Complex OsH Research Articles

Metathesis between E−C(sp n ) and H−C(sp 3 ) σ‐Bonds (E=Si, Ge; n =2, 3) on an Osmium‐Polyhydride

The silylation of a phosphine of OsH6(PiPr3)2 is performed via net-metathesis between Si−C(spn) and H−C(sp3) σ-bonds (n=2, 3). Complex OsH6(PiPr3)2 activates the Si−H bond of Et3SiH and Ph3SiH to give OsH5(SiR3)(PiPr3)2, which yield OsH4{κ1-P,η2-SiH-[iPr2PCH(Me)CH2SiR2H]}(PiPr3) and R−H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first-order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si-substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH6(PiPr3)2 with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH5(SiR2R′)(PiPr3)2, which evolve into OsH4{κ1-P,η2-GeH-[iPr2PCH(Me)CH2SiR2H]}(PiPr3) (R=Me, OSiMe3) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et3GeH. The latter reacts with OsH6(PiPr3)2 to give OsH5(GeEt3)(PiPr3)2, which loses ethane to form OsH4{κ1-P,η2-GeH-[iPr2PCH(Me)CH2GeEt2H]}(PiPr3).

Metathesis between E-C(spn ) and H-C(sp3 ) σ-Bonds (E=Si, Ge; n=2, 3) on an Osmium-Polyhydride.

The silylation of a phosphine of OsH6(PiPr3)2 is performed via net‐metathesis between Si−C(sp n ) and H−C(sp3) σ‐bonds (n=2, 3). Complex OsH6(PiPr3)2 activates the Si−H bond of Et3SiH and Ph3SiH to give OsH5(SiR3)(PiPr3)2, which yield OsH4{κ1‐P,η2‐SiH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) and R−H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first‐order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si‐substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH6(PiPr3)2 with dimethylphenylsilane, and 1,1,1,3,5,5,5‐heptamethyltrisiloxane afford OsH5(SiR2R′)(PiPr3)2, which evolve into OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) (R=Me, OSiMe3) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et3GeH. The latter reacts with OsH6(PiPr3)2 to give OsH5(GeEt3)(PiPr3)2, which loses ethane to form OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2GeEt2H]}(PiPr3).

Azolium Control of the Osmium-Promoted Aromatic C-H Bond Activation in 1,3-Disubstituted Substrates.

The hexahydride complex OsH6(PiPr3)2 promotes the C–H bond activation of the 1,3-disubstituted phenyl group of the [BF4]− and [BPh4]− salts of the cations 1-(3-(isoquinolin-1-yl)phenyl)-3-methylimidazolium and 1-(3-(isoquinolin-1-yl)phenyl)-3-methylbenzimidazolium. The reactions selectively afford neutral and cationic trihydride-osmium(IV) derivatives bearing κ2-C,N- or κ2-C,C-chelating ligands, a cationic dihydride-osmium(IV) complex stabilized by a κ3-C,C,N-pincer group, and a bimetallic hexahydride formed by two trihydride-osmium(IV) fragments. The metal centers of the hexahydride are separated by a bridging ligand, composed of κ2-C,N- and κ2-C,C-chelating moieties, which allows electronic communication between the metal centers. The wide variety of obtained compounds and the high selectivity observed in their formation is a consequence of the main role of the azolium group during the activation and of the existence of significant differences in behavior between the azolium groups. The azolium role is governed by the anion of the salt, whereas the azolium behavior depends upon its imidazolium or benzimidazolium nature. While [BF4]− inhibits the azolium reactions, [BPh4]− favors the azolium participation in the activation process. In contrast to benzimidazolylidene, the imidazolylidene resulting from the deprotonation of the imidazolium substituent coordinates in an abnormal fashion to direct the phenyl C–H bond activation to the 2-position. The hydride ligands of the cationic dihydride-osmium(IV) pincer complex display intense quantum mechanical exchange coupling. Furthermore, this salt is a red phosphorescent emitter upon photoexcitation and displays a noticeable catalytic activity for the dehydrogenation of 1-phenylethanol to acetophenone and of 1,2-phenylenedimethanol to 1-isobenzofuranone. The bimetallic hexahydride shows catalytic synergism between the metals, in the dehydrogenation of 1,2,3,4-tetrahydroisoquinoline and alcohols.

