Rhodium complexes ethylene

A series of olefin complexes with formula [Rh(/t-Rpz)(C2H4)2]2 (Rpz = pyrazolate (pz), 3-methylpyrazolate (Mepz), 3,5-dimethylpyrazolate (Me2pz)) was studied. The compound with Me2Pz showed the shortest olefmic C=C distance found in ethylene rhodium complexes reported until 1996. ... 

The treatment of many metal salts either in solution or in the solid state may give smooth addition of the olefin to the complex. The famous Zeise s salt, first isolated in 1827 [16], is prepared by bubbling ethylene through an aqueous solution of potassium tetrachloroplatinate(Il) from which the yellow crystals of the complex, K+[C2H4PtCh]".H20, are precipitated. The reaction is catalysed by tin(Il) chloride [17], The bis-ethylene rhodium complex, 1.1, is similarly prepared [18]. 

Pentapyrrolic macrocycles, 2,888 2,1,2-Pen tathiadiazol e-4,7-dicarbonitrile in hydrogen production from water, 6, 508 Pentatungstobis(organophosphonates), 3, 1053 4-Penten-l-al reaction with ethylene catalysts, rhodium complexes, 6, 300... 

It was elegantly shown later that the hydroamination of ethylene with piperidine or Et2NH can be greatly improved using cationic rhodium complexes at room temperature and atmospheric pressure to afford a high yield of hydroaminated products (Eq. 4.10) [111]. However, possible deactivation of the catalyst can be questioned [17]. 

The most recent catalysts that operate under thermal conditions were then based on the premise that a Cp M fragment with ligands that dissociate under thermal conditions could be a catalyst for alkane borylation. After a brief study of Cp IrH4 and Cp Ir(ethylene)2, Dr. Chen studied related rhodium complexes. Ultimately, he proposed that the Cp Rh(ri" -C6Me6) complex would dissociate CeMce as an iimocent side product, and that Cp Rh(Bpin)2 from oxidative addition of pinBBpin (pin=pinacolate) would be the active catalyst. The overall catalytic... 

Late transition metal boratabenzene complexes can catalyze C-H activation thus, the bis(ethylene)rhodium derivatives (HsCsB-R)Rh(C2H4)2 (R = Ph, NMe2) promote boration of alkanes faster than does the Cp analog Cp Rh(C2H4)2, although the boratabenzene compounds are thermally less stable.110... 

Thermolysis of (cycloheptatrienylmethyl)carbene complexes 554 [toluene, 1-2 h, 80-100°C MLn = Cr(CO)5, W(CO)5] affords an equilibrium mixture of 4,5-homotropilidenes 555 and 556. According to the NMR data and the results of AMI calculations, the formation of isomer 556 (equation 218) is strongly favored277. This course of events was called intramolecular cyclopropanation , and it was shown that the equilibrium between the 4,5-homotropilidene complexes is significantly different from that of the metal-free ligands. By reaction of the latter (555 and 556) with bis(ethylene)rhodium 1,3-pentanedionate 557, the complexes 558 and 559 of both 4,5-homotropilidenes were obtained in a 1 3 ratio. These complexes are non-fluxional and are configurationally stable at room temperature (equation 219)277. 

Other recent reports have also indicated that mixed-metal systems, particularly those containing combinations of ruthenium and rhodium complexes, can provide effective catalysts for the production of ethylene glycol or its carboxylic acid esters (5 9). However, the systems described in this paper are the first in which it has been demonstrated that composite ruthenium-rhodium catalysts, in which rhodium comprises only a minor proportion of the total metallic component, can match, in terms of both activity and selectivity, the previously documented behavior (J ) of mono-metallic rhodium catalysts containing significantly higher concentrations of rhodium. Some details of the chemistry of these bimetallic promoted catalysts are described here. 

Kaplan has proposed that ion pairing between rhodium complex anions and the positively charged counterions has an adverse effect on catalytic activity for ethylene glycol formation (96, 109, 110). The following scheme ... 

When the catalyst was used for simple olefin systems, it was not as active as with the amino acid precursors. Table III shows the relative rates for a variety of substrates, special care being taken in each case to purge oxygen. The slow rate of a-phenylacrylic acid was unexpected, but, it may be the result of a stable olefin-rhodium complex similar to the one Wilkinson (15) experienced with ethylene. Such a contention is consistent with the increased speed of hydrogenation with increased pressure. 

Industrial Applications. Several large scale industrial processes are based on some of the reactions listed above, and more are under development. Most notable among those currently in use is the already mentioned Wacker process for acetaldehyde production. Similarly, the production of vinyl acetate from ethylene and acetic acid has been commercialized. Major processes nearing commercialization are hydroformylations catalyzed by phosphine-cobalt or phosphine-rhodium complexes and the carbonylation of methanol to acetic acid catalyzed by (< 3P) 2RhCOCl. 

When ethylene was passed into a basic solution of Hg(OAc)2 containing a catalytic amount of [Rh2(OH)3(C5Me5)2]+, ethanol was formed.617 It appears that mercury salts of the type HOCH2CH2HgOAc are formed in a stoichiometric reaction so that this is not strictly a catalytic activation of ethylene by the rhodium complex. 

The directing group promoted C-H activation reaction is applicable to sp C-H bonds adjacent to the nitrogen in alkylamines, as shown in Scheme 5. Alkylation occurred when reaction of 25 with CO and ethylene was conducted in the presence of Ru3(CO)12 as catalyst [11], On the other hand, the use of a rhodium complex as catalyst resulted in C-H carbonylation [12],... 

The starting materials given to the computer were, according to Cramer s scheme (123), a bis(ethylene)rhodium(I) complex, an HX molecule (X = chloride atom) and a solvent molecule (L). TAMREAC finds, in the initial step, two possible product-intermediates (2 and 5, Fig. 6). We store them in the disk and we continue the generation of the synthetic sequences starting from the intermediate 2 or 5 in order to find the intermediates of the second step, which will be also stored. The same operation is repeated with all the intermediates until the generation of the initial catalyst (1, Fig. 6). 

Most of the ground states of complexes seem to have structure XXIV, but XXV reasonably could provide a mechanism for rotation about the metal-olefin bond axis with a low energy barrier. Cramer (II) found that 7r-cyclopentadienylbis(ethylene)rhodium(I), XXVI, gave two broad signals (r = 7.23, 8.88 ppm) for the ethylene protons at —25° and that... 

Ghosh CK, Graham AG. A rhodium complex that combines benzene activation with ethylene insertion — subsequent carbonylation and ketone formation. J Am Chem Soc 1989 111 375-376. 

Likewise, mononuclear complexes of rhodium and platinum containing only one meth-ylenecyclopropane ligand are prepared by ligand exchange reactions of the Feist s esters with (acac)Rh(CO)2 and rra 5-Cl2(pyr)Pt(ethylene), giving complexes (acac)(CO)Rh(tF) and trans-C 2(pyr)FiL (L = cF, tF), respectively (equation 311). 

The reaction of M3(CO)12 with both open-chain and cyclic poly-alkenes has attracted some attention, especially in the case of Ru3(CO)i2. In most of the examples reported, the organic fragment bonds to the metal framework in such a way as to interact with more than one of the three metal atoms (68-77). There are some exceptions to this general statement, however. One is the reaction of Ru3(CO)j 2 with cyclopentadiene, in which a mononuclear complex is obtained (78). In other cases, tetranuclear and hexanuclear compounds are obtained (79 81). Cluster breakdown has also been observed in the case of a rhodium complex upon reaction with ethylene (55) as shown in Fig. 3. 

---