Level 1 – Case 7
NaBH 4 Reduction of D D E E-Unsaturated Chromium
Carbene Complexes
Key point: Isotopic labeling
(CO) 5 Cr
OEt
Ph
NaBH 4
EtOH
Ph
EtO
EtO
Ph
NaBH 4 4 Reduction of D D E E-Unsaturated Chromium Carbene
Complexes
Conjugated chromium Fischer alkoxy carbene complex 1 is quantitatively transformed into a mixture of Z-vinyl ether
Z Z
2 and E-allyl ether 3 by NaBH 4 reduction in
EtOH (Scheme 7.1).
(CO) 5 Cr
OEt
Ph
NaBH 4
EtOH
Ph
EtO
EtO
Ph
1
2
3
2:3 (4:1)
Scheme 7.1
Propose a reasonable mechanism to account for the observed products and to explain all the following experimental data.
Experimental Data
1. The reduction of alkoxy carbene 1 with NaBD 4 in EtOH yielded the deuterated
products 4 and 5 (Scheme 7.2).
(CO) 5 Cr
OEt
Ph
NaBD 4
EtOH
Ph
EtO
D
EtO
Ph
H D
1
4
5
Scheme 7.2