Osmium-Acyl Decarbonylation Promoted by Tp-Mediated Allenylidene Abstraction: A New Role of the Tp Ligand

Abstract

Phenylacetylene and 1,1-diphenyl-2-propyn-1-ol displace the pyridyl and ethylene ligands of OsTp{κ 1 -C[NC 5 H 3 Me]}(η 2 -CH 2 CH 2 )(P i Pr 3 ) (1) to afford the alkynyl-vinylidene derivatives OsTp(CCR)(CCHR)(P i Pr 3 ) (Tp = hydridotris(pyrazolyl)borate; R = Ph, (2), C(OH)Ph 2 (3)). Stirring of toluene solutions of 3 in the presence of neutral aluminum oxide initially produces the dehydration of the vinylidene ligand to give the alkynyl-allenylidene OsTp{CCC(OH)Ph 2 }(CCCPh 2 )(P i Pr 3 ) (4), which subsequently undergoes a Meyer-Schuster rearrangement to yield the acyl-allenylidene OsTp{C(O)CHCPh 2 }(CCCPh 2 )(P i Pr 3 ) (5). In toluene, at 60 °C, the B−H bond of the Tp ligand of 5 abstracts the allene from the osmium coordination sphere by means of a 1,1-hydroboration of the Os−C α double bond. As a result, the acyl decarbonylation takes place to form Os( Ph2CCCH Tp)(CHCPh 2 )(CO)(P i Pr 3 ) (6). In acetonitrile at 60 °C, the allene tautomerizes into the alkyne to afford Os( Ph2HCCC Tp)(CHCPh 2 )(CO)(P i Pr 3 ) ( 7). The abstraction modifies the reactivity of the system toward HBF 4 . Thus, while the protonation of 5 leads to the alkylidyne [OsTp{C(O)CHCPh 2 }( CCHCPh 2 )(P i Pr 3 )]BF 4 (8), the protonation of 6 and 7 gives the alkylidenes [Os( Ph2CCCH Tp)(CHCHPh 2 )(CO)-(P i Pr 3 )]BF 4 ( 9) and [Os( Ph2HCCC Tp)(CHCHPh 2 )(CO)(P i Pr 3 )]BF 4 (10). Both 9 and 10 are unstable in solution. In dichloromethane, at room temperature, they evolve into the corresponding olefin derivatives [Os( Ph2CCCH Tp)(η 2 -CH 2  CPh 2 )(CO)(P i Pr 3 )]BF 4 (11) and [Os( Ph2HCCC Tp)(η 2 -CH 2 CPh 2 )(CO)(P i Pr 3 )]BF 4 (12) by means of a C β ,C α -hydrogen shift on the alkylidene ligand.

Catalytic Cyclization of o‐Alkynyl Phenethylamines via Osmacyclopropene Intermediates: Direct Access to Dopaminergic 3‐Benzazepines

“…[22] In this case,complex 5 is the key intermediate in the osmium-alkylidene to osmium-alkene transformation (II! [22] In this case,complex 5 is the key intermediate in the osmium-alkylidene to osmium-alkene transformation (II!…”

A Boron‐Fluorinated Tris(pyrazolyl)borate Ligand (FTp*) and Its Mono‐ and Dinuclear Copper Complexes [Cu(FTp*)2] and [Cu2(FTp*)2]: Synthesis, Structures, and DFT Calculations

“…Many Tp derivatives have been synthesised ever since, primarily focussing on the introduction of functional groups on the pyrazolyl moieties . Although much less common, modifications of the substituents on boron have been reported in recent years, most notably by the groups of Slugovc, Gunnou and Esteruelas for functionalised Tp's (Scheme ) and Messerle and Hill for related bis(pyrazolyl)borate derivatives.…”

Rhenium‐Promoted C−C Bond‐Cleavage Reactions of Internal Propargyl Alcohols

“…The reactiono f[ Re(dppm) 3 ]I (1)w ith PhCCC(OH)Ph 2 (2)t o give the vinylidenec omplex 3 is unusual when the reported reactions of terminal propargyl alcohols HCCC(OH)R 2 with coordinatively unsaturated d 6 metalc omplexes are considered. [10,11] The reported products include h 2 -HCCC(OH)RR' complexes,h ydroxyvinylidenes L n M=C=CHC(OH)R 2 and allenyli-denesL n M=C=C=CR 2 ,b ut not speciesd erived from the analogous CÀCcleavage reactions reportedh ere.…”