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POP-pincer osmium-polyhydrides: head-to-head (Z)-dimerization of terminal alkynes

AuthorsAlós, Joaquín ; Bolaño, Tamara ; Esteruelas, Miguel A. ; Oliván, Montserrat ; Oñate, Enrique ; Valencia, Marta
Issue Date2013
PublisherAmerican Chemical Society
CitationInorganic Chemistry 52(10): 6199-6213 (2013)
AbstractA wide range of osmium-polyhydride complexes stabilized by the POP-pincer ligand xant(PiPr2)2 (9,9-dimethyl-4,5- bis(diisopropylphosphino)xanthene) have been synthesized through cis-OsCl 2{κ-S-(DMSO)4} (1, DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this adduct with the diphosphine, under reflux, leads to OsCl2{xant(PiPr2) 2}(κ-S-DMSO) (2). The reaction of 2 with H2 in the presence of Et3N affords OsH3Cl{xant(PiPr 2)2} (3), which can be also prepared by addition of xant(PiPr2)2 to toluene solutions of the unsaturated d4-trihydride OsH3Cl(PiPr 3)2 (5). Complex 3 reductively eliminates H2 in toluene at 90 °C. In the presence of dimethyl sulfoxide, the resulting monohydride is trapped by the S-donor molecule to give OsHCl{xant(P iPr2)2}(κ-S-DMSO) (6). The reaction of 2 with H2 is sensible to the Brønsted base. Thus, in contrast to Et3N, NaH removes both chloride ligands and the hexahydride OsH 6{xant(PiPr2)2} (7), containing a κ2-P-binding diphosphine, is formed under 3 atm of hydrogen at 50 C. Complex 7 releases a H2 molecule to yield the tetrahydride OsH4{xant(PiPr2)2} (8), which can be also prepared by reaction of OsH6(PiPr3) 2 (9) with xant(PiPr2)2. Complex 8 reduces H+ to give, in addition to H2, the oxidized OsH4-species [OsH4(OTf){xant(PiPr 2)2}]+ (10, OTf = trifluoromethanesulfonate). The redox process occurs in two stages via the OsH5-cation [OsH 5{xant(PiPr2)2}]+ (11). The metal oxidation state four can be recovered. The addition of acetonitrile to 10 leads to [OsH2(η2-H2)(CH 3CN){xant(PiPr2)2}]2+ (12). The deprotonation of 12 yields the osmium(IV) trihydride [OsH 3(CH3CN){xant(PiPr2) 2}]+ (13), which is also formed by addition of HOTf to the acetonitrile solutions of 8. The latter is further an efficient catalyst precursor for the head-to-head (Z)-dimerization of phenylacetylene and tert-butylacetylene. During the activation process of the tetrahydride, the bis(alkynyl)vinylidene derivatives Os(C≡CR)2(=C=CHR) {xant(PiPr2)2} (R = Ph (14), tBu (15)) are formed. © 2013 American Chemical Society.
Identifiersdoi: 10.1021/ic400730a
issn: 0020-1669
e-issn: 1520-510X
Appears in Collections:(ISQCH) Artículos
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