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The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change.

Holmes AJ, Rayner PJ, Cowley MJ, Green GG, Whitwood AC, Duckett SB - Dalton Trans (2015)

Bottom Line: This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine.When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals.The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hyperpolarization in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, UK. simon.duckett@york.ac.uk.

ABSTRACT
The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

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Synthesis of d4-1 and d7-1. (a) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (98%, 95%D), (b) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (47%), (c) CO(g) (5 Bar), NaCO3, Pd(OAc)2, DPPB, EtOH, 100 °C, 16 h (55%), (d) 5% Pd/C, D2(g), Et3N, D2O/THF, rt, 5 h (82%, 98% D), (e) NaBD4, MeOD, 65 °C, 2 h (86%, 98% D), (f) SOCl2, THF, 65 °C, 1 h (93%), (g) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (99%), (h) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA-polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (57%).
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sch3: Synthesis of d4-1 and d7-1. (a) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (98%, 95%D), (b) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (47%), (c) CO(g) (5 Bar), NaCO3, Pd(OAc)2, DPPB, EtOH, 100 °C, 16 h (55%), (d) 5% Pd/C, D2(g), Et3N, D2O/THF, rt, 5 h (82%, 98% D), (e) NaBD4, MeOD, 65 °C, 2 h (86%, 98% D), (f) SOCl2, THF, 65 °C, 1 h (93%), (g) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (99%), (h) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA-polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (57%).

Mentions: The synthesis of d4-1 began by alkylation of borane di(tert-butyl)phosphine complex with 2,6-bis(chloromethyl)pyridine (5) as shown in Scheme 3.47 This gave the phosphine–borane complex d4-6 in 98% yield with 95% deuterium incorporation. We then developed a telescoped procedure to d4-1 in 47% yield over three steps; borane deprotection was effected using HBF4·OEt2 in MeOD, liberation of the free bisphosphine was achieved on polymer supported diisopropylamine (PS-DIPA) and finally complexation with [Ir(COD)2]BF4 under reported conditions.48 Importantly, this deprotection–complexation procedure proceeded with no observable deuterium–hydrogen exchange according to both mass spectrometry and NMR analysis.


The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change.

Holmes AJ, Rayner PJ, Cowley MJ, Green GG, Whitwood AC, Duckett SB - Dalton Trans (2015)

Synthesis of d4-1 and d7-1. (a) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (98%, 95%D), (b) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (47%), (c) CO(g) (5 Bar), NaCO3, Pd(OAc)2, DPPB, EtOH, 100 °C, 16 h (55%), (d) 5% Pd/C, D2(g), Et3N, D2O/THF, rt, 5 h (82%, 98% D), (e) NaBD4, MeOD, 65 °C, 2 h (86%, 98% D), (f) SOCl2, THF, 65 °C, 1 h (93%), (g) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (99%), (h) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA-polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (57%).
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sch3: Synthesis of d4-1 and d7-1. (a) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (98%, 95%D), (b) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (47%), (c) CO(g) (5 Bar), NaCO3, Pd(OAc)2, DPPB, EtOH, 100 °C, 16 h (55%), (d) 5% Pd/C, D2(g), Et3N, D2O/THF, rt, 5 h (82%, 98% D), (e) NaBD4, MeOD, 65 °C, 2 h (86%, 98% D), (f) SOCl2, THF, 65 °C, 1 h (93%), (g) (tBu)2PHBH3, 40% NaOD(D2O), TBAB, toluene, rt, 16 h (99%), (h) (i) HBF4·OEt2, MeOD, 80 °C, 16 h (ii) DIPA-polymer bound, MeOD, rt, 1 h (iii) [Ir(COD)2]BF4 (57%).
Mentions: The synthesis of d4-1 began by alkylation of borane di(tert-butyl)phosphine complex with 2,6-bis(chloromethyl)pyridine (5) as shown in Scheme 3.47 This gave the phosphine–borane complex d4-6 in 98% yield with 95% deuterium incorporation. We then developed a telescoped procedure to d4-1 in 47% yield over three steps; borane deprotection was effected using HBF4·OEt2 in MeOD, liberation of the free bisphosphine was achieved on polymer supported diisopropylamine (PS-DIPA) and finally complexation with [Ir(COD)2]BF4 under reported conditions.48 Importantly, this deprotection–complexation procedure proceeded with no observable deuterium–hydrogen exchange according to both mass spectrometry and NMR analysis.

Bottom Line: This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine.When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals.The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

View Article: PubMed Central - PubMed

Affiliation: Centre for Hyperpolarization in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, UK. simon.duckett@york.ac.uk.

ABSTRACT
The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(H2)]BF4.

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