Preparation of tricarbonyl(η<sup>6</sup>-pyridine)chromium(<scp>0</scp>) complexes

“…[235][236][237][238][239][240][241][242] For example, Davies et al report addition of diisobutyl aluminium hydride or alkyl lithium reagents to tricarbonyl(Z 6 -pyridine)chromium (55) to selectively afford the corresponding 1,2-dihydropyridine complexes, 56 (Scheme 24). [235][236][237] In contrast to the s-dihydropyridine complexes presented above, the p-bonded 1,2-dihydropyridines are far poorer reducing agents than when 'free' due to the overall electron-withdrawing effect of the bound metal center. Indeed, complex 56 was sufficiently stable to be isolated using chromatography in air.…”

Section: Direct Addition Of Hydride To Coordinated Pyridinesmentioning

confidence: 99%

The coordination chemistry of organo-hydride donors: new prospects for efficient multi-electron reduction

2013

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In biological reduction processes the dihydronicotinamides NAD(P)H often transfer hydride to an unsaturated substrate bound within an enzyme active site. In many cases, metal ions in the active site bind, polarize and thereby activate the substrate to direct attack by hydride from NAD(P)H cofactor. This review looks more widely at the metal coordination chemistry of organic donors of hydride ion--organo-hydrides--such as dihydronicotinamides, other dihydropyridines including Hantzsch's ester and dihydroacridine derivatives, those derived from five-membered heterocycles including the benzimidazolines and benzoxazolines, and all-aliphatic hydride donors such as hexadiene and hexadienyl anion derivatives. The hydride donor properties--hydricities--of organo-hydrides and how these are affected by metal ions are discussed. The coordination chemistry of organo-hydrides is critically surveyed and the use of metal-organo-hydride systems in electrochemically-, photochemically- and chemically-driven reductions of unsaturated organic and inorganic (e.g. carbon dioxide) substrates is highlighted. The sustainable electrocatalytic, photochemical or chemical regeneration of organo-hydrides such as NAD(P)H, including for driving enzyme-catalysed reactions, is summarised and opportunities for development are indicated. Finally, new prospects are identified for metal-organo-hydride systems as catalysts for organic transformations involving 'hydride-borrowing' and for sustainable multi-electron reductions of unsaturated organic and inorganic substrates directly driven by electricity or light or by renewable reductants such as formate/formic acid.

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“…Finally, it should be noted that the carbon-carbon interatomic distances within the metal-bound part of this ligand are somewhat unsymmetrical [C(14)-C( 15) 1.415 (7) and C(15)-C(16) 1.390 (7) A]. This, together with the bond distances C( 13)-C( 14) 1.439(6) and C( 13)-O( 3) 1.205 (5) A, implies some degree of n conjugation between the q3-allyl and the lactone carbonyl group. l4 The analogous q5-cyclopentadienyl system was also examined.…”

Section: Resultsmentioning

confidence: 96%