  Motivated by the recent discovery of a low temperature spin liquid phase in
layered organic compound $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ which becomes a
superconductor under pressure, we examine the phase transition of Mott
insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an
anisotropic triangular lattice. We use a renormalized mean field theory to
study the Gutzwiller projected BCS wavefucntions. The half filled electron
system is a Mott insulator at large on-site repulsion $U$, and is a
superconductor at a moderate $U$. The symmetry of the SC state depends on the
anisotropy, and is gapful with $d_{x^2-y^2}+id_{xy}$ symmetry near the
isotropic limit and is gapless with $d_{x^2-y^2}$ symmetry at small anisotropy
ratio.