Dihydroboration of Alkyl Nitriles Catalyzed by an Osmium-Polyhydride: Scope, Kinetics, and Mechanism

Complex OsH6(PiPr3)2 is an efficient catalyst precursor for the addition of pinacolborane and catecholborane to the C–N triple bond of alkyl nitriles. In this way, a variety of N,N-diborylamines ha...

Osmium- and Iridium-Promoted C–H Bond Activation of 2,2′-Bipyridines and Related Heterocycles: Kinetic and Thermodynamic Preferences

The d2-hexahydride complex OsH6(PiPr3)2 (1) promotes the activation of C–H bonds of 2,2′-bipyridines and related heterocycles. The study of the same reactions with the deuteride counterpart OsD6(Pi...

Osmium-Promoted Transformation of Alkyl Nitriles to Secondary Aliphatic Amines: Scope and Mechanism

The transformation of alkyl nitriles to symmetrical and asymmetrical secondary aliphatic amines promoted by the hexahydride complex OsH6(PiPr3)2 (1) is described, and the mechanisms of the reactions involved are established. Complex 1 catalyzes the aforementioned transformations of aryl-, pyridyl-, and alkoxy-functionalized alkyl nitriles with linear or branched chains. The formation of the secondary amines involves primary imines, primary amines, and secondary imines as organic intermediates. The reactions take place under mild conditions (toluene, 100 °C, and 4 bar of H2). Stoichiometric reactions of 1 with pivalonitrile and 2-methoxyacetonitrile have allowed us to isolate the trihydride azavinylidene derivatives OsH3{═N═CHR}(PiPr3)2 (R = tBu (3), CH2OMe (4)). Their formation involves the insertion of the N–C triple bond of the substrates into an Os–H bond of the unsaturated tetrahydride OsH4(PiPr3)2 (A), which is generated by reductive elimination of H2 from the hexahydride precursor. The reaction of these trihydride azavinylidene species with H2 is the key step for the reduction of the N–C triple bond of the nitriles. In the absence of H2, the attack of A to the azavinylidene ligand produces the rupture of its C(sp2)–C(sp3) bond. As a consequence of this attack and the presence of primary imines and amines in the reaction media, the binuclear complexes (PiPr3)2H4Os(μ-CN)OsH3{κ1-N-(NH═CHCH2OMe)}(PiPr3)2 (5) and (PiPr3)2H4Os(μ-CN)OsH3{κ1-N-(NH2CH2CH2OMe)}(PiPr3)2 (6) have been isolated and characterized by X-ray diffraction analysis, for 2-methoxyacetonitrile. DFT calculations reveal noticeable similarities between the hydrogenations of nitriles to primary imines and those of primary imines to primary amines.

Evidence for a Bis(Elongated σ)-Dihydrideborate Coordinated to Osmium.

The formation and Atoms in Molecules (AIM) analysis of osmium(IV) and osmium(II) complexes containing dihydrideborate groups and primary aminoborane ligands are reported. Complex OsH6(P iPr3)2 (1) loses a hydrogen molecule and the resulting unsaturated OsH4(P iPr3)2 species coordinates 9-borabicycle[3.3.1]nonane (HBbn) and pinacolborane (HBpin) to give the dihydrideborate derivatives OsH3{κ2- H, H-(H2BR2)}(P iPr3)2 (BR2 = Bbn (2), Bpin (3)). The bonding situation in these compounds and in the related osmium(II) derivative Os(Bcat){κ2- H, H-(H2Bcat)}(CO)(P iPr3)2 (4) (HBcat = catecholborane) has been analyzed by the AIM method. The Laplacian distributions in the Os-H-B plane exhibit a four-membered cyclic topology possessing two Os-H and two B-H bond critical points associated with one OsHHB ring critical point, which resembles that found for B2H6. The tetrahydride OsH4(P iPr3)2 also coordinates catecholborane, which initially affords OsH3{κ2- H, H-(H2Bcat)}(P iPr3)2 (5). In contrast to 2 and 3, complex 5 reacts with a second molecule of HBcat to give the elongated σ-borane-{bis(elongated σ) -dihydrideborate}-osmium(II) derivative OsH(η3-H2Bcat)(η2-HBcat)(P iPr3)2 (6). Complexes 5 and 6 have been also analyzed via the AIM method. Complex 5 displays the same topology as complexes 2-4. However, the OsH2B unit of 6 shows, besides the Os-H and B-H bond critical points, an additional Os-B bond critical point, which is associated with a bond path running between these atoms. This double triangular topology is completed with the respective ring critical points. Reactions of 1 with dimethylamine-borane (H3B·NHMe2) and tert-butylamine-borane (H3B·NH2tBu) give OsH2(η2:η2-H2BNR2)(P iPr3)2 (NR2 = NMe2 (7), NH tBu (8)). The AIM analyses of 7 and 8 also reveal the occurrence of an Os-B bond critical point associated with a bond path running between those atoms. However, neither Os-H bond critical points nor bond paths are observed in the latter species.

