Rhodium complexes pyridyl

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... 

A highly active catalytic system for direct arylation reactions of nonactivated arenes relied on a homobimetallic rhodium complex. Thus, treatment of [bis(2-pyridyl) amino]diphenylphosphane (109) with [Rh(cod)Cl]2 led to the formation of a complex 108, which, according to X-ray crystal structure analysis, consisted of [Rh(cod) Cl2] anion and a rhodium cation stabilized by two P,N-ligands (Scheme 9.34) [73]. This bimetallic rhodium complex (108) allowed the direct arylation of benzene (87) with the aryl chloride 106 with a turnover number (TON) of 780 under comparably mild reaction conditions. 

For rhodium, several studies concerning the use of amphiphilic ligands have been reported. Rhodium catalysts derived from tris(2-pyridyl)phosphine achieve selective hydroformylation of 1-hexene both in a homogeneous acetophenone system and, at a much lower rate, in a two-phase water/1-hexene system [13]. Attempts to extract the rhodium complex from the homogeneous system with water were not successful the use of HC1 or HBF4 resulted in rapid evolution of H2 and about half the rhodium could not be extracted from the orange, organic phase. 

N,N,N-Tri((6-methyl-2-pyridyl)methyl)amine and N-methyl-N,N-bis ((6-methyl-2-pyridyl)methyl)amine with [(r/ -C2H4)Ir(Cl)] and potassium hexafluorophosphate in methanol give the bis(ethene) iridium(I) 151 and 152, respectively. Both readily dissociate one ethene molecule. In the case of 151, the mono-ethene 139 (M = Ir, R = Me) slowly transforms to the cyclometalated 153 in acetonitrile. The rhodium complex reacts with molecular oxygen with displacement of ethene and formation of a per-oxo-species. Both iridium mono-ethene species, in contrast, bind... 

The rhodium-catalyzed conversion of aryl pyridyl ethers into arylboronates has been achieved using an NHC-supported rhodium catalyst (Scheme 6.31) [62]. The main theme of this work was the use of rhodium complexes to promote the cleavage of the pyridyl ether fragment and borylation of the arene. The reaction was carried out at elevated temperatures and afforded moderate to good yields of the arylboronates. One of the most impressive aspects of this chemistry was its tolerance to a wide range of functional groups. Heteroaryl ethers as well as substrates bearing esters, amides, and even a free amine were successfully converted into arylboronates. If the substrate is appropriately functionalized, this would be a reasonable approach to the formation of arylboronates. 

A mechanistic study by Haynes et al. demonstrated that the same basic reaction cycle operates for rhodium-catalysed methanol carbonylation in both homogeneous and supported systems [59]. The catalytically active complex [Rh(CO)2l2] was supported on an ion exchange resin based on poly(4-vinylpyridine-co-styrene-co-divinylbenzene) in which the pendant pyridyl groups had been quaternised by reaction with Mel. Heterogenisation of the Rh(I) complex was achieved by reaction of the quaternised polymer with the dimer, [Rh(CO)2l]2 (Scheme 11). Infrared spectroscopy revealed i (CO) bands for the supported [Rh(CO)2l2] anions at frequencies very similar to those observed in solution spectra. The structure of the supported complex was confirmed by EXAFS measurements, which revealed a square planar geometry comparable to that found in solution and the solid state. The first X-ray crystal structures of salts of [Rh(CO)2l2]" were also reported in this study. 

Optimized reaction conditions call for the use of Wilkinson s catalyst in conjunction with the organocatalyst 2-amino-3-picoline (60) and a Br0nsted add. Jun and coworkers have demonstrated the effectiveness of this catalyst mixture for a number of reactions induding hydroacylation and C—H bond fundionalization [25]. Whereas, in most cases, the Lewis basic pyridyl nitrogen of the cocatalyst ads to dired the insertion of rhodium into a bond of interest, in this case the opposite is true - the pyridyl nitrogen direds the attack of cocatalyst onto an organorhodium spedes (Scheme 9.11). Hydroamination of the vinylidene complex 61 by 3-amino-2-picoline gives the chelated amino-carbene complex 62, which is in equilibrium with a-bound hydrido-rhodium tautomers 63 and 64. 

Introduction of a bulky pyridyl ligand again results in a reduced ligating ability of the pyridine functionality [41], which this time could be visualised using the rhodium(I) cod complexes instead of the palladium allyl ones (see Figure 3.5). 

Figure 3.14 Synthesis of rhodium and iridium pyridyl functionalised carbene complexes.

Chelation v. cyclometalation in a cationic dipyridylpyridazine-Rh(I) complex. Milstein and co-workers reported the results of a study of the interaction of rhodium norbomadiene tetrafluoroborate (Rh(NBD)2) with the tetradentate ligand 3,6-bis-(2-pyridyl)pyridazine (DPPN) (241). Mononuclear complexes, 242, were obtained quantitatively. Treatment of the complex of DPPN Rh(NBD)2BF4 with a second equivalent of the metal precursor (Rh(NBD)(CH3CN)2)BF4 led to a dinuclear complex, 243, that involves a unique rearrangement of the norbomadienyl moiety. 

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