Ligand dependent structural changes in the acid–base chemistry of electron deficient benzoheterocycle triosmium clusters

The reactions of the electron deficient benzoheterocycle clusters Os3(CO)9(μ3-η2-LH)(μ-H) (L=phenanthridine, 2; 5,6-benzoquinoline, 3; quinoxaline, 4; 2-methyl benzimidazole, 5; 2-methyl benzotriazole, 6; 2-methyl benzothiazole, 7; benzothiazole, 8; 2-methyl benzoxazole, 9; benzoxazole, 10) with n-butylamine and with the protic acids HBF4 and CF3CO2H are reported. Complexes 2 and 3 behave very similarly to the analogous quinoline complex (L=quinoline, 1) forming adducts with n-butylamine with similar spectral properties to 1 and undergoing simple protonation at the metal core with both HBF4 and CF3CO2H. Complexes 4–10 on the other hand form an additional amine adduct with different spectral characteristics than 1–3 and in the case of 5 this is the only detectable product. In addition, these compounds also form adducts with acetonitrile while 1–3 do not. Compounds 4–9 also exhibit much more complex behavior in the presence of CF3CO2H than 1–3, giving trifluoroacetate adducts subsequent to initial protonation. Although 4, 5 and 10 behave differently than 1 with n-butylamine and protic acids they form exactly the same triphenyl phosphine adduct as 1 and 3 based on multinuclear NMR data. The solid-state structure for the amine adduct of 2 is reported and suggested structures for the other amine and acid adducts, based on NMR data, are presented. The reasons for the differences in the behavior of the three distinct groups of benzoheterocycles (1–3, 4 and 5–10) are discussed.