Pedro Valerga

Ruthenium and osmium vinylidene complexes and some related compounds

Abstract A review of the large number of studies completed during the current decade on the chemistry of ruthenium and osmium vinylidene complexes is presented. Interest in these studies arises not only from the reactivity modes and structural properties, but also because vinylidene species play an important role in the selective catalytic transformation of terminal alkynes (polymerization, CC bond formation in the condensation of alkynes with other substrates, etc.). Attention is mainly focused on the mononuclear compounds, studying their preparative methods where coordinatively unsaturated species and good donor ligands are often involved. Recent methods of synthesis from polyhydrides are also summarized. Metal alkynyl derivatives are closely related to vinylidene complexes, both being common precursors to, and reaction products of vinylidene complexes. Subsequently, 1-alkyne and π-alkyne to vinylidene rearrangements on these metal centers are studied. The transformations from vinyl 14 electron to hydride-vinylidene 16 electron species and from hydride–vinylidene to ethylidyne species, etc. are also considered.

Cleavage of Palladium Metallacycles by Acids: A Probe for the Study of the Cyclometalation Reaction

Useful mechanistic information about the cyclometalation reaction may be obtained by studying the reverse reaction, namely, the protonation of metallacycle 1 by acids of different coordinating anions (see scheme). Ar=3,5-(F3C)2C6H3; Tf=F3CSO2.

Synthetic, spectral and structural aspects of some mono- and binuclear (homo/hetero) Ru(II) hydrido carbonyl complexes

Abstract Reactions of the poly-pyridyl bridging ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine; 2,3-bis(2-pyridyl)-pyrazine and 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (referred hereafter as tptz, bppz and bptz respectively) with [RuH(CO)Cl(PPh3)3] in methanol, gave highly stable cationic complexes with the formulation [RuH(CO)(PPh3)2(L)]+. Further, the mononuclear complex [RuH(CO)(PPh3)2(bppz)]PF6 reacted with K2PtCl4, [PdCl2(benzonitrile)2], [{Ru(η6-C10H14)(μ-Cl)Cl}2], [{Ru(η6-C6Me6)(μ-Cl)Cl}2], [RuCl(η5-C5H5)(PPh3)2] and [{Rh(η5-C5Me5)(μ-Cl)Cl}2] in methanol under refluxing conditions to give bppz bridged binuclear complexes with the formulation [RuH(CO)(PPh3)2(bppz)PtCl2]PF6, [RuH(CO)(PPh3)2(bppz)PdCl2]PF6, [RuH(CO)(PPh3)2(bppz)(η6-C10H14)RuCl](PF6)2, [RuH(CO)(PPh3)2(bppz)(η6-C6Me6)Cl2Ru](PF6)2, [RuH(CO)(PPh3)2(bppz)(η5-C5H5)(PPh3)Ru](PF6)2 and [RuH(CO)(PPh3)2(bppz)Rh(η5-C5Me5)Cl](PF6)2 in quantitative yield. The reaction products have been characterized by elemental analyses, IR, 1H-, 1H–1H-COSY, 13C-, 31P-NMR, ESMS, FAB mass spectroscopy, electronic spectra and cyclic voltammetry. Molecular structure of the representative mononuclear complex [RuH(CO)(PPh3)2(tptz)]BF4 has been confirmed by X-ray crystallography. Crystal structure determination revealed η2-coordination of the ligand tptz with the metal center. Crystal data: monoclinic, P21/n, a=17.810(6) A, b=22.233(9) A, c=12.156(4) A, β=90.06(3)°, Z=4, R=0.078.

The interaction of [Cp∗RuCl(dippe)] and [CpRuCl(dippe)] with alkynols: hydroxyvinylidene, allenylidene and related derivatives (dippe 1,2-bis(diisopropylphosphino)ethane)