Dihydrobis(methimazolyl)borato complexes of ruthenium and osmium.

The reaction of Na[H2B(mt)2] (mt = 2-mercapto, 3-methylimidazol-1-yl, methimazolyl) with [Ru(X)Cl(CO)(PPh3)n] (n = 3 X = H; n = 2 BO2C6H4, SiCl3, SiMe3) affords the complexes [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}]. Evidence is presented to also support the transient formation of [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] (X = CH[double bond, length as m-dash]CHPh, Ph) via a similar strategy, although these are unstable. The osmium complex [OsH(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] is similarly obtained from [OsHCl(CO)(PPh3)3] or [OsH(NCMe)2(CO)(PPh3)2]BF4. The reaction of [RuH(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] with chloroform or diphenyldiselenide provides [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] (X = Cl, SePh), the latter reaction also providing traces of [Ru(SeH)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}]. Spectroscopic and structural data for the series [Ru(X)(CO)(PPh3){κ2-H,S,S'-H2B(mt)2}] are discussed in terms of perturbations on the B-H-Ru interaction by the trans-ligand X.

Osmium(II) Complexes Containing a Dianionic CCCC-Donor Tetradentate Ligand

The preparation of osmium(II) complexes containing a CC6H4,CBzIm,CBzIm,CC6H4-tetradentate ligand with a −CH2CH2– link between the benzimidazolidene (BzIm) groups is described, and the influence of the link on their structures and emissive properties is analyzed. The hexahydride complex OsH6(PiPr3)2 (1) reacts with 1,1′-diphenyl-3,3′-ethylenedibenzimidazolium bromide in dimethylformamide to afford OsBr{κ3-C,C,C-(C6H4-BzIm-CH2CH2-BzIm-Ph)}(CO)(PiPr3)2 (2), as a result of the direct metalation of both benzimidazolium moieties of the salt, the o-CH bond activation of a phenyl substituent, and the carbonylation of the metal center by action of the solvent. Treatment of 2 with Na[BH4] leads to the hydride derivative OsH{κ3-C,C,C-(C6H4-BzIm-CH2CH2-BzIm-Ph)}(CO)(PiPr3)2 (3), which evolves into Os{κ4-C,C,C,C-(C6H4-BzIm-CH2CH2-BzIm-C6H4)}(CO)(PiPr3)2 (4) as a consequence of the assisted C–H bond activation of the second phenyl substituent. The use of dimethyl sulfoxide instead of dimethylformamide allows the genera...

2-Azetidinones as Precursors of Pincer Ligands: Preparation, Structure, and Spectroscopic Properties of CC'N-Osmium Complexes.

A metal-promoted degradation of 2-azetidinones to afford CC'N-pincer ligands is reported. The hexahydride complex OsH6(P(i)Pr3)2 (1) reacts with (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(pyridin-2-yl)azetidin-2-one (I), (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(isoquinolin-2-yl)azetidin-2-one (II), and (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(quinolin-2-yl)azetidin-2-one (III) to give the respective OsH2(P(i)Pr3)2(CC'N) (2-4) complexes, which add HBF4·OEt2 to yield [OsH2(P(i)Pr3)2(CC″N)]BF4 (5-7). These salts are the result of the addition of the proton of the acid to the dianionic CC'N-pincer ligand. The hydride ligands of these compounds undergo quantum mechanical exchange coupling, which has been experimentally quantified according to a two-dimensional harmonic oscillator model, where Jex is determined by the separation between the hydrides, their hard sphere radius, and a ν parameter describing the H-M-H vibrational wag mode allowing the movement along the H-H vector. The comparison of the results reveals that the phenomenon is particularly intense for 5-7. Furthermore, in these compounds, the separation between the hydrides is ∼0.1 Å shorter than in the respective neutral species 2-4, whereas the hydride hard sphere radius increases by ∼10%, and the ν value decreases by ∼20%.

