Metal BINAP complexes

Other miscellaneous examples of this series are listed in Figure 5.[ i [53],[54] Complex 22 showed large distortion from the normal square planar geometry, and the bite angle of the BINAP ligand (92.69°) was among the largest values for transition metal-BINAP complexes.f ... 

A model proposed for rationalizing the stereochemical outcome is also shown in Scheme 5.112. It seems plausible that the skewed structure 441, typical for transition metal BINAP complexes, has just one open space that is filled by a coordination of rhodium to the carbon - carbon bond of cyclohexenone. As a consequence, the insertion of the phenyl group then occurs from the Sf-face to the enone to give the / -rhodium complex 442 that subsequently tautomerizes to the more stable oxallyl-type enolate [205a]. It seems that a transmetallation at the stage of the enolate - from rhodium to boron enolate, as indicated in cycle B (Scheme 5.111) - doesnot occur in all these rhodium-mediated domino reactions without exception. Thus, Hayashi and coworkers produced evidence in support of a rhodium enolate as an active nucleophile in the aldol step when phenyl-9-BBN 438 was reacted with acyclic enones in the presence of [Rh(OH)-(S)-BINAP]2. In this case, the catalytic cycle is maintained by a transmetallation of the rhodium to the boron aldolate [221]. 

Other chiral ligands such as BINAP (where BINAP is bis(diarylphosphino)-1,1 binaphthyl) or aminophosphines are also efficient for stereoselective synthesis of chiral-at-metal Ru complexes [39-41]. 

Aldol reactions of silyl enolates are promoted by a catalytic amount of transition metals through transmetallation generating transition metal enolates. In 1995, Shibasaki and Sodeoka reported an enantioselective aldol reaction of enol silyl ethers to aldehydes using a Pd-BINAP complex in wet DMF. Later, this finding was extended to a catalytic enantioselective Mannich-type reaction to a-imino esters by Sodeoka s group [Eq. (13.21)]. Detailed mechanistic studies revealed that the binuclear p-hydroxo complex 34 is the active catalyst, and the reaction proceeds through a palladium enolate. The transmetallation step would be facilitated by the hydroxo ligand transfer onto the silicon atom of enol silyl ethers ... 

Zinc dibenzyl malonate complex 129, prepared by the action of Et2Zn on dibenzyl malonate, was found to be superior to alkali metal dibenzyl malonates, in terms of enantiomeric control, in the allylic substitution with ( )-130 catalysed by an in situ prepared Pd-(/ )-BINAP complex (equation 73)164. 

The high asymmetric inductions that can be attained in these reductions are above all to be attributed to steric interaetions of the substrate with the phosphorus-bound phenyl groups of the [Ru-f/fj-BINAP] complex R)-S (Scheme 5). It can be assumed that hydride, being the smallest ligand, coordinates cis to both phosphine ligands. The P-bound phenyl groups occupy equatorial (parallel to the substrate coordination plane) and axial positions (perpendicular to the substrate coordination plane) with respect to the metal-ligand cycle. The skewed BINAP skeleton requires the equatorial phenyl substituents to protrude directly into two of four coordination quadrants that are accessible to the substrate. 

If the metal-binaphthyl complex is not fitted directly into the cyclic transition state, it becomes difficult to explain the asymmetric inductions observed. The following rule seems to be generally valid for both BINOL and BINAP complexes The complexation of carbonyl or imine moieties by (R)-binaphthyl-metal complexes results in a shielding of the si face, the reaction proceeds from the re face. Correspondingly, the opposite principle applies when (STbinaphthyl complexes are used. All aldol reactions and carbonyl-ene reactions which are catalyzed by binaphthyl complexes abide by this rule [18], and the scheme can also be applied to the addition of ketene-silyl-acetals to imines with boron-BINOL catalysts [19]. 

Metal complexes can be attached to membranes. For example, Ru BINAP complexes (cf. Scheme 22-VII) and a Brpnsted acid attached to a polydimethyl-siloxane membrane act as effective heterogenized catalysts for asymmetric hydrogenations.172... 

