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1. Synthesis and Evaluation of C2-Symmetric SPIROL-Based bis-Oxazoline Ligands

   https://doi.org/10.3390/sym13091667  

   Sun, Siyuan; Diaz, Nicolas A.; Nagorny, Pavel (September 2021, Symmetry)

   This communication describes the synthesis of new bis-oxazoline chiral ligands (SPIROX) derived from the C2-symmetric spirocyclic scaffold (SPIROL). The readily available (R,R,R)-SPIROL (2) previously developed by our group was subjected to a three-step sequence that provided key diacid intermediate (R,R,R)-7 in 75% yield. This intermediate was subsequently coupled with (R)- and (S)-phenylglycinols to provide diastereomeric products, the cyclization of which led to two diastereomeric SPIROX ligands (R,R,R,R,R)-3a and (R,R,R,S,S)-3b in 85% and 79% yield, respectively. The complexation of (R,R,R,R,R)-3a and (R,R,R,S,S)-3b with CuCl and Cu(OTf)2 resulted in active catalysts that promoted the asymmetric reaction of α-diazopropionate and phenol. The resultant O–H insertion product was formed in 88% yield, and with excellent selectivity (97% ee) when ligand (R,R,R,R,R)-3a was used. 

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2. Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out

   https://doi.org/10.1039/D2SC04724A  

   Zhu, Yun; Stollenz, Michael; Zarcone, Samuel R.; Kharel, Sugam; Joshi, Hemant; Bhuvanesh, Nattamai; Reibenspies, Joseph H.; Gladysz, John A. (November 2022, Chemical Science)

   The diphosphine complexes cis - or trans -PtCl 2 (P((CH 2 ) n ) 3 P) ( n = b/12, c/14, d/16, e/18) are demetalated by MCX nucleophiles to give the title compounds (P((CH 2 ) n ) 3 )P (3b–e, 91–71%). These “empty cages” react with PdCl 2 or PtCl 2 sources to afford trans -MCl 2 (P((CH 2 ) n ) 3 P). Low temperature 31 P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in , in (major) and out , out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: Δ H ‡ 7.3/8.2 kcal mol −1 , Δ S ‡ −19.4/−11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60–51) : (40–49) mixtures of ( in , in / out , out ) :  in , out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH 3 . The configurational stabilities of in , out -3b, c, e preclude phosphorus inversion in the interconversion of in , in and out , out isomers. Low temperature 31 P NMR spectra of in , out -3b, c reveal degenerate in , out / out , in homeomorphic isomerizations (Δ G ‡Tc 12.1, 8.5 kcal mol −1 ). When ( in , in / out , out )-3b, c, e are crystallized, out , out isomers are obtained, despite the preference for in , in isomers in solution. The lattice structures are analyzed, and the D 3 symmetry of out , out -3c enables a particularly favorable packing motif. Similarly, ( in , in / out , out )-3c, e·2BH 3 crystallize in out , out conformations, the former with a cycloalkane solvent guest inside. 

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3. The reaction of thiourea and 1,3-dimethylthiourea towards organoiodines: oxidative bond formation and halogen bonding

   https://doi.org/10.1107/S205322962100869X  

   Peloquin, Andrew J.; Ragusa, Arianna C.; McMillen, Colin D.; Pennington, William T. (October 2021, Acta Crystallographica Section C Structural Chemistry)

