Three-Fold Intramolecular Ring Closing Alkene Metatheses of Square Planar Complexes with cis Phosphorus Donor Ligands P(X(CH2)mCH═CH2)3 (X = −, m = 5–10; X = O, m = 3–5): Syntheses, Structures, and Thermal Properties of Macrocyclic Dibridgehead Diphosphorus Complexes

Macrocyclic Sulfur Ligand Stabilized Trans-Palladium Dichloride Complex: Syntheses, Structure, Chlorine Rotation, and Application in α-Olefination of Nitriles by Primary Alcohols

Herein, we have reported the synthesis of a macrocyclic organosulfur ligand (L1) having a seventeen-membered macrocyclic ring. Subsequently, the corresponding trans-palladium complex (C1) of bulky macrocyclic organosulfur ligand (L1) was synthesized by reacting it with PdCl2 (CH3 CN)2 salt. The newly synthesized ligand and complex were characterized using various analytical and spectroscopic techniques. The complex showed a square planar geometry with trans orientation of two ligands around the palladium center. The complex possesses intramolecular SCH…Cl interactions of 2.648 Å between the macrocyclic ligand and palladium dichloride. The potential energy surface (PES) for the rotational process of C1 suggested a barrier of ~23.81 kcal/mol for chlorine rotation. Furthermore, the bulky macrocyclic organosulfur ligand stabilized palladium complex (C1) was used as a catalyst (2.5 mol %) for α-olefination of nitriles by primary alcohols. The α,β-unsaturated nitrile compounds were found to be the major product of the reaction (57-78 % yield) with broad substrate scope and large functional group tolerance. Notably, the saturated nitrile product was not observed during the reaction. The mechanistic studies suggested the formation of H2 and H2 O as only by-products of the reaction, thereby making the protocol greener and sustainable.

First Example of Cage P4N4-Macrocycle Copper Complexes with Intracavity Location of Unusual Cu2I Fragments

In this study, 28-membered macrocyclic 1,5(1,5)-di(1,5-diaza-3,7-diphosphacyclooctana)-2,4,6,8(1,4)-tetrabenzenacyclooctaphane were synthesized by condensation of pyridinephosphine, paraformaldehyde, and primary diamines (bis(4-aminophenyl)methane or -sulfide. The first representatives of binuclear copper(I) complexes of P,N-containing cyclophanes with two 1,5-diaza-3,7-diphosphacyclooctane rings incorporated into a macrocyclic core and intracavity location of unusual, developed angle Cu₂I moiety were obtained. The structure of one complex was established by X-ray diffraction analysis. The complexation led to a slight distortion of the cyclophane conformations.

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

The diphosphine complexes cis- or trans-[upper bond 1 start]PtCl₂(P((CH₂) _n )₃P[upper bond 1 end]) (n = b/12, c/14, d/16, e/18) are demetalated by MC[triple bond, length as m-dash]X nucleophiles to give the title compounds (P((CH₂) _n )₃)P (3b-e, 91-71%). These "empty cages" react with PdCl₂ or PtCl₂ sources to afford trans-[upper bond 1 start]MCl₂(P((CH₂) _n )₃P[upper bond 1 end]). Low temperature ³¹P 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: ΔH ^‡ 7.3/8.2 kcal mol^-1, ΔS ^‡ -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·2BH₃. The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature ³¹P NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (ΔG ^‡ _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·2BH₃ crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.

