Ricardo Hernández

Reaction of [RhCl(CO)2]2 or [RhCl(COD)]2 with o-(diphenylphosphino)benzaldehyde. Formation of hemiaminals in the subsequent reaction with dihydrazones

Abstract [RhCl(CO) 2 ] 2 reacts with o -(diphenylphosphino)benzaldehyde (PCHO) to afford a monocarbonylated rhodium(I) complex containing P-monodentate PCHO, trans -[RhCl(CO)(PCHO) 2 ] ( 1 ) while [RhCl(COD)] 2 undergoes the oxidative addition of one PCHO, with displacement of 1,5-cyclooctadiene, and coordination of the second PCHO molecule as P-(σ-aldehyde) chelate to give [RhH(PCO)Cl(PCHO)] ( 2 ) which contains trans P-atoms. Compound 2 reacts with H 2 NNCHCHNNH 2 (gdh) to give selectively a complex [RhH(PCO)(Pgdh)] + containing a stable hemiaminal in a new tridentate ligand, Pgdh, coordinated via the imino nitrogens and the phosphorus and the atom. The reaction of Rh(COD)(gdh)Cl with PCHO gives a mixture of the hemiaminal containing compound and the hydroxyalkyl complex [Rh(PCO)(PCHOH)(gdh)] + which contains trans P-atoms and is formed from precursors containing cis P-atoms. The transformation of the hemiaminal group in [RhH(PCO)(PNN)] + (PNN=Pgdh or Ppvdh (pvdh, H 2 NNCHC(CH 3 )NNH 2 )) into imine to give new tridentate PaNN ligands in complexes [RhH(PCO)(PaNN)] + has also been studied.

Redox-Robust Pentamethylferrocene Polymers and Supramolecular Polymers, and Controlled Self-Assembly of Pentamethylferricenium Polymer-Embedded Ag, AgI, and Au Nanoparticles.

We report the first pentamethylferrocene (PMF) polymers and the redox chemistry of their robust polycationic pentamethylferricenium (PMFium) analogues. The PMF polymers were synthesized by ring-opening metathesis polymerization (ROMP) of a PMF-containing norbornene derivative by using the third-generation Grubbs ruthenium metathesis catalyst. Cyclic voltammetry studies allowed us to determine confidently the number of monomer units in the polymers through the Bard-Anson method. Stoichiometric oxidation by using ferricenium hexafluorophosphate quantitatively and instantaneously provided fully stable (even in aerobic solutions) blue d(5) Fe(III) metallopolymers. Alternatively, oxidation of the PMF-containing polymers was conducted by reactions with Ag(I) or Au(III) , to give PMFium polymer-embedded Ag and Au nanoparticles (NPs). In the presence of I2 , oxidation by using Ag(I) gave polymer-embedded Ag/AgI NPs and AgNPs at the surface of AgI NPs. Oxidation by using Au(III) also produced an Au(I) intermediate that was trapped and characterized. Engineered single-electron transfer reactions of these redox-robust nanomaterial precursors appear to be a new way to control their formation, size, and environment in a supramolecular way.

Living ROMP Synthesis and Redox Properties of Diblock Ferrocene/Cobalticenium Copolymers.

Using the third-generation Grubbs catalyst, the living ring-opening metathesis polymerization of ferrocene/cobalticenium copolymers is conducted with theoretical numbers of 25 monomer units for each block, and their redox and electrochemical properties allow using the Bard-Anson electrochemical method to determine the number of metallocenyl units in each block.

Rhodium(I) complexes with 2-(aminoalkyl)pyridines or 2-(2-aminomethyl)-1-methylpyrrol. Crsytal structure of RhCl(C8H12)(C7N2H12) and [Rh(C8H12)(C7N2H10)][Rh(C8H12)Cl2]

