  Among the silicon bearing species discovered in the interstellar medium, SiS
and SiO stand out as key tracers due to their distinct chemistry and abundances
in interstellar and circumstellar environments. Our objective is to enhance the
network of Si- and S-bearing chemical reactions for a gas-grain model in
molecular clouds, encompassing both low and high metallicities. We have
calculated the energies and rate coefficients for 6 neutral atom-diatom
reactions involved in the SiCS triatomic system, with a special focus on the
C+SiS and S+SiC collisions. We employ the coupled cluster method with single
and double substitutions and a perturbative treatment of triple substitutions
(CCSD(T)) refined at the explicitly correlated CCSD(T)-F12 level. With these
computational results in conjunction with data from the literature, we
construct an extended network of neutral-neutral chemical reactions. We
performed time-dependent models employing the Nautilus gas-grain code, setting
the gas temperature to 10 K and the density to 2x10$^4$ cm$^{-3}$. The
temperature dependence for the reactions involving SiS were modelled using
$k(T)=\alpha \left( T/300 \right)^{\beta} \exp{(-\gamma/T)}$. The
high-metallicity models significantly boost the SiS production. Higher initial
abundances of C, S, and Si, roughly $\sim$2, 190, and 210 times higher,
respectively, contribute to this. Around 10$^3$ yr, destruction mechanisms
become relevant. The proposed production reaction S + SiC $\rightarrow$ C +
SiS, mitigates these effects. By expanding the gas reaction network using a
high metallicity model, we derived estimates for the abundances of interstellar
molecules. The inclusion of neutral-neutral mechanisms, particularly via Si+HS
and S+SiC channels, played a pivotal role in determining SiS abundance. These
mechanisms carry a significance on a par with the well-known and fast
ion-neutral reactions.
