RESUMEN

The discovery of cycloosmathioborane compounds is reported. These species, which are prepared by the simultaneous dehydrogenation of a trihydride hydrogensulfide osmium(IV) complex and a BH3NHR2 amine-borane, bear an Os-S-B three-membered ring, being a manifestation of the 4 n + 2 Hückel aromaticity in which n = 0 and where the two π electrons of the ring are provided by the S atom.

RESUMEN

Nonclassical and classical osmium polyhydrides containing the diphosphine 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(PiPr2)2), coordinated in κ3-mer, κ3-fac, and κ2-P,P fashions, have been isolated during the cyclic formation of H2 by means of the sequential addition of H+ and H- or H- and H+ to the classical trihydride OsH3Cl{xant(PiPr2)2} (1). This complex adds H+ to form the compressed dihydride dihydrogen complex [OsCl(H···H)(η2-H2){xant(PiPr2)2}]+ (2). Under argon, cation 2 loses H2 and the resulting unsaturated fragment dimerizes to give [(Os(H···H){xant(PiPr2)2})2(µ-Cl)2]2+ (3). During the transformation the phosphine changes its coordination mode from mer to fac. The benzofuran counterpart of 1, OsH3Cl{dbf(PiPr2)2} (4; dbf(PiPr2)2 = 4,6-bis(diisopropylphosphino)dibenzofuran), also adds H+ to afford the benzofuran counterpart of 2, [OsCl(H···H)(η2-H2){xant(PiPr2)2}]+ (5), which in contrast to the latter is stable and does not dimerize. Acetonitrile breaks the chloride bridge of 3 to form the dihydrogen [OsCl(η2-H2)(CH3CN){xant(PiPr2)2}]+ (6), regenerating the mer coordination of the diphosphine. The hydride ion also breaks the chloride bridge of 3. The addition of KH to 3 leads to 1, closing a cycle for the formation of H2. Complex 1 reacts with a second hydride ion to give OsH4{xant(PiPr2)2} (7) as consequence of the displacement of the chloride. Similarly to the latter, the oxygen atom of the mer-coordinated diphosphine of 7 has a tendency to be displaced by the hydride ion. Thus, the addition of KH to 7 yields [OsH5{xant(PiPr2)2}]- (8), containing a κ2-P,P-diphosphine. Complex 8 is easily protonated to afford OsH6{xant(PiPr2)2} (9), which releases H2 to regenerate 7, closing a second cycle for the formation of molecular hydrogen.

RESUMEN

The aromatic osmacyclopropenefuran bicycles [OsTp{κ3 -C1 ,C2 ,O-(C1 H2 C2 CHC(OEt)O)}(Pi Pr3 )]BF4 (Tp=hydridotris(1-pyrazolyl)borate) and [OsH{κ3 -C1 ,C2 ,O-(C1 H2 C2 CHC(OEt)O)}(CO)(Pi Pr3 )2 ]BF4 , with the metal fragment in a common vertex between the fused three- and five-membered rings, have been prepared via the π-allene intermediates [OsTp(η2 -CH2 =CCHCO2 Et)(OCMe2 )(Pi Pr3 )]BF4 and [OsH(η2 -CH2 =CCHCO2 Et)(CO)(OH2 )(Pi Pr3 )2 ]BF4 , and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(Pi Pr3 )2 ]+ metal fragment is a key intermediate in the [OsH(CO)(OH2 )2 (Pi Pr3 )2 ]BF4 -catalyzed regioselective anti-Markovnikov hydration of ethyl buta-2,3-dienoate to ethyl 4-hydroxycrotonate.

RESUMEN

A novel osmium-catalyzed cyclization of o-alkynyl phenethylamines to give 3-benzazepines is reported. The procedure allows the straightforward preparation of a broad range of dopaminergic 3-benzazepine derivatives. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, which were isolated and characterized by X-ray crystallography.

Asunto(s)

RESUMEN

A new synthetic route to dihydrobiphenylenes has been developed. The process involves a mild Ru(II) -catalyzed [2+2+2] dimerization of ortho-alkenylarylacetylenes or its more versatile variant, the Ru-catalyzed [2+2+2] cycloaddition of ortho-ethynylstyrenes with alkynes. Mechanistic aspects of this [2+2+2] cycloaddition are discussed.

Asunto(s)

RESUMEN

The complex [H(EtOH)2][{OsCl(eta4-COD)}2(mu-H)(mu-Cl)2] (1) has been prepared in high yield by treatment of OsCl3.3H2O (54% Os) with 1,5-cyclooctadiene in ethanol under reflux. Under air, it is unstable and undergoes oxidation by action of O2 to afford the neutral derivative {OsCl(eta4-COD)}2(mu-H)(mu-Cl)2 (2). The terminal chlorine ligands of the anion of 1 are activated toward nucleophilic substitution. Thus, reaction of the salt [NBu4][{OsCl(eta4-COD)}2(mu-H)(mu-Cl)2] (1a) with NaCp in toluene gives [NBu4][{Os(mu1-C5H5)(eta4-COD)}(mu-H)(mu-Cl)2{OsCl(eta4-COD)}] (3) as a result of the replacement of one of the terminal chlorine atoms by the cyclopentadienyl ligand. The CH2 group of the latter can be deprotonated by the bridging methoxy ligand of the iridium dimer [Ir(mu-OMe)(eta4-COD)]2. The reaction leads to the trinuclear derivative [NBu4][{(eta4-COD)Ir(mu5-C5H4-mu1)Os(eta4-COD)}(mu-H)(mu-Cl)2{OsCl(eta4-COD)}] (4) containing a bridging C5H4 ligand that is eta1-coordinated to an osmium atom of the dimeric unit and mu5-coordinated to the Ir(eta4-COD) moiety. Salt 1a also reacts with LiC[triple bond]CPh. In this case, the reaction produces the substitution of both terminal chlorine ligands to afford the bis(alkynyl) derivative [NBu4][{Os(C[triple bond]CPh)(eta4-COD)}2(mu-H)(mu-Cl)2] (5). Complexes 1, 2, 3, and 4 have been characterized by X-ray diffraction analysis. Although the separations between the osmium atoms are short, between 2.6696(4) and 2.8633(5) A, theoretical calculations indicate that only in 2 is there direct metal-metal interaction, as the bond order is 0.5.