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.

Gyroscopes and the Chemical Literature, 2002-2020: Approaches to a Nascent Family of Molecular Devices.

Research directed toward the goal of molecular gyroscopes since the coverage of a previous review (2002) is described. Such species are a subclass of molecular rotors, which are comprised of rotators and stators. Major categories include (1) systems in which a rotator is embedded in a cage-like stator reminiscent of mechanical toy gyroscopes and (2) molecules that have been engineered to crystallize with parallel rotators and voids or other features that enable the rotator to rotate in the solid state (amphidynamic crystals). Particular attention is given to structural data and strategies for the minimization of rotational barriers. Synthetic routes are also described. Some allied types of molecules and supramolecular assemblies are also treated.

Shortwave Infrared Fluorofluorophores for Multicolor In Vivo Imaging.

Developing chemical tools to detect and influence biological processes is a cornerstone of chemical biology. Here we combine two tools which rely on orthogonality- perfluorocarbons and multiplexed shortwave infrared (SWIR) fluorescence imaging- to visualize nanoemulsions in real time in living mice. Drawing inspiration from fluorous and SWIR fluorophore development, we prepared two SWIR-emissive, fluorous-soluble chromenylium polymethine dyes. These are the most red-shifted fluorous fluorophores- "fluorofluorophores"-to date. After characterizing the dyes, their utility was demonstrated by tracking perfluorocarbon nanoemulsion biodistribution in vivo. Using an excitation-multiplexed approach to image two variables simultaneously, we gained insight into the importance of size and surfactant identity on biodistribution.

Mechanism of Coupling of Methylidene to Ethylene Ligands in Dimetallic Assemblies; Computational Investigation of a Model for a Key Step in Catalytic C1 Chemistry.

Methylidene complexes often couple to ethylene complexes, but the mechanistic insight is scant. The path by which two cations [(η5-C5H5)Re(NO)(PPh3)(═CH2)]+ (5+) transform (CH2Cl2/acetonitrile) to [(η5-C5H5)Re(NO)(PPh3)(H2C═CH2)]+ (6+) and [(η5-C5H5)Re(NO)(PPh3)(NCCH3)]+ is studied by density functional theory. Experiments provide a number of constraints such as the second-order rate in 5+; no prior ligand dissociation/exchange; a faster reaction of (S)-5+ with (S)-5+ than with (R)-5+ ("enantiomer self-recognition"). Although dirhenium dications with Re(µ-CH2)2Re cores represent energy minima, they are not accessible by 2 + 2 cycloadditions of 5+. Transition states leading to ReCH2CH2Re linkages are prohibitively high in energy. However, 5+ can give non-covalent SRe/SRe or SRe/RRe dimers with π interactions between the PPh3 ligands but long ReCH2···H2CRe and H2CRe···H2CRe distances (3.073-3.095 Å and 3.878-4.529 Å, respectively). In rate-determining steps, these afford [(η5-C5H5)Re(NO)(PPh3)(µ-η2:η2-H2C···CH2)(Ph3P)(ON)Re(η5-C5H5)]2+ (132+), in which one rhenium binds the bridging ethylene more tightly than the other (2.115-2.098 vs 2.431-2.486 Å to the centroid). In the SRe/RRe adduct, Dewar-Chatt-Duncanson optimization leads to unfavorable PPh3/PPh3 contacts. Ligand interactions are further dissected in the preceding transition states via component analyses, and ΔΔG‡ (1.2 kcal/mol, CH2Cl2) favors the SRe/SRe pathway, in accordance with the experiment. Acetonitrile then displaces 6+ from the more weakly bound rhenium of 132+. The formation of similar µ-H2C···CH2 intermediates is found to be rate-determining for varied coordinatively saturated M═CH2 species [M = Fe(d6)/Re(d4)/Ta(d2)], establishing generality and enhancing relevancy to catalytic CH4 and CO/H2 chemistry.

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.

Tracking Energy Transfer across a Platinum Center.