Abstract [Rh(L 2 )Cl] 2 (L 2 = COD, NBD; L = CO) complexes react with 2-(2-aminoethyl)-1-methylpyrrol to give only neutral tetracoordinated RhCl(L 2 )(aempyr) species, irrespective of the stoichiometric rations employed. In solution, dynamic behaviour through pentacoordinated compounds is observed. The X-ray structure of RhCl(COD)(C 7 N 2 H 12 ) indicates coordination through the primary amino group. Aminopyridines such as 2-(2-aminoethyl)pyridine or 2-(aminomethyl)pyridine afford, from the 1:2 reaction pentacoordinated RhCl(L 2 )(LL′) compounds or ionic [Rh(L 2 )(LL′)] + species. The cationic species show association processes in solution. From the 1:1 reaction Rh 2 (L 2 )Cl 2 (LL′) complexes are obtained. When LL′ = 2-(2-aminoethyl)pyridine the X-ray diffraction indicates an ionic structure [Rh(C 8 H 12 )(C 7 H 2 H 10 )[Rh(C 8 H 12 )Cl 2 ] in the solid state. In solution, evidence of an equilibrium between this species and the corresponding dimer [Rh(C 8 H 12 )Cl] 2 (μ-C 7 N 2 H 10 ) is observed.

Rhodium(I) complexes with diimines. 1H and 119Sn NMR study of the trichlorostannato compounds

Abstract Reactions of [RhL 2 Cl] 2 (L 2 COD or NBD, LCO) with α-diimines, RN:C(CH 3 )C(CH 3 ):NR′(LL); RR′NH 2 (bdh); RNH 2 , R′OH (boh); RR′N(CH 3 ) 2 (bdnh) or RR′C 6 H 5 (bda) or with 2,2′-biquinoline (biqui) and SnCl 2 afford trichlorostannato complexes. Rh(SnCl 3 )(NBD)(LL) compounds are neutral and according to their 1 H and 119 Sn NMR spectra undergo tin halide dissociation and intramolecular rearrangements. Rh(SnCl 3 )(COD)(LL) are ionic or neutral and also undergo SnCl 3 − or SnCl 2 dissociation. In the absence of SnCl 2 , [RhL 2 Cl] 2 dimers react with α-diimines to give fluxional pentacoordinated [Rh(Cl)L 2 (LL)] complexes (L 2 COD or NBD) irrespective of the stoichiometric ratios employed, or ion-pair [RhL 2 (LL)] + [RhL 2 Cl 2 ] − compounds (LCO).

Rhodium(I) complexes with unsymmetric aliphatic diamines. Crystal structure of [Rh(C8H12)(C7N2H16)][RhCl2(C8H12)] and [Rh(C8H12)(C7N2H16)]ClO4

Abstract Reactions of [Rh(COD)Cl]2 with unsymmetric aliphatic diamines (LL′) have been studied. The 1:1 ligand:dimer reactions yield ionic products [Rh(C8H12)(LL′)][RhCl2(C8H12)] that in solution are in equilibrium with the respective binuclear compounds {[RhCl2(C8H12)]2(μ-LL′)}. The X-ray structure of [Rh(C8H12)(C7N2H16)][RhCl2(C8H12)] is presented. When the reactions are performed in media saturated with CO, carbonylated ion-pair complexes are obtained. The 2:1 ligand:dimer reactions afford neutral tetracoordinated [Rh(COD)(LL′)Cl] compounds bonded through the primary amino group, and show rapid interchange of olefinic protons at room temperature. The synthesis and properties of cationic complexes of general formulae [Rh(COD)(LL′)]Cl2 and [Rh(CO)(PPh3)(LL′)]CO4 are also discussed. Cyclooctadiene compounds show association processes in acetone solution, though they are monomeric in the solid state. The X-ray structure of [Rh(C8H12)(C7N2H16)]ClO4 indicates the existence of hydrogen bonding between the oxygens in the perchlorate anion and the primary amino group in the cation.

Diblock metallocopolymers containing various iron sandwich complexes: living ROMP synthesis and selective reversible oxidation

The design of redox-robust metallocopolymers is expected to produce new nanomaterials with multiple applications. Here the ROMP syntheses using Grubbs’ 3rd generation catalyst of three new living diblock copolymers each containing two distinct redox-stable iron sandwich complexes of the ferrocene, pentamethylferrocene and cyclopentadienyl-iron-arene families in the side chain are reported. The electrochemical properties of these diblock metallocopolymers investigated by cyclic voltammetry show complete chemical and electrochemical reversibilities of the redox waves, which also allow using the Bard–Anson method to determine the number of monomer units. The selective and reversible “chemical” oxidation of one of the blocks in two of these metallocopolymers afforded the syntheses of mixed-valent FeIIFeIII polymers.

