Oxygenation studies part IV. Decomposition of RhCl(Ph3P)3O2 in anaerobic solutions

Dioxygen adducts of rhodium N-heterocyclic carbene complexes

“…Although the precise determination of O-O bond lengths by crystallography has its challenges, 32,[47][48][49]56 it is clear that Rh-O 2 compounds can be grouped into two basic classes: (1) those that display properties typical of metal peroxo species, namely O-O bond lengths of ca. 1.43-1.5 Å, 30,34,[42][43][44][45][46] and octahedral geometry about Rh, and (2) those that are square planar (with O 2 occupying a single site) and have O-O bond lengths less than 1.40 Å. 31,32,35,40,41 Of the Rh-O 2 complexes discussed in this report, 1-6 and 11-14 appear to belong to the latter class and 7-10 belong to the former class of compounds.…”

“…Although peroxide stretches are typically observed in the 800-900 cm −1 region, 34,[43][44][45][46]61 as the O-O bond order increases, the stretching frequencies are expected to move to higher wave-number. 47 For RhCl(IPr) 2 (O 2 ) (4), the IR spectrum in the region where we expect the O-O stretch to appear is complicated by the presence of other transitions, and thus both the 16 O 2 and 18 O 2 -isotopomers were examined by Raman spectroscopy.…”

“…37 Other key differences between the two types of compounds include the observation of O-O bond lengths for the former and related compounds that are unusually short (1.24-1.39 Å) 31,32,35,[38][39][40][41] compared to the typical peroxidic lengths (1.43-1.50 Å) which are observed in the latter and in other Rh III -peroxides. 30,34,[42][43][44][45][46] The use of techniques other than X-ray crystallography to characterize the bonding in such complexes is critically important due to the potential for difficulties in the accurate determination of O-O bond lengths in metal complexes in general, [47][48][49] and in the specific case of square planar complexes which can be susceptible to positional disorder of the ligands, which complicates the assignment of O-O bond lengths. 32,49 In addition to the crystallographic data, X-ray absorption spectroscopy, IR and Raman spectroscopies all demonstrate that complexes 1-6 differ substantially from typical peroxo complexes and are most consistent with a Rh I { 1 O 2 } formulation of their electronic structure.…”

Intramolecular Cyclopropanation of 1,4‐Dienes through Hydroboration–Homologation: Easy Access to Bicyclo[3.1.0]hexanes

“…Hydroboration of the 1,4‐diene 2 a with catecholborane catalyzed by fresh [RhCl(PPh 3 ) 3 ] leads, after oxidative workup, to significant amounts of aldehyde from an intermediate vinylboronate ester or gem ‐bisborylated product. By using the partially oxidized Wilkinson's catalyst described by Evans and co‐workers, hydroboration of 2 a with catecholborane followed by oxidation gave the desired primary alcohol 5 a in 83 % yield (Scheme ). Similar results for the hydroboration of a silylated allylic alcohol were reported by Burgess and co‐workers …”

Intramolecular Cyclopropanation of 1,4‐Dienes through Hydroboration–Homologation: Easy Access to Bicyclo[3.1.0]hexanes

“…Hydroboration of the 1,4-diene 2awith catecholborane catalyzed by fresh [RhCl(PPh 3 ) 3 ]l eads,a fter oxidative workup,t os ignificant amounts of aldehyde from an intermediate vinylboronate ester or gem-bisborylated product. By using the partially oxidized Wilkinsons catalyst described by Evans and coworkers, [29][30][31][32] hydroboration of 2a with catecholborane followed by oxidation gave the desired primary alcohol 5a in 83 %y ield (Scheme 3). Similar results for the hydroboration of asilylated allylic alcohol were reported by Burgess and coworkers.…”