Synthesis, Structure, and Bonding Properties of Ruthenium Complexes Possessing a Boron-Based PBP Pincer Ligand and Their Application for Catalytic Hydrogenation

Abstract

In addition to our previous works for PBP-pincer metal complexes, four PBP-pincer Ru complexes, [PBP]Ru(Cl)(CO) (2), [PBP]Ru(CO)(η2-BH4) (3), [PBP](μ-H)2Ru(OAc-κ2 O) (4), and [PBP](μ-H)2Ru(η2-BH4) (5) were synthesized. All the obtained complexes were characterized by NMR and IR spectroscopy, X-ray crystallography, elemental analysis, and DFT calculation with AIM analysis. Through the structural analysis, two types of interaction between boron atoms and ruthenium atoms in 3–5 were revealed. One is the typical two-center–two-electron bond between the boron atom of the PBP ligand and the Ru atom, associated with bridging hydride ligand(s) on the Ru(IV) center. The other is an ionic interaction between the Ru fragment and the tetrahydroborate anion. On comparison of the structural features, vibrational analysis, NBO analysis, and AIM analysis of the obtained compounds with those of the previously reported complexes having “similar” interactions among B, H, and Ru atoms, the interactions in 4 and 5 were proven to be different from that previously reported. The obtained complexes 3–5 were applied as catalysts for the hydrogenation of aldehyde. Complex 5 showed the highest catalytic activity and widest range of substrate scope. Two mechanisms for the catalytic cycle were proposed with an initial dissociation of BH3 or anionic ligand, according to the control experiments.

Rapid reversible borane to boryl hydride exchange by metal shuttling on the carborane cluster surface

“…The Ru1–B1 bond length is 2.086(2) Å, which is comparable to a two-center-two-electron (2c-2e) Ru–B bond length in previously reported ruthenium diazaborolyl PBP pincer complexes (2.022(4)–2.080(14) Å). 2 , 7 – 9 The short Ru1···B2 (2.417(2) Å) and Ru···H2 (1.96(2) Å) distances are indicative of a strong bridging B–H···Ru interaction. This apparently strong 3c-2e bond attracts the metal center to the B2 vertex, and, as a consequence, results in a significant distortion of the vicinal 2c-2e Ru1–B1 bond.…”

Boron-Based Lewis Acid Transition Metal Complexes as Potential Bifunctional Catalysts

“…Complex 66 adopts a four coordination square planar structure, in which N 2 coordinates with the cobalt center trans to the boron atom. By reacting with RuH(OAc)(PPh 3 ) 2 , Yamashita et al [58] further synthesized complex PBP-(μ-H) 2 Ru(OAc-κ 2 O). Interestingly, this PBP-(μ-H) 2 Ru(OAcκ 2 O) (67, Figure 28) possesses two Ru-H-B bridge bonds.…”

“…[PBP](μ-H) 2 Ru(OAc-κ 2 O) (67) was found to be the catalyst for the hydrogenation of 1-hexanal under 6 MPa H 2 with low catalyst loadings (0.01 mol%). [58] The catalytic transfer dehydrogenation reactions were also been achieved with the sp 2 boron-based LA-TM catalysts ( Figure 32). [63] By using PBP-Ir complex 65, cyclooctane can be catalytic transfer dehydrogenated to tert-butylethylene.…”

The Organometallic Chemistry of Boron-Containing Pincer Ligands based on Diazaboroles and Carboranes

“…72 Reaction of 1a with Ru(H)(Cl)(CO)(PPh 3 ) 3 furnished (PBP)Ru(Cl)(CO) complex 65. Treatment of 65 with NaBH 4 resulted in a substitution of the chloride ligand with tetrahydroborate to afford (PBP)Ru-(CO)(η 2 -BH 4 ) (66).…”