Molecular Dihydrogen Activation by (C5Me5)M/N (M=Rh, Ir) Transition Metal Frustrated Lewis Pairs: Reversible Proton Migration to, and Proton Abstraction from, the C5Me5 Ligand.

The masked transition-metal frustrated Lewis pairs [Cp*M(κ3N,N',N''-L)][SbF6] (Cp*=η5-C5Me5; M=Ir, 1, Rh, 2; HL=pyridinyl-amidine ligand) reversibly activate H2 under mild conditions rendering the hydrido derivatives [Cp*MH(κ2N,N'-HL)][SbF6] observed as a mixture of the E and Z isomers at the amidine C=N bond (M=Ir, 3Z, 3E; M=Rh, 4Z, 4E). DFT calculations indicate that the formation of the E isomers follows a Grotthuss type mechanism in the presence of water. A mixture of Rh(I) isomers of formula [(Cp*H)Rh(κ2N,N'-HL)][SbF6] (5 a-d) is obtained by reductive elimination of Cp*H from 4. The formation of 5 a-d was elucidated by means of DFT calculations. Finally, when 2 reacts with D2, the Cp* and Cp*H ligands of the resulting rhodium complexes 4 and 5, respectively, are deuterated as a result of a reversible hydrogen abstraction from the Cp* ligand and D2 activation at rhodium.

Dynamic Configuration on a Chiral-at-Rhodium Catalyst Featuring a Flexible Tetradentate Ligand.

The unique dynamic configuration of an enantioselective chiral-at-metal catalyst based on Rh(III) and a non-chiral tetradentate ligand is described and resolved. At room temperature, the catalyst undergoes a dynamic configuration process leading to the formation of two interconvertible metal-stereoisomers, remarkably without racemization. Density functional theory (DFT) calculations indicate that this metal-isomerization proceeds via a concerted transition state, which features a trigonal bipyramidal geometry stabilized by the tetradentate ligand. Furthermore, the resolved enantiopure complex shows high catalytic enantioinduction in the Friedel-Crafts reaction, achieving enantiomeric ratios as high as 99 : 1.

Activation of H-H, HO-H, C(sp2)-H, C(sp3)-H, and RO-H Bonds by Transition-Metal Frustrated Lewis Pairs Based on M/N (M = Rh, Ir) Couples.

Reaction of the dimers [(Cp*MCl)2(µ-Cl)2] (Cp* = η5-C5Me5) with Ph2PCH2CH2NC(NH(p-Tolyl))2 (H2L) in the presence of NaSbF6 affords the chlorido complexes [Cp*MCl(κ2N,P-H2L)][SbF6] (M = Rh, 1; Ir, 2). Upon treatment with aqueous NaOH, solutions of 1 and 2 yield the corresponding complexes [Cp*M(κ3N,N',P-HL)][SbF6] (M = Rh, 3; Ir, 4) in which the ligand HL presents a fac κ3N,N',P coordination mode. Treatment of THF solutions of complexes 3 and 4 with hydrogen gas, at room temperature, results in the formation of the metal hydrido-complexes [Cp*MH(κ2N,P-H2L)][SbF6] (M = Rh, 5; Ir, 6) in which the N(p-Tolyl) group has been protonated. Complexes 3 and 4 react with deuterated water in a reversible fashion resulting in the gradual deuteration of the Cp* group. Heating at 383 K THF/H2O solutions of the complexes 3 and 4 affords the orthometalated complexes [Cp*M(κ3C,N,P-H2L-H)][SbF6] [M = Rh, 7; Ir, 8, H2L-H = Ph2PCH2CH2NC(NH(p-Tolyl))(NH(4-C6H3Me))], respectively. At 333 K, complexes 3 and 4 react in THF with methanol, primary alcohols, or 2-propanol giving the metal-hydrido complexes 5 and 6, respectively. The reaction involves the acceptorless dehydrogenation of the alcohols at a relatively low temperature, without the assistance of an external base. The new complexes have been characterized by the usual analytical and spectroscopic methods including the X-ray diffraction determination of the crystal structures of complexes 1-5, 7, and 8. Notably, the chlorido complexes 1 and 2 crystallize both as enantiopure conglomerates and as racemates. Reaction mechanisms are proposed based on stoichiometric reactions, nuclear magnetic resonance studies, and X-ray crystallography as well as density functional theory calculations.

