Reactions of an Osmium(IV)-Hydroxo Complex with Amino-Boranes: Formation of Boroxide Derivatives

Abstract

The discovery of a reaction which allows preparation of boroxide complexes of platinum group metals and study of their behavior under CO atmosphere is described. The trihydride-osmium(IV)-hydroxo complex OsH 3 (OH){κ 3-P,O,P-[xant(P i Pr 2) 2 ]} (1, xant(P i Pr 2) 2 = 4,5-bis-(diisopropylphosphino)xanthene) reacts with the amino-boranes i Pr(H)NBCy 2 and i Pr(H)NBBN to give the osmium(IV)boroxide derivatives OsH 3 (OBR 2){κ 3-P,O,P-[xant(P i Pr 2) 2 ]} (BR 2 = BCy 2 (2), BBN (3); BBN = 9-borabicyclo[3.5.1]nonane) and i PrNH 2 as a consequence of the addition of the O−H bond of the hydroxo ligand of 1 to the B−N bond of the amino-boranes. At room temperature under CO atmosphere, complexes 2 and 3 eliminate H 2 to afford the osmium(II)− boroxide compounds OsH(OBR 2)(CO) 2 {κ 2-P,P-[xant(P i Pr 2) 2 ]} (BR 2 = BCy 2 (4), BBN (5)) bearing a κ 2-P,P-coordinated ether-diphosphine. The subsequent reductive elimination of the borinic acids R 2 BOH needs heating and a long duration and leads to the tricarbonyl-osmium(0) derivative Os(CO) 3 {κ 2-P,P-[xant(P i Pr 2) 2 ]} (6) with the phosphorus atoms of the diphosphine lying in the equatorial plane of a pentagonal bypyramid of donor atoms around the metal center. In contrast to 2 and 3, under CO atmosphere, precursor 1 eliminates water to initially give the trans-dihydride OsH 2 (CO){κ 3-P,O,P-[xant(P i Pr 2) 2 ]} (7), which subsequently evolves to the cis-dihydride-cis-dicarbonyl derivative OsH 2 (CO) 2 {κ 2-P,P-[xant-(P i Pr 2) 2 ]} (8) and finally into the tricarbonyl 6.

Influence of the Bite Angle of Dianionic C,N,C-Pincer Ligands on the Chemical and Photophysical Properties of Iridium(III) and Osmium(IV) Hydride Complexes

“…Pincer ligands are flexible or rigid. The former can change their coordination mode from mer to fac , in addition to displaying hemilability . As a consequence, they adapt to the requirements of the different intermediates of the catalytic cycles .…”

Insertion of Diphenylacetylene into Rh–Hydride and Rh–Boryl Bonds: Influence of the Boryl on the Behavior of the β-Borylalkenyl Ligand

“…22 Complex 5 reacts with pinacolborane, in benzene, at 60 °C to quantitatively give trans-4,4,5,5-tetramethyl-2-(2-styrylphenyl)-1,3,2-dioxaborolane (I) and to regenerate the monohydride 1. 23 The reaction takes place via the hydride-boryl-rhodium-(III) intermediate RhH (Bpin){C 6 H 4 -2-(E-CHCHPh)}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (6), which undergoes reductive elimination of the boronic ester. Noticeable spectroscopic features of 6 are a broad resonance at −5.99 ppm in the 1 H NMR spectrum, corresponding to the hydride ligand, and a doublet at 69.5 ppm in the 31 P{ 1 H} NMR spectrum, due to the diphosphine, which displays a typical P−Rh(III) coupling constant of 128.7 Hz.…”

“…2 H NMR (76.77 MHz, C 6 H 6 , 298 K): δ 9.14 (s, =CD). 6). The 1 H NMR spectrum shows a hydride resonance at -5.99 ppm.…”

“…It changes the coordination from mer to fac to minimize the steric hindrance between the P i Pr 2 groups, when the complex is a dimer (a), 5 or releases the oxygen atom to act as κ 2 -P,P-bidentate when replacing hydride by carbonyl (b). 6 The change mer to fac is a consequence of the structural flexibility of the xanthene linker. In contrast to the latter, the more rigid dibenzofuran prevents the change and the formation of the dimer (c).…”

“…The 1 H NMR (400 MHz, C 6 D 6 , 298 K) data were identical to those reported for 5 with the exception of the intensity of the signals at 9.17 (0.15H, CH) and a singlet at 7.53 ppm. 2 (6). The 1 H NMR spectrum shows a hydride resonance at −5.99 ppm.…”