C-S BOND SCISSION OF SUBSTITUTED THIOPHENES AT RHODIUM - FACTORS INFLUENCING THE REGIOSELECTIVITY OF THE INSERTION AND THE STABILITY OF THERESULTING METALLATHIACYCLES
C. Bianchini et al., C-S BOND SCISSION OF SUBSTITUTED THIOPHENES AT RHODIUM - FACTORS INFLUENCING THE REGIOSELECTIVITY OF THE INSERTION AND THE STABILITY OF THERESULTING METALLATHIACYCLES, Organometallics, 14(7), 1995, pp. 3196-3202
The fragment [(triphos)RhH], generated in situ by thermolysis of the t
rihydride (triphos)RhH3 in refluxing tetrahydrofuran, reacts with a va
riety of substituted thiophenes to give C-S insertion products of the
formula (triphos)Rh(eta(3)-SCR=CR'CH-CH2) (R' = H, R = Me, Et, COMe, C
O(2)Et; R = H, R' = Me, COMe, OMe; triphos = MeC(CH(2)PPh(2))(3)). Irr
espective of the position and electronic character of the substituent
in the thiophene, insertion is seen exclusively into the C-S bond away
from the substituent, consistent with a determinant steric control. T
he electronic properties of the substituent in the thiophene play an i
mportant role in determining the stability of the C-S insertion produc
ts in chlorinated solvents. Among the thiophenes investigated, only 2,
5-Me(2)T, for steric reasons, and 2-OMeT, for electronic reasons, do n
ot form butadienethiolate complexes by reaction with [(triphos)RhH]. T
he competitive reactivity of various substituted thiophenes toward the
fragment [(triphos)RhH] has been studied by NMR spectroscopy. The rea
ctivity decreases in the order: 2-CO(2)EtT > 2-COMeT > 3-COMeT much gr
eater than 3-OMeT > T congruent to 2-MeT > 3-MeT, consistent with a pr
edominant electronic effect.