Bis(di-t-butylphosphino)methane complexes of rhodium: homogeneous alkyne hydrosilylation by catalyst-dependent alkyne insertion into Rh---Si or Rh---H bonds. Molecular structures of the dimer [(dtbpm)RhCl]2 and of the silyl complex (dtbpm) Rh[Si(OEt)3](PMe3)

The homogeneous, Rh-catalysed hydrosilylation of but-2-yne with triethoxysilane has been studied. All rhodium complexes employed as catalyst precursors contain ^tBu₂PCH₂P^tBu₂ (“dtbpm”) as a chelating ligand. The crystal and molecular structure of the dimer [(dtbpm)RhCl]₂ (10) has been determined by X-ray diffraction. Complex 10 is shown to be a sluggish catalyst in hydrosilylation reactions of hex-1-ene, whereas but-2-yne is hydrosilylated more rapidly. A much more efficient and highly selective catalyst is 10 with added PPh₃, equivalent to the use of monomeric (dtbpm)RhCl(PPh₃). (E)-2-Triethoxysilylbut-2-ene is formed exclusively and with high turnover numbers in this case. For both 10 and its PPh₃ derivative, the 14-electron fragment [(dtbpm)RhCl], formed by dissociation processes, is the most likely active intermediate in a Harrod-Chalk-type catalytic cycle. The PPh₃ dissociation equilibrium has been studied in detail for (dtbpm)RhCl(PPh₃) and its thermodynamic parameters have been determined. With rhodium alkyl complexes as catalyst precursors, a different type of alkyne hydrosilylation catalysis, involving direct alkyne insertion into the Rh---Si bond of an intermediate rhodium silyl complex, (dtbpm)Rh[Si(OEt)₃](PMe₃) (14), has been found. Complex 14 was synthesized independently from (dtbpm)RhMe(PMe₃) and characterized by X-ray diffraction. It is an equally active catalyst itself, yielding (E)-2-triethoxysilylbut-2-ene as the major product (90%) from but-2-yne and HSi(OEt)₃ (turnover number 1000 per 30 min). The insertion step of the alkyne into the Rh---Si bond of 14 and the formation of two stereoisomeric rhodium vinyl complexes were established independently for MeO₂CCCCO₂Me as a more reactive alkyne substrate. A catalytic cycle is proposed for this unprecedented hydrosilylation reaction. The synthesis of the ν³-benzyl complex (dtbpm)Rh(η³-CH₂C₆H₅) (23) is described. This compound allows an alternative, more efficient access to the new silyl complex (dtbpm)Rh[Si(OEt)₃](PMe₃).     

Rhodium(I) and rhodium(III) complexes formed by coordination and C-H activation of bulky functionalized phosphanes

