A combined experimental and theoretical study of bimetallic bis- and tris-homocubane analogues
Abstract
Synthesis of various metal-incorporated bis- and tris-homocubane analogues has been reported. Room temperature reactions of [Cp*MCl2](2) (Cp* = eta(5)-C5Me5, M = Ir or Rh) with chalcogenated borohydride reagents, Li[BH2E3] (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)(mu-E)(2)(mu(3)-E)(4)(mu(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)(mu-S)(2)(mu(3)-S)(4)(mu-BH2)(2)], 3, can be described as an unusual bishomocubane having two (mu-BH2) units with a missing-bond. In addition to these bishomocubanes, two trishomocubane derivatives [(Cp*M)(2)(mu-E)(3)(mu(3)-E)(4)(mu(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[BH2E3] (E = S or Se) led to the formation of Co-1,3-bishomocubane analogues, [(Cp*Co)(2)(mu-E)(2)(mu(3)-E)(4)(mu(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.