An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

The hexahydride complex OsH6(PiPr3)2 (1) activates the C–OMe bond of 1-(2-methoxy-2-oxoethyl)-3-methylimidazolium chloride (2), in addition to promoting the direct metalation of the imidazolium group, to afford a five-coordinate OsCl(acyl-NHC)(PiPr3)2 (3) compound. The latter coordinates carbon monoxide, oxygen, and molecular hydrogen to give the corresponding carbonyl (4), dioxygen (5), and dihydrogen (6) derivatives. Complex 3 also promotes the heterolytic bond activation of pinacolborane (HBpin), using the acyl oxygen atom as a pendant Lewis base. The hydride ligand and the Bpin substituent of the Fischer-type carbene of the resulting complex 7 activate the O–H bond of alcohols and water. As a consequence, complex 3 is a metal ligand cooperating catalyst for the generation of molecular hydrogen, by means of both the alcoholysis and hydrolysis of pinacolborane, via the intermediates 7 and 6.

Azole Assisted C–H Bond Activation Promoted by an Osmium-Polyhydride: Discerning between N and NH

The capacity of the hexahydride complex OsH6(PiPr3)2 (1) to discern between the nitrogen atom and the NH unit in the azole assisted aryl C–H bond activation has been investigated. Complex 1 reacts with 2-phenylimidazole to give OsH3{κ2-C,N-(C6H4-imidazole)}(PiPr3)2 (2), which has been characterized by X-ray diffraction analysis. The structure proves the higher affinity of the metal center for the N atom in the presence of the NH unit, which remains unchanged, and reveals that in the solid state the molecules of this complex form infinite chains by means of intermolecular asymmetric 3-center bifurcated dihydrogen bonds. In solution, 1H-DOSY NMR experiments suggest that the association degree decreases as the temperature increases. The fused six-membered ring of benzimidazole weakens the NH bond, enhancing its reactivity. As a consequence, complex 1 cannot discern between the N atom and the NH unit of 2-phenylbenzimidazole. Thus, the treatment of 1 with this substrate leads to a mixture of OsH3{κ2-C,N-(C6H4...

Osmium(II)–Bis(dihydrogen) Complexes Containing Caryl,CNHC–Chelate Ligands: Preparation, Bonding Situation, and Acidity

The hexahydride complex OsH6(PiPr3)2 (1) reacts with the BF4-salts of 1-phenyl-3-methyl-1-H-benzimidazolium, 1-phenyl-3-methyl-1-H-5,6-dimethyl-benzimidazolium, and 1-phenyl-3-methyl-1-H-imidazolium to give the respective trihydride-osmium(IV) derivatives OsH3(κ2-Caryl,CNHC)(PiPr3)2 (2–4). The protonation of these compounds with HBF4·OEt2 produces the reduction of the metal center and the formation of the bis(dihydrogen)-osmium(II) complexes [Os(κ2-Caryl,CNHC)(η2-H2)2(PiPr3)2]BF4 (5–7). DFT calculations using AIM and NBO methods reveal that the Os–NHC bond of the Os-chelate link tolerates a significant π-backdonation from a doubly occupied dπ(Os) atomic orbital to the pz atomic orbital of the carbene carbon atom. The π-accepting capacity of the NHC unit of the Caryl,CNHC-chelate ligand, which is higher than those of the coordinated aryl group and phosphine ligands, enhances the electrophilicity of the metal center activating one of the coordinated hydrogen molecules of 5–7 toward the heterolysis. As a result, these compounds are strong Brønsted acids with pKawater values between 2.5 and 2.8. In acetonitrile the hydrogen molecules of 5 and 6 are displaced by the solvent, the resulting bis(solvento) compounds [Os(κ2-Caryl,CNHC)(CH3CN)2(PiPr3)2]BF4 (8, 9) react with acetylacetonate (acac) and cis-1,2-bis(diphenylsphosphino)ethylene (bdppe) to give Os(κ2-Caryl,CNHC)(acac)(bdppe) (10, 11) as a mixture of the two possible isomers, namely with P trans to the aryl group or to the NHC moiety.