The reaction of [[RhCl(C(8)H(14))(2)](2)] (2) with iPr(2)PCH(2)CH(2)C(6)H(5) (L(1)) led, via the isolated dimer [[RhCl(C(8)H(14))(L(1))](2)] (3), to a mixture of three products 4 a-c, of which the dinuclear complex [[RhCl(L(1))(2)](2)] (4 a) was characterized by Xray crystallography. The mixture of 4a-c reacts with CO, ethene, and phenylacetylene to give the square-planar compounds trans-[RhCl(L)(L(1))(2)] (L=CO (5), C(2)H(4) (6), C=CHPh (9)). The corresponding allenylidene(chloro) complex trans-[RhCl(=C=C=CPh(2))(L(1))(2)] (11), obtained from 4 a-c and HC triple bond CC(OH)Ph(2) via trans-[RhCl[=C=CHC(OH)Ph(2)](L(1))(2)] (10), could be converted stepwise to the related hydroxo, cationic aqua, and cationic acetone derivatives 12-14, respectively. Treatment of 2 and [[RhCl(C(2)H(4))(2)](2)] (7) with two equivalents of tBu(2)PCH(2)CH(2)C(6)H(5) (L(2)) gave the dimers [[RhCl(C(8)H(14))(L(2))](2)] (15) and [[RhCl(C(2)H(4))(L(2))](2)] (16), which both react with L(2) in the molar ratio of 1:2 to afford the five-coordinate aryl(hydrido)rhodium(III) complex [RhHCl(C(6)H(4)CH(2)CH(2)PtBu(2)-kappa(2)C,P)(L(2))] (17) by C-H activation. The course of the reactions of 17 with CO, H(2), PhC triple bond CH, HCl, and AgPF(6), leading to the compounds 19-21, 24, and 25 a, respectively, indicate that the coordinatively unsaturated isomer of 17 with the supposed composition [RhCl(L(2))(2)] is the reactive species. Labeling experiments using D(2), DCl, and PhC triple bond CD support this proposal. With either [Rh(C(8)H(14))(eta(6)-L(2)-kappaP]PF(6) or [Rh(C(2)H(4))(eta(6)-L(n)-kappaP]PF(6) (n=1 and 2) as the starting materials, the corresponding halfsandwich-type complexes 27, 28, and 32 were obtained. The nonchelating counterpart of the dihydrido compound 32 with the composition [RhH(2)(PiPr(3))(eta(6)-C(6)H(6))]PF(6) (35) was prepared stepwise from [Rh(C(2)H(4))(PiPr(3))(eta(6)-C(6)H(6))]PF(6) and H(2) in acetone via the tris(solvato) species [RhH(2)(PiPr(3))(acetone)(3)]PF(6) (34) as intermediate. The synthesis of the bis(chelate) complex [Rh(eta(4)-C(8)H(12))(C(6)H(5)OCH(2)CH(2)PtBu(2)-kappa(2)O,P)]BF(4) (39) is also described. Besides 4 a, the compounds 17, 25 a, and 39 have been characterized by Xray crystal structure analysis.     

Phosphabenzenes as monodentate pi-acceptor ligands for rhodium-catalyzed hydroformylation

A new class of phosphinine/rhodium catalysts for the hydroformylation of terminal and internal alkenes is presented in this study. A series of phosphabenzenes 1-14 has been prepared by condensation of phosphane or tris(trimethylsilyl)phosphane with the corresponding pyrylium salt. Trans-[(phosphabenzene)2RhCl(CO)] complexes 21-25 have been prepared and studied spectroscopically and by X-ray crystal-structure analysis. The hydroformylation of oct-1-ene has been used to identify optimal catalyst preformation and reaction conditions. Hydroformylation studies with 15 monophosphabenzenes have been performed. The catalytic performance is dominated by steric influences, with the phosphabenzene 8/rhodium system being the most active catalyst. Turnover frequencies of up to 45370 h(-1) for the hydroformylation of oct-1-ene have been determined. In further studies, hydroformylation activity toward more highly substituted alkenes was investigated and compared with the standard industrial triphenylphosphane/rhodium catalyst. The reactivity differences between the phosphabenzene and the triphenylphosphane catalyst increase on going to the more highly substituted alkenes. Even tetrasubstituted alkenes reacted with the phosphabenzene catalyst, whereas the triphenylphosphane system failed to give any product. In situ pressure NMR experiments have been performed to identify the resting state of the catalyst. A monophosphabenzene complex [(phosphinine 8)Ir(CO)3H] could be detected as the predominant catalyst resting state.     