Bulky selenium ligand stabilized trans-palladium dichloride complexes as catalyst for silver-free decarboxylative coupling of coumarin-3-carboxylic acids

This report describes synthesis of three new trans -palladium dichloride complexes of bulky selenium ligands. These complexes possess a Cl-Pd-Cl rotor spoke attached to a Se-Pd-Se axle. The new ligands and palladium complexes ( C1 - C3 ) were characterized with the help of NMR, HRMS, UV-Vis., IR, and elemental analysis. The single crystal structure of metal complex C2 confirmed a square planer geometry of complex with trans -orientation. The X-ray structure revealed intramolecular secondary interactions (SeCH---Cl) between chlorine of PdCl 2 and CH 2 proton of selenium ligand. Variable temperature NMR data shows coalescence of diastereotopic protons, which indicates pyramidal inversion of selenium atom at elevated temperature. The relaxed potential energy scan of C2 suggests a rotational barrier of ~12.5 kcal/mol for rotation of chlorine atom through Cl-Pd-Cl rotor. The complex C3 possess dual intramolecular secondary interactions (OCH 2 ---Cl and SeCH 2 ---Cl) with stator ligand. Molecular rotor C2 was found to be most efficient catalyst for the decarboxylative Heck-coupling under mild reaction conditions. The protocol is applicable to a broad range of substrates with large functional group tolerance and low catalyst loading (2.5 mol %). The mechanism of decarboxylative Heck-coupling reaction was investigated through experimental and computational studies. Importantly the reaction works under silver-free conditions which reduces the cost of overall protocol. Further, the catalyst also worked for decarboxylative arylation and decarboxylative Suzuki-Miyaura coupling reactions with good yields of the coupled products.

Platinum(II) alkyl complexes of chelating dibridgehead diphosphines P((CH2)n)3P (n = 14, 18, 22); facile cis/trans isomerizations interconverting gyroscope and parachute like adducts

The gyroscope like dichloride complexes trans-Pt(Cl)₂(P((CH₂)_n)₃P) (trans-2; n = c, 14; e, 18; g, 22) and MeLi (2 equiv.) react to yield the parachute like dimethyl complexes cis-Pt(Me)₂(P((CH₂)_n)₃P) (cis-4c,e,g, 70-91%). HCl (1 equiv.) and cis-4c react to give cis-Pt(Cl)(Me)(P((CH₂)₁₄)₃P) (cis-5c, 83%), which upon stirring with silica gel or crystallization affords trans-5c (89%). Similar reactions of HCl and cis-4e,g give cis/trans-5e,g mixtures that upon stirring with silica gel yield trans-5e,g. A parallel sequence with trans-2c/EtLi gives cis-Pt(Et)₂(P((CH₂)₁₄)₃P) (cis-6c, 85%) but subsequent reaction with HCl affords trans-Pt(Cl)(Et)(P((CH₂)₁₄)₃P) (trans-7c, 45%) directly. When previously reported cis-Pt(Ph)₂(P((CH₂)₁₄)₃P) is treated with HCl (1 equiv.), cis- and trans-Pt(Cl)(Ph)(P((CH₂)₁₄)₃P) are isolated (44%, 29%), with the former converting to the latter at 100 °C. Reactions of trans-5c and LiBr or NaI afford the halide complexes trans-Pt(X)(Me)(P((CH₂)₁₄)₃P) (trans-9c, 88%; trans-10c, 87%). Thermolyses and DFT calculations that include acyclic model compounds establish trans > cis stabilities for all except the dialkyl complexes, for which energies can be closely spaced. The σ donor strengths of the non-phosphine ligands are assigned key roles in the trends. The crystal structures of cis-4c, trans-5c, trans-7c, and trans-10c are determined and analyzed together with the computed structures.

Solid-State 2H NMR Study for Deuterated Phenylene Dynamics in a Crystalline Gyroscope-Like Molecule

Molecular rotors have earned substantial popularity in recent times, owing to the unique dependence of its crystalline properties on the rotational dynamics of the rotor. We have recently reported the synthesis and crystal structure of a phenylene-bridged macrocage as a gyroscope-like molecule in the crystalline state. The dynamics of the phenylene moiety was probed by solid-state 13C CP/MAS proton dipolar dephasing NMR spectroscopy. Herein, solid-state 2H NMR studies were performed to study the dynamics of the gyroscope-like molecule with a deuterated rotor in the crystalline state. A spectrum with a narrow line shape was obtained at 300 K. The facile exchange among three stationary states, which was observed by X-ray crystallography, was clearly confirmed. Additionally, a crystal-to-crystal phase transition that switches the motion of the rotor was observed in the DSC analysis of the powdered sample.