Reversible Activation of Water by an Air- and Moisture-Stable Frustrated Rhodium Nitrogen Lewis Pair.

[Cp*Rh(κ3 N,N',P-L)][SbF6 ] (Cp*=C5 Me5 ), bearing a guanidine-derived phosphano ligand L, behaves as a "dormant" frustrated Lewis pair and activates H2 and H2 O in a reversible manner. When D2 O is employed, a facile H/D exchange at the Cp* ring takes place through sequential C(sp3 )-H bond activation.

Metal as Source of Chirality in Octahedral Complexes with Tripodal Tetradentate Ligands.

The challenging control of the absolute configuration of chiral-at-metal complexes is efficiently achieved using the tripodal tetradentate ligand L. The optical resolution of rac-[RhCl2(κ4C,N,N',P-L)] mediated by (S)-α-phenylglycine provides access to enantiopure complexes of general formula [Rh(κ4C,N,N',P-L)A(Solv)][SbF6]n that enantioselectively catalyze the Diels-Alder reaction between methacrolein and HCp with enantiomeric ratio of up to >99/1. The nature of the active species, the origin of the enantioselectivity and mechanistic details are disclosed by means of NMR spectroscopy and DFT studies.

The Stepwise Reaction of Rhodium and Iridium Complexes of Formula [MCl2 (κ4 C,N,N',P-L)] with Silver Cations: A Case of trans-Influence and Chiral Self-Recognition.

Acetonitrile suspensions of the dichlorido complexes [MCl2 (κ4 C,N,N',P-L)] [M=Rh (1), Ir (2)] react with AgSbF6 in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ4 C,N,N',P-L)(NCMe)2 ][SbF6 ]2 (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ4 C,N,N',P-L)}2 (µ-Cl)][SbF6 ] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ4 C,N,N',P-L)(Solv)][SbF6 ] (Solv=H2 O, MeCN, 7-10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ4 C,N,N',P-L)(NCMe)(µ-Cl)}2 Ag][SbF6 ]3 in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ4 C,N,N',P-L)(NCMe)]+ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh2 group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods.

Temperature Dual Enantioselective Control in a Rhodium-Catalyzed Michael-Type Friedel-Crafts Reaction: A Mechanistic Explanation.

By changing the temperature from 283 to 233 K, the S (99 % ee) or R (96 % ee) enantiomer of the Friedel-Crafts (FC) adduct of the reaction between N-methyl-2-methylindole and trans-ß-nitrostyrene can be obtained by using (SRh ,RC )-[(η(5) -C5 Me5 )Rh{(R)-Prophos}(H2 O)][SbF6 ]2 as the catalyst precursor. This catalytic system presents two other uncommon features: 1) The ee changes with reaction time showing trends that depend on the reaction temperature and 2) an increase in the catalyst loading results in a decrease in the ee of the S enantiomer. Detection and characterization of the intermediate metal-nitroalkene and metal-aci-nitro complexes, the free aci-nitro compound, and the FC adduct-complex, together with solution NMR measurements, theoretical calculations, and kinetic studies have allowed us to propose two plausible alternative catalytic cycles. On the basis of these cycles, all the above-mentioned observations can be rationalized. In particular, the reversibility of one of the cycles together with the kinetic resolution of the intermediate aci-nitro complexes account for the high ee values achieved in both antipodes. On the other hand, the results of kinetic measurements explain the unusual effect of the increment in catalyst loading.

Stereocontrol of Metal-Centred Chirality in Rhodium(III) and Ruthenium(II) Complexes with N2N'P Ligand.

