Bidentate P(III)−N(III) — Rh(I) Complexes : Synthesis from Bicyclophosphoranes and Applications in Homogeneous Catalysis

Diastereoselectivity of Borane Addition to Chiral Triquinphosphoranes. NMR, X-ray, and Molecular Modeling Studies

“…The axial P−N bond is remarkably longer (1.932(2) Å) , than all those yet reported for phosphoranes (1.70−1.83 Å) 19 or for the cyclenphosphorane bis(borane) adduct 1 (average bond length 1.865 Å) 2a. Nevertheless, this value comes closer to the axial P→N dative bond (1.986 Å) reported by Verkade et al .…”

“…This result is in accordance with those obtained by Riess et al . concerning the lack of reactivity of the equatorial nitrogen atom of the TBP toward Lewis acids 2a. The strong basic character exhibited by the axial nitrogen atom should be due to its sp 3 type hybridization, whereas the equatorial nitrogen adopts an sp 2 type hybridization that considerably decreases its basic character .…”

“…The minute structural distortion from TBP is reflected in the values of the axial and equatorial N−P−O angles of 176.7(1) and 122.6(1)°, respectively. By the use of the dihedral angle method and the unit bond lengths, it was estimated that the structure is displaced by only 5.9% along the Berry coordinate 15 from the ideal TBP (0%) toward the ideal SP (100%), P−H being the pivotal ligand in the pseudorotation process. , This distortion should be compared with that of the cyclenphosphorane bis(borane) adduct 1 that was shifted by 10.4% along the Berry coordinate from the ideal TBP 2c 1 X-ray structure of the major diastereomer of triquinphosphorane−borane adduct 28 ( 28M ). 2 X-ray Data for Triquinphosphorane−Borane Complex 28M C 12 H 28 N 2 O 2 BP d (calcd) = 1.19 g cm -3 fw = 274.15 recording temp: 18 °C space group: P2 1 Mo Kα radiation: λ = 0.710 69 a = 9.513(2) Å θ range: 5 ≤ 2θ ≤ 35° b = 6.134(1) Å data collected: 2778 c = 13.313(3) Å no.…”

“…Hydridophosphoranes have been the subject of numerous studies in coordination chemistry. − Depending on the structure of the phosphorane, the action of Lewis acids leads either to a complex preserving the pentacoordinated phosphorus pattern or to a structure resulting from the opening of the hydridophosphorane and exhibiting a tricoordinated phosphorus atom. For example, Riess and co-workers have shown that the cyclenphosphorane 1 reacts with diborane to give the bis(borane) adduct 2 with a nearly ideal TBP structure in which the two axial nitrogen atoms are coordinated to a BH 3 unit 2a.…”

“…Hydridophosphoranes have been the subject of numerous studies in coordination chemistry. − Depending on the structure of the phosphorane, the action of Lewis acids leads either to a complex preserving the pentacoordinated phosphorus pattern or to a structure resulting from the opening of the hydridophosphorane and exhibiting a tricoordinated phosphorus atom. For example, Riess and co-workers have shown that the cyclenphosphorane 1 reacts with diborane to give the bis(borane) adduct 2 with a nearly ideal TBP structure in which the two axial nitrogen atoms are coordinated to a BH 3 unit 2a. Conversely, the bicyclophosphorane 3 with a single equatorial nitrogen atom, which can in principle exist in different tautomeric P III and P V forms, reacts with diborane at both the phosphorus and the nitrogen atoms to afford the monocyclic bis(borane) adduct 4 . 3a,b The difference in behavior of 1 and 3 can be assigned both to a strong macrocyclic effect in 1 which favors the closed form and to the presence in 1 of two axial nitrogen atoms that are much more basic than the equatorial one in 3 .…”