Ligand-to-Metal Charge Transfer, LMCT)能量之和，恰好等于反式-[Ru(16-TMC或N₂O₂)(C≡CAr)₂]的配体内ππ*吸收能量。反式-[Ru((dmpe)₂){C≡C(C₆H₄C≡C)₂Ph}₂]的晶体结构显示，该分子的两条边缘间距为41.7埃(Å)。通过修饰L₄与Ar基团，可对这类配合物的电化学与光谱特性进行系统性调控：反式-[RuL₄(C≡CAr)₂]的氧化半波电位(E₁/₂)覆盖范围超过870 mV，其最大吸收对应的波数(λ_max)区间为19230~31750 cm⁻¹。综合所有实验结果可知，反式-[RuL₄(C≡CAr)₂]中的π反馈键相互作用较为微弱，且这类分子中的[RuL₄]结构单元可被视为在线性刚性π共轭棒状结构中扮演“掺杂剂”的角色。