Rhodium insertion

The initial step is an oxidative addition of RhCI(PPh3)3 to a C-0 bond of the ester moiety and produces rhodium-carbon and rhodium-oxygen bonds. Adjacent rhodium species can undergo further reaction with the formation of anhydride linkages. This anhydride formation may occur between adjacent pairs of reactants, between pairs in the same chain, or between pairs that are present in different chains. All of these reactions are observed, and in however the last reaction is the one of interest here since this leads to cross-linking and char formation. Rhodium is present in both the chary material and in the soluble fractions. From the reaction pathway in order for rhodium elimination to occur, two rhodium-inserted... 

Metal(II) species, homobimetallic complexes - During a rhodium insertion into H2(TPP) using [Rh(CO)2Cl]2 in HOAc/NaOAc, a paramagnetic rhodium(II) porphyrin was observed [57] which could be transformed into a hydridorho-dium(III) porphyrin with dihydrogen (path — p) and subsequently into its corresponding base, the anion [Rh(TPP)], which may be likewise regarded as... 

The possibility for the existence of two different metal-inserted BT products stems directly from the orbital structure of the BT LUMO and second LUMO (SLUMO) (Table 5). On the basis of Sargent s predicted insertion mechanism, the character of the LUMO is consistent with S-Cy insertion while the character of the SLUMO coincides with S-C insertion. While occupation of the LUMO is energetically preferred, the calculated LUMO/ SLUMO gap is small the small gap is consistent with the intramolecular pathway between the S-Cy and S-C products of the rhodium-inserted complex (CsMes)Rh(PMe3)(r -(7,y-2-MeC8HsS). Occupation of the SLUMO, therefore, is readily achievable. 

The rearrangement of cubane gives different types of products depending on the metal. With Ag+ ion catalysis, cuneane is produced, whereas with Rh(I), tricyclooctadiene is obtained (Scheme 6.36). Again, these reactions go through direct metal insertion. When, however, the [RhCl(CO)2]2 complex was applied in a stoichiometric amount, the rhodium-inserted cubane complex could be isolated. ... 

When hydroformylating a Linear Alpha Olefin (LAO), rhodium inserts the aldehyde group 52% onto carbon one (70% for cobalt) and 48% onto carbon two (30% for cobalt). 

Other oxygen-based nucleophiles have demonstrated efficient reactivity under our reported conditions. Para- and weta-substituted phenols were shown to add in high yield and excellent enantioselectivity (Scheme 10.5) [9]. The reaction proceeded well, even when aryl iodides were used, indicating that the rhodium insertion into the aryl iodide bond is slow compared to ring-opening. 

The reaction mechanism leading to advanced intermediate 85 starts with rhodium insertion into the aldehyde moiety. Rhodacycle formation follows to promote hydroacylation into the 4,6-diene providing cycloheptene compound 86. Then, rhodium catalyze a highly regioselective cycloisomerization reaction on the resulting triene to produce the final product 87 (Scheme 7.54 please refer also to Scheme 7.51). 

The catalytic cycle (Fig. 5) (20) is well estabUshed, although the details of the conversion of the intermediate CH COI and methanol into the product are not well understood the mechanism is not shown for this part of the cycle, but it probably involves rhodium in a catalytic role. The CH I works as a cocatalyst or promoter because it undergoes an oxidative addition with [Rh(CO)2l2]% and the resulting product has the CO ligand bonded cis to the CH ligand these two ligands are then poised for an insertion reaction. 

A simplified mechanism for the hydroformylation reaction using the rhodium complex starts by the addition of the olefin to the catalyst (A) to form complex (B). The latter rearranges, probably through a four-centered intermediate, to the alkyl complex (C). A carbon monoxide insertion gives the square-planar complex (D). Successive H2 and CO addition produces the original catalyst and the product ... 

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

Intermediate 37 can be transformed into ( )-thienamycin [( )-1)] through a sequence of reactions nearly identical to that presented in Scheme 3 (see 22— 1). Thus, exposure of /(-keto ester 37 to tosyl azide and triethylamine results in the facile formation of pure, crystalline diazo keto ester 4 in 65 % yield from 36 (see Scheme 5). Rhodium(n) acetate catalyzed decomposition of 4, followed by intramolecular insertion of the resultant carbene 3 into the proximal N-H bond, affords [3.2.0] bicyclic keto ester 2. Without purification, 2 is converted into enol phosphate 42 and thence into vinyl sulfide 23 (76% yield from 4).18 Finally, catalytic hydrogenation of 23 proceeds smoothly (90%) to afford ( )-thienamycin... 

Recently, Aumann et al. reported that rhodium catalysts enhance the reactivity of 3-dialkylamino-substituted Fischer carbene complexes 72 to undergo insertion with enynes 73 and subsequent formation of 4-alkenyl-substituted 5-dialkylamino-2-ethoxycyclopentadienes 75 via the transmetallated carbene intermediate 74 (Scheme 15, Table 2) [73]. It is not obvious whether this transformation is also applicable to complexes of type 72 with substituents other than phenyl in the 3-position. One alkyne 73, with a methoxymethyl group instead of the alkenyl or phenyl, i.e., propargyl methyl ether, was also successfully applied [73]. 

Scheme 15 Formation of 4-alkenyl(phenyl)-substituted 5-dialkylamino-2-ethoxycyclopen-tadienes 75 via transmetallated alkyne-inserted rhodium-carbene complexes 74 [73]. For further details see Table 2...

The insertion of a carbene into a Z-H bond, where Z=C, Si, is generally referred to as an insertion reaction, whereas those occurring from Z=0,N are based on ylide chemistry [75]. These processes are unique to carbene chemistry and are facilitated by dirhodium(II) catalysts in preference to all others [1, 3,4]. The mechanism of this reaction involves simultaneous Z-H bond breaking, Z-car-bene C and carbene C-H bond formation, and the dissociation of the rhodium catalyst from the original carbene center [1]. 

To date most of the nitriles studied have been simple alkyl or aromatic derivatives with little other functionality. We recently attempted to extend the reaction to iV-protected a-aminonitriles, derived by dehydration of a-aminoacid amides (Path A, Scheme 25), but this proved unsatisfactory, and therefore we investigated an alternative diazocarbonyl based route in which the order of steps was reversed, i.e. a rhodium catalysed N-H insertion reaction on the amide followed by cyclodehydration to the oxazole (Path B, Scheme 25). 

Rh(Por)l (Por = OEP. TPP, TMP) also acts as a catalyst for the insertion of carbene fragments into the O—H bonds of alcohols, again using ethyl diazoacetate as the carbene source. A rhodium porphyrin carbene intermediate was proposed in the reaction, which is more effective for primary than secondary or tertiary alcohols, and with the bulky TMP ligand providing the most selectivity. ... 

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