A combined experimental and theoretical study of bimetallic bis- and tris-homocubane analogues

Synthesis of various metal-incorporated bis- and tris-homocubane analogues has been reported. Room temperature reactions of [Cp*MCl 2 ] 2 (Cp* = η 5 -C 5 Me 5 , M = Ir or Rh) with chalcogenated borohydride reagents, Li[BH 2 E 3 ] (E = S or Se), yielded a series of bimetallic bis- and tris-homocubane derivatives ( 1-7 ). The bishomocubane analogues belong to the 1,3-bishomocubane family with the general formula [(Cp*M) 2 (μ-E) 2 (μ 3 -E) 4 (μ 3 -BH) 2 ] ( 1 : M = Ir, E = S; 2 : M = Ir, E = Se; 5 : M = Rh, E = S and 6 : M = Rh, E = Se), and [(Cp*Ir) 2 (μ-S) 2 (μ 3 -S) 4 (μ-BH 2 ) 2 ], 3 , can be described as an unusual bishomocubane having two (μ-BH 2 ) units with a missing-bond. In addition to these bishomocubanes, two trishomocubane derivatives [(Cp*M) 2 (μ-E) 3 (μ 3 -E) 4 (μ 3 -BH) 2 ] ( 4 : M = Ir, E = S and 7 : M = Rh, E = Se) were isolated from the above reactions. Trishomocubane 4 adopts a 1,2,4-trishomocubyl structure, whereas 7 is a D 3 -trishomocubyl analogue. In a similar fashion, thermolysis of [Cp*CoCl] 2 with Li[BH 2 E 3 ] (E = S or Se) led to the formation of Co-1,3-bishomocubane analogues, [(Cp*Co) 2 (μ-E) 2 (μ 3 -E) 4 (μ 3 -BH) 2 ] ( 8 : E = S and 9 : E = Se). All the compounds were characterized by multinuclear NMR and IR spectroscopies and mass spectrometric analysis. The core geometries of 1-4 and 8 were unequivocally established by single-crystal X-ray diffraction studies. Density functional theory (DFT) computations further demonstrated that metals and chalcogen atoms play an important role in determining the thermodynamic stability of the bis- and tris-homocubane species. Various bimetallic bis- and tris-homocubane analogues of group 9 transition metals have been isolated and structurally characterized employing Li[BH 2 E 3 ] (E = S or Se).