New binuclear heterocyclic ligands sharing an α‐diimine moiety and their ruthenium(II) tris‐chelates

Abstract

The detailed study on the binuciear neterocycies by using uv, (H-and 1%-nmr spectroscopy, as well as mass spectrometry, 18 also Provided. The synthesis and spectral data (uv, if, lH-and t3C-nmr) o f the ruthenium(l1) tris-chelates is also included. HTRODUCTIONA wide v a r i e t y of binuclear heterocyclic ligands which contatn a a-diimine moiety shared by b o t h rings, have been prepared in connection w i t h t h e search f o r 2,2'-bipyridine analogues. In addition, ruthentum(l1) t r i s -c h e l a t e s w i t h these ligands have also been obtained. Ground- atate, photophysical and photochemical p r o p e r t i e s of t h e resulting complexes have shown t o c o r r e l a t e w i t h t h e n a t u r e of t h e p r e c u r s o r l i g a n d~.~* 2 # 3The photochemical investigation on t h e Ru(ll) complexes has t e s t e d their abtlity t o a c t as e l e c t r o n -t r a n s f e r sensitizers, a class o f compounds which has received particular attention in the last years mainly by their r o l e ~n photoproduction o f hydrogen t h r o u g h water splitting processes4 o r in sensitized organic photoreauction reactions.5 Herein we r e p o r t t h e synthesis of several unsymmetrical chelating ligands o f t h e t y p e 2-(2'-pyridyl)-and 2-(2'-pyrazinyl)-l,3-heteroazole.The nature, number and positlon o f t h e h e t e r o a t o m s contained in t h e five-membered moiety as well as the 1-substitution in imidazole derivatives, have been systematically modified ( Table I). Most of t h e ltgands a r e described in this paper f o r t h e f i r s t time. Anyhow, t h e spectroscoptc charactertiation (uv. 1~-and 1 3~-nmr) and mass s p e c t r a o f these heterocyclic compounds had never reported, thus impeding t o establish some correlations between properties of t h e f r e e and complexed Iigands. F o r t h e sake o f completion, symmetrical binuclear h e t e r o c y c l e s (bi-l,3-heteroazole) and systems including benzoanellated r i n g s (2-(2'-pyridyl)benzoheteroazole) were also prepared.Since t h e main t a r g e t was t h e obtentton of t h e corresponding Ru(ll) tris-chelates, selection of synthettc r o u t e s has been accomplished w i t h a practical criterion: t o choose methods which involve t h e least number o f s t a g e s f r o m t h e most easily available r e a c t a n t s . Therefore, literature procedures have seldom been optimized -7 3 1 -

Perfluoroalkyl-Functionalized Thiazole–Thiophene Oligomers as N-Channel Semiconductors in Organic Field-Effect and Light-Emitting Transistors

“…On the other hand, 5,5′-dibromo-2,2′-bithiazole (11) is synthesized in accord with a standard literature procedure. 80,81 Thiazole is stannylated at the 2-position to give 9 in 65% yield, which was then coupled with 2-bromothiazole via Stille reaction using Pd(PPh 3 ) 4 /toluene as the catalyst/solvent system. Compound 10 is obtained in 74% yield and then brominated with NBS to give 11 in 80% yield.…”

Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations

“…The N-4 signal of monosubstituted pyrazines 1-4 can be easily identified due to its characteristic triplet structure (dt) in the 1 H-coupled 15 N NMR spectra (two geminal N,H couplings). [13] selected references: 2, [21] 3, [23,24] 4, [23,25,29,34] 5, [26] 6, [28] 7, [29] 11, [32] The exceptional position of compound 10 is best reflected by its 15 N NMR spectrum: The chemical shift of −190.9 ppm for N-4 definitely rules out an 'aromatic' pyrazine system (Scheme 3). The predominance of the NH-form is further confirmed by the distinctly smaller chemical shifts for H-5 (7.90 ppm) and H-6 (7.65 ppm) compared to the corresponding shifts in all other compounds (>8.17 ppm), furthermore by the larger H5,H6 coupling (3.7 Hz instead of ∼2.4 Hz, see above), by the markedly smaller 2 J(C6,H5) of 5.5 Hz (instead of 10.2-11.7 Hz) and by an obvious NOE on H-5 upon irradiation of the (broad) NH resonance (Scheme 3).…”

mer and fac isomerism in tris chelate diimine metal complexes

“…Despite the lack of general methodology to control and isolate diimine complexes of known and defined geometrical integrity, the possibility of mer/fac isomerism in such relatively simple systems has long been recognized. The kinetically inert systems such as the homoleptic pyridylpyrazole 24,25 and pyridyloxazole and thiazole [26][27][28] complexes of ruthenium(II) were identified and characterized using 1 H, 13 C and even 99 Ru NMR studies over 30 years ago. Such species have very well defined photophysical characteristics, 29 including a long lived metalto-ligand triplet states, but given the relatively small number of reported examples where they have been separated into the two isomeric forms, there is as yet, no clear indication as to what the effect the isomerism has on their behaviour, which will be addressed in the later sections of this article.…”