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1.1.4 Nickel–Alkene Complexes 73<br />
1.1.4.6 Method 6:<br />
Alkene Hydrosilylation<br />
The hydrosilylation of alkenes is an effective method for converting terminal or cyclic alkenes<br />
into functionalized silanes (Scheme 73). [12,166] Silicon is directed to the more electron-rich<br />
alkene terminus. Trichlorosilane is generally the most effective silane, and a variety<br />
of nickel catalysts may be employed. Relatively high temperatures are required<br />
(1208C), and nickel catalysts substituted with electron-rich phosphines generally are the<br />
most efficient.<br />
Scheme 73 Hydrosilylation of Alkenes [166]<br />
R 1<br />
R 2<br />
+<br />
HSiCl 3<br />
NiCl2(PR 3 3)2<br />
Alkene Hydrosilylation; General Procedure: [166]<br />
Alkene (1 equiv), hydrosilane (2 equiv), and nickel catalyst (10 –3 equiv) were placed in a<br />
glass ampule and degassed at –1968C, and the ampule was then sealed. After heating for<br />
a given period of time, the ampule was cooled to –788C before opening. Products were<br />
isolated by fractional distillation where possible, or by preparative GC after flash distillation.<br />
1.1.4.7 Method 7:<br />
Alkene Hydroalumination<br />
The nickel-catalyzed hydroalumination of alkenes has been extensively investigated in a<br />
variety of contexts. The interaction of aluminum hydrides with nickel(0) and the mechanism<br />
of alkene hydroalumination has been studied in detail by Wilke, [5] Eisch, [167] and<br />
Zweifel. [168] The most extensive synthetic applications from Lautens involve the hydroalumination<br />
of oxabicyclic alkenes followed by ring opening to produce substituted cyclohexenes<br />
and cycloheptenes (Scheme 74). [169–171] An asymmetric variant employing<br />
2,2¢-bis(diphenylphosphino)-1,1¢-binaphthyl (BINAP) is also quite general for various oxabicyclic<br />
starting materials.<br />
Cl 3Si<br />
Scheme 74 Nickel-Catalyzed Hydroalumination–Ring-Opening Sequence [169–171]<br />
O<br />
O<br />
O<br />
OMe<br />
OMe<br />
OBn<br />
OMe<br />
OMe<br />
DIBAL-H<br />
10 mol% Ni(cod) 2 2<br />
DIBAL-H<br />
10 mol% Ni(cod) 2 2<br />
DIBAL-H<br />
3 mol% Ni(cod) 2 2<br />
5 mol% (R)-BINAP<br />
95%<br />
O<br />
Bu<br />
H<br />
i 2Al<br />
O<br />
Bui H<br />
2Al<br />
R 1<br />
H<br />
R 2<br />
OMe<br />
OMe<br />
OMe<br />
OBn<br />
OH<br />
97% ee<br />
OMe<br />
iBu2AlCl<br />
HO<br />
OMe<br />
OH<br />
OBn<br />
OMe<br />
for references see p 79
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