Excited State Tuning of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores by Push–Pull Effects and Bite Angle Optimization: A Comprehensive Experimental and Theoretical Study

The synergy of push–pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the ¹MLCT absorption and the ³MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the ³MLCT excited‐state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC‐tpy)][PF₆]₂, [Ru(ddpd‐NH₂)(EtOOC‐tpy)][PF₆]₂, [Ru(ddpd){(MeOOC)₃‐tpy}][PF₆]₂, and [Ru(ddpd‐NH₂){(EtOOC)₃‐tpy}][PF₆]₂ the combination of the electron‐accepting 2,2′;6′,2′′‐terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron‐donating N,N′‐dimethyl‐N,N′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand decorated with none or one NH₂ group enforces spatially separated and orthogonal frontier orbitals with a small HOMO–LUMO gap resulting in low‐energy ¹MLCT and ³MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating ³MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time‐resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n=0–4) and on triplet excited states (³MLCT and ³MC) as well as by time‐dependent density functional calculations (excited singlet states).     

Synthesis and Characterization of Extended Bis(terpyridine)ruthenium Amino Acids

(Oligopyridine)ruthenium(II) complexes have been widely used in dye sensitized solar cells and other sophisticated optical devices due to their outstanding photophysical properties and their chemical stability. Herein, we describe the longitudinal extension of our previously reported bis(terpyridine)ruthenium(II) amino acid [Ru(tpy–NH₂)(tpy–COOH)]²⁺ (tpy = 4′‐substituted 2,2′:6′,2″‐terpyridine) by insertion of para‐phenylene spacers –C₆H₄– between the terpyridine and the functional groups. The influence of the para‐phenylene spacer on the absorption and emission properties is investigated using UV/Vis absorption and emission spectroscopy and is discussed within a qualitative molecular orbital picture.     

Substituent and Solvent Effects on the Electrochemical Properties and Intervalence Transfer in Asymmetric Mixed‐Valent Complexes Consisting of Cyclometalated Ruthenium and Ferrocene

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF₆) (Fcdpb=2‐deprotonated form of 1,3‐di(2‐pyridyl)‐5‐ferrocenylbenzene; L=2,6‐bis‐(N‐methylbenzimidazolyl)‐pyridine (Mebip), 2,2′:6′,2′′‐terpyridine (tpy), 4‐nitro‐2,2′:6′,2′′‐terpyridine (NO₂tpy), and trimethyl‐4,4′,4′′‐tricarboxylate‐2,2′:6′,2′′‐terpyridine (Me₃tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH₂Cl₂, CH₃NO₂, CH₃CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, ΔE_1/2 (E_1/2(Ru^II/III)?E_1/2(Fc^0/+)), decreased slightly with increasing solvent donocity. The mixed‐valent states of these complexes have been generated by electrolysis and the resulting intervalence charge‐transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, E_op, and ΔE_1/2 of four mixed‐valent complexes in a given solvent.     

Ligand‐Modification Effects on the Reactivity,Solubility, and Stability of Organometallic Tantalum Complexes in Water

