Dehydrogenating complexation of borolenes with carbonyls (Ru3(CO)12, Os3(CO)12), Wilkinson's catalyst (RhCl(PPh3)3) and related compounds (RuCl2(PPh3)3, RuHCl(PPh3)3, OSCl2(PPh3)3), and (η6-arene)ruthenium complexes (Ru(η-C6H6)(η4-C6H8), [Ru(η-C6H6)Cl2]2, [Ru(η-C6-Me6)Cl2]2) leads to the (η5-borole)metal complexes of Ru, Os, and Rh. Inter alia, the preparation of the complexes Ru(CO)3(η5-C4H4BF) (R