We present Li abundances for 14 solar–type stars in the intermediate age ( \sim 2 Gyr ) clusters IC 4651 and NGC 3680 .
The \log n ( Li ) vs. effective temperature distributions are compared with those of the similar age cluster NGC 752 , of the younger Hyades ( 600 Myr ) and of the older M 67 ( 4.5 Gyr ) and NGC 188 ( 6–7 Gyr ) clusters .
Neither IC 4651 nor NGC 3680 show the dispersion in Li which is observed in M 67 .
The 2 Gyr clusters have very similar Li vs. T _ { eff } distributions ; in addition , stars in the upper envelope of the M 67 distribution have the same Li content as stars in the 2 Gyr clusters , suggesting that either they have not suffered any significant depletion between \sim 2 and 4.5 Gyr or they had a much slower Li depletion .
Mechanisms that lead to Li depletion on the main sequence are discussed in the light of these observations .
None of the existing models seem to reproduce well the observed features .