Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex

Abstract

An unusual 1,3-hydrogen shift from the metal center to the C β atom of the C 3 -chain of the allenylidene ligand in a hydride-osmium(II)-allenylidene complex is the beginning of several interesting transformations in the cumulene. The hydride-osmium(II)-allenylidene complex was prepared in two steps, starting from the tetrahydride dimer [(Os(H···H){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ]}) 2 (μ-Cl) 2 ][BF 4 ] 2 ( 1 ). Complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give the hydride-osmium(II)-alkenylcarbyne [OsHCl(≡CCH=CPh 2 ){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ]}]BF 4 ( 2 ), which yields OsHCl(=C=C=CPh 2 ){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ]} ( 3 ) by selective abstraction of the C β –H hydrogen atom of the alkenylcarbyne ligand with K t BuO. Complex 3 is metastable. According to results of DFT calculations, the migration of the hydride ligand to the C β atom of the cumulene has an activation energy too high to occur in a concerted manner. However, the migration can be catalyzed by water, alcohols, and aldehydes. The resulting alkenylcarbyne-osmium(0) intermediate is unstable and evolves into a 7:3 mixture of the hydride-osmium(II)-indenylidene OsHCl(=C IndPh ){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ]} ( 4 ) and the osmanaphthalene OsCl(C 9 H 6 Ph){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ]} ( 5 ). Protonation of 4 with HBF 4 leads to the elongated dihydrogen complex [OsCl(η 2 -H 2 )(=C IndPh ){κ 3 - P , O , P -[xant(P i Pr 2 ) 2 ...

Dissimilarity in the Chemical Behavior of Osmaoxazolium Salts and Osmaoxazoles: Two Different Aromatic Metalladiheterocycles

“…Since the prediction of the metallabenzenes by Thorn and Hoffmann in 1979 and the preparation of the first osmabenzene by Roper and co-workers in 1982, the chemistry of these types of compounds has experienced a tremendous development, mainly from a conceptual point of view . Most of the effort has been centered on the metal counterparts of hydrocarbons: i.e., metallabenzenes, metallabenzynes, metallanaphthalenes, metallaanthracenes, metalloles, and some condensed species bearing the metal bonded to four carbons such as carbolongs and spiro metalloles . In contrast, organometallic metallaheteroaromatic compounds have received little attention .…”

Organometallic Chemistry of Transition Metal Alkylidyne Complexes Centered at Metathesis Reactions

“…The formally d 4 cationic alkyne-alkylidyne 119 (Scheme ) has been isolated from the reaction of the allenylidene complex OsHCl­(=C=C=CPh 2 )­{xant­(P i Pr 2 ) 2 } with PhCCH . Interestingly, the square-planar formally d 4 osmium alkylidyne 120 (Scheme ) reacted with terminal alkynes RCCH (R = Ph, CO 2 Me) to give the five-coordinate alkylidenes 123 , presumably via intermediates 121 which evolve to the hydrido-alkylidynes 122 followed by reductive elimination …”

“…179,180 The formally d 4 cationic alkyne-alkylidyne 119 (Scheme 25) has been isolated from the reaction of the allenylidene complex OsHCl(=C=C=CPh 2 ){xant(PiPr 2 ) 2 } with PhC�CH. 181 Interestingly, the square-planar formally d 4 osmium alkylidyne 120 (Scheme 26) reacted with terminal alkynes RC�CH (R = Ph, CO 2 Me) to give the five-coordinate alkylidenes 123, presumably via intermediates 121 which evolve to the hydridoalkylidynes 122 followed by reductive elimination. 31 [2 + 2]-Cycloaddition of low-valent alkylidyne complexes with alkynes to give MCBDs has been suggested as one of the key steps in several coupling reactions of alkynes with COcontaining alkylidyne complexes reported in 1980s and early 1990s.…”

Light‐ and Heat‐Controlled Formation of Osmanaphthalenes and Osmanaphthalynes

“…[ 13 ] Since then, metal heterocyclic compounds have developed rapidly. Metal heterocyclic compounds reported to date include metallabenzenes, [ 14‐15 ] metallafurans, [ 16 ] metallapyridines, [ 17‐18 ] metallabenzynes, [ 19 ] metallaindenes, [ 20‐21 ] metallanaphthalenes, [ 22‐24 ] metallanaphthalynes, [ 25‐28 ] metallaanthracene, [ 29 ] metallaphenanthrene, [ 30 ] metallaphenanthryne, metallaanthracyne, [ 31,32 ] metallapentalynes, and metallapentalenes. [ 33‐46 ] Among this range of metallaaromatics, fused ring tricyclic or polycyclic metallanaphthalenes are still relatively scarce, [ 47‐49 ] which is mainly due to the paucity of available synthetic methods.…”