Tantalum complexes [TaCp*Me{κ⁴‐C,N,O,O‐(OCH₂)(OCHC(CH₂NMe₂)?CH)py}] ( 4 ) and [TaCp*Me{κ⁴‐C,N,O,O‐(OCH₂)(OCHC(CH₂NH₂)?CH)py}] ( 5 ), which contain modified alkoxide pincer ligands, were synthesized from the reactions of [TaCp*Me{κ³‐N,O,O‐(OCH₂)(OCH)py}] (Cp*=η⁵‐C₅Me₅) with HC?CCH₂NMe₂ and HC?CCH₂NH₂, respectively. The reactions of [TaCp*Me{κ⁴‐C,N,O,O‐(OCH₂)(OCHC(Ph)?CH)py}] ( 2 ) and [TaCp*Me{κ⁴‐C,N,O,O‐(OCH₂)(OCHC(SiMe₃)?CH)py}] ( 3 ) with triflic acid (1:2 molar ratio) rendered the corresponding bis‐triflate derivatives [TaCp*(OTf)₂{κ³‐N,O,O‐(OCH₂)(OCHC(Ph)?CH₂)py}] ( 6 ) and [TaCp*(OTf)₂{κ³‐N,O,O‐(OCH₂)(OCHC(SiMe₃)?CH₂)py}] ( 7 ), respectively. Complex 4 reacted with triflic acid in a 1:2 molar ratio to selectively yield the water‐soluble cationic complex [TaCp*(OTf){κ⁴‐C,N,O,O‐(OCH₂)(OCHC(CH₂NHMe₂)?CH)py}]OTf ( 8 ). Compound 8 reacted with water to afford the hydrolyzed complex [TaCp*(OH)(H₂O){κ³‐N,O,O‐(OCH₂)(OCHC(CH₂NHMe₂)?CH₂)py}](OTf)₂ ( 9 ). Protonation of compound 8 with triflic acid gave the new tantalum compound [TaCp*(OTf){κ⁴‐C,N,O,O‐(OCH₂)(HOCHC(CH₂NHMe₂)?CH)py}](OTf)₂ ( 10 ), which afforded the corresponding protonolysis derivative [TaCp*(OTf)₂{κ³‐N,O,O‐(OCH₂)(HOCHC(CH₂NHMe₂)?CH₂)py}](OTf) ( 11 ) in solution. Complex 8 reacted with CNtBu and potassium 2‐isocyanoacetate to give the corresponding iminoacyl derivatives 12 and 13 , respectively. The molecular structures of complexes 5 , 7 , and 10 were established by single‐crystal X‐ray diffraction studies.     

Acid‐, Water‐ and High‐Temperature‐Stable Ruthenium Complexes for the Total Catalytic Deoxygenation of Glycerol to Propane

The ruthenium aqua complexes [Ru(H₂O)₂(bipy)₂](OTf)₂, [cis‐Ru(6,6′‐Cl₂‐bipy)₂(OH₂)₂](OTf)₂, [Ru(H₂O)₂(phen)₂](OTf)₂, [Ru(H₂O)₃(2,2′:6′,2′′‐terpy)](OTf)₂ and [Ru(H₂O)₃(Phterpy)](OTf)₂ (bipy=2,2′‐bipyridine; OTf^?=triflate; phen=phenanthroline; terpy= terpyridine; Phterpy=4′‐phenyl‐2,2′:6′,2′′‐terpyridine) are water‐ and acid‐stable catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOS(O)₂CF₃ (triflic acid) as a dehydration co‐catalyst they directly convert 1,2‐hexanediol to n‐hexanol and hexane. The terpyridine complexes are stable and active as catalysts at temperatures ≥250 °C and in either aqueous sulfolane solution or pure water convert glycerol into n‐propanol and ultimately propane as the final reaction product in up to quantitative yield. For the terpy complexes the active catalyst is postulated to be a carbonyl species [(4′‐R‐2,2′:6′,2′′‐terpy)Ru(CO)(H₂O)₂](OTf)₂ (R=H, Ph) formed by the decarbonylation of aldehydes (hexanal for 1,2‐hexanediol and 3‐hydroxypropanal for glycerol) generated in the reaction mixture through acid‐catalyzed dehydration. The structure of the dimeric complex [{(4′‐phenyl‐2,2′:6′,2′′‐terpy)Ru(CO)}₂(μ‐OCH₃)₂](OTf)₂ has been determined by single crystal X‐ray crystallography (Space group P (a=8.2532(17); b=12.858(3); c=14.363(3) Å; α=64.38(3); β=77.26(3); γ = 87.12(3)°, R=4.36 %).     