Formation of new acylhydride rhodium(III) complexes and hydroxyalkyl derivatives in the reaction of rhodium(I) compounds containing dinitrogen donor ligands with o-(diphenylphosphino)benzaldehyde

Abstract The complexes Rh(COD)(NN)Cl (NN=2,2′-bipyridine or 1,10-phenanthroline derivatives) react with o-(diphenylphosphino)benzaldehyde (PCHO) (Rh–PCHO=1:1) to give acylhydride [Rh(Cl)(H)(PCO)(NN)] species. When this reaction is performed in the presence of SnCl2, neutral trichlorostannate compounds with phosphorus trans to tin [Rh(SnCl3)(H)(PCO)(NN)] are obtained and the complexes containing bipyridine derivatives undergo deinsertion of SnCl2 from the RhCl bond in solution. The oxidative addition of PCHO to Rh(COD)(NN)Cl in the presence of PPh3 gives cationic species [Rh(H)(PCO)(PPh3)(NN)]+ containing mutually trans phosphorus atoms. The reaction of Rh(COD)(NN)Cl with PCHO (Rh–PCHO=1:2) affords cationic complexes [Rh(H)(PCO)(PCHO)(NN)]+ where PCHO behaves as P-monodentate ligand and contains a free aldehyde group. The aldehyde group in [Rh(H)(PCO)(PCHO)(bipy)]+, may undergo the insertion reaction into the RhH bond to give the hydroxyalkyl derivative [Rh(PCO)(PCHOH)(bipy)]+.

Formation of 18e− and 16e− Acyl(η3-cyclooctenyl)rhodium(III) Complexes in the Reaction of Cationic (Cycloocta-1,5-diene)rhodium(I) Compounds with 2-(Diphenylphosphino)benzaldehyde

The reaction of cationic diolefinic rhodium(I) complexes with 2-(diphenylphosphino)benzaldehyde (pCHO) was studied. [Rh(cod)2]ClO4 (cod=cycloocta-1,5-diene) reacted with pCHO to undergo the oxidative addition of one pCHO with (1,2,3-η)cyclooct-2-en-1-yl (η3-C8H13) formation, and the coordination of a second pCHO molecule as (phosphino-κP)aldehyde-κO(σ-coordination) chelate to give the 18e− acyl(allyl)rhodium(III) species [Rh(η3-C8H13)(pCO)(pCHO)]ClO4 (see 1). Complex 1 reacted with [Rh(cod)(PR3)2]ClO4 (R=aryl) derivatives 3–6 to give stable pentacoordinated 16e− acyl[(1,2,3-η)-cyclooct-2-en-1-yl]rhodium(III) species [Rh(η3-C8H13)(pCO)(PR3)]ClO47–10. The (1,2,3-η)-cyclooct-2-en-1-yl complexes contain cis-positioned P-atoms and were fully characterized by NMR, and the molecular structure of 1 was determined by X-ray crystal diffraction. The rhodium(III) complex 1 catalyzed the hydroformylation of hex-1-ene and produced 98% of aldehydes (n/iso=2.6).

Liquid–Liquid Interfacial Electron Transfer from Ferrocene to Gold(III): An Ultrasimple and Ultrafast Gold Nanoparticle Synthesis in Water under Ambient Conditions

Ferrocene (Fc) in ether reduces HAuCl4 in water within seconds under ambient conditions in air upon stirring, forming ferricinium chloride stabilized water-soluble 20 nm gold nanoparticles (AuNPs) that are redispersible in the presence of poly(N-vinylmethylpyrrolidone) or NaBH4 + thiol. After reduction with NaBH4 yielding Fc and 26 nm sodium poly(hydroxyborate) stabilized AuNPs, the core size no longer changes following reactions with thiols providing (RS)nAuNPs.