Abstract The reactions of [Cp∗RuCl(dippe)] and [CpRuCl(dippe)] (dippe  1,2-bis(diisopropylphosphino)ethane) with several alkynols HCCC(OH)RR′ (RR′H, Me; RMe, R′Ph) have been studied. These reactions leads to the formation of the corresponding allenylidene derivatives, although in some cases hydroxyvinylidene complexes were isolated as intermediates in such process. The X-ray crystal, structure of [CpRuCCCMePh(dippe)][BPh4] was determined. In the course of the reaction of [CpRuCl(dippe)] with HCCC(OH)Me2, there is evidence for the formation of a deep bluedimeric aklynyl-carbene (or alkenyl-allenylidene) complex [{CpRu(dippe)}2(μ-C10H11)][BPh4] resulting formally from the coupling of two allenylidene moieties followed by the loss of one proton. The reaction of [Cp∗RuCCCMePh(dippe)][BPh4] with KOBu′ leads to the ene-yne derivative [Cp∗Ru(CCC(Ph)CH2)(dippe)] as result of the deprotonation of the allenylidene ligand at the δ-position. This compound was structurally characterized by single crystal X-ray crystallography. In an attempt to obtain the primary allenylidene complex [Cp∗RuCCCH2(dippe)][BPh4] by dehydration of the hydroxyvinylidene [Cp∗RuCCHCH2OH(dippe)][BPh4] using P2O5, the previously reported carbonyl complex [Cp∗Ru(CO)(dippe)][BPh4] was obtained and its crystal structure determined. This is also accessible by aerial oxidation of the hydroxy-vinylidene derivative.

Hydride, dihydrogen, dinitrogen and related complexes of ruthenium containing the ligand hydrotris(pyrazolyl)borate. X-ray crystal structure of [{HB(pz)3}Ru(η2-H2)(dippe)] [BPh4] (dippe = 1,2-bis(diisopropylphosphino)ethane)

Abstract The complex [HB(pz)3)RuCl(PPh3)2] reacts with one equivalent ofdippe in toluene toyield [(HB(pz)3)RuCl(dippe)]. This compound reacts with NaBH4 in MeOH furnishing the monohydride [(HB(pz)3)RuH(dippe)], whereas [(HB(pz)3)RuH(PPh3)2] was obtained by reaction of [RuHCl(PPh3)3] with K[HB(pz)3]. Both monohydride complexes are protonated by HBF4·OEt2 at −80°C to give the corresponding dihydrogen adducts [(HB(pz)3)Ru(H2)(dippe)]+ and [(HB(pz)3]Ru(H2)(PPh3)2]+, as inferred from longitudinal relaxation time (T1) and 1J(H,D) measurements. The latter complex is unstable and decomposes at room temperature, but the former is a stable species which does not rearrange to the dihydride form when the temperature is raised. The X-ray crystal structure of [(HB(pz)3)Ru(H2)-(dippe)][BPh4] has been determined. The dihydrogen ligand in this compound is labile, and readily replaced by a range of neutral donor molecules, yielding the corresponding complexes [(HB(pz)3)Ru(L)(dippe)][BPh4] (L = CO, CNBu1, Me2CO, thf, N2). There is also supporting evidence for the formation of a paramagnetic RuIII methoxide complex, namely [(HB(pz)3)Ru(OMe)(dippe)][BPh4]. All compounds were characterized by IR, NMR and microanalysis.

Synthesis of new half-sandwich ruthenium complexes containing 1,2-bis(diisopropylphosphino)ethane (dippe); crystal structures of [Ru(C5Me5)Cl(dippe)] and [Ru(C5Me5)(O2)(dippe)][BPh4]

The complex [Ru(C5H5)Cl(PPh3)2] reacted with 1 equivalent of dippe [dippe = 1,2-bis(diisopropylphosphino)ethane] in refluxing toluene to yield [Ru(C5H5)Cl(dippe)]1. The complex [Ru(C5Me5)Cl(dippe)]2 was obtained by reaction of [{Ru(C5Me5)(µ3-Cl)}4] with a stoichiometric amount of dippe in CH2Cl2. The crystal structure of 2 has been determined. Both 1 and 2 are non-electrolytes in non-polar solvents. In alcohols, compound 2 has a strong tendency to dissociate chloride. In the presence of air, this compound binds O2 irreversibly, yielding the dioxygen complex [RuC5Me5(O2)(dippe)]+, which is isolable as the [BPh4]– salt (3). The crystal structure of this compound has also been determined. Both 1 and 2 reacted with SnCl2 in CH2Cl2 to yield the insertion derivatives [Ru(C5R5)(SnCl3)(dippe)](R = H 4 or Me 5). All compounds were characterized by NMR spectroscopy and microanalysis.

