Para-Quinone-Containing Bis(pyrazol-1-yl)methane Ligands: Coordination Behavior Toward Co^II and a C−H Activation Reaction with Ce^IV

Abstract

Two series of sterically demanding para-dimethoxyphenyl-substituted bis(pyrazol-1-yl)methane ligands have been synthesized, i.e., L2(R,R') = ((MeO)(2)C(6)H(3))C(H)(pz(R,R'))(2) and L3(R,R') = ((MeO)(2)C(6)H(3))C(Me)(pz(R,R'))(2) (R,R' = 3-Me,5-Me; 3-Ph,5-H; 3-tBu,5-H). In the solid state, already the sterically least encumbered derivative L2(Me2) is able to stabilize Co(II) complexes of the form [X(2)Co(L2(Me2))] (X = Cl, NO(3)); in solution, these complexes are at an equilibrium with the 1:2 species [Co(L2(Me2))(2)](2+). Oxidative demethylation of L3(Ph) and L3((t)Bu) with [Ce(NH(4))(2)(NO(3))(6)] leads to the corresponding para-benzoquinonyl-substituted bis(pyrazol-1-yl)methane ligands L4(Ph) and L4((t)Bu). Contrary to that, the methyl derivative L3(Me2) is transformed into the ortho-benzoquinone species L5(Me2), which still contains one methoxy substituent while one oxygen atom has been newly introduced. The formation of L5(Me2) requires (i) the admission of air, (ii) the presence of both methoxy substituents of L3(Me2), and (iii) the presence of (methyl) substituents both at the exocyclic carbon atom and at the 5- positions of the pyrazolyl rings. The parent ortho-hydroquinonyl-substituted bis(pyrazol-1-yl)methane ligand ((HO)(2)C(6)H(3))C(H)(pz(H,H))(2) is readily available from 3,4-dihydroxybenzaldehyde and (pz(H,H))(2)SO/pyridine.

Chemical behavior of ortho-hydroquinone-based bis(pyrazol-1-yl)methane ligands in the presence of palladium(II) chloride

“…In a preceding report we have already noted the ortho-hydroquinone-based bis(pyrazol-1-yl)methane ligand 1(H) [17], but synthetic details and analytical data of 1(H) such as metric parameters will be discussed here. The bis(pyrazol-1-yl)methane 1 (H) was prepared in a three-step one-pot procedure (Scheme 2): (i) At first pyrazole was deprotonated with sodium hydride in THF.…”

(Acetonitrile-κN)chloridobis[2-(pyridin-2-yl)phenyl-κ2C1,N]iridium(III)

“…For our work on redox active ligands, see: Jä kle et al (1996); Guo et al (2001); Margraf et al (2006); Kretz et al (2006); Phan et al (2011);Scheuermann et al (2008Scheuermann et al ( , 2009); Blasberg et al (2010Blasberg et al ( , 2011. For the synthesis of the starting materials, see: Blasberg et al (2011);Lowry et al (2004).…”

“…Up to now we have applied electro-active ligands with poly(pyrazol-1-yl)borate (Jäkle et al, 1996;Guo et al, 2001), diimine (Margraf et al, 2006;Kretz et al, 2006;Phan et al, 2011) and bis(pyrazol-1-yl)methane (Scheuermann et al, 2008;Scheuermann et al, 2009;Blasberg et al, 2010) donor groups. So far, ferrocenyl and mainly para-quinonyl units (quinone is used if the oxidation state is not defined) were used as the redox-active element.…”

“…This molecule might allow for light-driven redox-reactions, which in turn can switch catalysis on or off. The palladium(II) complex 1 (Blasberg et al, 2010;Blasberg et al, 2011) was deprotonated twice with lithium t-butoxide (LiOtBu) in a tetrahydrofuran solution in a glove box and subsequently Lowry et al, 2004) was added to the resulting dianion. After stirring overnight and recrystallization of the resulting crude material from acetonitrile, the only obtained product was (acet-…”

Development of ruthenium-based complexes as anticancer agents: toward a rational design of alternative receptor targets

“…Since then, several Ru half-sandwich complexes have been synthesized (Komiya and Hurano coordinating ligands to possibly mimic the feature of the best anticancer complex called cisplatin, which is characterized with two units of NH 2 ligand. In addition to the complexes from the Sadler research members that most often characterized heterocyclic nitrogen-containing ligands, many other researchers have equally characterized the Ru-based complexes that contained 1,10-phenanthroline (Hara et al 2001, Byabartta et al 2003, Himeda et al 2004, Nakabayashi et al 2004, Canivet et al 2005, Małecki et al 2009, Al-Lawati et al 2010, Chen et al 2010, bipyridine (Pruchnik et al 1999, Mitsopoulou et al 2007, Wei et al 2008, Tomaz et al 2012, terpyridine (Koizumi et al 2003, Bolink et al 2005, Sharma et al 2005, Zhou and Harruna 2005, Etienne and Beley 2006, Hofmeier et al 2006, Goze et al 2007, Rajalakshmanan and Alexander 2007, Jain et al 2009), and bis(pyrazoly-l-yl) (Burns et al 1998, Kopf et al 2006, Tampier et al 2008, Zhao et al 2009, Blasberg et al 2010, Türkoglu et al 2012 for different purposes, such as electrochemiluminescence, catalyst, photochemical, and anticancer complexes. However, the application of these type of Ru complexes as potential anticancer is predominant (Concepcion et al 2000, Peacock et al 2007a, Sun et al 2009, Zhu and Holliday 2010,...…”