Ruthenium tris(σ-B–H) borate complexes: synthesis, structure, and reactivity

Abstract

The coordination of the B-H bond to a transition metal is fundamentally intriguing due to its connection with the transition metal-mediated B-H bond activation mechanism and catalysis. Most of the...

Access to Bis(σ‐B−H) Complexes of Ruthenium Bearing Monoaryl Borate and Borane Ligands

“…Its 31 P{ 1 H} NMR spectrum at 51.2 ppm is shifted slightly downfield in comparison to the starting material Cp*Ru(PCy 3 )Cl (40.4 ppm in C 6 D 6 ) [18] . The spectroscopic parameters of 1 are similar to those of related ruthenium bis(σ‐B−H) borate complexes [Cp*Ru(PR 3 )(H 3 BMes), R= i Pr, Cy] [15a,16a] with a bulky mesityl group on the boron atom.…”

“…The broad resonance in the hydride region at −10.08 ppm is attributed to the chemical equivalent bridging Ru‐H 2 ‐B hydrides. The signals of HB(C 6 F 5 ) 3 and RuH 2 BMes are observed at −25.4 (d, 1 J ( 11 B, 1 H) ∼90 Hz) and 82.2 (broad singlet) ppm in the 11 B NMR spectrum, respectively, which are distinctly different from those of the starting material 4 ( 11 B: 41.2 ppm) [16a] and B(C 6 F 5 ) 3 ( 11 B: 60.0 ppm). Compound 5 shows a 31 P{ 1 H} signal at 57.9 ppm and three sharp 19 F NMR resonances [ 19 F: −133.9 (6F, o ‐C 6 F 5 ), −164.8 (3F, p ‐C 6 F 5 ), −167.7 (6F, m ‐C 6 F 5 )] of the anionic borate moiety [HB(C 6 F 5 ) 3 ] − with a typical small Δδ 19 Fm,p of 2.9 ppm chemical shift separation.…”

“…The selected spectroscopic data of bis(σ‐B−H) borates 3 and 4 are listed in Table 1. It is worth noting that an alternative synthesis of the complex 4 was previously reported by our group via the ligand substitution reaction of the tris(σ‐B‐H) borate Cp*Ru(H 3 BMes) with PCy 3 in 87 % yield [16a] . However, our previously reported method could not be applicable to synthesis of bis(σ‐B−H) borates with less sterically hindered aryl group in the ArBH 3 ligand.…”

“…The cation features a Cp*Ru(PCy 3 ) + fragment coordinated by a neutral H 2 BMes borane ligand through two geminal σ‐B−H bonds. The nearly linear Ru⋅⋅⋅B−C linkage (176.50(18)°) and remarkably short Ru⋅⋅⋅B distance (1.920(2) Å) are different with the starting material 4 , [16a] but comparable with the values of 172.24(17)° and 1.921(2) Å in similarly cationic bis(σ‐B−H) borane [Cp*Ru(P i Pr 3 )(H 2 BMes)] + [(C 6 F 5 ) 4 ] −[15] and 177.1(3)° and 1.938(4) Å in related neutral bis(σ‐B−H) borane RuH 2 (H 2 BMes)(PCy 3 ) 2 [8] . The Ru−H bond lengths of 1.57(2) and 1.60(2) Å are significantly shorter than those of 1.69(2) and 1.68(2) Å for 4 , [16a] which indicates a much stronger interaction between the ruthenium center and the two hydrogen atoms in 5 .…”