Synthesis of cationic arene complexes of iron and ruthenium with 1,2-bis(diisopropylphosphino)ethane (dippe): X-ray crystal structures of [RuCl(η6-C6H6)(dippe)][BPh4] and [RuH(η6-C6H6)(dippe)][BPh4]

Abstract The complex [FeCl2(dippe)] (dippe = 1,2-bis(diisopropylphosphino)ethane) reacts with cyclohexadienyl-lithium in tetrahydrofuran yielding a dark mixture, from which the hydrido-arene complex [FeH(C6H6)(dippe)][BPh4] (1) can be isolated in moderate yields upon treatment with MeOHNaBPh4. 1, as well as the toluene complex [FeH(C6H5Me)(dippe)][BPh4] (2), can be prepared by reaction of [FeCl2(dippe)] with LinBu in benzene or toluene respectively, followed by MeOHNaBPh4. The ruthenium complexes [RuCl(L)(dippe)]+ (L = C6H6, p-isopropylmethylbenzene (p-cymene)) are obtained by reaction of [{Ru(L)Cl2}2] wit dippe and Ag+, and isolated as the tetraphenylborate salts 3. These compounds react with NaBH4 in acetone-ethanol furnishing the hydrido-aerene derivatives [RuH(L)(dippe)][BPh4] (L = C6H6 5, p-cymene 6). All the compounds were characterized by IR, NMR and microanalysis. The X-ray crystal structures of 3 and 4 are also reported.

Synthesis and spectroscopic properties of cationic Ru(II) arene complexes [Ru(η6-arene)(P)Cl(L)]+. (P=PPh3, PEt3, MePPri2 and L=4-cyanopyridine or 1,4-dicyanobenzene)

Abstract Reactions of [Ru(η6-arene)(P)Cl2] (P=PPh3, PEt3 or MePPri2) with organonitriles 4-cyanopyridine or 1,4-dicyanobenzene (referred hereafter as CNPy or DCB) in methanol, in the presence of NH4PF6, gives the cationic arene complexes [Ru(η6-arene)(P)Cl(L)]+ (L=CNPy or DCB). The reaction products have been characterized by physico-chemical methods viz., elemental analyses, IR, 1H-, 13C-, 31P-NMR, electronic and FAB mass spectra. The spectral data of the complexes revealed the presence of a pendant nitrile group. These could behave as potential metallo-ligands and could find wide application in the syntheses of homo- or heterobimetallic mixed valence bridged complexes.

Reactivity of an anionic Pd(II) metallacycle with CH2X2(X = Cl, Br, I): formal insertion of methylene into a Pd–Caryl bond

Whereas the reaction of the anionic palladium metallacycle [K[Pd(CH2CMe2-o-C6H4)(kappa2-Tp)]] with CH2Cl2 leads to the isolation of the stable Pd(IV) chloromethyl complex [Pd(CH2CMe2-o-C6H4)(kappa3-Tp)(CH2Cl)], the analogous reactions with CH2Br2 and CH2I2 give rise to the six membered metallacycles [Pd(CH2CMe2-o-C6H4(CH2))(kappa3-Tp)X](X = Br or I), as a result of the formal insertion of CH2 into the Pd-C(aryl) bond.

Counteranion and Solvent Assistance in Ruthenium-Mediated Alkyne to Vinylidene Isomerizations

The complex [Cp*RuCl((i)Pr2PNHPy)] (1) reacts with 1-alkynes HC≡CR (R = COOMe, C6H4CF3) in dichloromethane furnishing the corresponding vinylidene complexes [Cp*Ru═C═CHR((i)Pr2PNHPy)]Cl (R = COOMe (2a-Cl), C6H4CF3 (2b-Cl)), whereas reaction of 1 with NaBPh4 in MeOH followed by addition of HC≡CR (R = COOMe, C6H4CF3) yields the metastable π-alkyne complexes [Cp*Ru(η(2)-HC≡CR)((i)Pr2PNHPy)][BPh4] (R = COOMe (3a-BPh4), C6H4CF3 (3b-BPh4)). The transformation of 3a-BPh4/3b-BPh4 into their respective vinylidene isomers in dichloromethane is very slow and requires hours to its completion. However, this process is accelerated by addition of LiCl in methanol solution. Reaction of 1 with HC≡CR (R = COOMe, C6H4CF3) in MeOH goes through the intermediacy of the π-alkyne complexes [Cp*Ru(η(2)-HC≡CR)((i)Pr2PNHPy)]Cl (R = COOMe (3a-Cl), C6H4CF3 (3b-Cl)), which rearrange to vinylidenes in minutes, i.e., much faster than their counterparts containing the [BPh4](-) anion. The kinetics of these isomerizations has been studied in solution by NMR. With the help of DFT studies, these observations have been interpreted in terms of chloride- and methanol-assisted hydrogen migrations. Calculations suggest participation of a hydrido-alkynyl intermediate in the process, in which the hydrogen atom can be transferred from the metal to the β-carbon by means of species with weak basic character acting as proton shuttles.