Synthesis of metallacarboranes containing group 16 donor ligands and application

Abstract

The chemistry of transition metal complexes containing group 16 donors has drawn considerable interest due to its relevance to metal-centered oxygen-transfer reactions in biological systems, metal-catalyzed oxidation and hydrodesulfurization processes for industrial catalysts, and the synthesis of high oxidation state organometallics. In particular, cyclopentadienyl ligands, among others, have been used very often as ancillary ligands because of their ability to stabilize both low and high formal oxidation states. On the other hand, the dicarbollide anion $[nido-7,8-C_2B_9H_{11}]^{2-}$, which is isolobal with the $η^5$-cyclopentadienyl ligands, has not been employed in synthesizing metal complexes containing group 16 donors in spite of its known ability to stabilize higher formal oxidation states in metallacarborane complexes. Consequently, a systematic synthetic search for metallacarboranes in high oxidation states was undertaken. The oxidative decarbonylation reactions of $[C_2B_9H_{11})Mo(CO)_3]_{2-}$(1) with tetraethylthiuram disulfide, aldrithiol, elemental sulfur, and phenyl disulfide gave oxidized monomeric products $[(C_2B_9H_{11})Mo^{II}(CO)_2X_2]^{2-or 1-} (X_2 = S_2CNEt_2$ (2), 2-pyridine thiolate (3), 2SPh(4), $S_2$), respectively. The further oxidation of 4 with iodosylbenzene (PhIO) resulted in two new oxomolybdacarboranes $[(η^1-C_2B_9H_{11})Mo^{VI}(O)_3]^{2-}$(5) and $[(C_2B_9H_{11})O_2Mo^{VI}(μ-O)Mo^{VI} O_2(C_2B_9H_{11})]^{2-}$(6). In contrast to the stepwise conversion of 1 to 5 and 6 via 4, direct treatment of 1 with PhIO provided 5 as well as two new products $[(C_2B_9H_{11}Mo^VO(μ-O))_2^{2-}$(7) and $[(C_2B_9H_{11})Mo^{II}(CO)_2(η^2-CO_3)]^{2-}$ (8). Interestingly, The oxidation of 1 with trimethylamine N-oxide generated another useful synthon dimer $[(C_2B_9H_{11}) Mo(CO)_3]_2^{2-}$ which in turn gave a dinuclear linear complex 6 in the presence of PhIO. Furthermore, in the course of investigating the reactivities of these oxomolybdaca...