Osmium pincer complexes

The only study on the direct reaction of carbon monoxide with osmium pincer complexes was reported by Milstein and coworkers in 2001 [52]. In this case, the pincer (PCP)Os(II) complex (131) was reacted with CO in benzene at room temperature to afford quantitatively the carbon monoxide adduct (132). This species further reacted with an additional equivalent of CO to yield the bis-carbonyl (PCP)Os(II) pincer complex (133) with the elimination of PPhs. Additionally, complex (133) can be directly generated by pressurizing the pincer compound (131) with 3 bar of CO or from the reaction of complex (134) with CO under mild conditions. The structure of... 

Gauvin, R. M. Rozenberg, H. Shimon, L. J. W. Ben-David, Y. Milstein, D. Osmium-mediated C—H and C—C bond cleavage of a phenolic substrate p-quinone methide and methylene arenium pincer complexes. Chem. Eur. J. 2007, 13, 1382-1393. 

Though in moderate yield, the reported conversion of ethanol to ethyl acetate by complex 14 and a related osmium dimer complex [37] by Gusev generated interest in the catalytic synthesis of ethyl acetate from ethanol because it is a widely used fine chemical. Very recently, Beller et al. [38] screened the catalytic activity of various known pincer complexes for this transformation and found thatTakasago s complex 15, known as Ru-MACHO catalyst, is very efficient and the reaction in the presence of a base resulted in very good TON (Table 1.4). 

In recent years, several structurally different osmium(II) ATH precatalysts have been developed, including those containing L-a-amino carboxylates, pybox ligands, monophosphinite-inositol complexes [169], and pincer complexes. Many of those reduce ketones with high enantioselectivities at very low loadings. 

A wide range of ruthenium and osmium complexes incorporating metallated pincer phosphines or pincer amines have been prepared and characterized and used in applications ranging from materials to catalysis. These will not be reviewed in great detail here—for information, readers are referred to the following citations. ... 

Alabau RG, EguUlor B, Esler J, et al. CCC-Pincer-NHC osmium complexes new types of blue-green emissive neutral compounds for organic light-emitting devices (OLEDs). Organometallics. 2014 33 5582-5596. 

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