The bridging function of an apparently nonbridging ligand: dinuclear rhodium complexes with Rh(mu-SbR3)Rh as a molecular unit

Novel dinuclear rhodium complexes of the general composition [Rh2Cl2(mu-CRR')2(mu-SbiPr3)] (4-6) were prepared by thermolysis of the mononuclear precursors trans-[RhCl(=CRR')(SbiPr3)2] in excellent yield. The X-ray crystal structure analysis of 4 (R = R' = Ph) confirms the symmetrical bridging position of the stibane ligand. Related compounds [Rh2Cl2(mu-CPh2)(mu-CRR')(mu-SbiPr3)] (7, 8) with two different carbene units were obtained either from trans-[RhCl(=CPh2)(SbiPr3)2] (1) and RR'CN2 or by a conproportionation of 4 and 5 (R = R' = p-Tol) or 4 and 6 (R= Ph, R' = p-Tol), respectively. While CO reacts with 4 to give the polymeric product [[RhCl(CPh2)(CO)]n] (9), tert-butyl isocyanide replaces the bridging stibane and yields [Rh2Cl2(mu-CPh2)2(mu-CNtBu)] (10). The reaction of 4 with tertiary phosphanes PR3 leads to complete bridge cleavage and affords the mononuclear compounds trans-[RhCl(=CPh2)(PR3)2] (11-15). In contrast, treatment of 4 with SbMe3 and SbEt3 yields the related triply bridged complexes [Rh2Cl2(mu-CPh2)2(mu-SbR3)] (16, 17) by substitution of SbiPr3 for the smaller stibanes. The displacement of the chloro ligands in 4-6 and 10 by n5-cyclopentadienyl gives the dinuclear complexes [(n5-C5H5)2Rh2(mu-CRR')2] (18-20) and [(n5-C5H5)2Rh2(mu-CPh2)2(mu-CNtBu)] (21), of which 18 (R = R' = Ph) was characterized crystallographically.     

Catalytic intermolecular ortho-arylation of phenols

The use of rhodium catalysts such as [RhCl(PPh3)3] or [[RhCl(COD)]2] with PiPr2(OAr) or P(NMe2)3 co-catalysts allows the ortho-selective intermolecular arylation of phenols. The reaction proceeds via orthometalation of P-OAr groups and then transesterification liberates the product phenol. When 2-substituted phenols are used as substrates, [RhCl(PPh3)3]/iPr2(OAr) mixtures are typically the catalysts of choice, whereas for substrates without 2-substitution [[RhCl(COD)]2]/P(NMe2)3 mixtures tend to give better results.     

Pentamethylcyclopentadienylrhodium(I) complexes incorporated into porous polysiloxanes prepared by a sol–gel process: catalysts for hydrogenation of crotonic acid in water

Pentamethylcyclopentadiene‐functionalized polysiloxanes were prepared by a sol–gel process from tetraethoxysilane and (pentamethylcyclopentadienylmethyl)methyldiethoxysilane without a catalyst. The polysiloxanes are microporous–mesoporous solids, of which the BET surface areas and micropore volumes are inversely proportional to the concentration of the functionalizing agent (5–21 mol%) in the starting mixture of alkoxysilanes. The polysiloxanes were also characterized by CP MAS ¹³C NMR spectroscopy, revealing essentially the same structure of organofunctional ligand as that in particulate materials with low surface areas prepared earlier in a sol–gel process catalyzed by dibutyltin diacetate. Novel alkoxysilyl‐substituted pentamethylcyclopentadienyl (1,5‐cyclo‐octadiene)rhodium(I) complexes were synthesized from the corresponding cyclopentadienes by deprotonation followed by reaction with [(cod)RhCl]₂ (cod = cyclo‐octadiene). Polysiloxane‐bound rhodium complexes were prepared by a sol–gel reaction analogous to the one mentioned above and were found to catalyze the hydrogenation of crotonic acid in water; to the best of our knowledge, this constitutes the first example of catalysis by a well‐defined polysiloxane‐bound transition metal complex in an aqueous system. Copyright © 2000 John Wiley & Sons, Ltd.     

