Synthesis and Characterization of Cu2(I,I), Cu2(I,II), and Cu2(II,II) Compounds Supported by Two Phthalazine-Based Ligands: Dramatic Influence of a Hydrophobic Pocket

The copper coordination chemistry of two phthalazine-based ligands of differing steric bulk was investigated. A family of dinuclear complexes were prepared from reactions Of Cu-2(bdptz)(MeCN)(2)](OTf)(2), 1(OTf)(2), where bdptz = 1,4-bis(2,2’-dipyridylmethyl)phthalazine. Treatment of 1(OTf)(2) with NaO2CCH3 afforded the class I mixed-valent compound Cu-2(bdPtZ)(2)](OTf)(3), 2(OTf)(3), by disproportionation of Cu(I). Compound 2(OTf)(3) displays an electron paramagnetic resonance spectrum, with g(parallel to) = 2.25 (A(parallel to) = 169 G) and g(perpendicular to) = 2.06, and exhibits a reversible redox wave at 452 mV versus Cp2Fe+/Cp2Fe. The complex Cu-2(bdptz)(mu-OH)(MeCN)(2)](OTf)(3), 3(OTf)(3), was prepared by chemical oxidation of 1 with AgOTf, and exposure of 1 to dioxygen afforded Cu-2(bdptz)(muOH)(2)](2)(OTs)(4), 4(OTs)(4), which can also be obtained directly from Cu(H2O)(6)](OTs)(2). In compound Cu-2(bdptz)(mu-vpy)](OTf)(2), 5(OTf)(2), where vpy = 2-vinylpyridine, the vpy ligand bridges the two Cu(I) centers by using both its pyridine nitrogen and the olefin as donor functionalities. The sterically hindered compounds Cu-2(Ph(4)bdptz)(MeCN)(2)](OTf)(2), 6(OTf)(2), and Cu-2(Ph(4)bdptz)(muO2CCH3)](OTf), 7(OTf), were also synthesized, where Ph(4)bdptz = 1,4-bisbis(6-phenyl-2-pyridyl)methyl]phthalazine. Complexes 1-7 were characterized structurally by X-ray crystallography. In 6 and 7, the four phenyl rings form a hydrophobic pocket that houses the acetonitrile and acetate ligands. Complex 6 displays two reversible redox waves with E-1/2 values of +41 and +516 mV versus Cp2Fe+/Cp2Fe. Analysis of oxygenated solutions of 6 by electrospray ionization mass spectrometry reveals probable aromatic hydroxylation of the Ph4bdptz ligand. The different chemical and electrochemical behavior of 1 versus 6 highlights the influence of a hydrophobic binding pocket on the stability and reactivity of the dicopper(l) centers. DOI: https://doi.org/10.1021/ic35009r Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-65674 Submitted Version Originally published at: Kuzelka, J; Mukhopadhyay, S; Spingler, Bernhard; Lippard, S J (2004). Synthesis and characterization of Cu-2(I,I), Cu-2(I,II), and Cu-2(II,II), compounds supported by two phthalazine-based ligands: Influence of a hydrophobic pocket. Inorganic Chemistry, 43(5):1751-1761. DOI: https://doi.org/10.1021/ic35009r Synthesis and Characterization of Cu2(I,I), Cu2(I,II), and Cu2(II,II) Compounds Supported by Two Phthalazine-Based Ligands: Dramatic Influence of a Hydrophobic Pocket Jane Kuzelka, Sumitra Mukhopadhyay, Bernhard Spingler, and Stephen J. Lippard* Contribution from the Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 and Institute of Inorganic Chemistry, University of Zürich, CH-8057 Zürich, Switzerland Received August 00, 2003 † Massachusetts Institute of Technology. ‡ University of Zürich. *Author to whom correspondence should be addressed. [email protected] Two phthalazine-based ligands of differing steric bulk were used to study the coordination chemistry of copper. A family of dinuclear complexes were prepared from reactions of [Cu2(bdptz)(MeCN)2](OTf)2 (1(OTf)2), where bdptz = 1,4-bis(2,2’-dipyridylmethyl)phthalazine. Treatment of 1(OTf)2 with NaO2CCH3 afforded the class I mixedvalent compound [Cu2(bdptz)2](OTf)3 (2(OTf)3) by disproportionation of Cu(I). Compound 2(OTf)3 displays an EPR spectrum with gÍÍ = 2.25 (AÍÍ = 169 G) and g^ = 2.06, and exhibits a reversible redox wave at –452 mV vs Cp2Fe/Cp2Fe. The complex [Cu2(bdptz)(m-OH)(MeCN)2](OTf)3 (3(OTf)3) was prepared by chemical oxidation of 1(OTf)2 with AgOTf, and exposure of 1(OTf)2 to dioxygen afforded [Cu2(bdptz)(mOH)2]2(OTs)4 (4(OTs)4), a compound that can also be obtained directly from [Cu(H2O)6](OTs)2. In compound [Cu2(bdptz)(m-vpy)](OTf)2 (5(OTf)2), where vpy = 2-