Rh(III) and Ru(II) complexes, [RhCl2(κ4-N2N'P-L)][SbF6] (1) and [RuCl2(κ4-N2N'P-L)] (2), were synthesised using the tetradentate ligand L (L=N,N-bis[(pyridin-2-yl)methyl]-[2-(diphenylphosphino)phenyl]methanamine). In each case only one diastereomer is detected, featuring cis-disposed pyridine groups. The chloride ligand trans to pyridine can be selectively abstracted by AgSbF6, with the ruthenium complex (2) reacting more readily at room temperature compared to the rhodium complex (1) which requires elevated temperatures. Rhodium complexes avoid the second chloride abstraction, whereas ruthenium complexes can form the chiral bisacetonitrile complex [Ru(κ4-N2N'P-L)(NCMe)2][SbF6]2 (5) upon corresponding treatment with AgSbF6. The complex [RhCl2(κ4-N2N'P-L)][SbF6] (1) has also been used to synthesise polymetallic species, such as the tetrametallic complex [{RhCl2(κ4-N2N'P-L)}2(µ-Ag)2][SbF6]4 (6) which was formed with complete diastereoselectivity and chiral molecular self-recognition. In addition, a stable bimetallic mixed-valence complex [{Rh(κ4-N2N'P-L)}{Rh(COD)}(µ-Cl)2][SbF6]2 (7) (COD=cyclooctadiene) was synthesised. These results highlight the significant differences in chloride lability between Rh3+ and Ru2+ complexes and demonstrate the potential for complexes to act as catalyst precursors and ligands in further chemistry applications.

Molecular hydrogen and water activation by transition metal frustrated Lewis pairs containing ruthenium or osmium components: catalytic hydrogenation assays.

The transition metal frustrated Lewis pair compounds [(Cym)M(κ3S,P,N-HL1)][SbF6] (Cym = η6-p-MeC6H4iPr; H2L1 = N-(p-tolyl)-N'-(2-diphenylphosphanoethyl)thiourea; M = Ru (5), Os (6)) have been prepared from the corresponding dimer [{(Cym)MCl}2(µ-Cl)2] and H2L1 by successive chloride abstraction with NaSbF6 and AgSbF6 and NH deprotonation with NaHCO3. Complexes 5 and 6 and the previously reported phosphano-guanidino compounds [(Cym)M(κ3P,N,N'-HL2)][SbF6] [H2L2 = N,N'-bis(p-tolyl)-N''-(2-diphenylphosphanoethyl) guanidine; M = Ru (7), Os (8)] and pyridinyl-guanidino compounds [(Cym)M(κ3N,N',N''-HL3)][SbF6] [H2L3 = N,N'-bis(p-tolyl)-N''-(2-pyridinylmethyl) guanidine; M = Ru (9), Os (10)] heterolytically activate H2 in a reversible manner affording the hydrido complexes [(Cym)MH(H2L)][SbF6] (H2L = H2L1; M = Ru (11), Os (12); H2L = H2L2; M = Ru (13), Os (14); H2L = H2L3; M = Ru (15), Os (16)). DFT calculations carried out on the hydrogenation of complex 7 support an FLP mechanism for the process. Heating 9 and 10 in methanol yields the orthometalated complexes [(Cym)M(κ3N,N',C-H2L3-H)][SbF6] (M = Ru (17), Os (18)). The phosphano-guanidino complex 7 activates deuterated water in a reversible fashion, resulting in the gradual deuteration of the three cymene methyl protons through sequential C(sp3)-H bond activation. From DFT calculations, a metal-ligand cooperative reversible mechanism that involves the O-H bond activation and the formation of an intermediate methylene cyclohexenyl complex has been proposed. Complexes 5-10 catalyse the hydrogenation of the CC double bond of styrene and a range of acrylates, the CO bond of acetophenone and the CN bond of N-benzylideneaniline and quinoline. The CC double bond of methyl acrylate adds to catalyst 9, affording complex 19 in which a new ligand exhibiting a fac κ3N,N',C coordination mode has been incorporated.

Reduced IL-8 Secretion by NOD-like and Toll-like Receptors in Blood Cells from COVID-19 Patients.