Synthesis of Five-Membered Osmacycles with Osmium–Vinyl Bonds from Hydrido Alkenylcarbyne Complexes

Treatment of the osmium hydrido butenylcarbyne complex [OsH{≡CC(PPh3)═CH(Et)}(PPh3)2Cl2]BF4 (1) with excess 2-chloro-4-cyanopyridine in the presence of H2O2 generates the fused osmacyclopentadiene 2. A detailed mechanism of the conversion has been investigated with the aid of in situ NMR experiments and the isolation of intermediates 3 and 4. In contrast, reaction of 1 with the propiolic acid ester HC≡CCOOMe produces the osmafuran 5. Analogous reactions of the osmium hydrido phenylethenylcarbyne complex [OsH{≡CC(PPh3)═CH(Ph)}(PPh3)2Cl2]BF4 (6) with nitriles/CO or HC≡CCOOMe were also studied, which result in the formation of five-membered osmacycles [Os{CHC(PPh3)CH(Ph)(OH)}(CH3CN)(PPh3)2CO](BF4)2 (7) and [Os{CHC(PPh3)CH(Ph)(OH)}(PhCN)(PPh3)2CO](BF4)2 (8). In the presence of NEt3, 6 can convert to the osmium hydrido phenylethenylcarbyne complex OsH{≡CC═CH(Ph)}(PPh3)2Cl2 (9) in wet acetonitrile, presumably involving P–C bond cleavage. Similarly, 9 can react with HC≡CCOOMe with the aid of HBF4 to give osmafur...

CCC–Pincer–NHC Osmium Complexes: New Types of Blue-Green Emissive Neutral Compounds for Organic Light-Emitting Devices (OLEDs)

Novel homoleptic and heteroleptic NHC carbene containing bis(tridentate) osmium(II) complexes have been designed, synthesized, and characterized, and their photophysical properties have been studied. The complex OsH6(PiPr3)2 (1) reacts with the tetrafluoroborate salts of 1,3-bis(3-methylbenzimidazolium-1-yl)benzene and 1,3-bis(3-methylimidazolium-1-yl)benzene, in dimethylformamide, under reflux to afford the hydride–carbonyl derivatives [OsH(CNHCCarylCbenzimidazolium)(CO)(PiPr3)2]BF4 (2) and [OsH(CNHCCarylCimidazolium)(CO)(PiPr3)2]BF4 (3), as a result of the direct metalation of one of the NHC units of the salts, the activation of the C–H bond at the 6-position of the bridged aryl group, and metal carbonylation by solvent decarbonylation. In contrast to the BF4 salts, under the same conditions, the iodide salts of 1,3-bis(3-methylbenzimidazolium-1-yl)benzene, 1,3-bis(3-methylimidazolium-1-yl)benzene, and 1,3-bis(3-methylbenzimidazolium-1-yl)-5-trifluoromethylbenzene undergo direct metalation of both NHC u...

Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe2CMe2NH2)(PPh3)2

The hydrido–amido complex OsH(NHCMe2CMe2NH2)(PPh3)2 (1) catalyzes the base-free hydrogenation of ketones in benzene. Kinetic studies using acetophenone revealed that the system has an induction period, after which the rate of the reaction increases. A constant rate was observed when a critical amount of the product alcohol was added, indicating that the reaction is autocatalytic in 1-phenylethanol. Varying the initial conditions showed that the reaction rate is dependent on hydrogen and catalyst concentration and independent of ketone concentration. Above the critical concentrations of 1-phenylethanol, the reaction rate is independent of alcohol concentration. The rate law for pressures up to 5 atm was found to be rate = d[alcohol]/dt = −d[ketone]/dt = k[Os][H2], with k = 30 mol L−1 s−1 at 293 K and the temperature dependence provided energy of activation parameters. Therefore, the heterolytic splitting of dihydrogen is rate determining under these conditions. Only small kinetic isotope effects were measured in contrast with the analogous ruthenium system. Complex 1 reacts with the product alcohol 1-phenylethanol and is partially converted into the dihydride complex trans-OsH2(NH2CMe2CMe2NH2)(PPh3)2 and acetophenone; with excess alcohol, an osmium alkoxide is observed at low temperature. As expected from these results, 1 is a ketone transfer hydrogenation catalyst in isopropanol.

