Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes

Abstract

A series of ruthenium(ii) complexes [{RuCl(CO)(PMe3)3(-CH[double bond, length as m-dash]CH-)}nX], (: n = 3, X = 3,3''-dimethyl-2,2':3',2''-terthiophene; : n = 2, X = 2,2'-bithiophene; : n = 2, X = 2,3-bis(3-methylthiophen-2-yl)benzothiophene) and [{Cp*(dppe)2Ru(-C[triple bond, length as m-dash]C-)}3X], (X = 3,3''-dimethyl-2,2':3',2''-terthiophene), were prepared and characterized by (1)H, (13)C and (31)P NMR. Their redox, spectroscopic and bonding properties were studied with a range of spectro-electrochemical methods in combination with density functional theory calculations. The first two anodic steps observed for and are largely localized on the lateral frameworks of the molecular triangle, the direct conjugation between them being precluded due to the photostable open form of the dithienyl ethene moiety. The third anodic step is then mainly localized on the centerpiece of the triangular structure, affecting both bithiophene laterals. The experimental IR and UV-vis-NIR spectroelectrochemical data and, largely, also DFT calculations account for this explanation, being further supported by direct comparison with the anodic behavior of reference diruthenium complexes and .

Delocalization-to-Localization Charge Transition in Divinylthiophene-Bridged Biruthenium Complexes as a Function of Length of the Bridging Chain by Both IR Spectroscopy and Theoretical Investigations

“…Winter et al, 28,29 Paul et al, 30 and some of the present authors 31,32 31 and bithiophene-bridged 33 divinyl biruthenium complexes. Herein, a series of biruthenium complexes linked by variable-length oligothiophene bridges (4a−4d, Scheme 1) have been prepared and investigated by electrochemical methods combined with spectroscopic studies with the aim of probing intramolecular electronic delocalization as a function of the chain length of the bridging ligand.…”

“…Winter et al, , Paul et al, and some of the present authors , have used “RuCl­(CO)­(PR 3 ) 2 L” (PR 3 = PPh 3 , PPr 3 i , or PMe 3 ; L = vacant coordination site or redox-innocent 2e – donor) as an indicator to successfully study the redox characteristics, electron density distribution, and interplay between the charge-transfer properties of the metal termini and the bridge. Recently, Liu et al and some of the present authors have reported a detailed account of the synthesis and electrochemical and UV–vis–NIR–IR properties of the monothiophene and bithiophene-bridged divinyl biruthenium complexes. Herein, a series of biruthenium complexes linked by variable-length oligothiophene bridges ( 4a – 4d , Scheme ) have been prepared and investigated by electrochemical methods combined with spectroscopic studies with the aim of probing intramolecular electronic delocalization as a function of the chain length of the bridging ligand.…”

“…We note that previous works of some of the present dication complexes 4a 2+ and 4b 2+ have shown only a single CO band at approximately 1970 cm −1 . 31,33 The ν(CO) band at approximately 1950 cm −1 is most likely to be assigned to the decomposition of dication species or other unstable intermediates. 43 Therefore, our IR spectroscopic data are in general agreement with those previously reported by Winter et al for the related diruthenium complexes.…”

Role of Substituents at 3‐position of Thienylethynyl Spacer on Electronic Properties in Diruthenium(II) Organometallic Wire‐like Complexes

“…The lowest energy transition in the NIR region at 1125 nm with an oscillator strength of 0.5525 corresponds to β‐HOSO→β‐LUSO transition having a dominant π‐π*(thienylethynyl) character mixed with some ML(bridge)CT . The vibrationally structured aromatic radical band centred at 536 nm with oscillator strength of 0.0242, arises predominantly from β‐HOSO‐9→β‐LUSO transition, exhibiting similar absorption characteristics bearing π‐π*(bridge) mixed with MLCT . Finally, in the UV region, the most intense band is calculated at λ max of 386 nm (oscillator strength 0.6015), being mainly assigned to electronic transition from α‐HOSO→α‐LUSO which can be attributed to intraligand π‐π* transition with some admixture of MLCT character.…”

“…The corresponding molecular orbitals involved in the major electronic excitations in [5 a‐H] + are displayed in Figure . The lowest energy transition in the NIR region at 1125 nm with an oscillator strength of 0.5525 corresponds to β‐HOSO→β‐LUSO transition having a dominant π‐π*(thienylethynyl) character mixed with some ML(bridge)CT . The vibrationally structured aromatic radical band centred at 536 nm with oscillator strength of 0.0242, arises predominantly from β‐HOSO‐9→β‐LUSO transition, exhibiting similar absorption characteristics bearing π‐π*(bridge) mixed with MLCT .…”