Severe inflammatory responses are associated with the misbalance of innate and adaptive immunity. TLRs, NLRs, and cytokine receptors play an important role in pathogen sensing and intracellular control, which remains unclear in COVID-19. This study aimed to evaluate IL-8 production in blood cells from COVID-19 patients in a two-week follow-up evaluation. Blood samples were taken at admission (t1) and after 14 days of hospitalization (t2). The functionality of TLR2, TLR4, TLR7/8, TLR9, NOD1, and NOD2 innate receptors and IL-12 and IFN-γ cytokine receptors was evaluated by whole blood stimulation with specific synthetic receptor agonists through the quantification of IL-8, TNF-α, or IFN-γ. At admission, ligand-dependent IL-8 secretion was 6.4, 13, and 2.5 times lower for TLR2, TLR4, and endosomal TLR7/8 receptors, respectively, in patients than in healthy controls. Additionally, IL-12 receptor-induced IFN-γ secretion was lower in COVID-19 patients than in healthy subjects. We evaluated the same parameters after 14 days and observed significantly higher responses for TLR2, TLR4, TLR7/8, TLR9, and NOD1, NOD2, and IFN-γ receptors. In conclusion, the low secretion of IL-8 through stimulation with agonists of TLR2, TLR4, TLR7/8, TLR9, and NOD2 at t1 suggests their possible contribution to immunosuppression following hyperinflammation in COVID-19 disease.

Synthesis of chiral-at-metal rhodium complexes from achiral tripodal tetradentate ligands: resolution and application to enantioselective Diels-Alder and 1,3-dipolar cycloadditions.

An improved synthesis of the racemic rhodium compound [RhCl2(κ4 C,N,N',P-L1)] (1) containing an achiral tripodal tetradentate ligand is reported. Their derived solvate complexes [Rh(κ4 C,N,N',P-L1)(Solv)2][SbF6]2 (Solv = NCMe, 2; H2O, 3) are resolved into their two enantiomers. Complexes 2 and 3 catalyze the Diels-Alder (DA) reaction between methacrolein and cyclopentadiene and the 1,3-dipolar cycloaddition reaction between methacrolein and the nitrone N-benzylidenphenylamine-N-oxide. When enantiopure (A Rh,R N)-2 was employed as the catalyst, enantiomeric ratios >99/1, in the R at C2 adduct, and up to 94/6, in the 3,5-endo isomer, were achieved in the DA reaction and in the 1,3-dipolar cycloaddition reaction, respectively. A plausible catalytic cycle that accounts for the origin of the observed enantioselectivity is proposed.

Catalytic Enantioselective Alkylation of Indoles with trans-4-Methylthio-ß-Nitrostyrene.

The reaction of the rhodium aqua-complex (S Rh,R C)-[Cp*Rh{(R)-Prophos} (OH2)][SbF6]2 [Cp* = C5Me5, Prophos = propane-1,2-diyl-bis(diphenylphosphane)] (1) with trans-4-methylthio-ß-nitrostyrene (MTNS) gives two linkage isomers (S Rh,R C)-[Cp*Rh{(R)-Prophos}(κ1 O-MTNS)]2+ (3-O) and (S Rh,R C)-[Cp*Rh{(R)-Prophos}(κ1 S-MTNS)]2+ (3-S) in which the nitrostyrene binds the metal through one of the oxygen atoms of the nitro group or through the sulfur atom, respectively. Both isomers are in equilibrium in dichloromethane solution, the equilibrium constant being affected by the temperature in such a way that when the temperature increases, the relative concentration of the oxygen-bonded isomer 3-O increases. The homologue aqua-complex of iridium, (S Ir,R C)-[Cp*Ir{(R)-Prophos}(OH2)][SbF6]2 (2), also reacts with MTNS; but only the sulfur-coordinated isomer (S Ir,R C)-[Cp*Ir{(R)-Prophos}(κ1 S-MTNS)]2+ (4-S) is detected in the solution by NMR spectroscopy. The crystal structures of 3-S and 4-S have been elucidated by X-ray diffractometric methods. Complexes 1 and 2 catalyze the Friedel-Crafts reaction of indole, N-methylindole, 2-methylindole, or N-methyl-2-methylindole with MTNS. Up to 93% ee has been achieved for N-methyl-2-methylindole. With this indole, the ee increases as conversion increases, ee at 263 K is lower than that obtained at 298 K, and the sign of the chirality of the major enantiomer changes at temperatures below 263 K. Detection and characterization of the catalytic intermediates metal-aci-nitro and the free aci-nitro compound as well as detection of the Friedel-Crafts (FC)-adduct complex involved in the catalysis allowed us to propose a plausible double cycle that accounts for the catalytic observations.