Monodentate and bridging behaviour of the sulfur‐containing ligand 4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine in two discrete zinc(II) complexes with acetylacetonate

The Zn complexes bis(acetylacetonato‐κ²O,O′)bis{4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine‐κN¹}zinc(II), [Zn(C₅H₇O₂)₂(C₂₂H₁₇N₃S)₂], (I), and {μ‐4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine‐κ²N¹:N^1′′}bis[bis(acetylacetonato‐κ²O,O′)zinc(II)], [Zn₂(C₅H₇O₂)₄(C₂₂H₁₇N₃S)], (II), are discrete entities with different nuclearities. Compound (I) consists of two centrosymmetrically related monodentate 4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine (L1) ligands binding to one Zn^II atom sitting on an inversion centre and two centrosymmetrically related chelating acetylacetonate (acac) groups which bind via carbonyl O‐atom donors, giving an N₂O₄ octahedral environment for Zn^II. Compound (II), however, consists of a bis‐monodentate L1 ligand bridging two Zn^II atoms from two different Zn(acac)₂ fragments. Intra‐ and intermolecular interactions are weak, mainly of the C—H...π and π–π types, mediating similar layered structures. In contrast to related structures in the literature, sulfur‐mediated nonbonding interactions in (II) do not seem to have any significant influence on the supramolecular structure.     

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of Ru^II polypyridyl complexes of the structural design [Ru^II(R?tpy)(NN)(CH₃CN)]²⁺ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO₂ to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru^II(tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 3 ]²⁺; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [Ru^II(tBu?tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 4 ]²⁺), in which the methyl group of the 6‐mbpy ligand is trans to the CH₃CN ligand, show electrocatalytic CO₂ reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH₃CN ligand dissociation, CO₂ coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.     

A Combined Experimental and Computational Study of Linear Ruthenium(II) Coordination Oligomers with End‐Capping Organic Redox Sites: Insight into the Light Absorption and Charge Delocalization

Two series of linear ruthenium coordination oligomers, [(Ntpy)Ru_n(tppz)_n?1(tpy)]²ⁿ⁺ (mono‐Ntpy series, n=1–3) and [(Ntpy)₂Ru_n(tppz)_n?1]²ⁿ⁺ (bis‐Ntpy series, n=1–3) have been prepared, where Ntpy is the capping ligand 4′‐di‐p‐anisylamino‐2,2′:6′,2′′‐terpyridine, tppz is tetra‐2‐pyridylpyrazine, and tpy is 2,2′:6′,2′′‐terpyridine. The electrochemical measurements evidence oxidation events from both the amine segments and the metal centers and reduction waves from tppz and the capping ligands. Both series complexes display much enhanced light absorption with respect to model complexes without terminal amine units. Density functional theory (DFT) calculations have been performed on both series and time‐dependent DFT (TD‐DFT) calculations have been performed on the bis‐Ntpy‐series compounds (n=1–4) to characterize their electronic structures and excited states and predict the electronic properties of long‐chain polymers. Upon one‐electron oxidation, the mono‐Ntpy‐series monoruthenium and diruthenium complexes display N⁺‐localized transitions and metal‐to‐nitrogen charge‐transfer (MNCT) transitions in the near‐infrared (NIR) region. DFT and TD‐DFT computations on the one‐electron‐oxidized forms of the mono‐Ntpy‐series compounds (n=1–4) provide insight into the nature of the MNCT transitions and the degree of charge delocalization.     

A Cytostatic Ruthenium(II)–Platinum(II) Bis(terpyridyl) Anticancer Complex That Blocks Entry into S Phase by Up‐regulating p27KIP1

