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The titanium complex [TiCp*(OSBz)(OBzSH)] (1) has been synthesized by reaction of [TiCp*(Me)3] (Cp* = η5-C5Me5) with 2-mercaptobenzyl alcohol (H2OSBz). The reaction of complex 1 with H2O gives the dinuclear oxo-bridged complex [{TiCp*(OSBz)}2(μ-O)] (2). Complex 1 reacts with [M(μ-OH)(cod)]2 (M = Rh, Ir) to yield the early–late heterobimetallic complexes [TiCp*(OSBz)2M(cod)] {M = Rh (3); Ir (4)}. Carbon monoxide easily replaces the cod ligand in 3 and 4, which leads to the corresponding dicarbonyl derivatives [TiCp*(OSBz)2M(CO)2] {M = Rh (5); Ir (6)}. Compound 5 reacts with PPh3 to yield the monocarbonyl complex [TiCp*(OSBz)2Rh(CO)(PPh3)] (7). The molecular structures of complexes 2 and 5 have been established by single-crystal X-ray diffraction studies. The structure of complex 1 and its coordination mode toward a rhodium moiety have been ascertained by means of calculations based on density functional theory. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The heterometallic complex [TiCp*(O(2)Bz)(2)AlMe(2)] (2) has been synthesised by reaction of [TiCp*(O(2)Bz)(OBzOH)] (1) with AlMe(3) (Cp*=eta(5)-C(5)Me(5); Bz=benzyl). Complex 1 reacts with HOTf to yield the cationic derivative [TiCp*(OBzOH)(2)]OTf (3) (HOTf=HSO(3)CF(3)). Compound 3 reacts with [{M(mu-OH)(cod)}(2)] (M=Rh, Ir; cod=cyclooctadiene) to render the early-late heterometallic complexes [TiCp*(O(2)Bz)(2){M(cod)}(2)]OTf (M=Rh (4); Ir (5)). The molecular structure of complex 4 has been established by single-crystal X-ray diffraction studies.

The new titanium guanidinido complexes [TiCp*Me2{(PhN)2CNH2}] (1), and [TiCp*Cl2- {(PhN)2CNH2}] (2) (Cp* = η5-C5Me5) have been synthesized. The reaction of complex 1 with [Rh(μ-OH)(cod)]2 affords the rhodium guanidinido complex [Rh{(PhNH)(PhN)CNH}(cod)]2 (3). The molecular structures of complexes 1 and 3 were studied by X-ray diffraction methods. Complex 3 can also be prepared by reaction of [Rh(μ-OH)(cod)]2 with N,N'-diphenylguanidine.

The titanium salycilate complex [Cp*Ti(sal)(salH)] 1 (salH 2 = salycilic acid) was synthesised by reacting Cp*TiMe 3 and salycilic acid. The molecular structure of 1 studied by X-ray shows it to be dinuclear with a carboxylate group acting as a bridge ligand. [Rh(μ-OH)COD] 2 reacts with 1 to yield the bimetallic complex 2 , or with the siloxanodiol (HOSiPh) 2 O to yield the bimetalic bis-siloxide Rh complex 3 . Carbon monoxide displaces COD in 2 and 3 to give the carbonylic complexes 4 and 5 respectively. Complex 4 can also be prepared from 2 and [Rh(acac)(CO) 2 ]. Compounds 2 , 3 , 4 and 5 can be envisaged as models of Rh complexes anchored on titania or silica. The catalytic performance of heterometallic complexes is studied in the CO hydrogenation reaction and compared to rhodium-based (Rh-based) catalysts prepared by impregnation from Rh(NO 3 ) 3 or [Rh(acac)(CO) 2 ] showing higher yields to oxygenated products.

The temperature of calcination in air of a Rh/γ-Al 2 O 3 catalyst affects its structure in, at least, two different ways. First, upon increasing calcination temperature from 400 to 700 °C, the amount of non-reducible Rh 2 O 3 increases. But the most important effect is the sintering of metal particles, especially when the calcination temperature is around 700 °C or above. Catalytic activity in CO hydrogenation is strongly influenced as a consequence of this phenomenon. CO conversion decreases on larger rhodium particles, although turnover frequency (TOF) follows the opposite trend. In addition, oxygenates formation is strongly suppressed on the sintered catalysts.

