María A. Garralda

Aldehyde C–H activation with late transition metal organometallic compounds. Formation and reactivity of acyl hydrido complexes

This perspective focuses on the aldehyde C-H activation promoted by late transition metals, including the chelation-assisted reactions. The mechanisms currently accepted for different metal complexes, the reactivity of acyl hydrido species formed, and the reactions promoted on further aldehyde when using excess reagent are discussed. Homogeneous catalytic aldehyde decarbonylation or dimerization reactions are also reviewed.

A readily accessible ruthenium catalyst for the solvolytic dehydrogenation of amine–borane adducts

The use of the readily available complex [Ru(p-Cym)(bipy)Cl]Cl as an efficient and robust precatalyst for homogeneously catalysed solvolysis of amine-borane adducts to liberate the hydrogen content of the borane almost quantitatively is being presented. The reactions can be carried out in tap water, and in aqueous mixtures with non-deoxygenated solvents. The system is also efficient for the dehydrocoupling of dimethylamine-borane under solvent-free conditions.

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.

Rhodium(I) complexes containing aliphatic diamine ligands

Abstract The reaction of [Rh(diolefin)Cl]2 and aliphatic diamines (LL) in 2 1 ratio, gave either the ion-pair species [Rh(diolefin)(LL)]+ [Rh(diolefin)Cl2]− or neutral pentacoordinated [Rh(Cl)(diolefin)(LL)] complexes depending on the degree of N-substitution in the ligands. When the reactions were performed in solutions saturated with CO only ion-pair [Rh(CO)2(LL)]+ [Rh(CO)2Cl2]− complexes were obtained; these carbonyl derivatives show some metal-metal interaction. Reaction of [Rh(NBD)Cl]2 with ethylenediamine and triphenylphosphine gives pentacoordinated [Rh(NBD)(en)(PPh3)]+ species.

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.

Efficient hydridoirida-β-diketone-catalyzed hydrolysis of ammonia- or amine-boranes for hydrogen generation in air

The dihydridoirida-β-diketone [IrH2{(PPh2(o-C6H4CO))2H}] (2) has been used as a homogeneous catalyst for the hydrolysis of ammonia- or amine-boranes to generate up to 3 equivalents of hydrogen in the presence of air. When using 0.5 mol% loading of 2, dimethylamine-borane is hydrolysed completely within 8 min at 30 °C and maintains its activity in consecutive runs. Ammonia-borane or tert-butylamine-borane is hydrolysed completely within 32 or 25 min respectively. Triethylamine-borane fails to be hydrolysed. Kinetic studies suggest a sequence of two consecutive first-order reactions, in which an intermediate builds up and finally falls, with the first step being the rate controlling step. ΔH1(‡) are in the range 65-85 kJ mol(-1) and negative values of ΔS1(‡) are obtained. A multinuclear NMR study of the catalyzed reaction shows the formation of a resting state (A) of the active catalyst proposed to be of the hydridodiacyl type [IrH(PPh2(o-C6H4CO))2(solvent)] with a hydride trans to the acyl group. In the absence of substrate a dormant species (B) is formed. By the reaction of hydridoirida-β-diketones with ammonia, the hydridoirida-β-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH))H}] (3) and the hydridobis(acylphosphane)aminoiridium(III) complex [IrH(PPh2(o-C6H4CO))2(NH3)] (4), with a hydride trans to phosphane, are formed. Aromatic amines such as aniline or anisidines afford cationic [IrH{(PPh2(o-C6H4CO))2H}(C6H4RNH2)]ClO4 (R = H (6); p-MeO (7); o-MeO (8)) hydridoirida-β-diketones with a coordinated amine group trans to the hydride. The dormant species B is proposed to be of the hydridobis(acylphosphine)aminoiridium(III) type with a hydride trans to the amine group.

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).