Cytostatic agents that interfere with specific cellular components to prevent cancer cell growth offer an attractive alternative, or complement, to traditional cytotoxic chemotherapy. Here, we describe the synthesis and characterization of a new binuclear Ru^II–Pt^II complex [Ru(tpy)(tpypma)Pt(Cl)(DMSO)]³⁺ (tpy=2,2′:6′,2′′‐terpyridine and tpypma=4‐([2,2′:6′,2′′‐terpyridine]‐4′‐yl)‐N‐(pyridin‐2‐ylmethyl)aniline), VR54, which employs the extended terpyridine tpypma ligand to link the two metal centres. In cell‐free conditions, VR54 binds DNA by non‐intercalative reversible mechanisms (K_b=1.3×10⁵ M ^?1) and does not irreversibly bind guanosine. Cellular studies reveal that VR54 suppresses proliferation of A2780 ovarian cancer cells with no cross‐resistance in the A2780CIS cisplatin‐resistant cell line. Through the preparation of mononuclear Ru^II and Pt^II structural derivatives it was determined that both metal centres are required for this anti‐proliferative activity. In stark contrast to cisplatin, VR54 neither activates the DNA‐damage response network nor induces significant levels of cell death. Instead, VR54 is cytostatic and inhibits cell proliferation by up‐regulating the cyclin‐dependent kinase inhibitor p27^KIP1 and inhibiting retinoblastoma protein phosphorylation, which blocks entry into S phase and results in G1 cell cycle arrest. Thus, VR54 inhibits cancer cell growth by a gain of function at the G1 restriction point. This is the first metal‐coordination compound to demonstrate such activity.     

A Metal‐Containing N‐Heterocyclic Germylene Based on an Oxalamidine Framework

A metal‐containing N‐heterocyclic germylene based on a N‐mesityl (Mes)‐substituted oxalamidine framework is reported. The precursor (MesN=)₂C–C(–N(H)Mes)₂ ( 1 H₂) was converted into its rhodium complex [Rh(κ²N‐ 1 H₂)(cod)][OTf] ( 2 ) (cod = 1,5‐cyclooctadiene; OTf = triflate) in 62 % isolated yield. Subsequent reaction of 2 with Ge{N(SiMe₃)₂}₂ gave the crystalline N‐heterocyclic germylene [Rh(cod)(μ‐ 1 )Ge][OTf] ( 3 ) in 50 % yield. The compounds under study were fully characterized by various methods, also including X‐ray crystallographic studies on single crystals of 2 and 3 . Density functional theory (DFT) calculations revealed that π conjugation in the bridging oxalamidine framework is increased and n(N)–p(Ge) π bonding is decreased upon κ²N metal coordination; a further weakening of the Ge–N bond occurs through triflate coordination to the Ge^II atom. Nevertheless, preliminary coordination studies revealed that 3 behaves as 2‐electron (L ‐type) germylene donor ligand. Treatment of 3 with [Ir(cod)Cl]₂ furnished the heterobimetallic complex [Rh(cod)(μ‐ 1 )Ge‐Ir(cod)Cl][OTf] ( 4 ), as evidenced by NMR spectroscopic investigations and DFT calculations.     

Crystalline Diuranium Phosphinidiide and μ‐Phosphido Complexes with Symmetric and Asymmetric UPU Cores

Reaction of [U(Tren^TIPS)(PH₂)] ( 1 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃) with C₆H₅CH₂K and [U(Tren^TIPS)(THF)][BPh₄] ( 2 ) afforded a rare diuranium parent phosphinidiide complex [{U(Tren^TIPS)}₂(μ‐PH)] ( 3 ). Treatment of 3 with C₆H₅CH₂K and two equivalents of benzo‐15‐crown‐5 ether (B15C5) gave the diuranium μ‐phosphido complex [{U(Tren^TIPS)}₂(μ‐P)][K(B15C5)₂] ( 4 ). Alternatively, reaction of [U(Tren^TIPS)(PH)][Na(12C4)₂] ( 5 , 12C4=12‐crown‐4 ether) with [U{N(CH₂CH₂NSiMe₂Bu^t)₂CH₂CH₂NSi(Me)(CH₂)(Bu^t)}] ( 6 ) produced the diuranium μ‐phosphido complex [{U(Tren^TIPS)}(μ‐P){U(Tren^DMBS)}][Na(12C4)₂] [ 7 , Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t)₃]. Compounds 4 and 7 are unprecedented examples of uranium phosphido complexes outside of matrix isolation studies, and they rapidly decompose in solution underscoring the paucity of uranium phosphido complexes. Interestingly, 4 and 7 feature symmetric and asymmetric UPU cores, respectively, reflecting their differing steric profiles.     

