Uptake, Trapping, and Release of Organometallic Cations in Redox-Active Cationic Hosts

The host-guest chemistry of metal-organic nanocages is typically driven by thermodynamically favorable interactions with their guests, such that uptake and release of guests can be controlled by switching affinity on/off. Herein, we achieve this effect by reducing porphyrin-walled cationic nanoprisms <b>1a¹²⁺</b> and <b>1b¹²⁺</b> to zwitterionic states that rapidly uptake organometallic cations Cp*₂Co⁺ or Cp₂Co⁺. Cp*₂Co⁺ binds strongly (<i>K</i>_a = 1.3 x 10³ M⁻¹) in the neutral state <b>1a⁰</b> of host <b>1a¹²⁺</b>, which has its three porphyrin walls doubly reduced and its six (bipy)Pt²⁺ linkers singly reduced. The less-reduced states of the host <b>1a³⁺</b> and <b>1a⁹⁺</b> also bind Cp*₂Co⁺, though with lower affinities. The smaller Cp₂Co⁺ cation binds strongly (<i>K</i>_a = 1.7 x 10³ M^-1) in the 3 e⁻ reduced state <b>1b⁹⁺</b> of (tmeda)Pt²⁺ linked host <b>1b¹²⁺</b>. Upon reoxidation of the hosts with Ag⁺, the guests become trapped to provide unprecedented metastable cation-in-cation complexes <b>Cp*₂Co⁺@1a¹²⁺ </b>and <b>Cp₂Co⁺@1b¹²⁺</b> that persist for >1 month. Thus, dramatic kinetic effects reveal a way to confine the guests in thermodynamically unfavorable environments. Experimental and DFT studies indicate that PF₆⁻ anions kinetically stabilize <b>Cp*₂Co⁺@1a¹²⁺ </b>through electrostatic interactions and by influencing conformational changes of the host that open and close its apertures. However, when <b>Cp*₂Co⁺@1a¹²⁺ </b>was prepared using ferrocenium (Fc⁺) instead of Ag⁺ to reoxidize the host, dissociation was accelerated >200-fold even though neither Fc⁺ nor Fc have any competing affinity for <b>1a¹²⁺</b>. This finding shows that metastable host-guest complexes can respond to subtler stimuli than are required to induce guest release from thermodynamically favorable complexes.

Uptake, Trapping, and Release of Organometallic Cations in Redox-Active Cationic Hosts

The host-guest chemistry of metal-organic nanocages is typically driven by thermodynamically favorable interactions with their guests, such that uptake and release of guests can be controlled by switching affinity on/off. Herein, we achieve this effect by reducing porphyrin-walled cationic nanoprisms <b>1a¹²⁺</b> and <b>1b¹²⁺</b> to zwitterionic states that rapidly uptake organometallic cations Cp*₂Co⁺ or Cp₂Co⁺. Cp*₂Co⁺ binds strongly (<i>K</i>_a = 1.3 x 10³ M⁻¹) in the neutral state <b>1a⁰</b> of host <b>1a¹²⁺</b>, which has its three porphyrin walls doubly reduced and its six (bipy)Pt²⁺ linkers singly reduced. The less-reduced states of the host <b>1a³⁺</b> and <b>1a⁹⁺</b> also bind Cp*₂Co⁺, though with lower affinities. The smaller Cp₂Co⁺ cation binds strongly (<i>K</i>_a = 1.7 x 10³ M^-1) in the 3 e⁻ reduced state <b>1b⁹⁺</b> of (tmeda)Pt²⁺ linked host <b>1b¹²⁺</b>. Upon reoxidation of the hosts with Ag⁺, the guests become trapped to provide unprecedented metastable cation-in-cation complexes <b>Cp*₂Co⁺@1a¹²⁺ </b>and <b>Cp₂Co⁺@1b¹²⁺</b> that persist for >1 month. Thus, dramatic kinetic effects reveal a way to confine the guests in thermodynamically unfavorable environments. Experimental and DFT studies indicate that PF₆⁻ anions kinetically stabilize <b>Cp*₂Co⁺@1a¹²⁺ </b>through electrostatic interactions and by influencing conformational changes of the host that open and close its apertures. However, when <b>Cp*₂Co⁺@1a¹²⁺ </b>was prepared using ferrocenium (Fc⁺) instead of Ag⁺ to reoxidize the host, dissociation was accelerated >200-fold even though neither Fc⁺ nor Fc have any competing affinity for <b>1a¹²⁺</b>. This finding shows that metastable host-guest complexes can respond to subtler stimuli than are required to induce guest release from thermodynamically favorable complexes.

Synthesis and characterization of group 13 dichloride (M = Ga, In), dimethyl (M = Al) and cationic methyl aluminum complexes supported by monoanionic NNN-pincer ligands

A series of monoanionic NNN-pincer ligands effectively stabilize five-coordinate gallium and indium dichloride complexes, as well as neutral dimethyl aluminum species, and organometallic cations thereof.

An 8-hydroxyquinoline–proline hybrid with multidrug resistance reversal activity and the solution chemistry of its half-sandwich organometallic Ru and Rh complexes

Synthesis and characterization of an 8-hydroxyquinoline–proline hybrid, and its complex formation with half-sandwich organometallic cations: aqueous chemistry, lipophilicity, cellular uptake and anticancer activity.

