Fernando J. Lahoz

Ligand-controlled regioselectivity in the hydrothiolation of alkynes by rhodium N-heterocyclic carbene catalysts.

Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(η(2)-olefin)](2) and RhCl(IPr)(py)(η(2)-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(η(2)-olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate-hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate-alkyne disposition, favoring formation of 2,2-disubstituted metal-alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl-hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium-thiolate bond is the rate-determining step.

Trimerisation of the Cationic Fragments [(η‐ring)M(Aa)]+ ((η‐ring) M=(η5‐C5Me5)Rh, (η5‐C5Me5)Ir, (η6‐p‐MeC6H4iPr)Ru; Aa=α‐amino acidate) with Chiral Self‐Recognition: Synthesis, Characterisation, Solution Studies and Catalytic Reactions of the Trimers [{(η‐ring)M(Aa)}3](BF4)3

The formation of [{(η-ring)M(Aa)}3](BF4)3trimers [(η-ring)M=(η5-C5Me5)Rh, (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru; Aa = α-amino acidate, one cation shown schematically] takes place by chiral self-recognition, the RMRMRM or SMSMSM trimers are equally configurated at the metal centres and are the only diastereomers detected. The equilibrium constant for the diastereomerisation process between both isomers depends on the solvent, amino acidate, and metal. The trimers catalyse the reduction of unsaturated aldehydes to unsaturated alcohols and the reduction of acetophenone to 2-phenylethanol with up to 75 % ee.

Mild and selective H/D exchange at the β position of aromatic α-olefins by N-heterocyclic carbene-hydride-rhodium catalysts

Financial support from the MICINN of Spain (project numbers CTQ2009-08089 and CTQ2010-15221), the ARAID Foundation under the program “jovenes investigadores”, and CONSOLIDER INGENIO-2010 program, under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015) is gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramon y Cajal” program.

On the Sense of the Enantioselection in Hydrogen Transfer Reactions from 2-Propanol to Ketones

An explanation for the reversal in the sense of the enantioselectivity observed in hydrogen transfer reactions from 2-propanol to ketones catalyzed by the ruthenium or osmium amino acidates [(η6-p-MeC6H4-i-Pr)M(Aa)Cl] and [(η6-p-MeC6H4-i-Pr)M(Aa)]3[BF4]3 [Aa=piperidine-2-carboxylate (pip), N-methyl-L-phenylalaninate (MePhe)] is given; the molecular structures of [(η6-p-MeC6H4-i-Pr)Os(Pip)Cl] (1), [(η6-p-MeC6H4-i-Pr)Os(Pip)]3[BF4]3 (2), [(η6-p-MeC6H4-i-Pr)M(MePhe)Cl] [M=Ru (3), Os (4)] are also reported.

Direct Access to Parent Amido Complexes of Rhodium and Iridium through NH Activation of Ammonia

Financial support from CONSOLIDER INGENIO-2010 program under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015). P.G.O. acknowledges financial support from the CSIC “JAE-Doc” program.

Optically active pseudoctahedral rhodium(III), iridium(III), and ruthenium(II) complexes with α-amino acidato ligands. Crystal structures of RIrSCSN- and SIrSCSN-[(C5Me5)Ir(pro)Cl] · 12H2O (Hpro = l-proline)

Abstract The synthesis and characterization of optically active amino acidato complexes of the types [(C 5 Me 5 )M(aa)Cl], [( p -cymene)Ru(aa)Cl], [(C 5 Me 5 )M(aa)(PPh 3 )]BF 4 , and [( p -cymene)Ru(aa)(PPh 3 )]BF 4 (M = Rh, Ir; Haa = l -alanine, l -proline), in which the metal is a chiral centre, are reported. The cationic species were prepared via the solvato-complexes [(C 5 Me 5 )M(aa)(MeOH)] + and [( p -cymene)Ru(aa)(MeOH)] + , which epimerize rapidly on the 1 H NMR time scale. The crystal structure of the complex [(C 5 Me 5 )Ir(pro)Cl] is reported; the asymmetric unit contains two independent molecules differing in the configuration at the metal.