Ligand‐to‐Ligand Charge‐Transfer Transitions of Platinum(II) Complexes with Arylacetylide Ligands with Different Chain Lengths: Spectroscopic Characterization,Effect of Molecular Conformations,and Density Functional Theory Calculations

The complexes [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1R}]⁺ (n=1: R=alkyl and aryl (Ar); n=1–3: R=phenyl (Ph) or Ph‐N(CH₃)₂‐4; n=1 and 2, R=Ph‐NH₂‐4; tBu₃tpy=4,4’,4’’‐tri‐tert‐butyl‐2,2’:6’,2’’‐terpyridine) and [Pt(Cl₃tpy)(C?CR)]⁺ (R=tert‐butyl (tBu), Ph, 9,9’‐dibutylfluorene, 9,9’‐dibutyl‐7‐dimethyl‐amine‐fluorene; Cl₃tpy=4,4’,4’’‐trichloro‐2,2’:6’,2’’‐terpyridine) were prepared. The effects of substituent(s) on the terpyridine (tpy) and acetylide ligands and chain length of arylacetylide ligands on the absorption and emission spectra were examined. Resonance Raman (RR) spectra of [Pt(tBu₃tpy)(C?CR)]⁺ (R=n‐butyl, Ph, and C₆H₄‐OCH₃‐4) obtained in acetonitrile at 298 K reveal that the structural distortion of the C?C bond in the electronic excited state obtained by 502.9 nm excitation is substantially larger than that obtained by 416 nm excitation. Density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations on [Pt(H₃tpy)(C?CR)]⁺ (R= n‐propyl (nPr), 2‐pyridyl (Py)), [Pt(H₃tpy){C?C(C₆H₄C?C)_n?1Ph}]⁺ (n=1–3), and [Pt(H₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺/+H⁺ (n=1–3; H₃tpy=nonsubstituted terpyridine) at two different conformations were performed, namely, with the phenyl rings of the arylacetylide ligands coplanar (“cop”) with and perpendicular (“per”) to the H₃tpy ligand. Combining the experimental data and calculated results, the two lowest energy absorption peak maxima, λ₁ and λ₂, of [Pt(Y₃tpy)(C?CR)]⁺ (Y=tBu or Cl, R=aryl) are attributed to ¹[π(C?CR)→π*(Y₃tpy)] in the “cop” conformation and mixed ¹[d_π(Pt)→π*(Y₃tpy)]/¹[π(C?CR)→π*(Y₃tpy)] transitions in the “per” conformation. The lowest energy absorption peak λ₁ for [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐H‐4}]⁺ (n=1–3) shows a redshift with increasing chain length. However, for [Pt(tBu₃tpy){C?C(C6H4C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺ (n=1–3), λ₁ shows a blueshift with increasing chain length n, but shows a redshift after the addition of acid. The emissions of [Pt(Y₃tpy)(C?CR)]⁺ (Y=tBu or Cl) at 524–642 nm measured in dichloromethane at 298 K are assigned to the ³[π(C?CAr)→π*(Y₃tpy)] excited states and mixed ³[d_π(Pt)→π*(Y₃tpy)]/³[π(C?C)→π*(Y₃tpy)] excited states for R=aryl and alkyl groups, respectively. [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺ (n=1 and 2) are nonemissive, and this is attributed to the small energy gap between the singlet ground state (S₀) and the lowest triplet excited state (T₁).     

Activating a Low Overpotential CO2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu₃tpy)(bpy)(NCCH₃)]²⁺ (tBu₃tpy=4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine; bpy=2,2′‐bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO₂ to CO. The methyl group enables CO₂ binding already at the one‐electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO₂ reduction catalysts.     

