A surprise landing on the terra incognita of macrocyclic dibridgehead diorganoarsines: syntheses, structures, and reactivities

Ring-closing metathesis of dialkenylcycloalkanes for the synthesis of fused bicycloalkanes and tricycloalkanes

Ring-closing metathesis of dialkenyldisilacycloalkane using the Grubbs catalyst, followed by hydrogenation, afforded a mixture of two disilabicycloalkanes and tetrasilatricycloalkanes. This method can synthesize a diastereomer mixture of disilabicycloalkanes with one differing alkyl side chain. The observed symmetries of the NMR spectra of anti-bicycloalkanes depend significantly on the length of the side chain. The findings may contribute to the molecular design of functional bicycloalkanes based on structural transformations of the stable forms.

Macrobicyclic Dibridgehead Di(trialkyl)pnictogens E((CH2) n )3E (E/n = As/10, As/12, As/14, Sb/14) and Their Cage-like Metal Complexes: Syntheses, Structures, and Homeomorphic Isomerizations

Photolyses of trans-Fe(CO)3(As((CH2) n )3As) (n = a, 10; b, 12; c, 14) in the presence of PMe3, or reactions of trans-[Fe(CO)2(NO)(As((CH2) n )3As)]+ BF4 - and n-Bu4N+ Cl-, afford the air stable title complexes As((CH2) n )3As (8a-c) in 79-34% yields. With 8a, the in, in and out, out isomers are separable and each is crystallographically characterized. With 8b,c, the isomers rapidly interconvert by homeomorphic isomerization, but each crystallizes (contrathermodynamically) as an out, out isomer. Reactions of 8c with H2O2 or 8b with BH3 give 8c·2O or 8b·2BH3, respectively (85-94%). Reactions of 8c with MCl2 (M = Pt, Pd, Ni), Rh(CO)(Cl), and Fe(CO)3 sources afford the corresponding cage-like complexes trans-ML n (As((CH2)14)3As) (86-51%). The crystal structures of 8c·2O and the PtCl2 and PdCl2 adducts are determined and compared to those of 8a-c and diphosphorus analogs. The corresponding distibine Sb((CH2)14)3Sb is analogously prepared, but precursors necessary for the bismuth analog could not be accessed due to the diminished BiR3 Lewis basicity.

Molecules that Turn Themselves Inside-Out: Tuning in/out Equilibria and Homeomorphic Isomerization in Macrobicyclic Dibridgehead Diphosphines P((CH2 )n )3 P Newly Accessible by Earth-Abundant-Metal Templates

Photolyses of trans-Fe(CO)3 (P((CH2 )n )3 P) (n=10 (a), 12 (b), 14 (c), 16 (d), 18 (e)) in the presence of PMe3 provide the first economical and scalable route to macrobicyclic dibridgehead diphosphines P((CH2 )n )3 P (1). These are isolated as mixtures of in,in/out,out isomers that equilibrate with degenerate in,out/out,in isomers at 150 °C via pyramidal inversion at phosphorus. For the entire series, VT 31 P NMR data establish or bound Keq , rates, and activation parameters for a variety of phenomena, many of which involve homeomorphic isomerizations, topological processes by which certain molecules can turn themselves inside out (e. g., in,in⇌out,out). This provides the first detailed mapping of such trends in homologous series of aliphatic bicyclic compounds XE((CH2 )n )3 EX with any type of bridgehead. Isomeric diborane adducts 1 a,d ⋅ 2BH3 are also characterized. Crystal structures of out,out-1 a and in,in-1 a ⋅ 2BH3 aid isomer assignments and reveal unusual cage 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.

Square-Planar and Octahedral Gyroscope-Like Metal Complexes Consisting of Dipolar Rotators Encased in Dibridgehead Di(triaryl)phosphine Stators: Syntheses, Structures, Dynamic Properties, and Reactivity

For a variety of purposes, it is of interest to embed metals in cagelike trans-spanning di(triaryl)phosphine ligands. Toward this end, a combination of P(p-C₆H₄O(CH₂)_mCH═CH₂)₃ [3; m = 4 (a), 5 (b), 6 (c), and 7 (d)], [Rh(COD)(μ-Cl)]₂, and CO gives square-planar trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_mCH═CH₂)₃]₂ (4a-4d). Reactions of 4b-4d with Grubbs' catalyst (first generation) and then H₂ (catalyst PtO₂) yield the title compounds trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P] (n = 2m + 2, 6b-6d; 26-41% from 4b-4d). Two are crystallographically characterized. The Cl-Rh-CO moieties rapidly rotate on the NMR time scale at -120 °C, per the ample clearance provided by the (CH₂)_n segments. Steric interactions with the PC₆H₄O linkages are analyzed. LiC≡CAr displaces the chloride ligand from 6b to give RhC≡CAr adducts (Ar = C₆H₅/p-C₆H₄CH₃, 7b/8b). The ArC≡C-Rh-CO rotator of 7b rapidly rotates on the NMR time scale (-70 °C), but with 8b, the longer p-CH₃C₆H₄C≡C group is confined between two (CH₂)₁₂ bridges, even at 120 °C. Reactions of Re(CO)₅(X) and 3c (140 °C) give octahedral mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₆CH═CH₂)₃]₂ (X = Cl/Br), and metathesis/hydrogenation sequences yield mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₁₄O-p-C₆H₄)₃P]. Reactions of 6c and 6d and excess PMe₃ give the free diphosphines P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P (14c and 14d, 83-75%). The addition of 14d to [Rh(CO)₂(μ-Cl)]₂ reconstitutes 6d (87%). Both in,in and out,out isomers of 14c and 14d are possible, but low-temperature NMR spectra show one set of signals, consistent with rapid homeomorphic isomerizations that turn the molecules inside out. Thermolyses (C₆D₅Br, 140 °C) effect phosphorus inversion to give in,out isomers.