-
[show abstract]
[hide abstract]
ABSTRACT: A parahydrogen based NMR study of the platinum(ii) bis-phosphine triflate catalysed hydrogenation of alkynes in methanol reveals that platinum bis-phosphine alkyl cations and methanol functionalised platinum bis-phosphine alkylether cations, are responsible for the observed alkene and vinylether products.
Dalton Transactions 04/2010; 39(14):3495-500. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The sensitivity of both nuclear magnetic resonance spectroscopy and magnetic resonance imaging is very low because the detected signal strength depends on the small population difference between spin states even in high magnetic fields. Hyperpolarization methods can be used to increase this difference and thereby enhance signal strength. This has been achieved previously by incorporating the molecular spin singlet para-hydrogen into hydrogenation reaction products. We show here that a metal complex can facilitate the reversible interaction of para-hydrogen with a suitable organic substrate such that up to an 800-fold increase in proton, carbon, and nitrogen signal strengths are seen for the substrate without its hydrogenation. These polarized signals can be selectively detected when combined with methods that suppress background signals.
Science 04/2009; 323(5922):1708-11. · 31.20 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The cationic iridium complexes [Ir(COD)(PR3)2]BF4 (1a-c) (a, R = Ph; b, R = p-tolyl; c, R = p-C6H4-OMe) react with parahydrogen in the presence of pyridine to give trans, cis, cis-[Ir(PR3)2(py)2(H)2]+ (2a-c) and small amounts of fac, cis-[Ir(PR3)(py)3(H)2]+ (3a-c), each of which exhibit polarized hydride resonances due to the magnetic inequivalence associated with the resultant AA"XX" spin system when 15N-labeled pyridine is employed. The pyridine ligands in 2 are labile, exchanging slowly into free pyridine with a rate constant of 0.4 s(-1) for 2a at 335 K in a dissociative process where DeltaH(double dagger) = 134 +/- 1 kJ mol(-1) and DeltaS(double dagger) = 151 +/- 5 J mol(-1) K(-1). Pyridine ligand exchange in 2 proves to be slower than that determined for 3. Parahydrogen induced polarization (PHIP) based on the hydride ligands of 2 and 3 is transferred efficiently to the 15N nuclei of the bound pyridine ligand by suitable insensitive-nuclei-enhanced-by-polarization-transfer (INEPT) based procedures. Related methods are then used to facilitate the sensitization of the free pyridine 15N signal by a factor of 120-fold through ligand exchange even though this substrate does not contain parahydrogen. This therefore corresponds to the successful polarization of an analyte by parahydrogen induced polarization methods without the need for the actual chemical incorporation of any parahydrogen derived nuclei into it.
Inorganic Chemistry 01/2009; 48(2):663-70. · 4.60 Impact Factor