(Nitro‐κN)[2‐(phenyldiazenyl‐κN2)pyridine‐κN](2,2′:6′,2′′‐terpyridine‐κ3N)ruthenium(II) tetrafluoroborate

The Ru—N bond distances in the title complex, [Ru(NO₂)(C₁₁H₉N₃)(C₁₅H₁₁N₃)]BF₄ or [Ru(NO₂)(tpy)(azpy)]BF₄, [tpy is 2,2′:6′,2′′‐ter­pyridine and azpy is 2‐(phenyl­azo)­pyridine], are Ru—N_py 2.063 (4), Ru—N_azo 2.036 (4), Ru—N_nitro 2.066 (3) Å, and Ru—N_tpy 2.082 (4), 1.982 (3) and 2.074 (4) Å. The azo N atom is trans to the nitro group. The azo N=N bond length is 1.265 (5) Å, which is the shortest found in such complexes to date. This indicates a multiple bond between Ru and the N atom of the nitro group, and π‐­backbonding [dπ(Ru) π*(azo)] is decreased.     

Terminal Redox‐Site Effect on the Long‐Range Electron Conduction of Fe(tpy)2 Oligomer Wires on a Gold Electrode

This article completes our comprehensive understanding of the electron transport properties of our original π‐conjugated redox‐active molecular wires comprising Fe bridged by p‐phenylene linkers (tpy=2,2′:6′,2′′‐terpyridine). The Fe(tpy)₂ oligomer wires comprise three types of tpy ligands: the anchor tpy ligand ( A series) makes a junction between the wire and electrode, the bridging bis‐tpy ligand ( L series) connects the Fe(tpy)₂ units, and the terminal tpy ligand ( T series) possesses a redox site as a probe for the long‐range electron transport ability. Taking advantage of the precise tunability of the composition of the Fe(tpy)₂ oligomer wires, thus far we investigated how A and L impacted on the electron‐transport ability. The excellent long‐range electron transport ability with ultrasmall attenuation constants (β^d, 0.002 Å^?1 as the minimum) depends on L significantly [Chem. Asian J. 2009 , 4, 1361], whereas A is unrelated to the β^d value, but influences the zero‐distance electron‐transfer rate constant, k_et⁰ [J. Am. Chem. Soc. 2010 , 132, 4524]. Herein we study the influence of terminal ligand T ^x (x=1–3). β^d is independent of T , however, T³ , with a cyclometallated Ru complex as the redox site, gives rise to a k_et⁰ value greater than T¹ and T² with ferrocene. This series of simple but definitive conclusions indicates that we have reached the stage of being able to precisely design molecular wires to attain desirable single‐molecule electron conduction.     

Structural and theoretical characterization of a new twisted 4′‐substituted terpyridine compound: 4′‐(isoquinolin‐4‐yl)‐2,2′:6′,2′′‐terpyridine

4′‐Substituted derivatives of 2,2′:6′,2′′‐terpyridine with N‐containing heteroaromatic substituents, such as pyridyl groups, might be able to coordinate metal centres through the extra N‐donor atom, in addition to the chelating terpyridine N atoms. The incorporation of these peripheral N‐donor sites would also allow for the diversification of the types of noncovalent interactions present, such as hydrogen bonding and π–π stacking. The title compound, C₂₄H₁₆N₄, consists of a 2,2′:6′,2′′‐terpyridine nucleus (tpy), with a pendant isoquinoline group (isq) bound at the central pyridine (py) ring. The tpy nucleus deviates slightly from planarity, with interplanar angles between the lateral and central py rings in the range 2.24 (7)–7.90 (7)°, while the isq group is rotated significantly [by 46.57 (6)°] out of this planar scheme, associated with a short H_tpy…H_isq contact of 2.32 Å. There are no strong noncovalent interactions in the structure, the main ones being of the π–π and C—H…π types, giving rise to columnar arrays along [001], further linked by C—H…N hydrogen bonds into a three‐dimensional supramolecular structure. An Atoms In Molecules (AIM) analysis of the noncovalent interactions provided illuminating results, and while confirming the bonding character for all those interactions unquestionable from a geometrical point of view, it also provided answers for some cases where geometric parameters are not informative, in particular, the short H_tpy…H_isq contact of 2.32 Å to which AIM ascribed an attractive character.     

