Osmium complexes deprotonated

The 7] -osmium complexes of a-unsubstituted thiophenes undergo Lewis acid-promoted addition with acetals at C-2 to give the thiophenium complexes in good yields <19990M2988>. These can be deprotonated to give the 2-substituted thiophene complexes. The electrophile attacks the substrate on the rivn-face (Scheme 83). 

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

Intermolecular addition of carbon nucleophiles to the ri2-pyrrolium complexes has shown limited success because of the decreased reactivity of the iminium moiety coupled with the acidity (pKa 18-20) of the ammine ligands on the osmium, the latter of which prohibits the use of robust nucleophiles. Addition of cyanide ion to the l-methyl-2//-pyr-rolium complex 32 occurs to give the 2-cyano-substituted 3-pyrroline complex 75 as one diastereomer (Figure 15). In contrast, the 1-methyl-3//-pyrrolium species 28, which possesses an acidic C-3-proton in an anti orientation, results in a significant (-30%) amount of deprotonation in addition to the 2-pyrroline complex 78 under the same reaction conditions. Uncharacteristically, 78 is isolated as a 3 2 ratio of isomers, presumably via epimerization at C-2.17 Other potential nucleophiles such as the conjugate base of malononitrile, potassium acetoacetate, and the silyl ketene acetal 2-methoxy-l-methyl-2-(trimethylsiloxy)-l-propene either do not react or result in deprotonation under ambient conditions. 

The isolation of the first stable oxo-terf-butylimido complexes of ru-thenium(VI) and osmium(VI) porphyrins by oxidative deprotonation of [M(porp)CBuNH2)2] has been reported (289). These complexes are diamagnetic and have been characterized by NMR and IR spectroscopy. The [RuVI(porp)(0)(N Bu)] complex rapidly reacts with PPh3 in solution to give 0=PPh3, Ph3P=N Bu, and [Ru(porp)(PPh3)2]. 

A related process has been reported for the synthesis of osmium nitrido complexes with 1,2-benzenedithiolate ligands. Thus, the synthesis of 173 was effected by treatment of (Bu4N)[OsNC14] with deprotonated 1,2-benzenedithiol (Eq. (70)). Interestingly, when 173 is treated with Me3OBF4 alkylation is observed to occur on the sulfur this contrasts the reaction of 173 with Ph3CPF6, for which reaction at the terminal nitride is observed [93]. 

It seems strange that no hydroxylamine complexes of osmium are established. There is a brief report of a deprotonated complex Os(NO)(NHOH)Cl2(PPh3)2, made from Os(NO)2(PPh3)2 and HC1. The vNO band is at 1860 cm-1.247... 

Several groups have completed computational studies on the relative stabilities of osmium carbyne, carbene, and vinylidene species. DFT calculations on the relative thermodynamic stability of the possible products from the reaction of OsH3Cl(PTr3)2 with a vinyl ether CH2=CH(OR) showed that the carbyne was favored. Ab initio calculations indicate that the vinylidene complex [CpOs(=C=CHR)L]+ is more stable than the acetylide, CpOs(-C=CR)L, or acetylene, [CpOs() -HC=CR)L]+, complexes but it doesn t form from these complexes spontaneously. The unsaturated osmium center in [CpOsL]+ oxidatively adds terminal alkynes to give [CpOsH(-C=CR)L]+. Deprotonation of the metal followed by protonation of the acetylide ligand gives the vinylidene product. 

Osmium pentacarbonyl is a convenient precursor to other osmium carbonyl complexes. Hydrogenation gives the dihydride OsH2(CO)4. This hydride is not acidic with a p/fa of 18.5 but it can be deprotonated by strong bases to give [OsH(CO)4] and reduced by sodium (Scheme 23). Substitution of CO on Os(CO)5 by trialkyl or triarylphosphines, arsines, or stibenes gives Os(CO)4L or Os(CO)3L2. Other carbonyl phosphine complexes result from the reduction of osmium halides by alcohols in the presence of the tertiary phosphine. 

The osmium hydride (CO)ioOs3H2 reacts with isonitriles to give monosubstituted products (CO)io(RNC)Os3H(/2-H), which react further via insertion to give (CO)io(ju-ri -RNCH))(/i-H)Os3. In weak donor solvents, hydride attacks at the carbon whereas strong donor solvents result in hydride attack at nitrogen. The latter reaction results from deprotonation of the hydride complex, followed by reprotonation at nitrogen. 

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