Syntheses, reactivities and crystal structures of triosmium clusters with imidazo(1,2-a)pyridine ligand

Treatment of the lightly stabilized cluster [Os-3(CO)(10)(MeCN)(2)] with ex cess imidazo(1,2-a)pyridine at 25 degrees C yields [(mu-H)Os-3(CO)(10)(mu-1 ,2-eta(2)-C7H5N2)] (7) and [(mu-H)Os-3(CO)(10)(mu-1,7-eta(2)-C7H5N2)] (8) i n 30 and 40% yields, respectively. The structures of 7 and 8 reveal that in the former the heterocyclic ligand is coordinated via the imino nitrogen a nd C(2) carbon atoms, whereas in the latter the ligand is coordinated via t he imino nitrogen and C(7) carbon atoms. The reaction of [Os-3(CO)(11)(MeCN )] with excess imidazo(1,2-a)pyridine at 25 degrees C gives the N-coordinat ed imidazo(1,2-a)pyridine compound [Os-3(CO)(11)(eta(1)-C7H6N2)] (9), which on refluxing in octane undergoes both C(2)-H and C(7)-H bond activation, p roducing 7 and 8 in 32 and 15% yields, respectively. Compound 9 is similar to [Os-3(CO)(11)(MeCN)] in that its N-coordinated ligand is labile and can easily be replaced by Various two-electron donors L yielding [Os-3(CO)(11)( L)] {L = PPh3; P(OMe)(3) or 'BuNC}. Compounds 7 and 8 further react with im idazo(1,2-n)pyridine to afford [(mu-H)(2)Os-3(CO)(8)(mu-1,2-eta(2)-C7H5N2)( 2)] (10) and [(mu-H)(2)Os-3(CO)(8)(mu-1,7-eta(2)-C7H5N2)(mu-1,2-eta(2)-C7H5 N3] (11), respectively. Compound II contains two imidazo(1,2-a)pyridine-der ived ligands formed by activation of C(2)-H and C(7)-H bonds, whereas both the heterocyclic ligands in 10 are formed by activation of C(2)-H bonds. Bo th compounds 7 and 8 react with PPh3 at 110 degrees C to yield the monosubs tituted products [(mu-H)Os-3(CO)(9)(mu-1,2-eta(2)-C7H5N2)(PPh3)] (12) and [ (mu-H)Os-3(CO)(9)(mu-1,7-eta(2)-C7H5N2)(PPh3)] (13). The structures of 7, 8 , 9 and 11 have been established by X-ray crystallography. (C) 1999 Elsevie r Science S.A. All rights reserved.