Unsaturated Osmium Research Articles

Osmium Hydride Acetylacetonate Complexes and Their Application in Acceptorless Dehydrogenative Coupling of Alcohols and Amines and for the Dehydrogenation of Cyclic Amines

The preparation of new osmium hydride complexes, starting from OsH6(PiPr3)2 (1) and OsH2Cl2(PiPr3)2 (2), and their catalytic activity in acceptorless dehydrogenative coupling of alcohols and amines and in dehydrogenation of cyclic amines are reported. Complex 1 reacts with acetylacetone (Hacac) to give the classical trihydride OsH3(acac)(PiPr3)2 (3). The protonation of 3 with triflic acid (HOTf) produces the release of H2 and the formation of the unsaturated osmium(IV) dihydride [OsH2(acac)(PiPr3)2]OTf (4), which is also prepared by starting from 2 via the intermediate OsH2Cl(acac)(PiPr3)2 (5). Treatment of an acetylacetone solution of 5 with KOH affords Os(acac)2(PiPr3)2 (6). In the presence of 5 mol % of KOH, complexes 3–6 promote the coupling of benzyl alcohol and aniline to give N-benzylideneaniline and H2. Under the same conditions, complex 3 catalyzes a wide range of analogous couplings to afford a variety of imines, including aliphatic imines, with yields between 90 and 40% after 1–48 h. Complex 3 ...

Hydroosmiation of Allenes and Reductive Elimination of Olefin in Unsaturated Osmium(IV) Polyhydrides: Hydride versus Chloride

The replacement of a chloride in OsH2Cl2(PiPr3)2 (1) by a hydride, to afford OsH3Cl(PiPr3)2 (2), produces dramatic changes in the behavior of the system. Complex 1 hydrogenates the sterically most hindered C–C double bond of gem-disubstituted allenes. In contrast, the trihydride 2 reacts with 1,1-dimethylallene and 1-methyl-1-(trimethylsilyl)allene to give the alkenyl derivates OsH2Cl{C(CH3)═C(CH3)R}(PiPr3)2 (R = CH3 (3), SiMe3 (4)), which do not undergo reductive elimination of olefin in spite of the coplanar cis disposition of the metalated carbon atom and one of the hydride ligands. The X-ray structure of 3 proves that the α-methyl substituent of the alkenyl group cancels the unsaturated character of the metal center. Complex 2 also reacts with ethyl allenecarboxylate. The reaction leads to the metallafuran OsH2Cl{κ2C,O-[C(CH3)═CHC(O)OEt]}(PiPr3)2 (5), which has been also characterized by X-ray diffraction analysis. DFT calculations suggest that the formation of 3 and 4 is a consequence of the coplanar cisoid disposition of the hydride ligand and the CH2 group of the allene in a hydride–dihydrogen−π-allene intermediate. The DFT calculations also show that 3 and 4 are thermodynamic sinks and that the reductive elimination of the olefin is kinetically disfavored.

Stoichiometric and Catalytic Deuteration of Pyridine and Methylpyridines by H/D Exchange with Benzene-d6 Promoted by an Unsaturated Osmium Tetrahydride Species

Treatment of toluene solutions of the hexahydride complex OsH6(PiPr3)2 (1) with pyridine, 3-methylpyridine, and 4-methylpyridine affords the tetrahydride derivatives OsH4(Rpy)(PiPr3)2 (Rpy = py (3), 3-methylpyridine (4), and 4-methylpyridine (5)). In benzene-d6, these compounds release the heterocycles, and the resulting unsaturated tetrahydride OsH4(PiPr3)2 (2) promotes the stoichiometric and catalytic deuteration of pyridine, 3-methylpyridine, and 4-methylpyridine by means of H/D exchanges between the heterocycles and the solvent. The deuteration rates of the pyridinic C−H bonds depend upon their positions in the heterocycles. For pyridine, they increase as the C−H bonds are separated from the heteroatom. A methyl substituent has a marked negative effect on the deuteration of its adjacent C−H bonds. The kinetic analysis of the deuteration reveals that the rate-determining step for the H/D exchanges is the C−H activation of the bond that is deuterated. DFT calculations show that this step is formed by tw...

