Synthesis and structural and spectroscopic properties of gorup 6 metallacarboranes containing a side-on bonded persulfide ligand

Abstract

Reactions of low valent dianionic metallacarboranes $[closo-3,3,3-(CO)_3-3,1,2-MC_2B_9H_11]^{2-}(M=Mo, Cr, W)$ (1), with elemental sulfur lead to novel side-on bonded disulfur metallacarboranes $[closo-3,3-(CO)_2-3-(7^2S_2)-3,1,2-MC_2B_9H_{11}]^{2-}(M-Mo, Cr, W)$ (2) via an oxidative addition process involving loss of a CO from (1). The nature of (2) was investigated by single crystal X-ray diffraction studies with M=Mo (2a), a successful refinement was made to reveal that central Mo atom deviate 2.384 Å from $C_2B_3$ plane, and d(Mo-Co) 1.879 Å, d (Mo-S) 2.502 Å, and d(S-S) 2.056 Å. Especially, d(S-S) and d(S-S) values of (2a) are compared with those of discrete diatomic sulfur species of $S_2, S_2^{-}$ and $S_2^{2-}$ demonstrating that approximate charge distribution in disulfur group in (2a) is somewhere between $S_2^{-}$ and $S_2^{2-}$. Its coordination number increases from 6 to 7 as Mo(0) is formally oxidised to Mo (II) during the addition of elemental sulfur.