Rigid, conjugated alkyne bridges serve as important components in various transition-metal complexes used for energy conversion, charge separation, sensing, and molecular electronics. Alkyne stretching modes have potential for modulating charge separation in donor-bridge-acceptor compounds. Understanding the rules of energy relaxation and energy transfer across the metal center in such compounds can help optimize their electron transfer switching properties. We used relaxation-assisted two-dimensional infrared spectroscopy to track energy transfer across metal centers in platinum complexes featuring a triazole-terminated alkyne ligand of two or six carbons, a perfluorophenyl ligand, and two tri(p-tolyl)phosphine ligands. Comprehensive analyses of waiting-time dynamics for numerous cross and diagonal peaks were performed, focusing on coherent oscillation, energy transfer, and cooling parameters. These observables augmented with density functional theory computations of vibrational frequencies and anharmonic force constants enabled identification of different functional groups of the compounds. Computations of vibrational relaxation pathways and mode couplings were performed, and two regimes of intramolecular energy redistribution are described. One involves energy transfer between ligands via high-frequency modes; the transfer is efficient only if the modes involved are delocalized over both ligands. The energy transport pathways between the ligands are identified. Another regime involves redistribution via low-frequency delocalized modes, which does not lead to interligand energy transport.

Launching Werner Complexes into the Modern Era of Catalytic Enantioselective Organic Synthesis.

Reactions catalyzed by transition metal complexes almost always entail binding of one or more reactants to the metal center, and nearly every corner of the "chiral pool" has been picked over in efforts to develop enantioselective catalysts. As reported by Alfred Werner in 1911-1912, salts of the formally D3-symmetric [Co(en)3]3+ trication (en = ethylenediamine) were among the first chiral inorganic compounds to be resolved into enantiomers. These air- and water-stable complexes are substitution-inert, so for 100 years they languished without application in organic synthesis. We then showed that when they are rendered soluble in organic media by lipophilic anions such as fluorinated tetraarylborates BArf-, they become potent catalysts for a variety of carbon-carbon and carbon-heteroatom bond forming reactions.These involve substrate activation by hydrogen bonding to the coordinated NH2 units (pKa ca. 15), a "second coordination sphere" mechanism. Only modest enantioselectivities are obtained with [Co(en)3]3+ 3BArf- or related chromium, rhodium, iridium, and platinum salts. However, high enantioselectivities are achieved when the three en ligands are replaced by the 1,2-diphenyl analogues (S,S)- or (R,R)-H2NCHPhCHPhNH2. Here only one BArf- anion is required to solubilize the trication, so a number of mixed-salt catalysts (2X-BArf-) have been evaluated. Alternatively, a dimethylamino group can be tethered to the backbone of one en ligand, providing bifunctional catalysts that obviate any need for an external base. Interestingly, the counteranions modulate the enantioselectivities somewhat. However, catalysts with chiral anions do not significantly outperform benchmark catalysts with achiral anions. Cagelike chiral hexaaminecobalt(III) complexes known as sepulchrates and sarcophagines, which feature secondary NH donor atoms, can also serve as catalysts, but the enantioselectivities are very low.In a spinoff application, certain salts are found to be superb "chiral solvating agents", leading to distinct sets of NMR signals for enantiomers of chiral analytes with Lewis basic functional groups. Loadings of 10-25 mol % generally suffice, providing the best way of assaying the enantiomeric purities of a host of compounds. Also, mixtures of several chiral compounds can be simultaneously analyzed. It is not surprising that complexes that perform well in chiral recognition phenomena also excel as enantioselective catalysts.In this Account, the stereochemical properties of the preceding complexes are treated, as well as arcana generally known only to specialists in the field. These include the use of charcoal for equilibrating configurations of the cobalt stereocenter and Sephadex for separating enantiomers and diastereomers. Other types of metal-containing hydrogen-bond-donor catalysts are briefly surveyed (noncoordinating NH units can also be effective), including several developed by other groups. However, the mechanisms of enantioselection in all of these transformations remain obscure. The optimum diastereomer and anion set varies from reaction to reaction, suggesting a "phenotypic plasticity" that allows adaption to a variety of processes.

Macrocyclic Complexes Derived from Four cis-L2 Pt Corners and Four Butadiynediyl Linkers; Syntheses, Electronic Structures, and Square versus Skew Rhombus Geometries.