The early–late heterometallic complexes [TiCp∗((OCH2)2Py)(μ-O)M(COD)] (M = Rh, Ir) behave as four-electron donor ligands yielding the polynuclear cationic complexes [TiCp∗(OCH2)2 Py(μ-O){M(COD)}2]OTf (M = Rh (1), Ir (2)). The molecular structure of complex 1 has been established through an X-ray diffraction study.

The effect of manganese promoter loading on the catalytic properties of Rh/Al2O3 catalysts (Mn/Rh=0, 0.5, 1 and 2, atomic ratio) for the synthesis of oxygenated compounds from synthesis gas was investigated. Catalysts were characterized by means of TPR, XPS, H2 chemisorption, FT-IR, and TPSR of chemisorbed CO. It is suggested that manganese oxide promotes CO conversion as a result of the change in the relative surface coverage of H* and C* (θH/θC). The manganese oxide promoter also affected the selectivity to oxygenated compounds, mainly to ethanol. The manganese promoter behaved as an electron-withdrawing, partially oxidizing the rhodium atoms at the Rh–MnO interface and thus creating new sites for CO insertion. The amount of promoter seemed to be an important parameter to achieve the highest yield of the desired reaction products. For oxygenates formation, the optimum Mn/Rh atomic ratio was found to be around 1.

In the present work, organometallic complexes were used as metal precursors for the synthesis of sulphur-resistant noble metal catalysts. The catalysts were tested in the hydrogenation reaction of diesel model-type molecules. Dibenzothiophene (DBT) was used as the source of sulphur. The organometallic-based catalysts activity was compared with the activity displayed by a commercial Pt/Al 2 O 3 hydrogenation catalyst. Comparable activity results were obtained when the reaction was carried in the presence of sulphur containing molecules. However, the organometallic-based catalysts were only active once the ligands had been removed from the metal coordination sphere, thus allowing the reactant molecules to adsorb on the metallic surface centres. Accordingly, the major advantage of this methodology may lie in improved metallic dispersion, which will be reflected in catalysts with greater sulphur resistance, rather than in the electronic or steric effects ascribed to organometallic precursors.

Modification of the multistep synthesis of the previously described bis[5-(diphenylphosphanyl)pyrazol-1-yl)]methane (bppzm, 1) produces the novel diphosphane (diphenylphosphanyl)-[5-(diphenylphosphanyl)pyrazol-1-yl](pyrazol-1-yl)methane (p4m, 2). Treatment of this ligand with [MCl2(PhCN)2] (M = Pd, Pt) or [M(COD)(THF)2]BF4 (M = Rh, Ir) produces [MCl2(p4m)] (M = Pd 3, Pt 4) or [M(COD)(p4m)]BF4 (M = Rh 5, Ir 6) complexes, which chelate in a P,P-bidentate fashion. Sulfidation of bppzm and p4m produces the disulfidophosphanes bppzmS2 (7) and p4mS2 (8). Treatment of 7 and 8 with [PdCl2(PhCN)2] produces [PdCl2(bppzmS2)] (9) and [PdCl2(pmS2)] (10), respectively, in which ligands 7 and 8 act in an N,N-bidentate chelate fashion. In contrast, ligand 8 reacts with [Rh(COD)(THF)2]BF4 to produce [Rh(COD)(p4mS2)]BF4, where ligand 7 acts in a dynamic S,S-chelate fashion. The activity of some of these complexes in the catalytic hydrogenation of olefins is reported and the single-crystal X-ray structures of 4, 8, and 9 have been obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Silica-supported rhodium catalysts prepared from nitrate and chloride precursors were tested in the CO hydrogenation reaction. Similar reaction rate and selectivities to the different product families were found for both catalysts, however the ex-chloride catalyst showed a lower 1-olefin/n-paraffin ratio. Characterisation by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), H2 chemisorption and Fourier transform infrared spectroscopy (FTIR) of CO chemisorbed did not evidence disparate features between ex-nitrate and ex-chloride samples. However, a much higher H2 desorption was found in the ex-chloride catalyst according to the hydrogen temperature-programmed desorption (TPD) studies. Residual chloride species seems to be involved in the H2 adsorption on silica enhancing the spillover of hydrogen from metal particles to the silica support. It is suggested that spilt-H atoms can create active sites on the silica surface where olefins can be hydrogenated to the corresponding paraffins.

