183675-07-2Relevant academic research and scientific papers
Rhenium dihydrogen complexes with isonitrile coligands: Novel displacement of chloride by hydrogen
Heinekey,Voges, Mark H.,Barnhart, David M.
, p. 10792 - 10802 (2007/10/03)
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, Fh (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 A?. [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 noncoordinating counteranions, due to the lability of the H2 ligand. [Re(RMe3)5HD]+ shows no H-D couplhig 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 ΔG298(+2=) = 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) A?.
