Rhenium Dihydrogen Complexes with Isonitrile Coligands:  Novel Displacement of Chloride by Hydrogen

• Published in: Journal of the American Chemical Society 1996-11, Vol.118 (44), p.10792-10802
• Main Authors: Heinekey, D. M, Voges, Mark H, Barnhart, David M
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja961994p

The syntheses, properties, and characterization of several new complexes, Re(CNtBu)3(PCy3)2H (1a), Re(CNtBu)3(PR3)2Cl [R = Cy, Ph (2a, 2b)], the 17-electron [Re(CNtBu)3(PCy3)2Cl]+ (3a), the dihydrogen complex, [Re(CNtBu)3(PR3)2(H2)]+ [R = Cy, Ph (4a, 4b)], the coordinatively unsaturated [Re(CNtBu)3(PCy3)2]+ (5a), and [Re(CNtBu)4(PCy3)2]+ (6a) are reported. In addition, spectroscopic evidence for the dinitrogen complex [Re(CNtBu)3(PCy3)2(N2)]+ and the dihydrogen complex [Re(CNtBu)5(H2)]+ is presented. Thermodynamic parameters have been obtained for the equilibrium system, Re(CNtBu)3(PCy3)2Cl (2a) + H2 ⇌ [Re(CNtBu)3(PCy3)2(H2)]Cl (4a). 1H and 31P{1H} NMR studies (CD2Cl2) over the temperature range 286−316 K afford values of ΔH° = −18.0 ± 0.7 kcal/mol, ΔS° = −44 ± 2 eu, and ΔG°298 = −4.8 ± 1.3 kcal/mol for this equilibrium. The complexes 4a and 4b are characterized as dihydrogen complexes. Their J HD (R = Cy, 30.3 Hz; R = Ph, 30.9 Hz) and T 1(min) values of 8 ms (300 MHz) are consistent with H−H distances of ca. 0.80 Å. [Re(CNtBu)5(HD)]+ is also characterized as a dihydrogen complex based on a J HD of 33.4 Hz. This complex could not be isolated at room temperature, even with non-coordinating counteranions, due to the lability of the H2 ligand. [Re(PMe3)5HD]+ shows no H−D coupling and is characterized as a dihydride complex. The unsaturated complex [Re(CNtBu)3(PCy3)2]+ (5a) is found to undergo a dynamic isonitrile rearrangement on the NMR time scale. 1H NMR spin saturation transfer studies over a temperature range of 254−297 K afford the activation parameters ΔH ⧧ = 11.4 ± 0.8 kcal/mol, ΔS ⧧ = −17.6 ± 1.6 eu, and ΔG ⧧ 298 = 16.6 ± 1.2 kcal/mol. The molecular structures of 2a and 3a have been determined by X-ray crystallography. 2a shows an unusually long Re−Cl bond distance of 2.596(2) Å.