C(sp2)−H Activation of RCHE−py (E = CH, N) and RCHCHC(O)R‘ Substrates Promoted by a Highly Unsaturated Osmium−Monohydride Complex

The 14-valence-electron monohydride OsH(SnPh2Cl)(PiPr3)2 (a), generated from (1), activates a C(sp2)−H bond of 2-vinylpyridine, (E)-N-(phenylmethylene)-2-pyridinamine, and α,β-unsaturated ketones. The activation of 2-vinylpyridine affords the elongated dihydrogen (dH-H = 1.41 A) derivative (2) in equilibrium (ΔH° = −2.5 ± 0.2 kcal mol-1 and ΔS° = −14.8 ± 1.0 cal mol-1 K-1) with the tautomer (3), where the stannane is bonded to the transition metal by an Os−H−Sn three-center bond (JH-Sn = 183 Hz). The activation of (E)-N-(phenylmethylene)-2-pyridinamine gives rise to (4; dH-H = 1.32 A), whereas the treatment of 1 with methyl vinyl ketone and benzylidenacetone leads to (R = H (5), Ph (6)), which show blocked rotation of the dihydrogen ligand (dH-H = 1.45 (5), dH-H = 1.42 (6) A) on the NMR time scale (ΔH⧧ = 11.7 ± 0.4 kcal mol-1 and ΔS⧧ = −1 ± 1 cal mol-1 K-1 (5), ΔH⧧ = 10.8 ± 0.5 kcal mol-1 and ΔS⧧ = 0.4 ± 1 cal mol-1 K-1 (6)). Complex 1 also reacts with benzylidenacetophenone. The reaction initially gives ...

Stepwise Conversion of an Osmium Trimethylstannyl Complex to a Triiodostannyl Complex and Nucleophilic Substitution Reactions at the Tin−Iodine Bonds

Treatment of the coordinatively unsaturated osmium complex Os(SnMe3)Cl(CO)(PPh3)2 with sodium dimethyldithiocarbamate gives the coordinatively saturated complex Os(SnMe3)(η2-S2CNMe2)(CO)(PPh3)2 (1). Complex 1 reacts with excess SnI4 to give Os(SnMeI2)(η2-S2CNMe2)(CO)(PPh3)2 (3) in high yield. A redistribution reaction of 3 with an equimolar amount of 1 provides Os(SnMe2I)(η2-S2CNMe2)(CO)(PPh3)2 (2). The last remaining methyl group bonded to tin in 3 is removed by treatment with a slight excess of I2, giving the triiodostannyl complex Os(SnI3)(η2-S2CNMe2)(CO)(PPh3)2 (4). Both 3 and 4 have been further derivatized by replacement of the halide groups on tin. Treatment of 3 with pyridinium tribromide gives Os(SnMeBr2)(η2-S2CNMe2)(CO)(PPh3)2 (5). Treatment of 3 with catechol provides Os(SnMe[1,2-O2C6H4])(η2-S2CNMe2)(CO)(PPh3)2 (6), while the similar reaction with 1,2-ethanedithiol gives Os(SnMe[1,2-S2C2H4])(η2-S2CNMe2)(CO)(PPh3)2 (7). Complex 4 undergoes reaction with an excess of KOH to give the trihydroxysta...

Diminishing π-Stabilization of an Unsaturated Metal Center: Hydrogen Bonding to OsHCl(CO)(PtBu2Me)2

The interaction between (CF3)2CHOH and OsHCl(CO)(PtBu2Me)2 in toluene and hexane is shown by 1H NMR (chemical shift, NOE and relaxation times) and IR (νCO, νOs-H, and νOs-Cl) spectroscopies to involve −ΔH° ≈ 3−4 kcal/mol and −ΔS° ≈ 7−9 cal mol-1 K-1. Integrated molecular orbital/molecular mechanics calculations show definitively that the hydrogen bond acceptor is chloride and that steric effects preclude any O→Os donation by the alcohol. Analysis of the calculated energies and structures shows that such hydrogen bonding increases the electrophilic character of the unsaturated osmium.