水/有机两相体系中单萜烯烃的氢甲酰化反应

考察了水溶性铑膦络合物RhCl(CO)(TPPTS)2(TPPTS为间-三苯基膦三磺酸钠)在水/有机两相体系中对不同单萜烯的氢甲酰化反应的催化性能.结果表明,添加表面活性剂对催化活性影响很大.在8.0 MPa,100℃的条件下,该催化体系对萜烯氢甲酰化反应具有较好的催化活性,月桂烯、莰烯和艹宁烯的转化率可分别达到92%,72%和86%.反应完成后,含水溶性铑膦络合物的水溶液与含产物的有机相分离方便,催化剂重复使用8次,其活性和选择性均未明显下降,易于实现催化剂的循环使用.     

Crescent-shaped rhodium(I) complexes with bis(o-carboxymethylphenyl)triazenide

Reaction of [[Rh(mu-Cl)(CO)2]2] with the triazene ArNNNHAr (Ar = o-CO2MeC6H4) produced the mononuclear complex [RhCl(ArNNNHAr)(CO)2] (1). Complex 1 reacted with KOH in methanol to give the dinuclear compound [[Rh(mu-ArNNNAr)(CO)2]2] (2), which showed a "mu-(1kappaN1,2kappaN3)-ArNNNAr" coordination mode for both bridging ligands. The dinuclear complex [[Rh(mu-ArNNNAr)(CO)2]2] (2) easily undergoes redistribution reactions in which the eight-membered "Rh2(NNN)2" core is broken. Thus, reaction of 2 with the anionic complex (NHEt3)[RhCl2(CO)2] gave the single-bridged complex (NHEt3)[Rh2(mu-ArNNNAr)Cl2(CO)4] (4), while the trinuclear complexes [Rh3(mu-ArNNNAr)(mu-Cl)(mu-CO)Cl(CO)4] (5) and [Rh3(mu-ArNNNAr)2(mu-Cl)(mu-CO)(CO)3] (6) were isolated by addition of the neutral compound [[Rh(mu-Cl)(CO)2]2] to 2, depending on the molar ratio employed. The formation of 5 and 6 involved the loss of carbonyl groups and the coordination of the oxygen atoms of the CO2Me groups. The structures of 4, 5, and 6 have been determined by X-ray diffraction methods, which show the ability of bis(o-carboxymethylphenyl)triazenide to act as bi-, tri-, and tetra-dentate ligand-spanning dinuclear moieties in trinuclear complexes.     

A new, easily recyclable arylating agent based on a diphosphino-digold(I) complex

The synthesis of two organogold(I) complexes, [(Au(NCN))2(dppbp)] (6) and [(Au(Phebox))2(dppbp)] (9), and their application in subsequent transmetalating reactions are described. A trinuclear organogold(I) complex, [(AuCl)3(tdpppb)] (4) is also reported, which exhibits a surprisingly high solubility in dichloromethane. It was found that 6 and 9 can cleanly transfer the anionic NCN-([C(6)H(3)(CH(2)NMe(2))2-2,6]-) or Phebox-([2,6-bis(oxazolinyl)phenyl]-) moiety to Ti(IV) and Pd(II) centers, respectively. The coproduct [(AuCl)2(dppbp)] (3, dppbp is [4-Ph(2)PC(6)H(4)]2 (1)) formed during this transmetalation reaction, precipitates almost quantitatively from the reaction mixture (toluene) and can thus be separated by simple filtration. In comparison, [AuCl(PPh3)], formed as the coproduct in the transmetalation reaction of [Au(NCN)(PPh3)] with metal salts, has a higher solubility in apolar solvents and thus is more difficult to separate from the resultant organometallic complex. Digold complex 6 has been characterized by NMR spectroscopy and crystallographic analyses. These analyses show that the two gold units are essentially independent. The formation of a dimetallic transmetalating agent based on gold(I) had no effect on its transmetalating properties.     

