Hydride-Alkenylcarbyne to Alkenylcarbene Transformation in Bisphosphine-Osmium Complexes

Abstract

The elongated dihydrogen complex [Os{C6H4C(O)CH3}(η 2 -H2)(H2O)(P i Pr3)2]BF4 (1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-π-alkynol derivatives [OsH{dCdCHC(OH)R2}{η 2 -HCtCC(OH)R2}(P i Pr3)2]BF4 (R ) Ph (2), Me (3)), where the π-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF4 and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH(tCCHdCR2)S2( 6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(dCHCHdCR2)(CH3CN)3(P i Pr3)2][BF4]2 (R ) Ph (7), Me (8)) by means of a concerted 1,2hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2(tCCHdCPh2)(P i Pr3)2 (10), which reacts with AgBF4 and acetonitrile to give [OsHCl-(tCCHdCPh2)(CH3CN)(P i Pr3)2]BF4 (11). In this solvent complex 11 is converted to [OsCl(dCHCHd CPh2)(CH3CN)2(P i Pr3)2]BF4 (12). Complex 5 reacts with CO to give [Os(dCHCHdCPh2)(CO)(CH3CN)2-(P i Pr3)2][BF4]2 (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as η 2 -carbene species (OsdC(R)H), increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported.

Osmabenzenes from Osmacycles Containing an η2‐Coordinated Olefin

“…Herein we present the transformations of osmacycle 9 under various conditions. As expected, introduction of benzonitrile into the reaction systems led to the cyclic osmium h (12) and osmabenzene (14) in high yields under different conditions. Moreover, osmacyclic h 2 -allene complex 12 can isomerise to osmabenzene 14.…”

“…[11] Hydride migration as a result of a decrease in electron density on the metallic centre by nitrile substitution has been reported. [12] Thus, in our case, it can be expected that the replacement of two chloride ligands in the neutral osmacycle 9 by nitrile ligands should greatly decrease the electron density on the metallic centre. As a consequence, hydrogen transfer on the metallacycle might be favourable and thus allow isomerisation of the osmacycle to the related osmabenzene.…”

“…In contrast, heating a chloroform solution of 9 to the reflux temperature in the presence of excess benzonitrile generated osmabenzene [OsA C H T U N G T R E N N U N G {CHC- (14). Complexes 11,12 and 14 are in fact isomers. In the absence of excess benzonitrile, the isolated dicationic 12 and 14 readily dissociate the benzonitrile ligands in solution to produce the neutral complex (13) and the monocationic os-…”

“…Whereas complex 2 is very stable, the PMe 3 -substituted analogue 3 slowly isomerises to osmaphenol 4 (Scheme 1). (12). In contrast, heating a chloroform solution of 9 to the reflux temperature in the presence of excess benzonitrile generated osmabenzene [OsA C H T U N G T R E N N U N G {CHC- (14).…”

Osmapyridine and Osmapyridinium from a Formal [4+2] Cycloaddition Reaction

“…Furthermore, the transformation of an osmium hydrido carbyne complex to an osmium carbene has already been reported. [17] In addition, when 1 was treated with HBF 4 and the reaction mixture in acetonitrile was heated at reflux, formation of 3 was observed together with other unidentified compounds by 1 H NMR spectroscopy. However, the yield was relatively low.…”