Synthesis and reactivity of coordinatively unsaturated osmium and ruthenium stannyl complexes

Abstract Treatment of MHCl(CO)(PPh 3 ) 3 (MRu, Os) with (CH 2 CH)SnR 3 is a good general route to the coordinatively unsaturated osmium and ruthenium stannyl complexes M(SnR 3 )Cl(CO)(PPh 3 ) 2 ( 1 : MRu, RMe; 2 : MRu, R = n-butyl; 3 : MRu, R = p -tolyl; 4 : MOs, RMe). These coordinatively unsaturated complexes readily add CO and CN- p -tolyl to form the coordinatively saturated compounds M(SnR 3 )Cl(CO)L(PPh 3 ) 2 ( 5 : MRu, RMe, LCO; 6 : M;Ru, R = n-butyl, LCO; 7 : MRu, R = p -tolyl, LCO; 8 : MOs, RMe, LCO; 9 : MRu, RMe, LCN- p -tolyl; 10 : MRu, R = n-butyl, L  CN - p -tolyl; 11 : MOs, RMe, LCN- p -tolyl). In addition, the chloride ligand in Ru(SnR 3 )Cl(CO)(PPh 3 ) 2 proves to be labile and treatment with the potentially bidentate anionic ligands, dimethyldithiocarbamate or diethyldithiocarbamate, affords the coordinatively saturated compounds Ru(SnR 3 )( η 2 -S 2 CNR′ 2 )(CO)(PPh 3 ) 2 ( 12 : RMe, R′ = Me; 13 : RMe, R′ = Et; 14 : R = n-butyl, R′ = Me; 15 : R = p -tolyl, R′ = Me; 16 : R = p -tolyl, R′ = Et). Chloride is also displaced by carboxylates forming the six-coordinate compounds Ru(SnR 3 )( η 2 -O 2 CR′)(CO)(PPh 3 ) 2 ( 17 : RMe, R′ = H; 18 : RMe, R′ = Me; 19 : RMe, R′ = Ph; 20 : R = n-butyl, R′ = Me; 21 : R = p -tolyl, R ′ = Me ). IR and 1 H NMR spectral data for all the new compounds and 31 P and 119 Sn NMR spectral data for selected compounds are reported.

Redox behavior of the electronically unsaturated osmium clusters Os3(.mu.-H)2(CO)9L and their saturated congeners Os3(.mu.-H)(H)(CO)10L (L = CO, PPh3, AsPh3)

Redox behavior of the electronically unsaturated osmium clusters Os3(.mu.-H)2(CO)9L and their saturated congeners Os3(.mu.-H)(H)(CO)10L (L = CO, PPh3, AsPh3)

A transient infrared spectroscopy study of coordinatively unsaturated osmium carbonyl compounds

Transient infrared spectroscopy is used to study the coordinatively unsaturated osmium carbonyl fragments generated by photolysis of gas-phase Os(CO) 5 . The nascent photoproducts, predominantly Os(CO) 3 with some Os(CO) 4 , are highly reactive toward combination with both CO and Os(CO) 5 . Infrared absorptions for a new unsaturated osmium species, Os 2 (CO) 8 , formed by reaction of Os(CO) 3 with Os(CO) 5 , are assigned

The high yield synthesis of an unsaturated osmium cluster; the X-ray crystal structure of [Os3(CO)8(H){Ph2PCH2P(Ph)C6H4}

Thermolysis of [Os3(CO)10(dppm)](dppm = Ph2PCH2PPh2) in refluxing toluene affords a high yield of the unsaturated cluster [Os3(CO)8(H){Ph2PCH2P(Ph)C6H4}] which has been characterized by X-ray crystallography, and which undergoes a facile reversible reaction with CO.