New diphosphine ligands containing ethyleneglycol and amino alcohol spacers for the rhodium-catalyzed carbonylation of methanol

The new diphosphine ligands Ph(2)PC(6)H(4)C(O)X(CH(2))(2)OC(O)C(6)H(4)PPh(2) (1: X=NH; 2: X=NPh; 3: X=O) and Ph(2)PC(6)H(4)C(O)O(CH(2))(2)O(CH(2))(2)OC(O)C(6)H(4)PPh(2) (5) as well as the monophosphine ligand Ph(2)PC(6)H(4)C(O)X(CH(2))(2)OH (4) have been prepared from 2-diphenylphosphinobenzoic acid and the corresponding amino alcohols or diols. Coordination of the diphosphine ligands to rhodium, iridium, and platinum resulted in the formation of the square-planar complexes [(Pbond;P)Rh(CO)Cl] (6: Pbond;P=1; 7: Pbond;P=2; 8: Pbond;P=3), [(Pbond;P)Rh(CO)Cl](2) (9: Pbond;P=5), [(P-P)Ir(cod)Cl] (10: Pbond;P=1; 11: Pbond;P=2; 12: Pbond;P=3), [(Pbond;P)Ir(CO)Cl] (13: Pbond;P=1; 14: Pbond;P=2; 15: Pbond;P=3), and [(Pbond;P)PtI(2)] (18: Pbond;P=2). In all complexes, the diphosphine ligands are trans coordinated to the metal center, thanks to the large spacer groups, which allow the two phosphorus atoms to occupy opposite positions in the square-planar coordination geometry. The trans coordination is demonstrated unambiguously by the single-crystal X-ray structure analysis of complex 18. In the case of the diphosphine ligand 5, the spacer group is so large that dinuclear complexes with ligand 5 in bridging positions are formed, maintaining the trans coordination of the P atoms on each metal center, as shown by the crystal structure analysis of 9. The monophosphine ligand 4 reacts with [[Ir(cod)Cl](2)] (cod=cyclooctadiene) to give the simple derivative [(4)Ir(cod)Cl] (16) which is converted into the carbonyl complex [(4)Ir(CO)(2)Cl] (17) with carbon monoxide. The crystal structure analysis of 16 also reveals a square-planar coordination geometry in which the phosphine ligand occupies a position cis with respect to the chloro ligand. The diphosphine ligands 1, 2, 3, and 5 have been tested as cocatalysts in combination with the catalyst precursors [[Rh(CO)(2)Cl](2)] and [[Ir(cod)Cl](2)] or [H(2)IrCl(6)] for the carbonylation of methanol at 170 degrees C and 22 bar CO. The best results (TON 800 after 15 min) are obtained for the combination 2/[[Rh(CO)(2)Cl](2)]. After the catalytic reaction, complex 7 is identified in the reaction mixture and can be isolated; it is active for further runs without loss of catalytic activity.     

A one-pot synthesis of (E)-disubstituted alkenes by a bimetallic [Rh-Pd]-catalyzed hydrosilylation/hiyama cross-coupling sequence

A bimetallic [Rh-Pd] catalyst was prepared by soaking into an iodide ionic gel an equimolar solution of [RhCl(PPh(3))(3)] and Pd(OAc)(2) in CH(2)Cl(2). Its catalytic activity was evaluated by rhodium-catalyzed hydrosilylation (H), palladium-catalyzed Hiyama coupling (C), and in the one-pot hydrosilylation/Hiyama coupling sequence (H/C). It was found that the homogeneous combination [RhCl(PPh(3))(3)]/NaI was a superior system compared to the polyionic mono- and bimetallic rhodium catalysts in the hydrosilylation of terminal alkynes. Interestingly, the most effective catalyst in terms of stereo- and chemoselectivities was observed to be the bimetallic ionic gel [Rh-Pd] in the one-pot process leading to (E)-alkenes with good yields. The remarkable stereocontrol is ascribed to a beneficial Pd-catalyzed isomerization from the mixture of stereoisomeric vinylsilanes obtained in the initial hydrosilylation step into the more stable (E)-adduct. The [Rh-Pd] heterogeneous catalyst also showed a higher chemoselectivity than the homogeneous catalytic combination, and no detrimental formation of Sonogashira side product was observed due to an ionic-gel-mediated kinetic modulation. To illustrate its scope and limitations, the described one-pot bimetallic catalytic sequence was extended to functionalized terminal alkynes and various iodide substrates. Conjugated systems, such as hydroxycinnamaldehyde, dienes, and trienes, were synthesized in good overall yields. To avoid deactivation of the Rh species, N-heterocyclic iodides had to be added sequentially after completion of hydrosilylation.     

