Redox-Induced Intramolecular C–C Coupling of Acyclic Bis(2-pyridylmethylene)ethylenediamine on a Ru(acac)₂ Platform

Abstract

The paper documents redox-triggered C–C coupling of acyclic N,N′-bis­(2-pyridylmethylene)­ethylenediamine (BPE) to yield 2,3-bis­(2-pyridyl)­pyrazine (DPP) upon coordination to an electron-rich {Ru­(acac)2} (acac = acetylacetonate) unit. This led to DPP-bridged [{Ru­(acac)2}2(DPP)]0/+ (2 and [2]­ClO4) along with the unperturbed BPE-bridged [{Ru­(acac)2}2(BPE)] (1). On the contrary, electron-poor {Ru­(Cl)­(H)­(CO)­(PPh3)3} yielded BPE-bridged [3]­(ClO4)2 as an exclusive product. Synergistic metal (Ru)–ligand (BPE) redox participation toward chemical noninnocence of the Schiff base ligand and DPP-mediated electronic communication in RuIIRuIII-derived [2]­ClO4 are addressed.

Metal–ligand synergy driven functionalisation of alkylene linked bis(aldimine) on a diruthenium(ii) platform. Cyclisation versus oxygenation

“…(ix) The bond distances related to Ru III -N(aldimine) in [2](ClO 4 ) 2 /[4] (ClO 4 ) 2 /[5](ClO 4 ) 2 , Ru III -N(carboxamido) in 2a/3a, Ru III -N( pyridine) and Ru III -O(acac) were in good agreement with those reported in analogous complexes. 10,14 The crystal structures of the earlier reported [{(PPh 3 ) 2 (CO) (H)Ru II } 2 (µ-L1)](ClO 4 ) 2 ([6](ClO 4 ) 2 ) 10 and the present set of complexes ([8](ClO 4 ) 2 ) established their trans and cis/trans configurations, respectively (Fig. 2, Table 2).…”

“…The bond parameters involving Ru II -N( pyridine/aldimine), Ru II -H, Ru II -PPh 3 , and Ru II -CO in the complexes agreed well with the analogous systems. 10,14 In principle, odd ((CH 2 ) n , n = 3) and even ((CH 2 ) n , n = 2, 4) numbers of the alkylene linker in the ligand frameworks should provide cis and trans isomers, respectively. 15 However,…”

“…9 In this regard, our recent work highlights C-C coupling of the ethylene linked bis(aldimine) core of L1 (syn-(CH 2 ) 2 ) on the electron-rich {Ru II (acac) 2 } (acac = acetylacetonate) platform in 1 to generate pyrazine (L1′) bridged 1a, whereas the same L1 in the corresponding 2 (anti-(CH 2 ) 2 ) remains unaltered under a N 2 atmosphere (Scheme 1). 10 In the pretext of the aforestated communication, 10 a simultaneous two-fold oxygenation of L1 (bis-aldimine) in 2 to L1″ (biscarboxamido) in 2a on O 2 purging has now been unveiled and thus the scope is further extended by following the oxygenation scenario of analogous L1-L3 containing varying alkylene linkers ((CH 2 ) n , n = 2 (L1), 3 (L2), 4 (L3)) in Ru II Ru II based 2-5 (Scheme 1). Interestingly, unlike 2-5, the aldimine function of L1-L3 in the corresponding oxidised Ru III Ru III based [2](ClO 4 ) 2 - [5](ClO 4 ) 2 and electron-poor {Ru II (H)(CO)(PPh 3 ) 2 } derived [6] (ClO 4 ) 2 -[8](ClO 4 ) 2 failed to undergo the oxygenation process, reemphasising the effective role of the Ru II -L redox interplay in the oxygenation event, which was monitored via synthetic, structural, spectro-electrochemical and theoretical investigations.…”

Tetracoordinated 15-Electron Ruthenium(I) in a Discrete Triruthenium Framework

“…The Ru−O(acac) and Ru−N(pyridine/imidazole) distances were in good agreement with the reported analogous systems. 8 The slight variation of the ring connecting C−C distances (C2−C13, C5−C6, C12− C13, and C2−C15) was also apparent upon moving from free L to the complexes.…”

“…The distorted octahedral situation around the metal ion in [ 1 ]ClO 4 , [ 2 ](ClO 4 ) 2 , [ 4 ]ClO 4 , and [ 3 ](ClO 4 ) 2 (Oh, Ru1/Ru3; square planar, Ru2; Scheme ) was evident from the deviation of their cis and trans angles with respect to the ideal values of 90° and 180°, respectively. The Ru–O(acac) and Ru–N(pyridine/imidazole) distances were in good agreement with the reported analogous systems . The slight variation of the ring connecting C–C distances (C2–C13, C5–C6, C12–C13, and C2–C15) was also apparent upon moving from free L to the complexes.…”