  Intensive studies of the interplay between spin-orbit coupling (SOC) and
electronic correlations in transition metal compounds have recently been
undertaken. In particular, $j_{\rm eff}$ = 1/2 bands on a honeycomb lattice
provide a pathway to realize Kitaev's exactly solvable spin model. However,
since current wisdom requires strong atomic SOC to make $j_{\rm eff}=1/2$
bands, studies have been limited to iridium oxides. Contrary to this
expectation, we demonstrate how Kitaev interactions arise in 4$d$-orbital
honeycomb $\alpha$-RuCl$_3$, despite having significantly weaker SOC than the
iridium oxides, via assistance from electron correlations. A strong coupling
spin model for these correlation-assisted $j_{\rm eff}$ = 1/2 bands is derived,
in which large antiferromagnetic Kitaev interactions emerge along with
ferromagnetic Heisenberg interactions. Our analyses suggest that the ground
state is a zigzag-ordered phase lying close to the antiferromagnetic Kitaev
spin liquid. Experimental implications for angle resolved photoemission
spectroscopy, neutron scattering, and optical conductivities are discussed.
