Homogeneous catalysis with polyhydride complexes

Abstract

This review analyzes the role of transition metal polyhydrides as homogeneous catalysts for organic reactions. Discussed reactions involve nearly every main organic functional group.

Reactions of an Osmium–Hexahydride Complex with 2-Butyne and 3-Hexyne and Their Performance in the Migratory Hydroboration of Aliphatic Internal Alkynes

“…As a consequence, the isomerization starts before the complete formation of 4. Furthermore, the isomerization affords two products, the ethylbutenediyl derivative OsH 2 (η 4 -CH 2 CHCHCHEt)(P i Pr 3 ) 2 (5) and the dimethylbutenediyl species OsH 2 (η 4 -MeCHCHCHCHMe)(P i Pr 3 ) 2 (6), the first of them being the main one in a 9:1 molar ratio (Scheme 6). The formation of both butenediyls takes place by metalmediated ethyl-to-C Os 1,3-hydrogen shifts.…”

“…The mixture was heated at 50 °C for 18 h. After this time, the 1 H and 31 P{ 1 H} NMR spectra of the reaction crude shows a mixture of complexes 4 and 5 in an 88:22 ratio along with 1-hexene and 3-hexene. The mixture was concentrated to dryness giving an orange oil, which was washed with cold methanol ( (5) and OsH 2 (η 4 -MeHCCHCHCHMe)(P i Pr 3 ) 2 (6). A mixture of complexes 4 and 5 in 88:22 molar ratio (30 mg, 0.05 mmol) was heated in toluene (0.5 mL) at 80 °C for 24 h. The mixture was concentrated to dryness obtaining a light-yellow oil.…”

“…The presence of metal–hydrogen bonds of different nature offers interesting chemical opportunities, as is evident in their ability to activate one of the widest ranges of σ-bonds . This property allows them to be relevant in a variety of fields including materials science, energy and environment, or organic synthesis based on metal-mediated catalysis . Thus, for example, this type of compounds are catalysts or catalyst precursors for some 40 different classes of organic reactions; the vast majority of them involve some σ-bond activation elemental step, in accordance with their tendency to activate σ-bonds.…”

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The current report about the accessibility of novel rhenium hydrido complexes and especially the tailoring of substitution patterns with the metal in the oxidation state " + 3" as well as the description of their reactivity gives some more insight into the structural chemistry of rhenium hydrides and is, thus, directly linked to the recently discussed relevance of rhenium hydrides for catalytic conversions. [4,[69][70][71] Experimental Section [ReCl 4 (PPh 3 ) 2 ] was prepared following a literature procedure. [72] All other chemicals were reagent grade and used as received.…”

Rupe-Type Rearrangement Intercepted by Diels–Alder Cycloaddition on Osmium

“…During the catalysis, the polyhydride is converted to the bis(γ-hydroxyalkynyl)-osmium(II)-(hydroxyvinylidene) Os{C�C−C(OH)Ph 2 } 2 {�C�CH−C(OH)Ph 2 }{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]}, which seems to be the true catalyst of the organic transformation, in agreement with what was observed for other osmium polyhydride precursors. 19 In methanol, the hydroxyvinylidene ligand of the catalyst is dehydrated to allenylidene, generating Os{C�C−C(OH)Ph 2 } 2 (�C�C� CPh 2 ){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} with allenylidene and γhydroxyalkynyl ligands (Scheme 4). 20 Because these γhydroxyalkynyl ligands could be in principle capable of isomerizing into acyl groups, this compound gives the opportunity that the aforementioned Tp complex denies.…”