The dialkyl malonate derived 1,3-diphosphines R2 C(CH2 PPh2 )2 (R=a, Me; b, Et; c, n-Bu; d, n-Dec; e, Bn; f, p-tolCH2 ) are combined with (p-tol3 P)2 PtCl2 or trans-(p-tol3 P)2 Pt((C≡C)2 H)2 to give the chelates cis-(R2 C(CH2 PPh2 )2 )PtCl2 (2 a-f, 94-69 %) or cis-(R2 C(CH2 PPh2 )2 )Pt((C≡C)2 H)2 (3 a-f, 97-54 %). Complexes 3 a-d are also available from 2 a-d and excess 1,3-butadiyne in the presence of CuI (cat.) and excess HNEt2 (87-65 %). Under similar conditions, 2 and 3 react to give the title compounds [(R2 C(CH2 PPh2 )2 )[Pt(C≡C)2 ]4 (4 a-f; 89-14 % (64 % avg)), from which ammonium salts such as the co-product [H2 NEt2 ]+ Cl- are challenging to remove. Crystal structures of 4 a,b show skew rhombus as opposed to square Pt4 geometries. The NMR and IR properties of 4 a-f are similar to those of mono- or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono-platinum or Pt(C≡C)2 Pt species, the UV-visible spectra show much more intense and red-shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt4 C16 cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt3 C12 and Pt5 C20 homologs and selected equilibria are explored computationally.

Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products.

Reactions of Li+ [(η5 -C5 H5 )Re(NO)(PPh3 )]- with 2- and 4-chloroquinoline or 1-chloroisoquinoline give the corresponding σ quinolinyl and isoquinolinyl complexes 3, 6, and 8. With 3 and 8 there is further protonation to yield HCl adducts, but additions of KH give the free bases. Treatment of 3 with HBF4 ⋅OEt2 or H(OEt2 )2 + BArf - gives the quinolinium salts [(η5 -C5 H5 )Re(NO)(PPh3 )(C(NH)C(CH)4 C(CH)(CH))]+ X- (3-H+ X- ; X- =BF4 - /BArf - , 94-98 %). Addition of CF3 SO3 CH3 to 3, 6, or 8 affords the corresponding N-methyl quinolinium salts. In the case of [(η5 -C5 H5 )Re(NO)(PPh3 )(C(NCH3 )C(CH)4 C(CH)(CH))]+ CF3 SO3 - (3-CH3 + CF3 SO3 - ), addition of CH3 Li gives the dihydroquinolinium complex (SRe RC ,RRe SC )-[(η5 -C5 H5 )Re(NO)(PPh3 )(C(NCH3 )C(CH)4 C(CHCH3 )(CH2 ))]+ CF3 SO3 - ((SRe RC ,RRe SC )-5+ CF3 SO3 - , 76 %) in diastereomerically pure form. Crystal structures of 3-H+ BArf - , 3-CH3 + CF3 SO3 - , (SRe RC , RRe SC )-5+ Cl- , and 6-CH3 + CF3 SO3 - show that the quinolinium ligands adopt Re⋅⋅⋅C conformations that maximize overlap of their acceptor orbitals with the rhenium fragment HOMO, minimize steric interactions with the bulky PPh3 ligand, and promote various π interactions. NMR experiments establish the Brønsted basicity order 3>8>6, with Ka (BH+ ) values >10 orders of magnitude greater than the parent heterocycles, although they remain less active nucleophilic catalysts in the reactions tested. DFT calculations provide additional insights regarding Re⋅⋅⋅C bonding and conformations, basicities, and the stereochemistry of CH3 Li addition.

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies.

The silylated hexatriynyl complex trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)3 SiEt3 (PtC6 TES) is converted in situ to PtC6 H (wet n-Bu4 N+ F- , THF) and cross coupled with the diyne H(C≡C)2 SiEt3 (HC4 TES; CuCl/TMEDA, O2 ) to give PtC10 TES (71 %). This sequence is repeated twice to afford PtC14 TES (65 %) and then PtC18 TES (27 %). An analogous series of reactions starting with PtC8 TES gives PtC12 TES (60 %), then PtC16 TES (43 %), and then PtC20 TES (17 %). Similar cross couplings with H(C≡C)2 Si(i-Pr)3 (HC4 TIPS) give PtC12 TIPS (68 %), PtC14 TIPS (68 %), and PtC16 TIPS (34 %). The trialkylsilyl species (up to PtC18 TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n-1 C=CHN(CH2 C6 H5 )N=N (29-92 % after workups). The most general procedure involves generating the terminal polyynes PtCx H (wet n-Bu4 N+ F- , THF) in the presence of benzyl azide in DMF and aqueous CuSO4 /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC20 TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.