Reactivity of ortho‐Substituted Aryl–Palladium Complexes towards Carbodiimides,Isothiocyanates, Nitriles,and Cyanamides

Complexes [Pd(C₆H₃XH‐2‐R′‐5)Y(N^N)] (X=O, NH; Y=Br, I; R′=H, NO₂; N^N=N,N,N′,N′‐tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (dtbbpy)) react with RN?C?E (E=NR, S) or RC≡N (R=alkyl, aryl, NR′′₂) and TlOTf (OTf=CF₃SO₃) to give, respectively, 1) products of the insertion of the C?E group into the C? Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{κ²‐X,E‐(XC₆H₃{EC(NHR)}‐2‐R′‐4)}(N^N)]OTf or [Pd(κ²‐X,N‐{ZC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{κ²‐C,N‐(C₆H₄{OC(NR)}NHR‐2)}(bpy)]OTf; or 2) products of the insertion of the C≡N group to Pd and N‐protonation, [Pd(κ²‐X,N‐{XC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf.     

Triamidoamine–Uranium(IV)‐Stabilized Terminal Parent Phosphide and Phosphinidene Complexes

Reaction of [U(Tren^TIPS)(THF)][BPh₄] ( 1 ; Tren^TIPS=N{CH₂CH₂NSi(iPr)₃}₃) with NaPH₂ afforded the novel f‐block terminal parent phosphide complex [U(Tren^TIPS)(PH₂)] ( 2 ; U–P=2.883(2) Å). Treatment of 2 with one equivalent of KCH₂C₆H₅ and two equivalents of benzo‐15‐crown‐5 ether (B15C5) afforded the unprecedented metal‐stabilized terminal parent phosphinidene complex [U(Tren^TIPS)(PH)][K(B15C5)₂] ( 4 ; U?P=2.613(2) Å). DFT calculations reveal a polarized‐covalent U?P bond with a Mayer bond order of 1.92.     

Synthesis of N,N,N-4,4＂-Di-（4-methylphenyl）-2,2＇：6＇,2＂- terpyridine-N,N,N-tris（isothiocyanato） Ruthenium（Ⅱ） and Application to Colorimetric Hg^2＋ Sensor

A terpyridine derivative DPTP [di-（4-methylphenyl）-2,2＇：6＇,2＂-terpyridine] was conveniently synthesized from 2-bromopyridine via halogen-dance reaction, Kharash coupling and Stille coupling reaction. Then its corresponding ruthenium complex Ru-DPTP [N,N,N-4,4＇＇-di-（4-methy,phenyl）-2,2＇：6＇,2＂-terpyridine-N,N,N-tris（is,-thi,cyanat,）- ruthenium（H） ammonium] was obtained and fully characterized by IR, UV-Vis, ESI MS and elemental analysis. The MLCT absorption band of Ru-DPTP was blue-shifted from 570 to 500 nm upon addition of Hg^2＋. Among a series of surveyed metal ions, the complex showed a unique recognition to Hg^2＋, indicating that it can be used as a selective colorimetric sensor for Hg^2＋.     

Masking of Lewis acidity trends in the solid‐state structures of trichlorido‐ and tribromido(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)gallium(III)

The molecular structures of trichlorido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaCl₃(C₁₅H₁₁N₃)], and tribromido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaBr₃(C₁₅H₁₁N₃)], are isostructural, with the Ga^III atom displaying an octahedral geometry. It is shown that the Ga—N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr₃. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2′:6′,2′′‐terpyridine donor as well.