   By varying the halogen-bond-donor molecule, 11 new halogen-bonding cocrystals involving thiourea or 1,3-dimethylthiourea were obtained, namely, 1,3-dimethylthiourea–1,2-diiodo-3,4,5,6-tetrafluorobenzene (1/1), C 6 F 4 I 2 ·C 3 H 8 N 2 S, 1 , thiourea–1,3-diiodo-2,4,5,6-tetrafluorobenzene (1/1), C 6 F 4 I 2 ·CH 4 N 2 S, 2 , 1,3-dimethylthiourea–1,3-diiodo-2,4,5,6-tetrafluorobenzene (1/1), C 6 F 4 I 2 ·C 3 H 8 N 2 S, 3 , 1,3-dimethylthiourea–1,3-diiodo-2,4,5,6-tetrafluorobenzene–methanol (1/1/1), C 6 F 4 I 2 ·C 3 H 8 N 2 S·CH 4 O, 4 , 1,3-dimethylthiourea–1,3-diiodo-2,4,5,6-tetrafluorobenzene–ethanol (1/1/1), C 6 F 4 I 2 ·C 3 H 8 N 2 S·C 2 H 6 O, 5 , 1,3-dimethylthiourea–1,4-diiodo-2,3,5,6-tetrafluorobenzene (1/1), C 6 F 4 I 2 ·C 3 H 8 N 2 S, 6 , 1,3-dimethylthiourea–1,3,5-trifluoro-2,4,6-triiodobenzene (1/1), C 6 F 3 I 3 ·C 3 H 8 N 2 S, 7 , 1,3-dimethylthiourea–1,1,2,2-tetraiodoethene (1/1), C 6 H 16 N 4 S 2 ·C 2 I 4 , 8 , [(dimethylamino)methylidene](1,2,2-triiodoethenyl)sulfonium iodide–1,1,2,2-tetraiodoethene–acetone (1/1/1), C 5 H 8 I 3 N 2 S + ·I − ·C 3 H 6 O·C 2 I 4 , 9 , 2-amino-4-methyl-1,3-thiazol-3-ium iodide–1,1,2,2-tetraiodoethene (2/3), 2C 4 H 7 N 2 S + ·2I − ·3C 2 I 4 , 10 , and 4,4-dimethyl-4 H -1,3,5-thiadiazine-3,5-diium diiodide–1,1,2,2-tetraiodoethene (2/3), 2C 5 H 12 N 4 S 2+ ·4I − ·3C 2 I 4 , 11 . When utilizing the common halogen-bond-donor molecules 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene, as well as 1,3,5-trifluoro-2,4,6-triiodobenzene, bifurcated I...S...I interactions were observed, resulting in the formation of isolated rings, chains, and sheets. Tetraiodoethylene (TIE) provided I...S...I cocrystals as well, but further yielded a sulfonium-containing product through the reaction of the S atom with TIE. This particular sulfonium motif is the first of its kind to be structurally characterized, and is stabilized in the solid state through a three-dimensional I...I halogen-bonding network. Thiourea reacted with acetone in the presence of TIE to provide two novel heterocyclic products, again stabilized in the solid state through I...I halogen bonding. 

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4. Aluminium( iii ) dialkyl 2,6-bisimino-4 R -dihydropyridinates(−1): selective synthesis, structure and controlled dimerization

   https://doi.org/10.1039/C9DT00847K  

   Gallardo-Villagrán, Manuel; Vidal, Fernando; Palma, Pilar; Álvarez, Eleuterio; Chen, Eugene Y.-X.; Cámpora, Juan; Rodríguez-Delgado, Antonio (June 2019, Dalton Transactions)