Toward Frameworks with Multiple Aligned and Interactive Fe(CO)3 Rotators: Syntheses and Structures of Diiron Complexes Linked by Two trans-Diaxial α,ω-Diphosphine Ligands Ar2P(CH2)nPAr2.

Reactions of (η4-benzylideneacetone)Fe(CO)3 and the α,ω-diphosphines Ar2P(CH2)nPAr2 afford the trigonal bipyramidal diiron tetraphosphorus complexes trans,trans-(CO)3Fe[Ar2P(CH2)nPAr2]2Fe(CO)3 (n/Ar = 3/Ph 3, 4/Ph 4a, 4/p-tol 4b; 56-19%). Crystal structures establish essentially parallel P-Fe-P axes, iron-iron distances of 5.894(9)-5.782(1) Å (3) and 6.403(1)-6.466(1) Å (4a,b), and van der Waals radii of 4.45 Å for the Fe(CO)3 rotators, the planes of which are offset by 0.029-1.665 Å. Analogous reactions of Ph2P(CH2)6PPh2 yield the square pyramidal monoiron complex trans-(CO)3Fe[Ph2P(CH2)6PPh2] (6', 31%), a rare case where a diphosphine spans trans basal positions (∠P-Fe-P 147.4(2)°). Both 3 and 6' exhibit two CO 13C NMR signals at room temperature, indicating slow exchange on the NMR time scale, which in the former could entail Fe(CO)3/Fe(CO)3 gearing. Under analogous conditions, 4a,b exhibit one signal. Previously reported adducts of Fe(CO)3 and Ph2P(CH2)nPPh2 are surveyed (1:1, n = 1-5; 2:2, n = 5), and the IR νC≡O band patterns and energies of all complexes analyzed with the aid of DFT calculations. The diiron complexes are preferred thermodynamically. Attention is given to limiting types of Fe(CO)3/Fe(CO)3 interactions in the diiron complexes.

An Air- and Water-Stable Hydrogen-Bond-Donor Catalyst for the Enantioselective Generation of Quaternary Carbon Stereocenters by Additions of Substituted Cyanoacetate Esters to Acetylenic Esters.

The chiral enantiopure cobalt(III) complex Δ-[Co((S,S)-dpen)3 ]3+ 2Cl- B(C6 F5 )4 - (Δ-(S,S)-23+ 2Cl- B(C6 F5 )4 - ; dpen=1,2-diphenylethylenediamine) is an effective catalyst, together with pyridine (10 mol % each), for enantioselective additions of substituted cyanoacetate esters NCCH(R)CO2 R' to acetylenic esters R''C≡CCO2 R'''. In the resulting adducts NC(R'O2 C)C(R)CR''C=CHCO2 R''', C=C isomers in which the CO2 R''' moiety is trans to the new carbon-carbon bond dominate (avg. ratio 98:2). These are obtained in 70-98 % ee (avg. 86 %; data for optimum R' and R'''), as determined by 1 H NMR with the chiral solvating agent Λ-(S,S)-23+ 2I- B(3,5-C6 H3 (CF3 )2 )4 - . NMR experiments show that the cyanoacetate and acetylenic esters and pyridine can hydrogen bond to certain NH groups of the catalyst. Rates are zero order in the cyanoacetate and acetylenic esters as well as the catalyst, and implications are discussed.

Λ-[Co((S,S)-dpen)3]3+ 2I-B(C6F5)4-: A Second Generation Air- and Water-Stable Chiral Solvating Agent for Chirality Sensing (dpen = NH2CHPhCHPhNH2).