Half-sandwich complexes of osmium containing guanidine-derived ligands.

Pyridinyl- and phosphano-guanidino complexes of formula [(η6-p-cymene)OsCl(H2L)][SbF6] (cymene = MeC6H4iPr; H2L = N,N'-bis(p-Tolyl)-N''-(2-pyridinylmethyl)guanidine, H2L1 (1) and N,N'-bis(p-Tolyl)-N''-(2-diphenylphosphanoethyl)guanidine, H2L2 (2)) have been prepared from the dimer [{(η6-p-cymene)OsCl}2(µ-Cl)2] and H2L in the presence of NaSbF6. Treatment of complex 2 with HCl renders the phosphano-guanidinium complex [(η6-p-cymene)OsCl2(H3L2)][SbF6] (3). Compounds 1 and 2 react with AgSbF6 rendering the cationic aqua complexes [(η6-p-cymene)Os(H2L)(OH2)][SbF6]2 (H2L = H2L1 (4), H2L2 (5)). Addition of monodentate ligands L to compound 4 affords complexes of formula [(η6-p-cymene)Os(H2L1)L][SbF6]2 (L = py (6), 4-(NHMe)py (7), CO (8), P(OMe)3 (9)). Treatment of complexes 4 and 5 with NaHCO3 renders the monocationic complexes [(η6-p-cymene)Os(κ3N,N',N''-HL1)][SbF6] (10) and [(η6-p-cymene)Os(κ3N,N',P-HL2)][SbF6] (11), respectively, in which the HL ligand adopts a fac-κ3 coordination mode. The new complexes have been characterised by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1-4, 6, 8, and 11, by X-ray diffractometric methods. The phosphano-guanidino complexes 2 and 5 exhibit a temperature dependent fluxional process in solution. The new 18 electron complexes 1, 2, 6, and 8-10 are active catalysts for the Friedel-Crafts reaction between trans-ß-nitrostyrene and N-methyl-2-methylindole. Conversions greater than 90% were obtained. Proton NMR studies support a mechanism involving the Brønsted-acid activation of trans-ß-nitrostyrene through the NH functionalities of the coordinated guanidine ligands.

Anchoring of Iron Oxyhydroxide Clusters at H and L Ferritin Subunits.

Ferritin (Fn) proteins or their isolated subunits can be used as biomolecular templates for the selectively heterogeneous nucleation and growth of nanoparticles, in particular of iron oxyhydroxides. To shed light on the atomistic mechanisms of ferritin-promoted mineralization, in this study we perform molecular dynamics simulations to investigate the anchoring sites for Fe(III) clusters on Fn subunit assemblies using models of goethite and ferrihydrite nanoparticles. For this aim, we develop and parametrize a classical force field for Fe(III) oxyhydroxides based on reference density functional theory calculations. We then reveal that stable Fn-nanoparticle contacts are formed not only via negatively charged amino acid residues (glutamic and aspartic acid) but also, in a similar amount, via positively charged (lysine and arginine) and neutral (histidine) residues. A large majority of the anchoring sites are situated at the inner side of protein cages, consistent with the natural iron storage function of ferritin in many organisms. A slightly different distribution of anchoring sites is observed on heavy (H) and light (L) Fn subunits, with the former offering a larger amount of negative and neutral sites than the latter. This finding is exploited to develop a Fn mineralization protocol in which immobilized Fn subunits are first loaded with Fe2+ ions in a long "activation" step before starting their oxidation to Fe3+. This leads to the formation of very dense and uniform iron oxide films, especially when H subunits are employed.