A selenium-coordinated palladium(ii) trans-dichloride molecular rotor as a catalyst for site-selective annulation of 2-arylimidazo[1,2-a]pyridines

This report describes the synthesis of a new class of secondary interaction (SeCHCl)-controlled molecular rotor having a Cl-Pd-Cl rotor spoke attached onto a Se-Pd-Se axle. NMR data acquired at various temperatures established ΔG/ΔG values of 15.5 and 17.2 kcal mol^-1 for a roughly 4.5 Å-long rotor. The molecular rotor showed excellent catalytic activity with reverse regioselectivity for annulation of 2-arylimidazo[1,2-a]pyridines (yields: ∼53-78%) with only 1.5 mol% catalyst loading.

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH₂Cl₂ solution of H₃B·P((CH₂)₆CH=CH₂)₃ (1·BH₃) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H₂ (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H₃B·P(n-C₈H₁₇)₃ (1%), H₃B·P((CH₂)₁₃CH₂)(n-C₈H₁₇) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H₃B·P((CH₂)₁₃CH₂)((CH₂)₁₄)P((CH₂)₁₃CH₂)·BH₃ (6·2BH₃, 10%), in,out-H₃B·P((CH₂)₁₄)₃P·BH₃ (in,out-2·2BH₃, 4%) and the stereoisomer (in,in/out,out)-2·2BH₃ (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH₄) to H₂P((CH₂)₁₄)PH₂ (10; 76% overall yield). The reaction with H₃B·SMe₂ gives 10·2BH₃, which is treated with n-BuLi (4.4 equiv) and Br(CH₂)₆CH=CH₂ (4.0 equiv) to afford the tetraalkenyl precursor (H₂C=CH(CH₂)₆)₂(H₃B)P((CH₂)₁₄)P(BH₃)((CH₂)₆CH=CH₂)₂ (11·2BH₃; 18%). Alternative approaches to 11·2BH₃ (e.g., via 11) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11·2BH₃ (0.0010 M in CH₂Cl₂) gives 6·2BH₃ (5%), in,out-2·2BH₃ (6%), and (in,in/out,out)-2·2BH₃ (7%). Despite the doubled yield of 2·2BH₃, the longer synthesis of 11·2BH₃ vs 1·BH₃ renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.

A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a "Crossed-Chain" Variant of in/out Stereoisomers

Reactions of (O=)PH(OCH2 CH3 )2 and BrMg(CH2 )m CH=CH2 (4.9-3.2 equiv; m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH2 )m CH=CH2 ]2 (2 a-c; 77-81 % after workup), which are treated with NaH and then α,ω-dibromides Br(CH2 )n Br (0.49-0.32 equiv; n=8 (a'), 10 (b'), 12 (c'), 14 (d')) to yield the bis(trialkylphosphine oxides) [H2 C=CH(CH2 )m ]2 P(=O)(CH2 )n (O=)P[(CH2 )m CH=CH2 ]2 (3 ab', 3 bc', 3 cd', 3 ca'; 79-84 %). Reactions of 3 bc' and 3 ca' with Grubbs' first-generation catalyst and then H2 /PtO2 afford the dibridgehead diphosphine dioxides (4 bc', 4 ca'; 14-19 %, n'=2m+2); 31 P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained, out,out-4 ca' and a conformer of in,out-4 ca' that features crossed chains, such that the (O=)P vectors appear out,out. Whereas 4 bc' resists crystallization, a byproduct derived from an alternative metathesis mode, (CH2 )12 P(=O)(CH2 )12 (O=)P(CH2 )12 , as well as 3 ab' and 3 bc', are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.