When CDCl3 solutions of chiral racemic molecules containing moderately Lewis basic functional groups are treated with the chiral solvating agent (CSA) Λ-[Co((S,S)-dpen)3]3+ 2I-B(C6F5)4- (Λ-(S,S)-13+ 2I-B(C6F5)4-), baseline-resolved NMR signals are observed for the enantiomers (29 diverse analytes). Only 0.62-100 mol % loadings are required (avg 14.5 or 11.6% for 24 analytes common to all tested CSAs). The overall performance is superior to those reported earlier for analogous salts with 2X-BArf- counter anion sets [BArf = B(3,5-C6H3(CF3)2)4]; 1.0-100 mol % loadings, avg 32.6% (X = Cl) or 14.0% (X = I) for 24 common analytes) and a new 2TfO-B(C6F5)4- salt (1.1-100 mol % loadings; avg 31.0% for 24 common analytes), including extensions to prochirality sensing. The effect of the solvent (Δδ in CDCl3 > CD2Cl2) is analyzed. The new CSAs are prepared in two steps from Λ-(S,S)-13+ 3Cl- by standard anion metathesis recipes (90-98% overall). The broad analyte scope and modest loading requirements for the title CSA distinctly surpass those of others in the literature.

Potentiometric Selectivities of Ionophore-Doped Ion-Selective Membranes: Concurrent Presence of Primary Ion or Interfering Ion Complexes of Multiple Stoichiometries.

The selectivities of ionophore-doped ion-selective electrode (ISE) membranes are controlled by the stability and stoichiometry of the complexes between the ionophore, L, and the target and interfering ions (I zi and J zj, respectively). Well-accepted models predict how these selectivities can be optimized by selection of ideal ionophore-to-ionic site ratios, considering complex stoichiometries and ion charges. These models were developed for systems in which the target and interfering ions each form complexes of only one stoichiometry. However, for a few ISEs, the concurrent presence of two primary ion complexes of different stoichiometries, such as IL zi and IL2 zi, was reported. Indeed, similar systems were probably often overlooked and are, in fact, more common than the exclusive formation of complexes of higher stoichiometry unless the ionophore is used in excess. Importantly, misinterpreted stoichiometries misguide the design of new ionophores and are likely to result in the formulation of ISE membranes with inferior selectivities. We show here that the presence of two or more complexes of different stoichiometries for a given ion may be inferred experimentally from careful interpretation of the potentiometric selectivities as a function of the ionophore-to-ionic site ratio or from calculations of complex concentrations using experimentally determined complex stabilities. Concurrent formation of JL zj and JL2 zj complexes of an interfering ion is shown here to shift the ionophore-to-ionic site ratio that provides the highest selectivities. Formation of IL n-1 zi and IL n zi complexes of a primary ion is less of a concern because an optimized membrane typically contains an excess of ionophore, but lower than expected selectivities may be observed if the stepwise complex formation constant, KILn, is not sufficiently large and the ionophore-to-ionic site ratio does not markedly exceed n.

Syntheses, Structures, and Spectroscopic Properties of 1,10-Phenanthroline-Based Macrocycles Threaded by PtC8 Pt, PtC12 Pt, and PtC16 Pt Axles: Metal-Capped Rotaxanes as Insulated Molecular Wires.

The platinum polyynyl complexes trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n/2 H undergo oxidative homocoupling (O2 , CuCl/TMEDA) to diplatinum polyynediyl complexes trans, trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n Pt(Pp-tol3 )2 (C6 F5 ) (n=4, 2; 6, 5; 8, 8; 92-97 %) as reported previously. When related reactions are conducted in the presence of CuI adducts of the 1,10-phenanthroline-based macrocycles 2,9-(1,10-phenanthrolinediyl)(p-C6 H4 O(CH2 )6 O)2 (1,3-C6 H4 ) (10, 33-membered) or 2,9-(1,10-phenanthrolinediyl)(p-C6 H4 O(CH2 )6 O)2 (2,7-naphthalenediyl) (11, 35-membered), excess K2 CO3 , and I2 (oxidant), rotaxanes are isolated that feature a Pt(C≡C)n Pt axle that has been threaded through the macrocycle (2⋅10, 9 %; 5⋅10, 41 %; 5⋅11, 28 %; 8⋅10, 12 %; 8⋅11, 9 %). Their crystal structures are determined and analyzed in detail, particularly with respect to geometric perturbations and the degree of steric sp carbon chain insulation. NMR spectra show a number of shielding effects. UV/Vis spectra do not indicate significant electronic interactions between the Pt(C≡C)n Pt axles and macrocycles, although cyclic voltammetry data suggest rapid reactions following oxidation.