Stereospecific control of the metal-centred chirality of rhodium(iii) and iridium(iii) complexes bearing tetradentate CNN'P ligands.

Ligands LH1-LH3 have been prepared by two successive condensation/reduction steps. These ligands react with MCl3 (M = Rh, Ir) rendering the trichlorido complexes [MCl3(κ3N,N',P-LH)] (M = Rh, LH = LH1 (1), LH2 (2), LH3 (3); M = Ir, LH = LH1, (4)) as racemic mixtures of fac and mer isomers. Only one of the two possible fac isomers was detected. The mer isomer of the rhodium compounds 1-3 quantitatively isomerizes to the more stable fac isomer, whereas the mer isomer of the iridium complex 4 does not. DFT calculations indicate a dissociative pathway for this isomerization. In the presence of acetate or trifluoroacetate, complexes 1-3 or 4, respectively, undergo cyclometallation of their free benzylic arm affording the corresponding dichlorido compounds [MCl2(κ4C,N,N',P-L)] (M = Rh, L = L1 (5), L2 (6), L3 (7); M = Ir, L = L1 (8)). Only one of the three possible enantiomeric pairs of coordination isomers was detected. The configuration at the stereogenic centres, namely the metal and the iminic nitrogen atom is stereospecifically predetermined. DFT calculations reveal that the cyclometallation follows an acetate-assisted mechanism and indicate that the isolated isomers are the most stable. Complexes 1-8 have been characterized by analytical and spectroscopic means and by the determination of the crystal structures of the complexes 1, 3 and 5-8 by X-ray diffractometry.

Half-sandwich complexes of iridium and ruthenium containing cysteine-derived ligands.

The dimers [{(ηn-ring)MCl}2(µ-Cl)2] ((ηn-ring)M = (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru) react with the modified cysteines S-benzyl-l-cysteine (HL1) or S-benzyl-α-methyl-l-cysteine (HL2) affording cationic complexes of the formula [(ηn-ring)MCl(κ2N,S-HL)]Cl (1, 2) in good yield. Addition of NaHCO3 to complexes 1 and 2 gave equilibrium mixtures of neutral [(ηn-ring)MCl(κ2N,O-L)] (3, 4) and cationic [(ηn-ring)M(κ3N,O,S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO3 to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-l-cysteine (HL3) and NaHCO3 to the dimers [{(ηn-ring)MCl}2(µ-Cl)2] affords the neutral compounds [(ηn-ring)MCl(κ2O,S-L3)] ((ηn-ring)M = (η5-C5Me5)Ir (5a), (η6-p-MeC6H4iPr)Ru (5b)). Complexes of the formula [(ηn-ring)MCl(κ3N,O,S-L)][SbF6] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF6 to the solutions of compounds 5 or to the mixtures of complexes 3/6Cl and 4/7Cl. The amide proton of compounds 8aSb and 8bSb can be removed by addition of NaHCO3 affording the neutral complexes [(ηn-ring)M(κ3N,O,S-L3-H)] ((ηn-ring)M = (η5-C5Me5)Ir (9a), (η6-p-MeC6H4iPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers [{(ηn-ring)MCl}2(µ-Cl)2] with HL3 and two equivalents of NaHCO3. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (RIr,RC,RS)-[(η5-C5Me5)Ir(κ3N,O,S-L1)][SbF6] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound [(η5-C5Me5)Ir(κ3N,O,S-L3-H)] (9a) undergoes have been determined through variable temperature 1H NMR studies.

Half-sandwich complexes of Ir(iii), Rh(iii) and Ru(ii) with the MaxPhos ligand: metal centred chirality and cyclometallation.

