A simple, high yielding catalytic method for the multigram
scale
selective epoxidation of electron-rich alkenes using near-stoichiometric
H2O2 under ambient conditions is reported. The
system consists of a Mn(II) salt (<0.01 mol %), pyridine-2-carboxylic
acid (<0.5 mol %), and substoichiometric butanedione. High TON
(up to 300 000) and TOF (up to 40 s–1) can
be achieved for a wide range of substrates with good to excellent
selectivity, remarkable functional group tolerance, and a wide solvent
scope. It is shown that the formation of 3-hydroperoxy-3-hydroxybutan-2-one
from butanedione, and H2O2 in situ, is central
to the activity observed.
Reaction of Cp*Ti{NC(Ar(F(2)))N(i)Pr(2)}Me(2) (1, Ar(F(2)) = 2,6-C(6)H(3)F(2)) with [Ph(3)C][B(C(6)F(5))(4)] gave the base-free structurally authenticated dication [Cp*(2)Ti(2){NC(Ar(F(2)))N(i)Pr(2)}(2)(mu-Me)(2)][B(C(6)F(5))(4)](2) (3-[BF(20)](2)) containing two doubly alpha-agostic bridging methyl groups. 3-[BF(20)](2) is a highly effective ethylene-propylene polymerization catalyst at 90 degrees C, and its performance is identical to the catalyst generated in situ from 1 and [Ph(3)C][B(C(6)F(5))(4)].
Because of the promising performance in olefin polymerization of 2,2'-bis(2-indenyldiyl)biphenyl zirconium dichloride, we developed a new and broadly applicable route to 2,2'-bis(2-indenyl)biphenyl derivatives. Reaction of the known 2,2'-diiodobiphenyl (26) with the new 2-indenyl boronic acid (23) did not result in the desired 2,2'-bis(2-indenyl)biphenyl (10); instead an isomer thereof, (spiro-1,1-(2,2'-biphenyl)-2-(2-indenyl)indane) (27), was obtained. It was found that compound 10 could be made via a palladium-catalyzed reaction of 2,2-biphenyldiboronic acid (31) with 2-bromoindene (21) under standard Suzuki reaction conditions. However, the yield of this reaction was low at low palladium catalyst loadings, due to a competitive hydrolysis reaction of 2,2-biphenyldiboronic acid (31). HTE techniques were used to find an economically viable protocol. Thus, use of the commercially available 1.0 molar solution of (n-Bu)(4)NOH in methanol with cosolvent toluene led to precipitation of the pure product in a fast and clean reaction, using only 0.7 mol % (0.35 mol % per C-C) of the expensive palladium catalyst.
We found that double-silicon-bridged bisindenyl complexes of early transition metals of group 4 are able to produce polyethylenes with high molecular weights and narrow molecularweight distributions having high a-olefin incorporation. The bottleneck for the synthesis of these complexes is the ligand synthesis. The corresponding ligands could be obtained via a three-step procedure with low (15%) overall yields. We found that the use of the new 2-lithioindenyllithium enhanced the overall yield to 50% in a one-pot procedure.Double-silicon-bridged bisindenyl derivatives were recently described by us (Scheme 1). 2 We found that reaction of 4a with 0.5 equivalent of dichlorodimethylsilane resulted in a mixture of 5 (70%) 3 and 6 (30%). The main drawback of this route is the low yield (15%) of the single-bridged 2-indenyl intermediate 4a, probably caused by proton abstraction by 2 from 3 or 4a. To avoid this exchange reaction, the starting materials and the reaction products should not contain acidic protons. Therefore, the 3-position should be protected, preferably with a metal like magnesium or lithium, since this gives the possibility of further reaction or facile deprotection via H-quench reactions. Given that several lithiated organometallic compounds are accessible via the bromoderivatives, such as lithioferrocene starting from bromoferrocene, 4 we set out to prepare 7 from the known 2-bromoindenyllithium (8) 5 (Scheme 2 and Scheme 3). (7) Mechanism of formation of 2-lithioindenyllithium (7): 2-Lithioindenyllithium (7) can be prepared from 2-bromoindene (1) with the aid of two equivalents of n-butyllithium in diethyl ether at -100 °C, followed by warming to room temperature (Scheme 4). The GC-MS spectrum of a sample quenched with D 2 O, taken at -40 °C, contained a peak with the retention time of 1. The corresponding MS spectrum contains a molecular ion with m/e = 195/197, which indicates the formation of [D]1 (8a), resulting from a D-quench of 8. Although hardly any L i L i 7 B r L i 8 ?
Scheme 2 Formation of 2-lithioindenyllithium
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