Eduardo Sola

Transition metal liquid crystals: Advanced materials within the reach of the coordination chemist

This review serve to open the field to many coordination chemistry who can use specific expertise of new transition metal liquid crystals. Bibliography

Iridium Compounds with κ-P,P,Si (biPSi) Pincer Ligands: Favoring Reactive Structures in Unsaturated Complexes

The structure, coordination properties, insertion processes, and dynamic behavior in solution of the five-coordinate complexes [IrXH(biPSi)] (biPSi = kappa-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2); X = Cl (1), Br (2), or I (3)) have been investigated. The compounds are formed as mixtures of two isomers, anti and syn, in slow equilibrium in solution. The equilibrium position depends on the halogen and the solvent. Both isomers display distorted square-based pyramidal structures in which the vacant position sits trans to silicon. The equatorial plane of the syn isomer is closer to the T structure due to distortions of steric origin. The small structural differences between the isomers trigger remarkable differences in reactivity. The syn isomers form six-coordinate adducts with chlorinated solvents, CO, P(OMe)(3), or NCMe, always after ligand coordination trans to silicon. The anti isomers do not form detectable adducts with chlorinated solvents and coordinate CO or P(OMe)(3) either trans to silicon (kinetic) or trans to hydride (thermodynamic). NCMe coordinates the anti isomers exclusively at the position trans to hydride. Qualitative and quantitative details (equilibrium constants, enthalpies, entropies, etc.) on these coordination processes are given and discussed. As a result of the different coordination properties, insertion reagents such as acetylene, diphenylacetylene, or the alkylidene resulting from the decomposition of ethyl diazoacetate selectively insert into the Ir-H bond of 1-syn, not into that of 1-anti. These reactions give five-coordinate syn alkenyl or alkyl compounds in which the vacancy also sits trans to silicon. Acetylene is polymerized in the coordination sphere of 1. The nonreactive isomer 1-anti also evolves into the syn insertion products via anti<-->syn isomerizations, the rates of which are notably dependent on the nature of the insertion reactants. H(2) renders anti<-->syn isomerization rates of the same order as the NMR time scale. The reactions are second order (k(obs) = k(anti<-->syn)[H(2)]) and do not involve H(2)/IrH hydrogen atom scrambling. A possible isomerization mechanism, supported by MP2 calculations and compatible with the various experimental observations, is described. It involves Ir(V) intermediates and a key sigma Ir-(eta(2)-SiH) agostic transition state. A similar transition state could also explain the anti<-->syn isomerizations in the absence of oxidative addition reactants, although at the expense of high kinetic barriers strongly dependent on the presence of potential ligands and their nature.

Bis-alkynyl- and hydrido-alkynyl-osmium(II) and ruthenium(II) complexes containing triisopropylphosphine as ligand

Abstract The five-coordinate bis-alkynyl complexes M(CCPh) 2 (CO)(P-i-Pr 3 ) 2 (M = Os, Ru) have been prepared by reaction of HCCPh with OsH 4 (CO)(P-i-Pr 3 ) 2 or MH( h 2 -H 2 BH 2 )(CO)(P-i-Pr 3 ) 2 (M = Os, Ru). They react with ligands L such as P(OMe) 3 , PMe 3 , CO and HCCPh to give the six-coordinate compounds M(CCPh) 2 (CO)(P-i-Pr 3 ) 2 L. Displacement of the chloride ligands in MHCl(CO)(PR 3 ) 2 L by CCPh − leads to the hydrido-alkynyl compounds MH(CCPh)(CO)(PR 3 ) 2 L. The selective reduction of phenylacetylene to styrene catalysed by the complex OsH 4 (CO)(P-i-Pr 3 ) 2 , prepared from OsHCl(CO)(P-i-Pr 3 2 and NaBH 4 in situ, is also described.

Reversible insertion of carbenes into ruthenium-silicon bonds.

The five-coordinate carbene complexes [Ru{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(═CHR)] (2, R = Ph; 3, R = SiMe3), analogues of the Grubbs catalyst, were prepared from the dimer [Ru(μ-Cl){κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2 (1) and the corresponding diazoalkane N2CHR. The particular structural features that result from the presence of a strongly trans directing silyl group at the pincer ligand of these complexes are discussed on the basis of NMR information and the crystal structure of the vinylidene analogue [Ru{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(═C═CHPh)] (4), which was also obtained from 1 and phenylacetylene. The reactions of 3 with reagents such as P(OMe)3, CO, NCMe, and K(acac) illustrate that the first response of these carbene complexes to an increase of the coordination number around ruthenium is the insertion of the carbene ligand into the Ru-Si bond. These reactions also indicate that the insertion process is reversible and allows typical transformations of carbene ligands such as C-H functionalizations via carbene insertion (in the acac ligand) or the formation of ketene from CO. In addition, the reactions of 3 with terminal alkynes such as phenylacetylene or 3,3-dimethyl-1-butyne show that the inserted carbenes can also undergo reactions typical of metal-bound alkyls such as alkyne insertion and C-H reductive elimination.

Synthesis and mesomorphism of stilbazole complexes of rhodium(I) and iridium(I)

The complexes cis-[MCl(CO)2(n-OPhVPy)](M = Rh, Ir; n-OPhVPy =trans-4-alkyloxy-4′-stilbazole) are mesomorphic showing nematic and smectic A phases at temperatures below 140 °C.