Rhodium complexes of the binucleating ligands pyridine-2-thiolate and benzothiazole-2-thiolate. Crystal structures of [{Rh(µ-SC5H4N)(CO)2}2] and [{Rh(µ-SC5H4N)(tfbb)}2]·Me2CO (tfbb = tetrafluorobenzobarrelene)

The binuclear complexes [(Rh)µ-SC5H4N)(diolefin)}2][SC5H4N = pyridine-2thiolate, diolefin = cycle-octa-1,5-diene (cod)(1), norborna-2,5-diene (nbd)(2), or tetrafluorobenzobarrelene (tetrafluorobenzo[5,6] bicyclo[2.2.2]octa-2,5,7-triene)(tfbb)(3)] are prepared by reaction of LiSC5H4N with the appropriate complex [{Rh(µ-Cl)(diolefin)}2] and show fluxional behaviour in solution associated with the bridging ligands. The related compounds [{Rh(µ-C7H4NS2)(diolefin)}2][C7H4NS2= benzothiazole-2-thiolate, diolefin = cod(5), nbd(6), or tfbb(7)] are prepared by a similar route. Carbonylation reactions of (1) and (5) give the tetracarbonyl complexes [{Rh(µ-L)(CO)2}2][L = SC5H4N (4) or C7H4NS2(8) respectively]. Triphenylphosphine replaces carbon monoxide stepwise in compound (4) yielding the mono-(10) and di-substituted (11) complexes whilst the disubstituted complex [{Rh(µ-C7H4NS2)(CO)(PPh3)}2](9) is obtained from compound (8). Methyl iodide adds to complexes (4) and (10) affording respectively the diacetyl complexes [{Rh(µ-SC5H4N)(COMe)I(CO)}2](12) and [{Rh)(µ-SC5H4N)(COMe)l}2(CO)(PPh3)](13). The molecular structures of (3) and (4) have been determined by X-ray analyses. Crystals of (3) are triclinic, space group P, with a= 13.772(7), b= 14.184(8), c= 9.738(4)A, α= 108.99(2), β= 75.65(3), γ= 106.04(3)°, and Z= 2. Crystals of (4) are orthorhombic, space group P21212 (no, 18), with a= 14.637(6), b= 6.734(4), c= 8.852(5)A, and Z= 2. Both complexes are binuclear with two pyridine-2-thiolate groups acting as bridges. In (4) both ligands, having a head-to-tail disposition, bridge the metal centres through the N and S atoms whereas in (3) one of the pyridine-2-thiolate ligands bridges through the S atom only. The square-planar environments of the Rh atoms are completed by two tfbb ligands [(3)] or four CO groups [(4)], with metal–metal separations of 3.028(2) and 2.941 (2)A respectively.

Rhodium and Iridium Pyrazolato Blues

The staggered arrangement of the two dimers in 1 facilitates the formation of an almost linear chain of four metal centers that is held together by a nonsupported metal-metal bond. The intense color of the compounds and the fractional oxidation states of the metal atoms can be explained by electron delocalization along the chain. M=Rh, Ir.

Chiral rhodium complexes as catalysts in Diels–Alder reactions

The first rhodium enantioselective catalysts for the Diels–Alder reaction between methacrolein and cyclopentadiene are described; the molecular structure of the catalyst precursor [(η5-C5Me5)Rh(R-Prophos)(H2O)][SbF6]2 is also presented.

Reversible Ethylene Dihydrogen Mediated 11-Vertex nido → closo → nido Conversion in a Metallathiaborane Cluster

The reaction of the unsaturated nido-rhodathiaborane [8,8-(PPh3)2-8,7-RhSB9H10] (1) with pyridine (py) generates the new nido-hydridorhodathiaborane [8,8,8-(PPh3)(H)-9-(py)-8,7-RhSB9H9] (2) that reacts with excess ethene to give ethane and the novel ethene-ligated closo cluster [1,1-(PPh3)(η2-C2H4)-3-(py)-1,2-RhSB9H8] (3). Reduction of 3 with dihydrogen regenerates 2, leading to a reaction cycle that opens new routes for potential catalytic hydrogenation of olefins.