Synthesis and characterization of MH⋯HOR dihydrogen bonded ruthenium and osmium complexes (η5-C5H4CH2OH)MH(PPh3)2 (M = Ru, Os)

Treatment of RuCl2(PPh3)3 with 6-dimethylaminopentafulvene in THF in the presence of water produced (η5-C5H4CHO) RuCl(PPh3)2, which was reduced by NaBH4 to give the Ru-H⋯HO dihydrogen bonded complex (η5-C5H4CH2OH) RuH(PPh3)2. The dihydrogen bonded complex (η5-C5H4CH2OH)RuH(PPh3)2 could also be synthesized by the reduction of complex (η5-C5H4CHO)RuH(PPh3)2, which was obtained by the reaction of RuHCl(PPh3)3 with 6-dimethylaminopentafulvene in the presence of water. The analogous dihydrogen bonded osmium complex (η5-C5H4CH2OH)OsH(PPh3)2 was similarly prepared. Single crystal structures and DFT calculations support the presence of intra-molecular H…H interaction, with separations of around 1.9 to 2.0 A.

Osmium-Promoted Dehydrogenation of Amine–Boranes and B–H Bond Activation of the Resulting Amino–Boranes

The five-coordinate osmium complex OsH(SH)(CO)(PiPr3)2, containing an electrophilic center bonded to the soft hydrogen sulfide ligand, promotes dehydrogenation of amine–boranes and captures the amino–borane products, forming hydrogenaminothioborate complexes.

Reactions of an Osmium-Hexahydride Complex with Cytosine, Deoxycytidine, and Cytidine: The Importance of the Minor Tautomers

Complex OsH(6)(P(i)Pr(3))(2) (1) deprotonates cytosine to give molecular hydrogen and the d(4)-trihydride derivative OsH(3)(cytosinate)(P(i)Pr(3))(2) (2), which in solution exists as a mixture of isomers containing κ(2)-N1,O (2a) and κ(2)-N3,O (2b) amino-oxo and κ(2)-N3,N4 (2c) imino-oxo tautomers. The major isomer 2b associates with the minor one 2c through N-H···N and N-H···O hydrogen bonds to form [2b·2c](2) dimers, which crystallize from saturated pentane solutions of 2. Complex 1 is also able to perform the double deprotonation of cytosine (cytosinate') to afford the dinuclear derivative (P(i)Pr(3))(2)H(3)Os(cytosinate')OsH(3)(P(i)Pr(3))(2) (3), where the anion is coordinated κ(2)-N1,O and κ(2)-N3,N4 to two different OsH(3)(P(i)Pr(3))(2) metal fragments. The deprotonation of deoxycytidine and cytidine leads to OsH(3)(deoxycytidinate)(P(i)Pr(3))(2) (4) and OsH(3)(cytidinate)(P(i)Pr(3))(2) (5), respectively, containing the anion κ(2)-N3,N4 coordinated. Dimer [2b·2c](2) and dinuclear complex 3 have been characterized by X-ray diffraction analysis.

Preparation, Structure, Bonding, and Preliminary Reactivity of a Six-Coordinate d4Osmium–Boryl Complex

The d4 ML6 bis-boryl complex OsH(Bcat)2Cl(PiPr3)2 (Bcat = catecholborate) has been prepared by the reaction of OsH2Cl2(PiPr3)2 with HBcat, via the monoboryl intermediate OsH2(Bcat)Cl(PiPr3)2, and its structure determined by X-ray diffraction analysis. The Os–B bonds and the stability and disposition of the boryl ligands have been analyzed by DFT calculations. The bis-boryl complex loses HBcat to give Os(Bcat)Cl(CO)2(PiPr3)2, under a CO atmosphere.