Entrapment of an organometallic complex within a metal: a concept for heterogeneous catalysis

A novel family of composite materials, organically doped metals, has been recently introduced. Here, we demonstrate their use as a new platform for heterogeneous catalysis, namely the doping of a metal with a catalytic organometallic complex. Specifically, a rhodium(I) catalyst, (RhCl(COD)(Ph2P(C6H4SO3Na))), ([Rh]), was physically entrapped within silver, thus creating a new type of catalytic material: [Rh]@Ag. Several aspects were demonstrated with the development of this heterogeneous catalyst: a metal can be used as a support for heterogenizing a homogeneous catalyst; the homogeneous catalyst is stabilized by the entrapment within the metal; the products of the composite catalyst are different compared to those obtained from the homogeneous one; and the adsorption of [Rh] on the surface of Ag and its entrapment are very different processes only the latter provided appreciable catalytic activity. Thus, while homogeneous [Rh] was entirely destroyed after converting styrene to ethylbenzne at 50%, [Rh]@Ag remained active after effecting the same reaction to a yield of 85% (compared to only 7% for [Rh] adsorbed on Ag), and while homogeneous [Rh] hydrogenated diphenylacetylene to bibenzyl (and was completely deactivated after one cycle) with no trace of cis-stilbene, [Rh]@Ag afforded that compound as the main product and could be reused.     

Efficient construction of the bicyclo[5.3.0]decenone skeleton based on the Rh(I)-catalyzed allenic Pauson-Khand reaction

A reliable procedure for constructing a bicyclo[5.3.0]deca-1,7-dien-9-one ring system by rhodium-catalyzed Pauson-Khand reaction (PKR) of allenynes with a sulfonyl group has been developed. Investigation of the rhodium-catalyzed PKR on 19 examples of 1,2-nonadien-8-yne derivatives demonstrated that (i) acceptable yields could be consistently achieved through the proper choice of the rhodium catalyst ([RhCl(CO)(2)](2) or [RhCl(CO)dppp](2)) depending on the starting allenyne and that (ii) an ester functionality as well as hydroxy and siloxy groups could be tolerated in this rhodium-catalyzed PKR.     

Oxidative C-arylation of free (NH)-heterocycles via direct (sp3) C-H bond functionalization

The development of a new chemical transformation, namely oxidative C-arylation of saturated (NH)-heterocycles, is described. This reaction combines dehydrogenation and arylation in one process, leading to cross-coupling of (NH)-heterocycles and haloarenes. Typical reaction conditions involve heating the reaction partners in anhydrous dioxane at 120-150 degrees C in the presence of RhCl(CO)[P(Fur)3]2 as the catalyst and Cs2CO3 as the base. Addition of tert-butylethylene as the hydrogen acceptor increases the chemical yield by diminishing the dehalogenation pathway. This method demonstrated a good substrate scope, allowing for cross-coupling of a variety of (NH)-heterocycles (e.g., pyrrolidine, piperidine, piperazine, morpholine) and halo(hetero)arenes to afford valuable heterocyclic products in one step. The preliminary mechanistic studies provided some insight regarding the key events in the proposed catalytic cycle, including beta-hydride elimination of an amido rhodium complex and carbometalation of the resulting imine. A large kinetic isotope effect [KIE (kC-H/kC-D) = 4.3] suggests that one or both beta-hydride elimination steps are rate determining. The central role for the phosphine ligand was established in controlling the partitioning between the oxidative C-arylation and N-arylation pathways.     

