Rhodium complexes 5-coordinate

Asymmetric hydrosilylation can be extended to 1,3-diynes for the synthesis of optically active allenes, which are of great importance in organic synthesis, and few synthetic methods are known for their asymmetric synthesis with chiral catalysts. Catalytic asymmetric hydrosilylation of butadiynes provides a possible way to optically allenes, though the selectivity and scope of this reaction are relatively low. A chiral rhodium complex coordinated with (2S,4S)-PPM turned out to be the best catalyst for the asymmetric hydrosilylation of butadiyne to give an allene of 22% ee (Scheme 3-20) [59]. 

For asymmetric hydrosilylation of ketones a rhodium complex coordinated with the ferrocenyl(dimethyl)phosphine 3b has been reported to be more effective than other ferrocenylphosphines to give optically active alcohols (up to 49% ee) after hydrolysis (Scheme 2-49) [7]. 

Catalytic asymmetric hydroboration has been most extensively studied with styrene (4) as the substrate which produces 1-phenylethanol (6) after treatment of the hydroboration product, l-phenyl-l,3,2-benzodioxaborole (5), with alkaline hydrogen peroxide (Scheme 2). The regioselectivity favoring the branched isomer 5 over the linear isomer 5 is usually high when the reaction is carried out with rhodium complexes coordinated with chelating ligands such as bisphos-... 

Styrylboronic ester 24 was subjected to the catalytic hydroboration with cat-echolborane in the presence of rhodium complexes coordinated with chiral bis-phosphine ligands. Oxidation of the resulting 1,2-diboryl product 25 gave optically active 1-phenyl-1,2-ethanediol (26) (Scheme 6) [26]. The reaction with BINAP (7) at -60 °C gave (S)-diol 26 of over 70% ee. 

Asymmetric hydroboration of norbornene (27) is a synthetically useful transformation forming optically active norbornanol (28) which is an important chiral synthon. The catalytic enantioselective hydroboration with catecholborane was examined using rhodium complexes coordinated with several chiral phosphine ligands (Scheme 7 and Table 4) [14,15,17,23,24,27]. For this reaction, DIOP (10) and its derivatives 21 and 22, which are modified on the diphenyl-phosphino group, are more enantioselective Hgands than BINAP (7) or chira-phos (9). The highest enantioselectivity was observed in the reaction at -25 °C... 

So far no definite carbon dioxide insertion into analogous metal carbon bonds has been reported. A rhodium complex coordinated with carbon dioxide was reported by Iwashita and Hayata 122>. 

Asymmetric cycloisomerization of nitrogen-bridged 1,6-enynes occurs in the presence of a cationic rhodium complex coordinated with a chiral diene/phosphine tridentate ligand to give chiral 3-azabicyclo[4.1.0]heptenes with high enantioselectivity (Scheme 149). " ... 

Unfortunately, thus far there has been only one example of the asymmetric version of rhodium-catalyzed asymmetric arylation of aldehydes. In this report, by Miyaura [44], a rhodium complex coordinated with axially chiral monodentate phosphine Ug-and, (S)-MeO-mop, catalyzed the addition of phenylboronic acid (2m) to 1-naph-... 

Rhodium complexes with oxygen ligands, not nearly as numerous as those with amine and phosphine complexes, do, however, exist. A variety of compounds are known, iucluding [Rh(ox)3] [18307-26-1], [Rh(acac)3] [14284-92-5], the hexaaqua ion [Rh(OH2)3] [16920-31 -3], and Schiff base complexes. Soluble rhodium sulfate, Rh2(804 )3-a H2 0, exists iu a yellow form [15274-75-6], which probably coutaius [Rh(H20)3], and a red form [15274-78-9], which contains coordinated sulfate (125). The stmcture of the soluble nitrate [Rh(N03)3 2H20 [10139-58-9] is also complex (126). Another... 

Rhodium complexes with chelating bis(oxazoline) ligands have been described to a lesser extent for the cyclopropanation of olefins. For example, Bergman, Tilley et al. [32] have prepared a family of bis(oxazoline) complexes of coordinatively unsaturated monomeric rhodium(II) (see 20 in Scheme 13). Interestingly, the use of complex 20 in the cyclopropanation reaction of styrene afforded mainly the cis cyclopropane cis/trans = 63137), with 74% ee and not the thermodynamically favored trans isomer. No mechanistic suggestions are proposed by the authors to explain this unusual selectivity. 

A few sulfonated bidentate ligands have been used for which the coordination behavior has been well established for their nonsulfonated analogs the sulfonated ligands showed a behavior that was very much the same as that of their parent ligands in organic solvents. NAPHOS as in rhodium complex (127) behaves the same as BISBI (58), as does its sulfonated analog BINAS (128), which was developed and extensively studied by Herrmann and co-workers.410"413 The catalytically active rhodium complexes [HRh(CO)2(P-P)] of NAPHOS and BINAS have been characterized by IR and NMR spectroscopy.414... 

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