Rhodium Silyl Boryl Hydride Complexes: Comparison of Bonding and the Rates of Elimination of Borane, Silane, and Dihydrogen

Abstract

Transition-metal "s complexes" [1] of dihydrogen [2] and of silanes [3] are common, and transition-metal s-borane complexes are now known. [4][5][6][7][8][9][10][11] Dihydrogen complexes are intermediates in the oxidative addition that occurs during hydrogenation, and they are intermediates of the reductive elimination that occurs during dehydrogenation. Similarly, silane complexes are probably intermediates in the oxidative additions of silanes that occur during hydrosilylation, [12] and borane complexes have been shown to be intermediates in catalytic hydroboration.[5] Borane complexes are also likely intermediates [13] in the borylation of alkanes [14,15] and arenes. [15][16][17][18][19] A complex with hydride, silyl, and boryl groups bound to the metal center of the same complex could adopt a structure with a s-dihydrogen, -silane, or -borane ligand. No complexes of this type have been isolated in pure form, but compounds with this collection of ligands would allow direct assessment of the similarities and differences between the three types of s complexes. Herein, we report the synthesis, experimental and calculated structures, as well as the reaction chemistry of [Cp*RhH 2 (Bpin)(SiR 3 )] (Cp* = C 5 Me 5 , Bpin = (pinacolato)-boryl) complexes, which contain two hydrides, one silyl and one boryl group. Our data suggests that this complex contains partial BÀH bonding and that borane eliminates from this complex faster than dihydrogen or silane.Reaction of the known bis(silyl) dihydride 1 a [20] with a large excess of HBpin in refluxing cyclohexane formed [Cp*RhH 2 (SiEt 3 )(Bpin)] (2 a) in 90 % yield, as determined by NMR spectroscopy with an internal standard [Eq. (1)]. In addition to a single pinacol methyl resonance at d = 1.09 ppm[*] Dr.

Addition of aluminium, zinc and magnesium hydrides to rhodium(iii)

“…10 In line with these findings, thermolysis of [Cp*Rh(H) 2 (SiEt 3 ) 2 ] in the presence of β-diketiminate stabilised aluminium, magnesium or zinc hydrides in C 6 D 6 solution led to the formation of the corresponding heterobimetallic complexes 1–3 along with a single equiv. of triethylsilane (Scheme 1).…”

“…Hartwig and co-workers have shown that H-Bpin reacts with [Cp*Rh(H) 2 (SiEt 3 ) 2 ] under thermal or photochemical conditions to give the corresponding metal boryl complex by B-H activation. 10 In line with these ndings, thermolysis of [Cp*Rh(H) 2 (SiEt 3 ) 2 ] in the presence of b-diketiminate stabilised aluminium, magnesium or zinc hydrides in C 6 D 6 solution led to the formation of the corresponding heterobimetallic complexes 1-3 along with a single equiv. of triethylsilane (Scheme 1).…”

“…It has also been concluded that [Cp*Rh(H) 2 (Bpin)(SiEt 3 )] contains a weak B···H interaction as evidenced by the line-broadening of the hydride resonances due to 1 J B–H coupling. 10 It is worth noting that a series of related complexes, including [Cp*Rh(PMe 3 )(η 2 -HSiR 3 )(SiR 3 )] + (R = Me, Et) and [CpRh(SiMe 3 ) 2 (η 2 -HSiEt 3 )] have been formulated as σ-silane adducts based on the observation of significant 1 J Si–H coupling constants > 20 Hz. 11e,f …”

Rhodium Indenyl NHC and Fluorenyl‐Tethered NHC Half‐Sandwich Complexes: Synthesis, Structures and Applications in the Catalytic C−H Borylation of Arenes and Alkanes

“…In comparison, [Rh(Cp)(Si i Pr 3 )(H)(PR 3 )] (R=Me [51] and Ph [52] ) were synthesised by photolytic ejection of ethylene [51,52] or η 2 ‐C 6 F 6 ligands [53] . [Rh(C 5 R 5 )(SiR 3 ) 2 (H) 2 ] complexes can be formed thermally, [54] whilst trans ‐[Rh(Cp*)(SiEt 3 )(H)(Bpin)(H)] was formed from the reaction of HBpin with [Rh(Cp*)(SiEt 3 ) 2 (H) 2 ] [55] …”

Rhodium‐Catalyzed ortho‐Selective C‐F Activation and Hydrodefluorination of Heterocycle‐Substituted Polyfluoroarenes: Dominated by Phosphine Ligands

“…The 1 HNMR spectrum of mixture solvent showed two broad signals at −19.97 ppm and −20.00 ppm. Noted 11 BNMR that for the Bpin ligand in the intermediate appeared δ= 40.41 ppm and 39.60 ppm , , . Besides, the 31 PNMR spectrum exhibited double peaks at 76.65 ppm and 72.55 ppm.…”