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.

Reactions of cis-PtCl2(P((CH2) mCH═CH2)3)2 and Grubbs' first generation catalyst and then hydrogenations afford cis- PtCl2(P((CH2) n)3 P) ( cis-2; n = 2 m + 2 = 12 (b), 14 (c), 16 (d), 18 (e), 20 (f), 22 (g); 6-40%), derived from 3-fold interligand metatheses. The phosphite complexes cis-PtCl2(P(O(CH2) m*CH═CH2)3)2 are similarly converted to cis- PtCl2(P(O(CH2) n*O)3 P) ( cis-5; n* = 8 (a), 10 (b), 12 (c), 10-20%). The substitution products cis- PtPh2(P((CH2) n)3 P) ( cis-6c,d) and cis- PtI2(P(O(CH2)10O)3 P) are prepared using Ph2Zn and NaI, respectively. Crystal structures of cis-2c,d,f, cis-5a,b, and cis-6c show one methylene bridge that roughly lies in the platinum coordination plane and two that are perpendicular. The thermal behavior of the complexes is examined. When the bridges are sufficiently long, they rapidly exchange via an unusual "triple jump rope" motion over the PtX2 moieties. NMR data establish Δ H⧧, Δ S⧧, and Δ G298K⧧/Δ G393K⧧ values of 7.8 kcal/mol, -27.9 eu, and 16.1/18.8 kcal/mol for cis-2d, and a Δ G393K⧧ of ≥19.6 kcal/mol for the shorter bridged cis-2c. While cis-2c,g gradually convert to trans-2c,g at 150-185 °C in haloarenes, trans-2c,g give little reaction under analogous conditions, establishing the stability order trans > cis. Similar metathesis/hydrogenation sequences with octahedral complexes containing two cis phosphine ligands, fac-ReX(CO)3(P((CH2)6CH═CH2)3)2 (X = Cl, Br), give fac- ReX(CO)3( P(CH2)13 CH2)((CH2)14)( P(CH2)13 CH2) (19-50%), which are derived from a combination of interligand and intraligand metathesis. The relative stabilities of cis/ trans and other types of isomers are probed by combinations of molecular dynamics and DFT calculations.

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.

Homeomorphic Isomerization as a Design Element in Container Molecules; Binding, Displacement, and Selective Transport of MCl2 Species (M = Pt, Pd, Ni).

The dibridgehead diphosphine ((CH2)14)3 P (1) can rapidly turn inside-out (homeomorphic isomerization) to give a mixture of in,in and out,out isomers. The exo directed lone pairs in the latter are able to scavenge Lewis acidic MCl2; cagelike adducts of the in,in isomer, trans- Cl2(P((CH2)14)3 P) (M = 2/Pt, 3/Pd, 4/Ni), then form. The NiCl2 unit in 4 may be replaced by PtCl2 or PdCl2, but 2 and 3 do not give similar substitutions. U-tubes are charged with CH2Cl2 solutions of 1 (lower phase), an aqueous solution of K2MCl4 (charging arm; M = Pt, Pd), and an aqueous solution of excess KCl (receiving arm). The MCl2 units are then transported to the receiving arm until equilibrium is reached (up to 22 d). When the receiving arm is charged with KCN, transport is much faster (ca. 100 h) and higher K2MX4 equilibrium ratios are obtained (≥96≤4). Analogous experiments with K2PtCl4/K2PdCl4 mixtures show PdCl2 transport to be more rapid. A similar diphosphine with longer methylene chains, P((CH2)18)3P, is equally effective. No transport occurs in the absence of 1, and other diphosphines or monophosphines assayed give only trace levels.

