Chemistry of Triple-Decker Sandwich Complexes Containing Four-Membered Open B<inf>2</inf>E<inf>2</inf> Rings (E = S or Se)

Building upon our earlier studies of cobaltaheteroboranes, we explore the chemistry with heavier group 9 metals. Reaction of [Cp*M(µ-Cl)Clx]2 (Cp* = η5-C5Me5; M = Co, x = 0; M = Rh or Ir, x = 1) with [LiBH4·THF], followed by thermolysis with an excess of chalcogen powders (S or Se), affords dimetallaheteroboranes nido-[(Cp*M)2B2H2E2], 1–4 (1: E = S; 2: E = Se, M = Co; 3 and 4: E = Se, M = Rh and Ir, respectively) in moderate-to-good yields. The solid-state structures of these compounds show open-cage triple-decker clusters. Attempts to isolate the Te analogue have failed; however, in the case of cobalt, we have isolated an 11 skeletal-electron-pair nido-[(Cp*Co)2B5H5Te2], 5. The X-ray diffraction structure of 5 shows monocapped square antiprismatic geometry, with two Te atoms in the core. To close the central four-membered B2E2 open ring of nido-1 and nido-2, we have performed a reaction with [Ru3(CO)12], which leads to the formation of closo-[(Cp*Co){µ-η5:η5-B2H2E2M}M{µ-Ru(CO)4}], 6 and 7 [6: E = S; 7: E = Se; M = Ru(CO)2]. In contrast, the reactions of nido-2 and nido-3 with [Fe2(CO)9] result in heterometallic clusters nido-[(Cp*M)Fe(CO)3B2H2Se2], 8 and 9 (8: M = Co; 9: M = Rh), [(Cp*Co)Fe3(CO)8Se2], 10, and [(Cp*Co)Fe2(CO)7Se], 11. As nido-8 also contains a four-membered open ring B2Se2, we have treated this with [Ru3(CO)12], which yields closo-[(Cp*Co){µ-η5:η5-B2H2Se2M}M{µ-Fe(CO)4}], 12 [M = Ru(CO)2], which is analogous to that of 7. In addition, we have analyzed the divergence in the reactivity of nido-[(Cp*M)2B2H2E2], 2–4, with the help of density functional theory calculations.