Nuclear magnetic resonance studies of molecular dynamics at below-ambient temperatures and crystal structures
- 1 January 1996
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 2,p. 203-209
- https://doi.org/10.1039/dt9960000203
Abstract
The octahedral complexes fac-[ReX(CO)3L][L = 6-(pyrazol-1-yl)-2,2′-bipyridine (pbipy), 6-(3,5-dimethylpyrazol-1-yl)-2,2′-bipyridine (dmpbipy) or 6-(4-methylpyrazol-1-yl)-2,2′-bipyridine (mpbipy); X = Cl, Br or I] have been studied by low-temperature NMR spectroscopy and in the first two cases by X-ray crystallography. The pendant pyrazol-1-yl ring is shown to be oriented considerably out of the plane of the adjacent co-ordinated pyridyl ring of the ligand. The crystal structure of [ReBr(CO)3(pbipy)] reveals this angle of orientation to be 36.3 and 48.1° in two crystallographically independent molecules. In solution, restricted rotation of the pendant ring occurs leading to distinct pairs of rotamers at low temperatures. Rotation barriers (ΔG‡) for the pbipy and mpbipy complexes are in the range 39–51 kJ mol–1 and the two rotamers have near-equal solution abundances. Methyl substitution at the 3 and 5 positions of the pyrazol-1-yl ring as in the dmpbipy complexes has a major effect on the orientation of the unco-ordinated pendant ring in the solid state as evidenced by the crystal structure of [ReBr(CO)3(dmpbipy)]. This in turn affects the relative rotamer populations in solution, with one rotamer being very dominant, and the barrier to pendant-ring rotation increases somewhat.Keywords
This publication has 12 references indexed in Scilit:
- Fluxional rhenium(I) tricarbonyl halide complexes of pyrazolylpyridine ligands. A detailed nuclear magnetic resonance investigationJ. Chem. Soc., Dalton Trans., 1994
- Rhenium(I) tricarbonyl halide complexes of pyrazolyl-bipyridine ligands. Part 1. Nuclear magnetic resonance studies of solution fluxionalityJ. Chem. Soc., Dalton Trans., 1994
- 2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 4. cis-[M(C6F5)2(terpy)](M = Pd or Pt): nuclear magnetic resonance studies of their solution dynamics and crystal structure of cis-[Pd(C6F5)2(terpy)]J. Chem. Soc., Dalton Trans., 1994
- 2,2′ : 6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 3. Ruthenium carbonyl halide complexes, [RuX2(CO)2(terpy)](X = Cl, Br or I) and metal tetracarbonyl complexes [M(CO)4(terpy)](M = Cr, Mo or W): nuclear magnetic resonance studies of their solution dynamics and synthesis of trans-[RuX2(CO)(terpy)](X = Cl, Br or I)J. Chem. Soc., Dalton Trans., 1994
- 2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 2. Rhenium carbonyl halide complexes, fac-[ReX(CO)3(terpy)](X = Cl, Br or I): NMR studies of their solution dynamics, synthesis of cis-[ReBr(CO)2(terpy)] and the crystal structure of [ReBr(CO)3(terpy)]J. Chem. Soc., Dalton Trans., 1993
- 2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 1. Trimethylplatinum(IV) halide complexes [PtXMe3(terpy)](X = Cl, Br or I): nuclear magnetic resonance studies of their solution dynamics and crystal structure of [PtIMe3(terpy)]J. Chem. Soc., Dalton Trans., 1993
- Some reactions of tetrakis(tert-butylimido)osmium(VIII). X-Ray crystal structures of Os(NBut)O(O2CBut)2(NH2But)2·ButCO2H, (ButN)2Os(µ-NBut)2Os(µ-NBut)X2(X = Cl or I) and [Os2(NBut)4(µ-NBut)2]I3J. Chem. Soc., Dalton Trans., 1991
- Phase annealing in SHELX-90: direct methods for larger structuresActa Crystallographica Section A Foundations of Crystallography, 1990
- Ruthenium carbonyl complexes. III. Peparations, properties and structures of Dicarbonyl- and Monocarbonyl-(2,2':6',2''-terpyridyl)ruthenium(II) complexesAustralian Journal of Chemistry, 1984
- An empirical method for correcting diffractometer data for absorption effectsActa Crystallographica Section A Foundations of Crystallography, 1983