Octahedral Gyroscope-like Molecules Consisting of Rhenium Rotators within Cage-like Dibridgehead Diphosphine Stators: Syntheses, Substitution Reactions, Structures, and Dynamic Properties.

Reactions of Re(CO)5(X) (X = Cl, Br) or [Re2(CO)4(NO)2(µ-Cl)2(Cl)2] and the phosphines P((CH2)mCH═CH2)3 (m = 6, a; 7, b; 8, c) give mer,trans-Re(CO)3(X)(P((CH2)mCH═CH2)3)2 (53-95%) or cis,trans-Re(CO) (NO) (Cl)2(P((CH2)6CH═CH2)3)2 (57%), respectively. Additions of Grubbs' catalyst (5-10 mol %, 0.0010-0.0012 M) and subsequent hydrogenations (PtO2, ≤5 bar) yield the gyroscope-like complexes mer,trans-R e(CO)3(X)(P((CH2)n)3 P) (n = 2m + 2; X = Cl, 7a,c; Br, 8a,c; 18-61%) or cis,trans-R e(CO)(NO)(Cl)2(P((CH2)14)3 P) (14%), respectively, and/or the isomers mer,trans-R e(CO)3(X)( P(CH2)n-1 CH2)((CH2)n)( P(CH2)n-1 CH2) (X = Cl, 7'a-c; Br, 8'b; 6-27%). The latter are derived from a combination of interligand and intraligand metatheses. Reactions of 7a or 8a with NaI, Ph2Zn, or MeLi give mer,trans-R e(CO)3(X)(P((CH2)14)3 P) (X = I, 11a; Ph, 12a; Me, 13a; 34-87%). The 13C NMR spectra of 7a-c, 8a-c, 11a, and 13a show rotation of the Re(CO)3(X) moieties to be fast on the NMR time scale at room temperature (and at -90 °C for 8a). In contrast, the phenyl group in 12a acts as a brake, and two sets of 13C NMR signals (2:1) are observed for the methylene chains. The crystal structures of 7a, 8a, 12a, and 13a are analyzed with respect to Re(CO)3(X) rotation in solution and the solid state.

Syntheses of Families of Enantiopure and Diastereopure Cobalt Catalysts Derived from Trications of the Formula [Co(NH2CHArCHArNH2)3]3.

Aerobic reactions of CoX2 (X = OAc, Cl) or Co(ClO4)2 with (S,S)-1,2-diphenylethylenediamine [(S,S)-dpen] in CH3OH, followed by HCl or HClO4 additions, give the diastereomeric lipophobic salts Λ-[Co((S,S)-dpen)3]3+3Cl- [Λ-(S,S)-13+3Cl-] or Δ-(S,S)-13+3ClO4- (60-65%) with high degrees of selectivity. Anion metatheses (room temperature) and equilibrations (charcoal, CH3OH, 70 °C) show that the former is more stable than Δ-(S,S)-13+3Cl-, and the latter is more stable than Λ-(S,S)-13+3ClO4-. Additional anion metatheses lead to large families of lipophilic salts Λ- and Δ-(S,S)-13+2X-X'- [X/X' = Cl/BArf [BArf = B(3,5-C6H3(CF3)2)4], PF6/BArf, BF4/BArf, PhBF3/BArf, Cl/BArf20 [BArf20 = B(C6F5)4], BArf/BArf, BArf20/BArf20, BF4/BF4, PF6/PF6]. Mixed salts of the formula Λ- and Δ-[Co((S,S)-NH2CHArCHArNH2)3]3+2Cl-BArf- are similarly prepared (Ar = 4-C6H4n-Bu, 4-C6H4Cl, 4-C6H4CF3, 4-C6H4OCH3, α-naphthyl, ß-naphthyl, 2-C6H4OBn). The diastereotopic NHH' protons exhibit different 1H NMR signals; one shifts far downfield when X/X' = Cl/BArf (δ ca. 8.0 vs 4.0 ppm). This is believed to arise from hydrogen bonding between the two Cl- anions and the two C3 faces of the D3-symmetric trication, each of which feature three synperiplanar NH groups. When all of the anions are poor hydrogen-bond acceptors (e.g., BArf-, BF4-, ClO4-), equilibria favor Δ diastereomers.