The rhodium thiopyrimidine complex [Rh(SPymMe 2 )(CO) 2 ] was tethered to chemically modified SiO 2 substrates and tested as a catalyst in the hydroformylation reaction of 1-heptene. Catalytic performance was monitored under different reaction conditions for several cycles, and compared with the catalytic behaviour of the Rh thiolate complex in a homogeneous medium. Anchoring of the rhodium complex to the modified SiO 2 surface was performed by displacement of a CO ligand of the rhodium complex by a PR 3 group, following a reaction pathway previously described for gem–dicarbonilic complexes. The XPS data revealed that the sulphur atom is released from the external surface of the solid catalyst during the hydroformylation reaction. However, the thiolate complex is still present in the inner pore network of the solid after the hydroformylation reaction.

Rhodium thiolate complexes intercalated in crystalline γ-zirconium phosphate or tethered to SiO2-modified γ-zirconium phosphate have been synthesised. It was observed that the addition of a solution of organic silicates to a colloidal suspension of γ-zirconium phosphate yielded amorphous substrates, which displayed very high specific areas (160–650 m2 g−1). Incorporation of a mercaptocarbonyl rhodium complex resulted in a highly selective and active catalyst precursor for the hydroformylation of 1-heptene in the liquid phase. Elemental analysis and photoelectron spectroscopy of the fresh and used samples revealed that some metal leaching occurs during the reaction, this being mainly confined to the outer layers of the solid particles. This observation, together with the high selectivity towards linear aldehydes, makes SiO2-modified γ-zirconium phosphate a good support candidate for immobilised Rh catalysts. Spectroscopic data obtained from the crystalline precursor and also from the amorphous catalyst showed that the interaction between the rhodium complex and the acid support was achieved ia hydrogen bonds, forming NH groups.

Rhodium supported on titania-silica is modeled by 1, which was obtained from [{Cp*TiMe(μ-O2 SiPh2 )}2 ] (2) and [{Rh(OH)(cod)}2 ]. Complex 2 and its triply bridged derivative [Cp*Ti(μ-O2 SiPh2 )3 TiCp*] (3) can be envisaged as molecular models of titania-silica systems. Compounds 1-3 could potentially provide insights into the nature of the catalytically active sites in these systems; cod=1,5-cycloctadiene, Cp*=η5 -C5 Me5 .

The reaction of Cp*TiMe3 with 3 equiv of [Ir(μ-OH)(COD)]2 affords the new heterometallic organometallic oxide Cp*Ti(μ3-O)3[Ir(COD)]3 (3). Reaction of Cp*TaMe4 with 4 equiv of [M(μ-OH)(COD)]2 (M = Rh, Ir) yields complexes Cp*Ta(μ3-O)4[M(COD)]4 [M = Rh (5), Ir (6)]. The structure of compound 5 has been determined by X-ray diffraction. Complexes 5 and 6 react with the alcohol 3-CN-4,6-Me2-2-OH−C5HN to yield the corresponding rhodium (7) or iridium (8) alkoxide complexes. The structure of complex 8 has been determined by X-ray diffraction. Reaction of [Rh(μ-OH)(COD)]2 with thiolacetic acid gives rise to a thioacetate complex [Rh(μ-SCOCH3)(COD)]2 (9).

