Octahedral Gyroscope-Like Molecules with M(CO)3(X) Rotators Encased in Three-Spoked Diphosphine Stators: Syntheses by Alkene Metathesis/Hydrogenation Sequences, Structures, Dynamic Properties, and Reactivities

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.

Sulfate Donor Based Dinuclear Heteroleptic Triple-Stranded Helicates from Sulfite and Ditopic Nitrogen Donor Ligands and Their Transformation to Dinuclear Homoleptic Double-Stranded Mesocates

Sulfate donor based supramolecular coordination complexes [{ fac-Re(CO)₃}(μ-SO₄)(L ⁿ)₂{ fac-Re(CO)₃}] (1-3) were obtained using ditopic N donors (L ⁿ; n = 1-3), NaHSO₃, and Re₂(CO)₁₀ in a one-pot, multicomponent, coordination-driven self-assembly approach, in which SO₃^2- becomes oxidized to SO₄^2- during the reaction and acts as a building framework. Complexes 1-3 were characterized using IR, ESI-TOF-MS, and ¹H NMR spectroscopy. The structures of complexes 1-3 were confirmed using single-crystal X-ray diffraction analysis. The transformation of the dinuclear heteroleptic triple-stranded helicate to the dinuclear homoleptic double-stranded mesocate [{Re(CO)₃Cl}₂(L ⁿ)₂] (L ⁿ = L¹, L², L³; 4a-6a) was achieved by the addition of BaCl₂. The direct treatment of Re(CO)₅X (X = Cl, Br) with L¹/L²/L³ yielded the dinuclear homoleptic double-stranded helicates [{Re(CO)₃X}₂ (L ⁿ)₂] (4b-6b and 7-9).

A family of cis-macrocyclic diphosphines: modular, stereoselective synthesis and application in catalytic CO2/ethylene coupling

The stereoselective synthesis of a family of cis-macrocyclic diphosphines was achieved in only three steps from white phosphorus and commercial materials. These new ligands showed activity in the nickel-catalyzed coupling of CO₂ and ethylene.

A family of cis-macrocyclic diphosphines was prepared in just three steps from white phosphorus and commercial materials using a modular synthetic approach. Alkylation of bicyclic diphosphane 3,4,8,9-tetramethyl-1,6-diphosphabicyclo(4.4.0)deca-3,8-diene, or P₂(dmb)₂, produced phosphino-phosphonium salts [R-P₂(dmb)₂]X, where R is methyl, benzyl and isobutyl, in yields of 90–96%. Treatment of these salts with organolithium or Grignard reagents yielded symmetric and unsymmetric macrocyclic diphosphines of the form cis-1-R-6-R′-3,4,8,9-tetramethyl-2,5,7,10-tetrahydro-1,6-DiPhospheCine, or R,R′-DPC, in which R′ is methyl, cyclohexyl, phenyl or mesityl, in yields of 46–94%. Alternatively, symmetric diphosphine Cy₂-DPC was synthesized in 74% yield from the dichlorodiphosphine Cl₂P₂(dmb)₂. As a first application, these cis-macrocyclic diphosphines were used as ligands in the nickel-catalyzed synthesis of acrylate from CO₂ and ethylene, for which they showed promising catalytic activity.

Crystal Fluidity Reflected by Fast Rotational Motion at the Core, Branches, and Peripheral Aromatic Groups of a Dendrimeric Molecular Rotor

Low packing densities are key structural features of amphidynamic crystals built with static and mobile components. Here we report a loosely packed crystal of dendrimeric rotor 2 and the fast dynamics of all its aromatic groups, both resulting from the hyperbranched structure of the molecule. Compound 2 was synthesized with a convergent strategy to construct a central phenylene core with stators consisting of two layers of triarylmethyl groups. Single crystal X-ray diffraction analysis confirmed a low-density packing structure consisting of one molecule of 2 and approximately eight solvent molecules per unit cell. Three isotopologues of 2 were synthesized to study the motion of each segment of the molecule in the solid state using variable temperature quadrupolar echo (2)H NMR spectroscopy. Line shape analysis of the spectra reveals that the central phenylene, the six branch phenylenes, and the 18 periphery phenyls all display megahertz rotational dynamics in the crystals at ambient temperature. Arrhenius analysis of the data gives similar activation energies and pre-exponential factors for different parts of the structure. The observed pre-exponential factors are 4-6 orders of magnitude greater than those of elementary site-exchange processes, indicating that the dynamics are not dictated by static energetic potentials. Instead, the activation energies for rotations in the crystals of 2 are controlled by temperature dependent local structural fluctuations and crystal fluidity.

Gyroscope like molecules consisting of trigonal or square planar osmium rotators within three-spoked dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties

The OsL_y moieties of the title complexes undergo rapid rotation within the diphosphine cages when L is restricted to Cl, Br, CO, H, and Me.

Synthesis, reactivity, structures, and dynamic properties of gyroscope like iron complexes with dibridgehead diphosphine cages: pre- vs. post-metathesis substitutions as routes to adducts with neutral dipolar Fe(CO)(NO)(X) rotors

Substitution reactions of 4c⁺ BF₄⁻ afford the title complexes 9c-X, the Fe(CO)(NO)(X) moieties of which rapidly rotate within the diphosphine cage. Trends are interpreted in terms of horizontal/vertical van der Waals clearance.

A pyrene-bridged macrocage showing no excimer fluorescence

A pyrene bridged macrocage shows fluorescence from a monomeric excited state without excimer due to cage effects.

Photochromic molecular gyroscope with solid state rotational states determined by an azobenzene bridge

We describe the synthesis, characterization, photochemical isomerization, and rotational dynamics of a crystalline molecular gyroscope containing an azobenzene bridge (trans-2) that spans from one end of the stator to other, with the intention of exploring its function as a molecular brake. While single crystal X-ray diffraction analysis of a photochemically inactive dichloromethane solvate was used to confirm the molecular and packing structures of trans-2, a nanocrystalline pseudopolymorph was shown to be photoactive, and it was analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy, and variable temperature solid state (2)H NMR before and after photoisomerization. It was shown that the nanocrystalline suspension irradiated with λ = 340 nm reaches a photostationary state with 34% of cis-isomer, as compared to that observed in solution where the corresponding value is 74%. Line shape analysis of solid state (2)H NMR spectra of a phenylene-d4 isotopologue, obtained as a function of temperature, indicated that rotation in crystals of the trans-2 isomer, with a mean activation energy of 4.6 ± 0.6 kcal/mol and a pre-exponential factor exp(29.4 ± 1.7), is ten times faster than that of samples containing the cis-2 isomer, which has a higher mean activation energy of 5.1 ± 0.6 kcal/mol and a lower pre-exponential factor of exp(27.9 ± 1.3).

Ring-closing metathesis for the synthesis of a molecular gyrotop

A molecular gyrotop was synthesized by ring-closing metathesis (RCM) under reflux, indicating that the cage is a thermodynamically controlled product.

A crystalline molecular gyrotop with germanium junctions between a phenylene rotor and alkyl spokes

A molecular gyrotop with germanium junctions was synthesized, and the dynamics of the phenylene and the optical properties were discussed.