Rhodium borate

Ghosh CK, Graham AG. Efficient and selective carbon-hydrogen activation by a tris(pyrazolyl)borate rhodium complex. J Am Chem Soc 1987 109 4726-4727. 

Zaric S, Hall MB. Prediction of the reactive intermediates in alkane activation by tris(pyrazolyl borate)rhodium carbonyl. J Phys Chem A 1998 102(11) 1963—1964. 

The single crystal X-ray structure of fra s-methyliodo difluoro[3,3 -(trimethylenedinitrolo)bis(2-pentanone oximato)]borate rhodium(III) (62) shows that the Rh sits in the plane established by the four N atoms, with the I and the Me in the axial positions (2.813 A and 2.090 A, respectively). The two six-membered rings resemble a chair conformation, with the BF2 bridge bent toward the axial methyl group, and the propylene bent toward the iodine atom.896... 

Jones reported an overview of the use of tris(pyrazolyl)borate rhodium complexes for the activation of arene and alkane C-H bonds, in particular detailing the fundamental studies with [Rh(CNR)(R)H(Tp )j. Selected example is reported in Fig. 8.12.154 Jones and coworkers155 also carried out some experiments in order to verify the involvement of... 

Alkyne hydroamination has been extensively reviewed [3, 4, 10] and important contributions using late transition metals have been realized to give the Markovnikov-type products most typically. Interestingly, in 2007, Fukumoto reported a tris(pyrazolyl borate)rhodium(l) complex for the anti-Markovnikov hydroamination of terminal aUcynes with both primary and secondary amine substrates, although yields with primary amines are always reduced compared to those with secondary amines (Scheme 15.26). Desirable functional group tolerance is also noteworthy for this regioselective hydroamination catalyst [187]. 

C2 5H3 2BF2Nn02RhSe21 trans-Bis(benzeneselenido)(difluoro-3,3 -(tri-methylenedinitrilo)bis(2 pentanoneoximato)borate)rhodium(III), 42B, 944... 

Rhodium catalysts have also been used. Benzylic halides were converted to carboxylic esters with CO in the presence of a rhodium complex. In this case, the R could come from an ether R20, a borate ester B(OR )3, or an Al, Ti, or Zr alkoxide. Reaction with an a,co-diiodide, BU4NF and Mo(CO)e gave the corresponding lactone. ... 

One problem apparently associated with the process is the loss of catalyst during the reaction. It is suggested that rhodium losses may be significantly reduced when the reaction is conducted in the presence of a trialkonolamine borate, B(OR)3N (63). Borates of type 17, where R R2, R3 = H or Me, were found to be particularly effective. 

It is thought that these trialkonolamine borates may enhance the reactivity of the rhodium carbonyl anions by minimizing their tendency to form contact ion pairs in solution under the reaction conditions employed. The same patent discloses that ammonium salts and salts of Groups I and II, especially cesium and ammonium carboxylate salts, function as promoters (63). 

The two-substituted-Quinazolinap-derived rhodium complexes proved extremely efficient catalysts for the hydro-boration-oxidation of vinylarenes (Table 6). For styrene derivatives, in most cases quantitative conversions were obtained after just 2 h at the relevant temperature (entries 1-6). Higher enantioselectivities were afforded with a 4-methoxy substituent (up to 95% ee, entry 3) compared to the 4-chloro or unsubstituted styrene analogs (entries 5 and 1), a trend also observed in hydroboration with rhodium complexes of QUINAP 60. This highlights that both the electronic nature of the substrate combined with the inherent steric properties of the catalyst are important for high asymmetric induction. It is noteworthy that in most cases, optimum enantioselectivities were afforded by the... 

Scheme 39.2 Examples of typical rhodium-based catalyst systems and modified derivatives of triphenylphosphine as used to control their solubility with scC02 in homogeneous or multiphase systems (BARF=tetrakis[3,5-bis (trifluoromethyl)phenyl]borate).

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... 

NaOH-HiOz) or to carboxylic acids (with w-chloroperbenzoic acid).-190 Double bonds can be hydroborated in the presence of triple bonds if the reagent is 9-BBN.191 On the other hand, dimesitylborane selectively hydroborates triple bonds in the presence of double bonds.192 Furthermore, it is often possible to hydroborate selectively one particular double bond of a nonconjugated diene.191 When the reagent is catecholborane, hydroboration is catalyzed by rhodium complexes, such as Wilkinson s catalyst.194 Enantioselective hydro-boration-oxidation has been achieved by the use of optically active rhodium complexes.195... 

Among the preformed enol derivatives used in this way have been enolates of magnesium, lithium,526 titanium,527 rhodium,528 zirconium,522 and tin,529 silyl enol ethers,530 enol bori-nates,531 and enol borates R CH=CR"—OB(OR)2.532 In general, metallic Z enolates give... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

Hydrothermal methods, for molecuarlar precursor transformation to materials, 12, 47 Hydrotris(3,5-diisopropylpyrazolyl)borate-containing acetylide, in iron complex, 6, 108 Hydrotris(3,5-dimethylpyrazolyl)borate groups, in rhodium Cp complexes, 7, 151 Hydrotris(pyrazolyl)borates in cobalt(II) complexes, 7, 16 for cobalt(II) complexes, 7, 16 in rhodium Cp complexes, 7, 151 Hydrovinylation, with transition metal catalysts, 10, 318 Hydroxides, info nickel complexes, 8, 59-60 Hydroxo complexes, with bis-Cp Ti(IV), 4, 586 Hydroxyalkenyl complexes, mononuclear Ru and Os compounds, 6, 404-405 a-Hydroxyalkylstannanes, preparation, 3, 822 y-Hydroxyalkynecarboxylate, isomerization, 10, 98 Hydroxyalkynes, in hexaruthenium carbido clusters, 6, 1015 a-Hydroxyallenes... 

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