Rhodium(I) complexes containing 4-pyridylmethylene-4′-alkoxyanilines as ligands: Formation of rhodium containing liquid crystals by coordination of non-mesogenic organic ligands

Abstract The complexes [RhCl(COD)L] (COD = cyclocta-1,5-diene; L = NC5H4CH=NC6H4OCnH2n+1) have been prepared by reaction of the corresponding L (n = 8, 14) ligands with [RhCl(COD)]2. They react with CO to give cis-[RhCl(CO)2L] (n = 2, 4, 6–10, 12, 14). Reaction of cis-dicarbonyl compounds with L in the presence of Me3NO gives trans-[RhCl(CO)L2] (n = 4, 8). Monocarbonyl compounds of formulae [RhCl(CO)L(P(OMe)3)] (n = 6, 8, 14) have been made by reaction of cis-[RhCl(CO)2L] with P(OMe)3 in dichloromethane. The mesogenic properties of the compounds [RhCl(CO)2L] (n = 8–10, 12, 14) are described.

Evidence for a dinuclear mechanism in alkyne hydrogenations catalyzed by pyrazolate-bridged diiridium complexes

The products obtained from the sequential reaction of [Ir2(mu-H)(mu-Pz)2H3(NCCH3)(PiPr3)2] (1) with diphenylacetylene and their subsequent reactions with hydrogen have been investigated in order to deduce the mechanisms operating in the hydrogenation reactions catalyzed by 1. The reaction of 1 with an excess of diphenylacetylene gives cis-stilbene and [Ir2(mu-H)(mu-Pz)2-[eta1-C6H4-2-[eta1-(Z)-C=CHPh]]((Z)-C(Ph) =CHPh](NCCH3)(PiPr3)2] (2), the structure of which has been determined by X-ray diffraction. The formation of 2 involves the intermediate species [Ir2(mu-H)(mu-Pz)2H2((Z)-C(Ph)=CHPh](NCCH3)-(PiPr3)2](3),[Ir2(mu-H)(mu-Pz)2H[(Z)-C(Ph)=CHPh]2(NCCH3)(PiPr3)2] (4), and [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C=CHPh](NCCH3)(PiPr3)2] (5), which have been isolated and characterized. These three complexes react with hydrogen to give cis-stilbene and 1 and are possible intermediates of the diphenylacetylene hydrogenation under catalytic conditions. Nevertheless, the rate of formation of 5 is very slow compared with the rate of catalytic hydrogenation, which excludes its participation during catalysis. Compound 2 also reacts with hydrogen in benzene, but in this case the hydrogenation gives 1,2-diphenylethane as the sole organic product. The course of this reaction in acetone has been investigated, and deuteration experiments were carried out. The formation of [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C=CHPh]](OC(CD3)2)(PiPr3)2] (6) and [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C-CHPh]](NCCH3)(PiPr3)2] (7) was observed under these conditions. The experimental evidence obtained supports two alternative mechanisms for the alkyne hydrogenation catalyzed by 1, one of them being dinuclear and the other mononuclear. The experimental data suggest that the former is favored.

Addition of water across Si-Ir bonds in iridium complexes with κ-P,P,Si (biPSi) pincer ligands.

Electrophiles such as Me(+), Ag(+), or protons react with the five-coordinate Ir(III) complex [IrClH(biPSi)] (biPSi = κ-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2)) by abstracting its chloride ligand. The resulting species can be stabilized by a variety of L ligands to give the cationic complexes [IrH(biPSi)L(2)](+). The derivative [IrH(biPSi)(NCMe)(2)](+) has been subjected to a kinetic study regarding the facile dissociations of its acetonitrile ligands. The presence of water changes the course of the reaction producing dihydride complexes that contain the silanol ligand κ-O,P,P-HOSi(Me){(CH(2))(3)PPh(2)}(2) (biPSiOH). The water activation product [IrH(2)(biPSiOH)(NCMe)](CF(3)SO(3)) undergoes insertion reactions with ethylene and phenylacetylene. The use of hydrolyzable fluorinated counterions such as PF(6)(-) or BF(4)(-) further modifies the reaction by provoking the incorporation of fluoride at the silicon atom of the former biPSi ligand. The dihydride resulting after such a process, [IrH(2)(biPSiF)(NCMe)(2)]BF(4) (biPSiF = κ-P(2)-FSi(Me){(CH(2))(3)PPh(2)}(2)), displays a trans-chelating diphosphine ligand. When dehydrogenating the Ir center, spontaneously or using ethylene as hydrogen acceptor, the diphosphine backbone undergoes a Si-C bond cleavage leading to a new Ir(III) species with κ-P,Si and κ-C,P chelate ligands.

Alkene C-H activations at dinuclear complexes promoted by oxidation.

We are grateful to the Plan Nacional de Investigacion, Ministerio de Ciencia y Tecnologia, for the support of this research (Project No. BQU2000-1170).

Synthesis of [Ir2(μ-Pz)2(CH3)(CO)2(PiPr3)2]+. A key intermediate in SN2 oxidative addition of halocarbons to dinuclear complexes

Abstract The unusual compound of formula [Ir2(μ-Pz)2(CH3)(CO)2(PiPr3)2](ClO4) (3) has been prepared. This complex is the proposed intermediate species for the SN2 oxidative addition of methyl iodide to the dinuclear compound [Ir(μ-Pz)(CO)(PiPr3)]2 (1). The spectroscopic and X-ray diffraction data obtained for 3, together with EHMO calculations and reactivity studies, indicate that the compound can be described as an Ir(III)–Ir(I) species containing a weak metal–metal bond. The implications of these electronic features in the regioselectivity of halocarbons oxidative additions to dinuclear complexes are discussed.