The reaction of Cp2ZrCl2 (Cp = η5-C5H5) with 2 equiv of the lithium amide derivative LiNHC6H4-o-SMe affords the new zirconium complex Cp2Zr(NHC6H4-o-SMe)2 (2). The structure of 2 has been determined by X-ray diffraction. When the reaction is carried out in an 1:1 ratio, the complex Cp2ZrCl(NHC6H4-o-SMe) (3) is generated as the major product. Reaction of “Cp*2Zr” (Cp* = η5-C5Me5) with 2-(methylmercapto)aniline yields a hydride−amide complex Cp*2ZrH(NHC6H4) (4). Reaction of complex 2 with [RhCl(COD)]2 generates complex 3 and the new rhodium amide complex Rh(NHC6H4-o-SMe)(COD), which has been also directly synthesized by reacting [RhCl(COD)]2 with LiNHC6H4-o-SMe. Thermolysis of complex 6, at 100 °C, produces to a new rhodium thiolate complex [Rh(μ-SC6H4-o-NHMe)(COD)]2 (5). Its structure has been determined by X-ray diffraction methods. Reaction of [IrCl(COD)]2 with LiNHC6H4-o-SMe gives the iridium(III) complex Ir(Me)(SC6H4NH)(COD) (7) by oxidative addition of the S−Me bond.

The perfluorothiolate dinuclear compounds [Rh( μ -SC 6 F 5 )(COD)[ 2 1 and [Rh( μ -SC 6 F 5 )(CO) 2 [ 2 2 react with PPh 3 to give monomeric and dimeric complexes, the particular product depending upon the PR 3 /Rh ratio and reaction conditions. Reaction of 2 with 2 moles of PPh 3 renders cis - 7 and trans -[Rh( μ -SC 6 F 5 )((CO)(PPh 3 )[ 2 8 , while with 4 moles of PPh 3 trans [Rh(SC 6 F 5 )(CO)(PPh 3 ) 2 [ 10a is obtained. This latter product can otherwise be prepared by Cl metathesis from trans -[RhCl(CO(PPh 3 ) 2 [ in toluene. This same reaction in dichloromethane however yields the cis isomer 10b . When a larger excess of PPh 3 is used, a mixture of compounds 11a and 11b is formed. An X-ray crystal structure study shows trans [Rh(SC 6 F 5 )(CO)(PPh 3 ) 2 [ to exit as two polymorphs. 11a crystallises in the space group P2 1 /n of the monoclinic system with a = 12.489(1), b = 15.430(5), c = 19.719(1) A, α = γ = 90, β = 92.84(1)°, and 11b is triclinic, space group P1¯ with a = 9.764(2), b = 12.197(6), c = 17.880 A, α = 100.18(5), β = 101.92(2), γ = 113.61(2)°. Both PPh 3 ligands are mutually trans and the difference in v (CO) stretching frequencies 1989 and 1939 cm −1 , can be explained in terms of o-phenyl H…CO interactions in the latter. The [Rh( μ -SC 6 F 5 )(COD)[ 2 1 and [Rh( μ -SC 6 F 5 )(CO) 2 [ 2 2 /nPPh 3 systems have been studied as catalyst precursors for the hydroformylation of 1-heptene in toluene at 30 bar and 343 K. Selectivity towards the linear aldehyde is enhanced when dimeric complexes are used.

RhNaY and RhHY zeolites have been prepared either by ion exchange with RhCl3 or by Rh6(CO)12 sublimation under vacuum. Except in the latter case, very small rhodium aggregates were obtained within the supercages of faujasitic zeolite. Photoelectron spectra and IR of chemisorbed carbon monoxide revealed that the interaction of these clusters with the zeolite matrix differs substantially, depending on the acidity of the zeolite. These clusters become aggregated during reduction or on-stream mainly at the outer zeolite surface irrespective of the degree of protonation of the zeolite. The RhNaYi catalyst proved to be interesting for the conversion of CO/H2 mixtures to low carbon number alkenes and alkanes with a propensity to form butenes/butanes. However, the parent RhHYi homologue produced a higher proportion of saturated and branched hydrocarbons, mainly the C4 fraction. These important differences in product distribution in the RhHYizeolite have been associated with the presence of cationic rhodium species as revealed by X-ray photoelectron spectroscopy and carbon monoxide chemisorption.

Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies.