The reaction of the acetylacetonates [(η5-C5Me5)M(acac)Cl] with (SP)-[HMaxPhos][BF4] afforded cationic complexes with the formula (SM,RP)-[(η5-C5Me5)MCl(MaxPhos)][BF4] (M = Rh (1), Ir (2)). The reaction of (SP)-MaxPhos with [RuCl(µ-Cl)(η6-p-MeC6H4iPr)]2 and NH4X afforded (SRu,RP)-[(η6-p-MeC6H4iPr)RuCl(MaxPhos)][X] (X = BF4 (3), PF6 (3')). The complexes have been completely characterized by analytical and spectroscopic means, including the determination of the crystal structures of 1, 2 and 3'. Treatment of the iridium complex 2 with AgBF4, at 253 K, resulted in the intramolecular cyclometallation of one of the tert-butyl substituents of the MaxPhos diphosphane ligand, affording a mixture of isomers of (SIr,RP1,SP2 and RIr,RP1,RP2)-[(η5-C5Me5)Ir(MaxPhos)][BF4] (4a and 4b). However, rhodium complex 1 and ruthenium complex 3 reacted with AgBF4 forming the expected unsaturated intermediates "(ηn-ring)M(MaxPhos)" which were trapped by MeCN, affording the cationic adducts (SM,RP)-[(ηn-ring)M(MaxPhos)(MeCN)][BF4]2 (M = Rh (5), Ru (6)). Only one epimer at the metal was isolated in high yield for the complexes 1, 2, 3, 3', 5 and 6 and the metallation of 2 to give 4 occurs with high diastereoselectivity.

Half-sandwich complexes of rhodium containing cysteine-derived ligands.

The modified cysteine ligand, S-benzyl-α-methyl-l-cysteine (HL2), was prepared from l-cysteine hydrochloride methyl ester. The reaction of commercial S-benzyl-l-cysteine (HL1) or HL2 with the dimer, [{(η(5)-C5Me5)RhCl}2(µ-Cl)2], gives rise to the cationic complexes, [(η(5)-C5Me5)RhCl(HL)]Cl (HL = HL1 (1), HL2 (2)), in which the cysteine ligand exhibits a κ(2)N,S coordination mode. In a basic medium, HL1 or HL2 reacts with [{(η(5)-C5Me5)RhCl}2(µ-Cl)2] to afford mixtures of two epimers at the metal centre of the neutral complexes, [(η(5)-C5Me5)RhCl(κ(2)N,O-L)] (HL = HL1 (3), HL2 (4)), in which amino carboxylate adopts a κ(2)N,O mode of coordination along with variable amounts of the cationic compounds, [(η(5)-C5Me5)Rh(κ(3)N,O,S-L)]Cl (HL = HL1 (6Cl), HL2 (7Cl)), which contain κ(3)N,O,S coordinated cysteine-derived ligands. However, in a basic medium, the N-Boc substituted cysteine S-benzyl-N-Boc-l-cysteine (HL3) only yields the κ(2)O,S coordinated derivative, [(η(5)-C5Me5)RhCl(κ(2)O,S-L3)] (5), as a mixture of two diastereomers depending on the configuration of the metal centre. The bidentate chelate complexes 3-5 react with AgSbF6 to give the hexafluoroantimonates [(η(5)-C5Me5)Rh(κ(3)N,O,S-L)][SbF6] (HL = HL1 (6Sb), HL2 (7Sb), HL3 (8Sb)) with tridentate coordination. Compound 8Sb reacts with NaHCO3 to give the neutral complex [(η(5)-C5Me5)Rh(κ(3)N,O,S-L3-H)] (9), which can also be prepared by reacting the dimer [{(η(5)-C5Me5)RhCl}2(µ-Cl)2] with HL3 in the presence of two equivalents of NaHCO3. The new compounds contain up to four stereogenic centres, namely, Rh, S, N, and C. The absolute configuration of the complexes has been established by spectroscopic and diffractometric investigations, including the crystal structure determination of [(η(5)-C5Me5)RhCl(κ(2)O,S-L3)] (5), [(η(5)-C5Me5)Rh(κ(3)N,O,S-L1)][SbF6] (6Sb), [(η(5)-C5Me5)Rh(κ(3)N,O,S-L2)][SbF6] (7Sb) and [(η(5)-C5Me5)Rh(κ(3)N,O,S-L3-H)] (9). Variable temperature (1)H NMR studies reveal the existence of epimerization processes and theoretical calculations were used to discriminate their nature.

