Lutetium triflate

The use of Ln(OTf)3 in the activation of aldehydes other than formaldehyde was also investigated [18]. The model reaction of 1-trimethylsiloxycyclohexene (2) with benzaldehyde under the influence of a catalytic amount of Yb(OTf)3 (10 mol%) was examined. The reaction proceeded smoothly in H20-THF (1 4), but the yields were low when water or THF was used alone. Among several Ln(OTf)3 screened, neodymium triflate (Nd(OTf)3), gadolinium triflate (Gd(OTf)3), Yb(OTf)3, and lutetium triflate (Lu(OTf)3) were quite effective, while the yield of the desired aldol adduct was lower in the presence of lanthanum triflate (La(OTf)3), praseodymium triflate (Pr(OTf)3) or thulium triflate (Tm(OTf)3) (Table 2). 

The effect of other Ln(OTf)3 was also examined. As shown in table 31, the choice of lanthanide element strongly influenced the yields and selectivities. A slight difference between the two catalyst systems (catalysts A and B) on the effect of the lanthanide elements was also observed. In catalyst A, lutetium triflate (Lu(OTf)3) was also effective in generating the endo Diels-Alder adduct in 93% ee. The yields and selectivities diminished rapidly in accordance with the enlargement of the ionic radii. In catalyst B, on the other hand, the best results were obtained when thulium triflate (Tm(OTf)3) or erbium triflate (Er(OTf)3) was employed. Deviations to either larger or smaller ionic... 

Pioneering work by Lubineau and coworkers showed that the aldol type reaction between a silyl enol ether and an aldehyde (the so-called Mukaiyama aldol reaction) occurred in water at room temperature with high syn stereoselectivity, albeit in low yields.However, the development of water-tolerant Lewis acids for this reaction has led to improved rates and chemical yields. Various lanthanides triflates, such as ytterbium triflate [Yb(OTf)3], scandium triflate [Sc(OTf)3], gadolinium triflate [Gd(OTf)3], or lutetium triflate [Lu(OTf)3], have been found to afford the aldol products between various aldehydes and silyl enol ethers in high yields in aqueous media, with good to moderate syn/anti diastereoselectivi-ties (Scheme 8.3, Table 8.1). ... 

Most of the known monocyclopentadienyl compounds of trivalent lanthanoids are dichloride complexes of CpLnCl2(THF) type. Besides these compounds, the ytterbium p-diketonates, lanthanum and cerium iodides (Me5C5)Lnl2 and the lutetium triflate complex CpLu(0S02CF3)2(THF)3 have been obtained (Table 111.14)... 

Eanthanide triflates reacts with PhsPO in ethanol forming [En(OTf)2(Ph3PO)4] OTf (Ln = La, Nd, Er, Lu). The erbium and lutetium compounds have octahedral coordination, with monodentate triflates, but the complexes of the larger La and Nd have seven-coordination with one triflate being bidentate. 

Reactions of Lu(03SCF3)3 with Na(C5H5) in THF generate readily the title monocy-clopentadienyl- and biscyclopentadienyl-lutetium complexes when the appropriate stoichiometric amount of Na(C5H5) is added. The highly reactive monocyclopentadi-enyl-lutetium unit seems to be stabilized by the bulky triflate anions. 

The A, stretching frequencies were found to increase steadily in magnitude across the lanthanide period for the [Ln(H20)x(NC>3)](0Tf)2 salts starting at 1450 cm-1 for lanthanum (r3+ = 1.172 A, Z/r = 2.56) and ending at a value of 1497 cm1 for lutetium (r3+ = 1.00, Z/r = 3.00) (Table 4). This structural data correlates extremely well with the observed reactivity of the respective lanthanide(m) triflates for nitration and can be taken as strong evidence for the proposed mode of action. 

From the above structural analysis it becomes clear that metal triflates with charge-to-size ratios greater than "3" (i.e. greater than that of the smallest lanthanide lutetium) should be more effective nitration catalysts. We considered that the group IV metals hafnium (r4+ = 0.78 A, Z/r = 5.13) and zirconium (r4 = 0.79 A, Z/r = 5.06) might be suitable for such a purpose. In line with this reasoning we noted that hafnium(IV) triflate has been shown to be an effective catalyst for Friedel-Crafts acylations and alkylations where the corresponding lanthanide salts were less active.20... 

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