Heteroatom exchange reactions in imidoosmium(II) systems: Cleavage of Os-N multiple bonds and formation of Os-X bonds (X = O, S, C)

Article abstract of DOI:10.1021/om00015a021

The monomeric imido complex CymOsN-t-Bu (2) (Cym = η⁶-p-cymene) was used as a convenient precursor in exchange reactions with a variety of H-X bonds (X = O, S, C). Complex 2 reacts with alkoxides HOCMe(CF₃)₂, pinacol, catechol, and 1,2-(H₂N)(HO)C₆H₄ to give CymOs(NH-t-Bu)[OCMe(CF₃)₂] (4), CymOs[OC(CH₃)₂C(CH₃)₂O] (5), CymOs[1,2-O₂C₆H₄] (6), and CymOs[1,2-O(HN)C₆H₄] (7), respectively. CymOs(O-t-Bu)₂ (3) was not formed by this method but was generated by treatment of [CymOsCl₂]₂ (1) with KO-t-Bu. Addition of H₂N-t-Bu to 3 gave 2, and reaction of 5 with catechol gave 6. Complex 6 adds PMe₃ to give CymOs[1,2-O₂C₆H₄](PMe₃) (8). Catechol, 1,2-(H₂N)₂C₆H₄, or H₂N-p-tol hydrogen bond or coordinate to the metal in 6 or CymOs[1,2-(NH)₂C₆H₄] (10). Reactivity patterns generally correlate with the pK_a of the substrate, but other factors are also involved. Several analogous thiolate complexes were also prepared. For example, imido complex 2 or bis(tert-butoxide) 3 reacted readily with t-Bu-SH to give CymOs(S-t-Bu)₂ (13). The analogous osmium complexes with 2,6-Me₂C₆H₃ and 2,4,6-Me₃C₆H₂ groups attached to the sulfur atoms (14 and 15, respectively) were obtained by treatment of imido complex 2 with the appropriate thiols. However, reaction of 2 with p-tol-SH gave the dimeric thiolate complex [CymOs(S-p-Me-C₆H₄)₂]₂ (16). Complex 2 also reacts with carbon acids. The more acidic C-H bond of H₂C(COMe)₂ (acacH) caused the addition of 2 mol of diketone with tert-butylamine loss to give CymOs[CH(COMe)₂][(OC(Me))₂CH-O,O] (18) whereas the weaker acid (H₂C(CO₂Me)₂) added only once across the Os-N bond to give CymOs(NH-t-Bu) [CH(CO₂Me)₂] (17). Treatment of dichloro dimer [CymOsCl₂]₂ with K₂CO₃ and acacH quantitatively provided yellow CymOs(acac-O,O)Cl (19). Monoacetylacetonato complex 19 was treated with AgOAc (Ac = COMe) to give CymOs(acac)(OAc) (21). Dimethyl malonate complex 17 was independently treated with acacH and H₂C(CO(Ph))₂ to give CymOs[CH(C0₂Me)₂][(OC(Me))₂CH] (22) and bright red CymOs[CH(CO₂Me)₂][(OC(Ph))₂CH] (23). Carbon-proton NMR coupling data provided evidence for the presence of carbon-metal bound diketonate ligands in 17, 18, 22, and 23.