   A family of stable and otherwise selectively unachievable 2,6-bisimino-4- R -1,4-dihydropyridinate aluminium (III) dialkyl complexes [AlR' 2 (4-R- i PrBIPH)] (R = Bn, Allyl; R′ = Me, Et, i Bu) have been synthesized, taking advantage of a method for the preparation of the corresponding 4- R -1,4-dihydropiridine precursors developed in our group. All the dihydropyrdinate(−1) dialkyl aluminium complexes have been fully characterized by 1 H- 13 C-NMR, elemental analysis and in the case 2′a , also by X-ray diffraction studies. Upon heating in toluene solution at 110 °C, the dimethyl derivatives 2a and 2′a dimerize selectively through a double cycloaddition. This reaction leads to the formation of two new C–C bonds that involve the both meta positions of the two 4- R -1,4-dihydropyridinate fragments, resulting the binuclear aluminium species [Me 2 Al(4-R- i PrHBIP)] 2 (R = Bn ( 3a ); allyl ( 3′a )). Experimental kinetics showed that the dimerization of 2′a obeys second order rate with negative activation entropy, which is consistent with a bimolecular rate-determining step. Controlled methanolysis of both 3a and 3′a release the metal-free dimeric bases, (4-Bn- i PrHBIPH) 2 and (4-allyl- i PrHBIPH) 2 , providing a convenient route to these potentially useful ditopic ligands. When the R′ groups are bulkier than Me ( 2b , 2′b and 2′c ), the dimerization is hindered or fully disabled, favoring the formation of paramagnetic NMR-silent species, which have been identified on the basis of a controlled methanolysis of the final organometallic products. Thus, when a toluene solution of [AlEt 2 (4-Bn- i PrBIPH)] ( 2b ) was heated at 110 °C, followed by the addition of methanol in excess, it yields a mixture of the dimer (4-Bn- i PrHBIPH) 2 and the aromatized base 4-Bn- i PrBIP, in ca . 1 : 2 ratio, indicating that the dimerization of 2b competes with its spontaneous dehydrogenation, yielding a paramagnetic complex containing a AlEt 2 unit and a non-innocent (4-Bn- i PrBIP) ˙− radical-anion ligand. Similar NMR monitoring experiments on the thermal behavior of [AlEt 2 (4-allyl- i PrBIPH)] ( 2′b ) and [Al i Bu 2 (4-allyl-iPrBIPH)] ( 2′c ) showed that these complexes do not dimerize, but afford exclusively NMR silent products. When such thermally treated samples were subjected to methanolysis, they resulted in mixtures of the alkylated 4-allyl- i PrBIP and non-alkylated i PrBIP ligand, suggesting that dehydrogenation and deallylation reactions take place competitively. 

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5. Syntheses, Structural Studies, and Copper Iodide Complexes of Macrocycles Derived from Williamson Ether Syntheses Involving 2,9-Bis(4-hydroxyphenyl)-1,10-phenanthroline, α,ω-Dibromides, and Resorcinol or 2,7-Dihydroxynaphthalene

   https://doi.org/10.1071/CH16587  

   Baranová, Zuzana; Amini, Hashem; Neupane, Madhav; Garrett, Sydney C.; Ehnbom, Andreas; Bhuvanesh, Nattamai; Reibenspies, Joseph H.; Gladysz, John A. (January 2017, Australian Journal of Chemistry)

   1,3-Bis(6-bromohexyloxy)benzene, 2,7-bis(6-bromohexyloxy)naphthalene, 1,3-bis(4-bromomethylbenzyloxy)benzene, and 1,3-bis(3-bromomethylbenzyloxy)benzene were prepared via Williamson ether synthesis using resorcinol or 2,7-dihydroxynaphthalene and 1,6-dibromohexane, 1,4-bis(bromomethyl)benzene, or 1,3-bis(bromomethyl)benzene (21–47 % yield). These dibromides were condensed with 2,9-bis(4-hydroxyphenyl)-1,10-phenanthroline in the presence of K2CO3 to give the corresponding 31- to 35-membered macrocycles (3a–d, 22–63 % yield). When 3a–d were treated with CuI, mononuclear 1 : 1 complexes formed, in which the CuI chelates to the nitrogen donor atoms of the phenanthroline moiety (4a–d, 40–80 % yield). The crystal structures of 3a–c and 4a–c were determined and analyzed using density functional theory calculations and in the context of rotaxanes that could be formed by treatment of 4a–d with terminal alkynes (e.g. macrocycle dimensions, void volumes). The copper and iodide atoms in 4a–c significantly protrude from the least-squares plane of the phenanthroline moiety (0.46–0.63 Å and 1.65–2.07 Å). 

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