Study of the effects on coordination of thioether sites. 1. Complexation study of bromopentacarbonylmanganese(I) with tripodal P3-nSn (n = 0-3) ligands
Resource
Organometallics 12 (6): 2277-2283
Journal
Organometallics
Journal Volume
12
Journal Issue
6
Pages
2277-2283
Date Issued
1993
Author(s)
Abstract
Manganese(I) complexes fac-(η2-P3−nSn)Mn(CO)3Br (n = 0–3) [P3 W = Z = PPh2; P2S W = PPh2, Z = SPh; PS2 Z = SPh, W = PPh2; S3 W = Z = SPh in CH3C(CH2W)2(CH2Z)] formed from the corresponding tripodal ligand have been prepared and isolated as pairs of isomers. The reaction of P2S with BrMn(CO)5 in chloroform produced a pair of stereoisomers, syn-fac(P,P′-P2S)Mn(CO)3Br (1a) and anti-fac-(P,P′-P2S)Mn(CO)3Br (1b), which were separated and fully characterized. Equilibration (K1 = 2/3) between 1a and 1b was established. For PS2, the equilibrium constant (K2) between syn-fac-(P,S-PS2)Mn(CO)3Br (2a) and anti-fac-(P,S-PS2)Mn(CO)3Br (2b) was unity. Kinetic studies of isomerization of 1a to 1b and 2a to 2b were carried out by using an NMR spectrometer. The activation parameters were obtained: ΔH‡1a = 30.5 ± 0.4 kcal/mol, ΔS‡1a = 11 ± 1 eu for complex 1a; ΔHǂ2a = 24.9 ± 0.7 kcal/mol, ΔSǂ2a = 7 ± 2 eu for complex 2a. A mechanistic pathway for these isomerizations is proposed. Crystal structures were determined for three complexes: 1a, 1b, and 2a. X-ray data were collected on a CAD-4 diffractometer at room temperature and were refined by a least-squares treatment. For 1a: a = 10.669(2) Å,b = 17.864(3) Å,c = 18.841(12) Å, β = 105.30(2)°, monocliniC., Z = 4, P21/c, R(Fo) = 0.051, Rw(Fo) = 0.042 for 3043 reflections with Io > 2σ(Io). For 2b: a = 10.855(3) Å, b = 20.322(7) Å, c = 17.887(9) Å, β = 104.73(3)°, monoclinic, Z = 4, P21/n, R(Fo) = 0.059, Rw(Fo) = 0.047 for 3316 reflections with Io > 2σ(Io). For 2a: a = 8.670(5) Å, b = 9.539(3) Å, c = 18.921(9) Å, a = 93.09(3)°, β = 90.27(5)°, γ = 101.21(4)°, triclinic, Z = 2, P1̅,R(Fo) = 0.052, Rw(Fo) = 0.054 for 2513 reflections with Io > 2σ(Io). The conformations of the chelate rings are discussed. © 1993, American Chemical Society. All rights reserved.
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journal article
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