Synthesis, Characterization, and Theoretical Study of Stable Hydride−Azavinylidene Osmium(IV) Complexes

Abstract

The dihydride-dichloro complex OsH 2 Cl 2 (P i Pr 3 ) 2 (1) reacts with cyclohexanone oxime in toluene under reflux to give after 12 h OsHCl 2 {NdC(CH 2 ) 4 CH 2 }(P i Pr 3 ) 2 (2), which can be also obtained by reaction of the oximate compound, OsH 2 Cl{κ-N,κ-O[ONdC(CH 2 ) 4 CH 2 ]}-(P i Pr 3 ) 2 (3) with HCl. Complex OsHCl 2 {NdC(CH 3 ) 2 }(P i Pr 3 ) 2 (4) has been similarly prepared by treatment of compound OsH 2 Cl{κ-N,κ-O[ONdC(CH 3 ) 2 ]}(P i Pr 3 ) 2 (5) with HCl. When the reaction of 1 and cyclohexanone oxime, in toluene under reflux, was quenched after 1 h, a mixture of 1, 2, 3, and the trichloroazavinylidene OsCl 3 {NdC(CH 2 ) 4 CH 2 }(P i Pr 3 ) 2 (6) was obtained. The structures in the solid state of 2 and 6 have been determined by X-ray diffraction studies. In both cases, the geometry around the metal center can be described as a distorted octahedron with the phosphorus atoms of the phosphines occupying trans positions and the CdN group and the carbon atoms bonded to this group lying in a plane that is parallel to the Cl-Os-Cl plane. CCSD(T)//B3LYP calculations on the model complexes OsXCl 2 (NdCH 2 )(PH 3 ) 2 [X ) H (2t), X ) Cl (6t)] state that the above-mentioned conformation is 15.3 (2t) or 12.1 (6t) kcal mol -1 more stable than that with the azavinylidene ligand parallel to the P-Os-P plane. In solution the azavinylidene ligands of 2 and 4 rotate around the Os-N-C axis. The activation parameters of the process are ∆H q ) 14.4 ( 0.8 kcal mol -1 and ∆S q ) -1.1 ( 1.3 cal mol -1 K -1 for 2 and ∆H q ) 13.1 ( 0.8 kcal mol -1 and ∆S q ) 0.0 ( 2.8 cal mol -1 K -1 for 4.

Synthesis of Cyclic Vinylidene Complexes and Azavinylidene Complexes by Formal [4+2] Cyclization Reactions

“…The X‐ray indicates that 4 a contains a metal–azavinylidene moiety (Os=N=C) inside a six‐membered osmacycle. The Os1=N1 bond length (1.806(10) Å) is within the typical range of bond lengths for azavinylidene–osmium complexes (1.777–1.881 Å),–– and the N1=C4 bond length (1.261(15) Å) is in the expected range for C=N double‐bond lengths. The Os1−C1 (2.095(11) Å) and C1=C2 (1.350(16) Å) bond lengths are similar to those found in other osmium–vinyl metallacycles and support the presence of a vinyl moiety.…”

Reduction of Benzonitriles via Osmium–Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers

“…The most noticeable features of this species are the angles in this plane of 116.4 (14)º (N(1)-Os-H(01)), 57.0(18)º (H(01)-Os-H(02)), 76.0(19)º (H(02)-Os-H(03)), and 111.0 (14)º (H(03)-Os-N(1)), which markedly deviate from 90º. These six-coordinate osmium(IV) species undergo distortion to destabilize one of the t2g set orbitals and to stabilize the other two, resulting to be diamagnetic.…”

Generation of Stable Ruthenium(IV) Ketimido Complexes by Oxidative Addition of Oxime Esters to Ruthenium(II): Reactivity Studies Based on Electronic Properties of the Ru−N Bond

“…Fine crystals of 2 a and 3 a , obtained by recrystallization from dichloromethane/hexane or benzene/hexane, were subjected to X‐ray crystallographic analysis, which showed that a pivalate ligand is coordinated to the Ru IV centers in η 2 fashion. The Ru−N bond in complex 2 a is 1.790 Å in length, which is similar to the bond length in the congener Os ketimido complex (Os−N 1.777 Å) . The Ru−N bond is much shorter than those in second‐row late transition metal ketimido complexes (Rh−N 2.039, Pd−N 1.999 Å), which implies stronger interaction between the nitrogen atom and the Ru center.…”

“…Metal ketimido complexes are considered to be key intermediates that can undergo 1,2‐insertion into C−C unsaturated bonds or N−C reductive elimination from high‐valent metal complexes to afford nitrogen‐containing heterocycles involving an N(sp 2 )−C bond . However, mechanistic studies based on isolation of the ketimido complexes that are generated by oxidative addition of oxime derivatives to low‐valent metal species (M=Ti, Re, Os, Pd; Scheme ) are still relatively scarce compared with the well‐documented access to ketimido complexes by stoichiometric reactions such as nucleophilic attack on metal nitrile complexes (M=W,, Re, Ru), migratory insertion of MR into nitriles (M=Th, U, Ti,, Zr, W, Fe, Rh), and deprotonation–metalation starting from ketimines HN=CRR′ (M=Zr, Cr, Mo, Fe) . Therefore, a better understanding of the inherent nature of ketimido complexes prepared from oxime derivatives is significant for further developments in efficient catalytic reactions of oxime derivatives.…”