Cationic and neutral diphenyldiazomethanerhodium(I) complexes as catalytically active species in the C-C coupling reaction of olefins and diphenyldiazomethane

Cationic rhodium(I) complexes cis-[Rh(acetone)2(L)(L')]+ (2: L = L'=C8H14; 3: L=C8H14; L'=PiPr3; 4: L=L'=PiPr3), prepared from [RhCl(C8H14)2]2] and isolated as PF6 salts, catalyze the C-C coupling reaction of diphenyldiazomethane with ethene, propene, and styrene. In most cases, a mixture of isomeric olefins and cyclopropanes were obtained which are formally built up by one equivalent of RCH=CH2 (R = H, Me, Ph) and one equivalent of CPh2. The efficiency and selectivity of the catalyst depends significantly on the coordination sphere around the rhodium(I) center. Treatment of 4 with Ph2CN2 in the molar ratio of 1:1 and 1:2 gave the complexes trans-[Rh(PiPr3)2(acetone)(eta1-N2CPh2)]PF6 (8) and trans-[Rh(PiPr3)2(eta1-N2CPh2)2]PF6 (9), of which 8 was characterized by X-ray crystallography. Since 8 and 9 not only react with ethene but also catalyze the reaction of C2H4 and free Ph2CN2, they can be regarded as intermediates (possibly resting states) in the C-C coupling process. The lability of 8 and 9 is illustrated by the reactions with pyridine and NaX (X=Cl, Br, I, N3) which afford the mono(diphenyldiazomethane)rhodium(I) compounds trans-[Rh(PiPr3)2(py)(eta1-N2CPh2)]PF6 (10) and trans-[RhX(eta1-N2CPh2)(PiPr3)2] (11-14), respectively. The catalytic activity of the neutral complexes 11 - 14 is somewhat less than that of the cationic species 8, 9 and decreases in the order Cl > Br> I > N3.     

Trimethylammonium-containing rhodacarborane [(9-NMe3-7,8-C2B9H10)RhCl2]2 as a catalyst for the annulation of arylcarboxylic acids with alkynes

Russian Chemical Bulletin - Rhodacarborane [(9-NMe3-7,8-C2B9H10)RhCl2]2 exhibited moderate catalytic activity in the reaction of annulation of arylcarboxylic acids with alkynes, giving naphthalenes...     

Synthesis of silica‐supported rhodium carbene complex as efficient catalyst for the addition of phenylboronic acid to aldehydes

Silica‐supported catalytically active functional materials, such as the rhodium(I) carbene complex with 1‐(triethoxysilylpropyl)‐3‐(2,4,6‐trimethylbenzyl)imidazolidine‐2‐ylidine (L), were prepared using the sol–gel method. The complex ( 1 ; COD = 1,5‐cyclooctadiene) RhCl(COD)[1‐(triethoxysilylpropyl)‐3‐(2,4,6‐trimethylbenzyl)imidazolidin‐2‐ylidine] was characterized by conventional spectroscopic methods and elemental analyses and the silica‐supported functional material RhCl(COD)(L) were tested for the catalytic addition of phenylboronic acid to aldehydes. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly efficient asymmetric epoxidation of alkenes with a D(4)-symmetric chiral dichlororuthenium(IV) porphyrin catalyst.