Hydroxo and methoxo organometallic rhodium complexes [Rh(μ-OX)(COD)] 2 (X=H, OMe) have been anchored on supports such as SiO 2 , TiO 2 -SiO 2 and zeolite HY and they have been used as catalysts for the syngas reaction providing moderate good yield in oxygenated products. Their behaviour is compared with early-late heterobimetallic μ-oxo model complexes [Cp * Ti(μ 3 -O) 3 {Rh(COD)} 3 ] under different reaction conditions.

The catalytic performance for the hydroformylation reaction of hept-1-ene at 343 K and 30 atm total pressure has been studied over some rhodium-(I) complexes anchored to 2% DVB crosslinked phosphinated polystyrene. The catalysts were prepared from the common [RhCl(COD)] 2 precursor and characterized by FTIR and photoelectron (XPS) spectroscopy techniques. The activity profiles and the number of cycles operative in the reactor were found to depend markedly on the Rh:P ratio. A joint discussion involving the data obtained from the homogeneous process is also presented.

The reaction of dinuclear [M(μ-Cl)(COD)]2 (M = Rh, Ir) with mercaptopyrimidine and its methylated derivatives affords monomeric complexes. Depending on the nature of the solvent used, the pyrimidine behaves as both a monodentate ligand, bonded to the metal directly through the sulfur atom, and as a bidentate ligand, bonded to the metal atom through both the sulfur and a nitrogen atom, acting as a chelating ligand. Reaction of these complexes with CO yields dicarbonyl complexes through displacement of the COD ligand. Displacement of one of the CO molecules occurs in the presence of PPh3. Both rhodium and iridium phosphinated complexes may accept a second PPh3 molecule within their coordination sphere, with no displacement of the remaining CO ligand. Thiolate rhodium complexes have proved to be good catalysts in the hydroformylation reaction of 1-heptene in the presence of PPh3. The donor capacity of mercaptopyrimidine ligands has been correlated with the activity of the catalysts tested. In the present work, an increase in ligand basicity gave rise to a faster reaction. However, no significant modifications in the distribution of the final products were observed.

Electron-rich olefins of general type [[graphic omitted]R]2(LR2; R = Me, Et, Ph, 4-MeC6H4, 4-MeOC6H4, or 2-MeOC6H4) undergo reaction with a variety of rhodium(I) precursors via ligand displacement or chloride-bridge cleavage to afford monocarbenerhodium(I) complexes, such as [RhCl(LR)(PPh3)2], [Rh(cod)Cl(LR)], or [Rh(CO)Cl(LR)(PPh3)][LR=[graphic omitted]R, cod = cyclo-octa-1,5-diene]; complexes [RhCl(L′Me)(PPh2)X][L′Me=[graphic omitted]Me, X = CO or PPh3] have similarly been obtained from the olefin L′Me2. From these, further complexes may be obtained by ligand (neutral or anionic) exchange processes: trans-[RhBr(LR)(PPh3)2], trans-[Rh(CO)(LR)(PPh3)2]X (X = Br, Cl, ClO4, or I), [Rh(CO)X(LR)(PPh3)](X = BH4 or ClO4), cis-[Rh(CO)2X(LR)](X = Cl or NO3), [Rh(cod)X(LR)](X = CH2SiMe3, ClO4, or NO3), cis-[Rh(cod)-(LR)(PPh3)][ClO4], and [Rh(CO)3(LR)][ClO4]. In many of the reactions some of these ligand displacements at RhI proceed without retention of stereochemistry and it is likely that the observed product is the thermodynamically preferred isomer. Other chemical properties of the monocarbene-rhodium(I) complexes relate to (i) rare examples of the displacement of LR from Rh by PPh3 or Ph2PCH2CH2PPh2 under rather forcing conditions, and (ii) oxidative addition (not particularly facile) of HCl, [NMe2CHCl]Cl, or C2(CN)4. The 45 new complexes have been characterised by analysis and spectroscopy (i.r. and 1H and 31P n.m.r.) and, where appropriate, relative molecular mass determination, and electrical conductivity. From J(31P–103Rh) coupling constants it is concluded that LR has a greater trans influence than PPh3[also indicated by ν(Rh–Cl)] but a lower cis influence.