The first catalysts used were Co(I)-DIOP (DIOP, see Figure 11b) based systems. Up to 32% ee was achieved with 39% yield in the isomerization of (A, AO-diethylgeranylamine to (i )-citronellal. Subsequently, some rhodium (I)-DIOP or BINAP (BINAP = 2,2 -bis(diphenylphosphino)-1,1 -binaphthyl) systems proved to be very active. In particular, cationic rhodium(I)-BINAP complexes show very high selectivities and catalytic activities for this isomerization. BINAP is an atropoisomeric diphosphine (Figure 20) which was first synthesized by Noyori and Takaya and since then its metal complexes have been extensively used as catalysts in a variety of asymmetric syntheses. 

Pyridine complexes can show analogous hindered rotation to that observed with metal-aryl complexes. This has been observed for over SOyears, but recent interest in supramolecular chemistry, particularly by Fujita and Stang, wherein bipyridyls have been used as linkers has spurred renewed interest in the phenomenon. Several articles on dynamics provide leading references for applications of EXSY and other DNMR methods in these systems. BINAP complexes with picolines and methyl-substituted isoquinolines, which show syn and anti isomerism, have been investigated, for example, (48), (49), and (50). ... 

Of the BINOL/BINAP-metal catalyst complexes, only the allylation procedure described by Keck using the BINOL-Ti(IV) catalyst 451 has been applied in the synthesis of natural products, presumably because it has the most substrate generality and the field is so new. In a preliminary report, Evans disclosed the synthesis of the 4-hydroxy buteneolide terminus 470 of mucocin, where he uses Keck s original catalytic asymmetric allylation procedure to effect conversion of aldehyde 469 to the homoallylic alcohol 470 in good yield and high diastereoselectivity (Scheme 11-36) [312]. 

A bidentate ligand possesses two atoms which have an electron pair that can be shared with a metal. On complexation, two bonds are formed to the metal and a ring results. This process is called chelation. A commonly used example is BINAP ... 

The invention of Ru-binap dicarboxylate complexes extends the scope of asymmetric hydrogenations . Simple acyclic acids are hydrogenated with enantioselectivities from 80 to 100%. The procedure is applicable to /3,y-unsaturated carboxylic acids with about 80% e.e. . Deuterium incorporation indicates that a mechanism involving a metal monohydride complex operates. An amino group on the chiral phosphine ligand enhances the efficacy of ferrocenylphosphine-Rh complexes toward trisubstituted acyclic acids . 

If, however, the metal is complexed to a chiral organic molecule, H2 will be delived to only one face of the double bond. One such chiral catalyst—using Ru(II) as the metal and BINAP (2,2 -bis(diphenylphosphino)-l,l -binaphthyl) as the chiral molecule— has been used to synthesize (5)-naproxen, the active ingredient in Aleve and several other over-the-counter nonsteroidal anti-inflammatory drugs, in greater than 98% enantiomeric excess. 

In 1985, Manning and N6th first reported the hydroboration of alkenes catalyzed by Wilkinson s catalystJ Since this pioneering work, the development of transition-metal-catalyzed hydroboration has been investigated extensively. Burgess and Ohlmeyer demonstrated asymmetric catalysis with the use of BINAP and Diop-derived Rh-catalysts. Hayashi et al. later reported improvement of the enantioselectivity for the hydroboration of styrenes using Rh-BINAP complexes (up to 96% ee at -78 Other catalyst systems have also been shown to be effective... 

Ally lie amines are isomerised by transition metal catalysts to enamines. The isomerisation can be rendered asymmetric with rhodium-BINAP complexes. 

A review describing the recent advances in transition-metal-catalysed 2-I-2-1-2-cyclotrimerization reactions has been published. A cationic rhodium (I)/(l )-Hg-BINAP complex catalysed the 2-I-2-I-2-cycloaddition reaction of 1,6-enynes with acrylamides to synthesize annulated cyclohexenes in high yields and excellent... 

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