Handbook of Functionalized Organometallics Applications in S

( +
- )
14.3 Unsymmetrically Placed Substituents in Stoichiometric Electrophilic Multihapto-Complexes
Me
Ph
Fe(CO) 3
1) LiCMe 2CN,
2) CO, then MeI, 87%
CMe 2CN
48 Ref. 204
( +
-)
Fe(CO) 3
( +
-)
+
Fe(CO)2P(OPh)3
50
Scheme 14.19
1) LiSiMe 2Ph, THF, 0 ºC,
then 25 ºC, 20 h,
2) F 3CCO 2H, 0 ºC,
then 25 ºC, 1 h, 41%
LiCCPh,
Ref. 235
THF, -78 ºC - rt, 1 h, 59%
Ref. 236
Me
O
SiMe 2Ph
Ph
( +
-)
Fe(CO) 2P(OPh) 3
Ph
49
( +
-)
central atom of the allyl ligand, producing two metal±carbon r bonds [216±218],
and with neutral stoichiometric g 3 allyl complexes, this seems to be quite a common
outcome [219]. Catalytic substitution of Cl from the center of an allyl ligand
has been reported using cationic platinum complexes [220]. Cationic g 3 allyl complexes
of Ir(C5Me5)(PMe3) + [221], Rh(C5Me5)(PMe3) + + +
[221], MoCp2 [222], WCp2
[222] are also known to react with nucleophiles at the central carbon atom.
Cycloheptadienyliron complexes also frequently show examples of internal
nucleophile addition [214,215,224±227]. Steric effects are conventionally cited to
explain the tendency of cycloheptadienyl complexes to give internal addition products
(whereas cyclohexadienyl complexes react at the termini). There is kinetic evidence
to support this, as cycloheptadienyl complexes have been shown to be less
reactive than cyclohexadienyl complexes [223]. The CH2 of the cyclohexadienyl
complexes, and the CH2CH2 of the cyclohepadienyl complexes fold out away from
the metal in these structures, and in the cycloheptadienyl case, each CH2 blocks a
terminus of the p system. Nucleophilic attack is displaced to the internal positions,
forming g 1 ,g 3 products in competition with the g 4 products from the normal
addition pathway [214,215,224±230]. With larger metals [Ru(CO) 3 and Os(CO) 3],
this effect becomes more pronounced, and the g 1 ,g 3 products can predominate
[230,231]. The nature of the nucleophile can also influence the preferred pathway
(see Section 14.4). With ªsoftº nucleophiles, cycloheptadienyl complexes show the
terminal addition pathway, while hard nucleophiles add internally [232]. Further
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