Cycloreversion of Rhenium(V) Diolates Containing the Hydridotris(3,5-dimethylpyrazolyl)borate Ancillary Ligand

Abstract

Hydridotris(3,5-dimethylpyrazolyl)boratorhenium(V) diolates cyclorevert to Tp‘ReO3 and alkene at elevated temperatures in nonpolar solvents. Comparison of activation parameters to those of the analogous pentamethylcyclopentadienyl complexes show the former have similar ΔS ⧧'s, but higher ΔH ⧧'s by 2−4 kcal/mol. Computation of the frontier orbitals for this ligand system show that the appropriate acceptor orbital on the metal is pushed to higher energy compared to the case where the ligand is pentamethylcyclopentadienyl, consistent with predictions for the proposed stepwise mechanism of this reaction.

Rhenium‐Catalyzed Deoxydehydration of Diols and Polyols

“…[49] The recently proposed alkene extrusion from a rhenium(III) diolate [19] will be discussed in Section 3.2. [49] The recently proposed alkene extrusion from a rhenium(III) diolate [19] will be discussed in Section 3.2.…”

A Cptt‐Based Trioxo‐Rhenium Catalyst for the Deoxydehydration of Diols and Polyols

“…Interestingly, a slight change of the ligand (removing one tert-butyl group) resulted in a different DODH reactivity of the trioxo-rhenium complex. [17] We observed an induction period in the Cp ttt ReO 3 -catalyzed DODH of 1,2octanediol, while there was almost no induction period in the reaction catalyzed by the Cp tt ReO 3 complex (Cp tt = 1,3-di-tertbutylcyclopentadienyl, Scheme 1,right). This result encouraged us to further investigate the catalytic properties of the less bulky Cp tt ReO 3 complex.…”

“…In this very early work, a Cp*ReO 3 complex (Scheme , left) was used to catalytically convert polyols into olefins. Later, Gable and co‐workers studied olefin extrusion reactions from Tp*Re(glycolate) complexes (Tp*=hydrido‐ tris ‐(3,5‐dimethylpyrazolyl)borate), and in doing so used the 6e − Tp* ligand as an alternative for the 6e − Cp* ligand . Recently, we reported on a bulky Cp‐based trioxo‐rhenium catalyst, Cp ttt ReO 3 (Cp ttt =1,2,4‐tri‐ tert ‐butylcyclopentadienyl, Scheme , middle) .…”

“…Later, Gable and co-workers studied olefin extrusion reactions from Tp*Re(glycolate) complexes (Tp* = hydrido-tris-(3,5-dimethylpyrazolyl)borate), and in doing so used the 6e À Tp* ligand as an alternative for the 6e À Cp* ligand. [15] Recently, we reported on a bulky Cp-based trioxorhenium catalyst, Cp ttt ReO 3 (Cp ttt = 1,2,4-tri-tert-butylcyclopentadienyl, Scheme 1, middle). [16] This trioxo-rhenium complex is able to effectively catalyze the DODH of a series of different diols and polyols.…”

Ruthenium (II) sulfoxides-catalyzed hydrogenolysis of glycols and epoxides

“…The potential of catalyzing DODH reactions by oxo-metal complexes (Cp*ReO 3 ) was demonstrated by Andrews and Cook [12] in the presence of PPh 3 as reductant. Gable and coworkers, with the help of experimental and computational studies, provided mechanistic insight of the reaction involving LReO 3 complexes as catalysts, especially the olefin-producing metallo-glycolate fragmentation step [25][26][27][28][29][30]. Abu-Omar et al recently [13] achieved deoxygenation of epoxides and deoxydehydration of glycols to alkenes and alkanes using MeReO 3 as catalyst with the more practical reductant H 2 .…”