Synthesis and ligand substitution of tri-metallic triply bridging borylene complexes

Abstract

To build upon our earlier results of heterometallic metallaboranes employing metal carbonyls, we performed the reaction of nido-[(Cp*Rh)2B3H7] (1) (nido-1) with [M(CO)5·THF] (M = Mo or W) that yielded the trimetallic metallaborane clusters [(Cp*Rh)2M(CO)3(μ-CO)(μ3-BH)(B2H4)] (3: M = Mo; 4: M = W) having a capped borylene fragment and trimetallic triply bridging borylene complexes [(Cp*Rh)2(μ3-BH)(μ-CO)M(CO)5] (5: M = Mo; 6: M = W). The chemistry of trimetallic triply bridging borylene complexes (5 and 6) were explored with Lewis bases such as tert-butyl isocyanide and bisphosphine ligands. Photolysis of 5 and 6 with tert-butyl isocyanide yielded [(Cp*Rh)2(μ3-BH)(μ-CO)M(CO)4(CN-tBu)] (7: M = Mo; 8: M = W) and with phosphines, PPh2(CH2)nPPh2 (n = 1, 2) they resulted in the formation of [(Cp*Rh)2(μ3-BH)(μ-CO)M(CO)4((PPh2)2(CH2)n)] (9: n = 1, M = Mo; 10: n = 1, M = W; 11: n = 2, M = Mo; 12: n = 2, M = W). All the new compounds have been characterized in solution by mass spectrometry and NMR spectroscopic techniques. The structural aspects were unambiguously established by X-ray crystallographic analysis of 3–4 and 7–10.