Synthesis and X-ray Structural Characterization of Binuclear Iridium (I) and Rhodium(I) Hydroxypyridinate Complexes. 1. Complete Assignment of the 1H NMR Spectra by Two-Dimensional and NOE Techniques. The Nature of “Inside” and “Outside” 1H Chemical Shift Differences

Gary S. Rodman, Kent R. Mann

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

Six new d8-d8 complexes, [Ir(COD)(µ-hp)]2, [Ir(COD)(µ-mhp)]2, [Ir(COD)(µ-chp)]2, [Ir(COD)(µ-2hq)]2, [Rh(COD)(µ-hp)]2, and [Rh(COD)(µ-mhp)]2 (hp = 2-hydroxypyridinate, mhp = 6-methyl-2-hydroxypyridinate, chp = 6-chloro-2-hydroxypyridinate, 2hq = 2-hydroxyquinolate, COD = 1,5-cyclooctadiene), were synthesized and characterized by 1H NMR, 13C NMR, and IR spectroscopy and FAB mass spectrometry. Other than our preliminary communication, these are the first rhodium(I) and iridium(I) hydroxypyridinate complexes reported to date. X-ray crystallographic analyses of the isostructural [M(COD)(µ-mhp)]2 (M = Ir and Rh) complexes confirmed the binuclear nature of the complexes. Both [M(COD)(µ-mhp)]2 complexes crystallize in the P21 space group with Z = 4. For M = Rh, V = 2544 (4) Å3, a = 14.963 (8) Å, b = 12.038 (2) Å, c = 14.673 (10) Å, and β = 105.75 (4)°. Full-matrix least-squares refinement (307 variables, 4006 reflections) converged to give R and Rw values of 0.028 and 0.036, respectively. For M = Ir, V = 2521 (4) Å3, a = 14.847 (5) Å, b = 11.991 (2) Å, c = 14.661 (11) Å, and β= 104.99 (4)°. Full-matrix least-squares refinement (307 variables, 3335 reflections) converged to give R and Rw values of 0.030 and 0.031, respectively. The complexes have a “nonpolar” structure with “head-to-tail” bridging ligands that persists in solution and the gas phase. The M-M separations (Rh-Rh, 3.367 (1) Å; Ir-Ir, 3.242 (2) Å) indicate significant metal-metal interactions are present in both complexes. A twist angle (27° and 25° for M = Ir and Rh, respectively) in the flexible eight-membered (MNCO)2 framework, not present in the six-membered ring of the analogous [M(COD)(µ-pz)]2 (pz = pyrazolate) complexes, relieves steric strain between the two bulky COD ligands. The “open book” geometry and asymmetry of the bridging ligands attributes the molecules low-point symmetry, leading to complex NMR spectra. The complete assignment of the 1H NMR spectrum of [Ir(COD)(µ-hp)]2 (and by analogy, the spectra of the other five complexes) was carried out with selective decoupling, NOE, and two-dimensional NMR techniques. The NOE observed between hp proton H5 and COD proton HI5 allowed the precise assignment of all 12 COD resonances. Olefinic proton H12 (trans to N and “outside”) resonates downfield of olefinic proton HI 1 (trans to N and “inside”). Olefinic proton H15 (trans to O and “outside”) resonates upfield of olefinic proton H16 (trans to O and inside). The endo methylene protons resonate upfield of the exo methylene protons. The “inside”/“outside” chemical shift differences observed for these compounds are ascribed to steric and magnetic anisotropy effects.

Original languageEnglish (US)
Pages (from-to)3338-3346
Number of pages9
JournalInorganic Chemistry
Volume27
Issue number19
DOIs
StatePublished - Sep 1 1988

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