Diastereoselective formation of chiral iridium hydrides containing the chiral P,N-chelate ligand (4S)-2-(2-(diphenylphosphino)phenyl)-4-isopropyl-1,3-oxazoline.

The iridium complex [Ir(mu-Cl)(PN)(PPh3)]2 (1) reacts with H2 affording only the kinetic isomer OC-6-55-C of the dihydride [IrClH2(PN)(PPh3)] (2) and with methanol yielding, also exclusively, the thermodynamic isomer OC-6-53-C (2b) of the same dihydride; complex 2b has been characterised by X-ray diffractometric methods.

Synthesis and Characterization of Heterodinuclear IrCo, RuCo, IrNi, and RuNi Complexes Containing Pyrazolate and Pyrazolylborate Ligands.

Treatment of the metallo ligands [ML(pz)(2)(Hpz)] (pz = pyrazolate; L = C(5)Me(5), M = Ir (1); L = mesitylene, M = Ru (3)) with [M'Cl{HB(3-i-Pr-4-Br-pz)(3)}] (M' = Co (4), Ni (5)) yields heterodinuclear complexes of formula [LM(&mgr;-pz)(2)(&mgr;-Cl)M'{HB(3-i-Pr-4-Br-pz)(3)}] (L = C(5)Me(5); M = Ir; M' = Co (6), Ni (7). L = mesitylene; M = Ru; M' = Co (8)). The related complex [Ru(eta(6)-p-cymene)(pz)(2)(Hpz)] (2) reacts with equimolar amounts of 4 or 5 to give mixtures of the corresponding bis(&mgr;-pyrazolato) &mgr;-chloro complexes [(eta(6)-p-cymene)Ru(&mgr;-pz)(2)(&mgr;-Cl)M'{HB(3-i-Pr-4-Br-pz)(3)}] (M' = Co (9), Ni (10)) and the triply pyrazolato-bridged complexes [(eta(6)-p-cymene)Ru(&mgr;-pz)(3)M'{HB(3-i-Pr-4-Br-pz)(3)}] (M' = Co (11), Ni (12)). Complex 1 reacts with 5 in the presence of KOH to give the IrNi complex [(eta(5)-C(5)Me(5))Ir(&mgr;-pz)(3)Ni{HB(3-i-Pr-4-Br-pz)(3)}] (13) whereas its reaction with 4 and KOH rendered the bis(&mgr;-pyrazolato) &mgr;-hydroxo complex [(eta(5)-C(5)Me(5))Ir(&mgr;-pz)(2)(&mgr;-OH)Co{HB(3-i-Pr-4-Br-pz)(3)}] (14). The molecular structure of the heterobridged IrCo complex (6) and those of the homobridged RuNi (12) and IrNi (13) complexes have been determined by X-ray analyses. Compound 6 crystallizes in the monoclinic space group P2(1)/n, with a = 10.146(5) Å, b = 18.435(4) Å, c = 22.187(13) Å, beta = 97.28(4) degrees, and Z = 4. Complex 12 is monoclinic, space group P2(1), with a = 10.1169(7) Å, b = 21.692(2) Å, c = 11.419(1) Å, beta = 112.179(7) degrees, and Z = 2. Compound 13 crystallizes in the monoclinic space group Cc, with a = 13.695(2) Å, b = 27.929(6) Å, c = 13.329(2) Å, beta = 94.11(4) degrees, and Z = 4. All the neutral complexes 6, 12, and 13 consist of linear M.M'.B backbones with two (6) or three (12, 13) pyrazolate ligands bridging the dimetallic M.M' units and three substituted 3-i-Pr-4-Br-pz groups joining M' to the boron atoms. The presence in the proximity of the first-row metal M' of the three space-demanding isopropyl substituents of the pyrazolate groups induces a significant trigonal distortion of the octahedral symmetry, yielding clearly different M'-N bond distances on both sides of the ideal octahedral coordination sphere of these metals.