Abstract
Tris[bis(trimethylsilyl)amide] has been shown to be an effective catalyst for the
hydroboration of representative alkenes and styrenes by pinacolborane.
Key words
hydroboration - lanthanides - catalysis
References
<A NAME="RS12004ST-1">1 </A>
Pelter A.
Smith K.
Brown HC.
Borane Reagents
Academic Press;
New York:
1988. and references cited therein
2a </A>
Evans DA.
Fu GC.
Hoveyda AH.
J. Am. Chem. Soc.
1992,
114:
6671 ; and references cited therein
2b </A>
Hayashi T.
Matsumoto Y.
Ito Y.
J. Am. Chem. Soc.
1989,
111:
3426
2c </A>
Burgess K.
Ohlmeyer MJ.
J. Org. Chem.
1988,
53:
5179
3a </A>
Harrison KN.
Marks TJ.
J. Am. Chem. Soc.
1992,
114:
9220
3b </A>
Bijpost EA.
Duchateau R.
Teubin JH.
J. Mol. Catal. A
1995,
95:
121
<A NAME="RS12004ST-4">4 </A>
Molander GA.
Pfeiffer D.
Org. Lett.
2001,
3:
361
5a </A>
Kim YK.
Livinghouse T.
Bercaw JE.
Tetrahedron Lett.
2001,
42:
2933
5b </A> For the use of novel group 3 chelates to accelerate intramolecular aminoalkene
hydroaminations, see:
Kim YK.
Livinghouse T.
Angew. Chem. Int. Ed.
2002,
41:
3645
5c </A>
Kim YK.
Livinghouse T.
Horino Y.
J. Am. Chem. Soc.
2003,
125:
9560
<A NAME="RS12004ST-6">6 </A>
Horino Y.
Livinghouse T.
Organometallics
2004,
23:
12
<A NAME="RS12004ST-7">7 </A>
Garrett CE.
Fu GC.
J. Org. Chem.
1996,
61:
3224
<A NAME="RS12004ST-8">8 </A> Srebnik has reported the use of (Ph3 P)3 RhCl as a catalyst for the hydroboration of representative alkenes by 2 :
Pereira S.
Srebnik M.
Tetrahedron Lett.
1996,
37:
3283
<A NAME="RS12004ST-9">9 </A> By way of contrast, Knochel has reported that crude 2 (2 equiv, prepared in situ from BH3 ·SMe2 and pinacol) is capable of hydroborating alkenes (ClCH2 CH2 Cl, 50 °C, 48 h):
Tucker CE.
Davidson J.
Knochel P.
J. Org. Chem.
1992,
57:
3482
<A NAME="RS12004ST-10">10 </A>
1 H NMR revealed >99% conversion of 3a to the corresponding boronic pinacolate.
<A NAME="RS12004ST-11">11 </A> Evans has reported that SmI3 is a catalyst for the hydroboration of alkenes with catecholborane:
Evans DA.
Muci AR.
Stürmer R.
J. Org. Chem.
1993,
58:
5307
<A NAME="RS12004ST-12">12 </A> Temperatures of 125-200 °C are required for effecting the hydroboration of alkenes
using BH3 ·NEt3 :
Hawthorne F.
J. Org. Chem.
1958,
23:
1788
<A NAME="RS12004ST-13">13 </A>
A General procedure for alkene hydroborations is as follows: In an argon-filled glove
box, La[N(TMS)2 ]3 (1a , 18.6 mg, 0.03 mmol) and C6 D6 (1.0 mL) were introduced into a J. Young NMR tube equipped with teflon screw cap
and then pinacolborane (2 , 256 mg, 2.0 mmol) and the appropriate alkene (1.0 mmol) were added by micro syringe.
The homogeneous reaction mixture was maintained at 90 °C or 120 °C, respectively,
using an oil bath until the hydroboration reaction was judged complete by the disappearance
of the appropriate olefinic resonances in the 1 H NMR spectrum. The resulting solution was transferred to a 25 mL round-bottomed flask
and was cooled to 0 °C with stirring whereupon 1:1 = THF:EtOH (6 mL), 2 N NaOH (3
mL) and 30% H2 O2 (3 mL) were added. The reaction mixture was allowed to warm to r.t. and was stirred
for 9 h. It was then extracted with Et2 O (3 × 10 mL) and the combined organic phases were dried over MgSO4 . After removal of the solvents in vacuo, the crude product was purified by column
chromatography on silica gel (5% EtOAc-hexane for elution) to provide the corresponding
alcohol as a colorless oil.
<A NAME="RS12004ST-14">14 </A>
An analogous catalytic cycle has been proposed in connection with the hydroboration
of alkenes by catecholborane (4 ) catalyzed by permethyllanthanocene complexes.
[3a
<A NAME="RS12004ST-15">15 </A>
Available from Gelest Inc., 612 William Leigh Drive, Tullytown, PA 19007-6308, USA.