A dichlororuthenium(IV) complex of 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,2:5,8-dimethanoanthrance-9-yl]porphyrin, [Ru(IV)(D(4)-Por)Cl(2)] (1), was prepared by heating [Ru(II)(D(4)-Por)(CO)(MeOH)] (2) in refluxing CCl(4). Complex 1 is characterized by (1)H NMR (paramagnetically shifted pyrrolic protons at delta(H) = -52.3 ppm), FAB-mass spectroscopies, and magnetic susceptibility measurement (mu(eff) = 3.1 mu(B)). The ruthenium complex exhibits remarkable catalytic activity toward enantioselective alkene epoxidation using 2,6-dichloropyridine N-oxide (Cl(2)pyNO) as terminal oxidant. The Ru(IV)-catalyzed styrene epoxidation is achieved within 2 h (versus 48 h for the 2-catalyzed reaction), and optically active styrene oxide was obtained in 69% ee and 84% yield (875 turnovers). Likewise, substituted styrenes and some conjugated cis-disubstituted alkenes (e.g., cis-beta-methylstyrene, cis-1-phenyl-3-penten-1-yne, 1,2-dihydronaphthalene, and 2,2-dimethylchromenes) are converted effectively to their organic epoxides in 50-80% ee under the Ru(IV)-catalyzed conditions, and more than 850 turnovers of epoxides have been attained. When subjecting 1 to four repetitive uses by recharging the reaction mixture with Cl(2)pyNO and styrene, styrene oxide was obtained in a total of 2190 turnovers and 69% ee. UV-vis and ESI-mass spectral analysis of the final reaction mixture revealed that a ruthenium-carbonyl species could have been formed during the catalytic reaction, leading to the apparent catalyst deactivation. We prepared a heterogeneous chiral ruthenium porphyrin catalyst by immobilizing 1 into sol-gel matrix. The heterogeneous catalyst is highly active toward asymmetric styrene epoxidation producing styrene oxide in 69% ee with up to 10,800 turnovers being achieved. The loss of activity of the Ru/sol-gel catalyst is ascribed to catalyst leaching and/or deactivation. On the basis of Hammett correlation (rho(+) = -1.62, R = 0.99) and product analysis, a dioxoruthenium(VI) porphyrin intermediate is not favored.     

Complexes amines du rhodium(I) : I. Complexes du type chloro-monoamine cyclooctadiène- 1,5 rhodium(I) et leurs produits de réaction avec l''oxyde de carbone

The reaction of amines with [(RhClCod)₂] (Cod = 1,5-cyclooctadiene) gives monomeric compounds [RhCl(Am)Cod](Am = amine). Elementary analyses as well as IR and NMR spectra are consistent with their structure.On treatment with carbon monoxide at atmospheric pressure these compounds give a series of complexes, [RhCl(Am)(CO)₂], identified by elementary analyses and IR spectra.The thermolysis of [RhCl(Aam)(CO)₂] with Aam = allyamine gives [{RhCl(Aam)CO_n}] not perfectly isolated. The reaction of [{RhCl(CO)₂}₂] with 2-vinylpyridine leads to the same kind of compound [{RhCl(Vpy)CO_m}] with Vpy = 2 -vinylpyridine. This latter complex is identified by elementary analysis. The IR spectra of these two complexes show that the olefinic double bond of amines β,γ-insaturated interacts with a rhodium atom. Their properties are discussed.     

Development of an Improved Rhodium Catalyst for Z‐Selective Anti‐Markovnikov Addition of Carboxylic Acids to Terminal Alkynes

To develop more active catalysts for the rhodium‐catalyzed addition of carboxylic acids to terminal alkynes furnishing anti‐Markovnikov Z enol esters, a thorough study of the rhodium complexes involved was performed. A number of rhodium complexes were characterized by NMR, ESI‐MS, and X‐ray analysis and applied as catalysts for the title reaction. The systematic investigations revealed that the presence of chloride ions decreased the catalyst activity. Conversely, generating and applying a mixture of two rhodium species, namely, [Rh(DPPMP)₂][H(benzoate)₂] (DPPMP=diphenylphosphinomethylpyridine) and [{Rh(COD)(μ₂‐benzoate)}₂], provided a significantly more active catalyst. Furthermore, the addition of a catalytic amount of base (Cs₂CO₃) had an additional accelerating effect. This higher catalyst activity allowed the reaction time to be reduced from 16 to 1–4 h while maintaining high selectivity. Studies on the substrate scope revealed that the new catalysts have greater functional‐group compatibility.