Template-Free Synthesis of a Macrocyclic Bis(pyridine-dienamine) Proligand and Metal Complexes of Its Bis(pyridine-diimine) and Bis(pyridine-dienamido) Forms

Abstract

We describe the template-free synthesis of the bis­(pyridine-dienamine) proligand [4,5-(m-xylylenediamine)­NH–C(CH)­(9-butyl-octahydroacridine)]2 (2′), a variant of Burrows’s macrocyclic bis­(pyridine-diimine) (bis-PDI) ligand [2,6-(m-xylylenediamine)­NC­(py)]2 (A), using octahydroacridine as the ligand backbone. The octahydroacridine backbone favors macrocyclization by constraining the PDI units in the (s-cis)2 conformation. The template-free synthesis of 2′ enables facile access to a wide array of bis-PDI and bis­(pyridine-dienamido) (bis-PDE) metal complexes. Five-coordinate binuclear bis-PDI (2)­M2Cl4 complexes {2 = [4,5-(m-xylylenediamine)­NC­(9-butyl-octahydroacridine)]2; M = Zn, Co, or Fe} and a four-coordinate bis-PDI [(2)­Pd2Br2]­[B­(3,5-(CF3)2-Ph)4]2 complex were synthesized and characterized. (2)­Zn2Cl4 undergoes macrocyclic ring inversion on the nuclear magnetic resonance (NMR) time scale with a free energy barrier ΔG ⧧ of 15.5(3) kcal/mol at 295 K. In contrast, (2)­Fe2Cl4 and (2)­Co2Cl4 undergo slow ring inversion on the NMR chemical shift time scale at 295 K. The amine elimination reaction of 2′ with Zr­(NMe2)4 yields the bis-PDE complex (2′-4H)­Zr2(NMe2)4, which was alkylated with AlMe3 and Al­(CH2SiMe3)3 to generate (2′-4H)­Zr2Me4 and (2′-4H)­Zr2(CH2SiMe3)2(NMe2)2, respectively.

Synthesis and Ethylene Reactivity of Dinuclear Iron and Cobalt Complexes Supported by Macrocyclic Bis(pyridine-diimine) Ligands Containing o-Terphenyl Linkers

“…The metal–metal distances for ( 1 – 3 )­M 2 Br 4 are given in Table and range from 5.7600(8) to 6.232(1) Å. Similar distances were observed for macrocyclic bis-PDI complexes in which the PDI units are bridged by m -xylylene linkers, including ([ D ]­Cu 2 Im]­[CF 3 SO 3 ] 3 (Cu–Cu = 5.9181(9) Å), [ E ]­Zn 2 Ox]­[CF 3 SO 3 ] 2 (Zn–Zn = 5.3849(6) Å), ( F )­Zn 2 Cl 4 (Zn–Zn = 5.515(1) Å), and ( F )­Co 2 Cl 4 (Co–Co = 5.501(1) Å), which are shown in Chart . − In contrast, the Co–Co distance in ( A )­Co 2 Cl 4 (R 1 = R 2 = H; 7.731(2) Å) is much longer. While the syn -double-decker complexes ( B )­Fe 2 Cl 4 have not been crystallographically characterized, Groysman has reported a similar [( B )­Co 2 (CH 3 CN) 4 ]­[Co­(CO) 4 ] 2 complex with a Co–Co distance of 4.628(1) Å .…”

Macrocycle-Induced Modulation of Internuclear Interactions in Homobimetallic Complexes

“…This procedure represents an update to a previously reported procedure from our group. 45 FeCl 2 (0.3089 g, 2.44 mmol), NaBArF 24 (2.1427 g, 2.41 mmol), and ( 3 PDI 2 )Sr(OTf) 2 (1.0901 g, 1.21 mmol) were loaded to a 100 mL Schlenk tube in the glovebox. On the Schenk line, approximately 30 mL of THF was added, and the mixture was stirred at room temperature overnight, resulting in a dark purple slurry.…”

“…Examples from the Jordan and Groysman groups have made use of bridging aryl linkers to form PDI macrocycles with 22- and 24-atom rings; these systems were shown to accommodate dinuclear complexes with M–M distances of 5.3–5.6 Å (Figure ). , Work from our group has employed alkyl linkers to form smaller 18- and 20-atom PDI-containing macrocyclic ligands that are derivatives of the early Drew and Nelson macrocycles (Figure ). The enhanced solubility profiles afforded by the inclusion of both p - t Bu groups on the pyridyl rings and weakly coordinating anions has allowed for investigation into small molecule activation chemistry under reducing conditions. − Examples of highly reactive dicobalt and diiron nitrides as well as unique dinitrogen, cyanide, and methyl group coordination chemistry have been enabled by these ligands (Figure ).…”

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

“…The combination with aromatic N atom may result for example in bidentate chelating 4e κ 2 -N,N' mode as in diruthenium complex (AZEQOL) [153] or in a more extended pincer type species (6e κ 3 -N,N'N" mode, MOTZUT), which may be further used to construct macrocyclic oligonuclear ligands [154] (Figure 9a,b). An example of imine fused with O ligating atom may be a series of acylhydrazone derivatives forming binucleating template for coordination of Ru(II) complexes, which were studied on antiproliferative activity and apoptosis induction showing higher cytotoxicity than cis-platin and low IC50 values against the screened cancer HeLa, MDA-MB-231 and Hep-G2 cell lines (Figure 9c; QESSUF) [155].…”

“…The presence of additional O atoms enabled formation of six-membered chelate rings. [153] (CSD Refcode AZWQOL); (b) cyclic binuclear complex with robust pincer type 6e κ 3 -N,N'N" coordination mode [154] (CSD Refcode MOTZUT); (c) binuclear complex of ruthenium(II) arene benzil bis(benzoylhydrazone) with coordination chelating κ 2 -N,O pockets [155] (CSD Refcode QESSUF); (d) binuclear Ru complex with non-innocent diimine ligand binding through coordination chelating κ 2 -N,S pockets [123] (CSD Refcode KEHSOH); (e) octaplatinum complex with Pt 3 metallic clusters stabilized by bridging and chelating dimethylglyoxime ligand molecules [156] (CSD Refcode MEMLUL). Hydrogen atoms, solvent and counterion molecules were omitted for clarity.…”