Gas-Phase Reactions of the Group 10 Organometallic Cations, [(phen)M(CH3)]+ with Acetone: Only Platinum Promotes a Catalytic Cycle via the Enolate [(phen)Pt(OC(CH2)CH3)]+

Electrospray ionisation of the ligated group 10 metal complexes [(phen)M(O2CCH3)2] (M = Ni, Pd, Pt) generates the cations [(phen)M(O2CCH3)]+, whose gas-phase chemistry was studied using multistage mass spectrometry experiments in an ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reactions (IMR). A new catalytic cycle has been discovered. In step 1, decarboxylation of [(phen)M(O2CCH3)]+ under CID conditions generates the organometallic cations [(phen)M(CH3)]+, which react with acetone to generate the [(phen)M(CH3)(OC(CH3)2)]+ adducts in competition with formation of the coordinated enolate for M = Pt (step 2). For M = Ni and Pd, the adducts regenerate [(phen)M(CH3)]+ upon CID. In the case of M = Pt, loss of methane is favored over loss of acetone and results in the formation of the enolate complex, [(phen)Pt(OC(CH2)CH3)]+. Upon further CID, both methane and CO loss can be observed resulting in the formation of the ketenyl and ethyl complexes [(phen)Pt(OCCH)]+ and [(phen)Pt(CH2CH3)]+ (step 3), respectively. In step 4, CID of [(phen)Pt(CH2CH3)]+ results in a beta-hydride elimination reaction to yield the hydride complex, [(phen)Pt(H)]+, which reacts with acetic acid to regenerate the acetate complex [(phen)Pt(O2CCH3)]+ and H2 in step 5. Thus, the catalytic cycle is formally closed, which corresponds to the decomposition of acetone and acetic acid into methane, CO, CO2, ethene and H2. All except the last step of the catalytic cycle are modelled using DFT calculations with optimizations of structures at the M06/SDD 6-31G(d) level of theory.

Intermolecular hydrogen bonding H···Cl in crystal structure of palladium(II)-bis(diaminocarbene) complex

The reaction of bis(isocyanide)palladium complex cis-[PdCl2(CNXyl)2] (Xyl=2,6-Me2C6H3) with excess of 4,5-dichlorobenzene-1,2-amine in a C2H4Cl2/MeOH mixture affords monocationic bis(diaminocarbene) complex cis-[PdClC{(NHXyl)=NHC6H2Cl2NH2}{C(NHXyl)=NHC6H2Cl2NH2}]Cl (3) in moderate yield (42%). Complex 3 exists in the solid phase in the H-bonded dimeric associate of two single charged organometallic cations and two chloride anions according to X-ray diffraction data. The Hirshfeld surface analysis for the X-ray structure of 3 reveals that the crystal packing is determined primarily by intermolecular contacts H–Cl, H–H, and H–C. The intermolecular hydrogen bonds N–H···Cl and C–H···Cl in the H-bonded dimeric associate of 3 were studied by DFT calculations and topological analysis of the electron density distribution within the framework of QTAIM method, and estimated energies of these supramolecular contacts vary from 1.6 to 9.1 kcal/mol. Such non-covalent bonding means that complex 3 is an anionic receptor for the chloride anions.

Formation and reactions of the 1, 8-naphthyridine (napy) ligated geminally dimetallated phenyl complexes [(napy)Cu2(Ph)]+, [(napy)Ag2(Ph)]+ and [(napy)CuAg(Ph)]+

Gas-phase ion trap mass spectrometry experiments and density functional theory calculations have been used to examine the routes to the formation of the 1,8-naphthyridine (napy) ligated geminally dimetallated phenyl complexes [(napy)Cu2(Ph)]+, [(napy)Ag2(Ph)]+ and [(napy)CuAg(Ph)]+ via extrusion of CO2 or SO2 under collision-induced dissociation conditions from their corresponding precursor complexes [(napy)Cu2(O2CPh)]+, [(napy)Ag2(O2CPh)]+, [(napy)CuAg(O2CPh)]+ and [(napy)Cu2(O2SPh)]+, [(napy)Ag2(O2SPh)]+, [(napy)CuAg(O2SPh)]+. Desulfination was found to be more facile than decarboxylation. Density functional theory calculations reveal that extrusion proceeds via two transition states: TS1 enables isomerization of the O, O-bridged benzoate to its O-bound form; TS2 involves extrusion of CO2 or SO2 with the concomitant formation of the organometallic cation and has the highest barrier. Of all the organometallic cations, only [(napy)Cu2(Ph)]+ reacts with water via hydrolysis to give [(napy)Cu2(OH)]+, consistent with density functional theory calculations which show that hydrolysis proceeds via the initial formation of the adduct [(napy)Cu2(Ph)(H2O)]+ which then proceeds via TS3 in which the coordinated H2O is deprotonated by the coordinated phenyl anion to give the product complex [(napy)Cu2(OH)(C6H6)]+, which then loses benzene.

Cation templated improved synthesis of pillar[6]arenes

Improved high yield syntheses of the larger pillar[6]arenes (P[6]) bearing different alkoxy substituents through cation templated syntheses using a series of small organic and organometallic cations is reported.