Flexible κ4-PNN′O-tetradentate ligands: synthesis, complexation and structural studies

Durran, Sean E.; Elsegood, Mark R. J.; Hammond, Shelly R.; Smith, Martin B.

doi:10.1039/c0dt00200c

“…[38][39][40][41] Previously detected gas phase NH•••P interactions, are characterized by much longer (calculated) bond lengths. [38,[41][42][43] Structurally characterised examples of NH•••P hydrogen bonds are surprisingly scarce, with few displaying the favourable close-to-linear alignment of the three atoms seen in 4 a-c. [38,41,[44][45][46][47] The xanthene backbone in all three cases displays a near planar geometry (xanthene fold angles of 4 a: 10) °), rather than being puckered, thereby increasing the distance between the P and B substituents, and allowing for accommodation of the close-to-linear NH•••P unit. Density functional theory (DFT) calculations (using the R 2 SCAN-3c method) allow visualisation of hydrogen bonding through Non Covalent Interaction (NCI) plots, [48] and for 4 a-c these reveal unequivocal H-bonding regions between the P and NÀ H fragments (see Figure 3 for 4 c).…”

Section: Results and Discussion (I) Syntheses Of Xanthene-supported S...mentioning

confidence: 95%

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

Crumpton,

Heilmann,

Aldridge

2024

Angew Chem Int Ed

0

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Xanthene‐backbone FLPs featuring secondary borane functions –B(ArX)H (where ArX = C6F5 (ArF) or C6Cl5 (ArCl)) have been targeted through reactions of the dihydroboranes Me2S·BArXH2 with [4,5‐xanth(PR2)Li]2 (R = Ph, iPr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N–H bond ‘activation.’ We find that in the case of four‐coordinate boron systems (cationic or change neutral), the N–H linkage remains intact, supported by a NH···P hydrogen bond which is worth up to 17 kcal mol‐1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N‐to‐P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH2]‐ conjugate base through N‐to‐B p bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B‐bound ArX group. It is viable in the case of C6F5 substituents, but is prevented by the more sterically encumbering and secondary donor‐stabilising capabilities of the C6Cl5 substituent.

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“…[38][39][40][41] Previously detected gas phase NH•••P interactions, are characterized by much longer (calculated) bond lengths. [38,[41][42][43] Structurally characterised examples of NH•••P hydrogen bonds are surprisingly scarce, with few displaying the favourable close-to-linear alignment of the three atoms seen in 4 a-c. [38,41,[44][45][46][47] The xanthene backbone in all three cases displays a near planar geometry (xanthene fold angles of 4 a: 5.67 (6) °; 4 b: 4.97 (7) °; 4 c: 0.45(10) °), rather than being puckered, thereby increasing the distance between the P and B substituents, and allowing for accommodation of the close-to-linear NH•••P unit. Density functional theory (DFT) calculations (using the R 2 SCAN-3c method) allow visualisation of hydrogen bonding through Non Covalent Interaction (NCI) plots, [48] and for 4 a-c these reveal unequivocal H-bonding regions between the P and NÀ H fragments (see Figure 3 for 4 c).…”

Section: Results and Discussion (I) Syntheses Of Xanthene-supported S...mentioning

confidence: 96%

“…Structurally characterised examples of NH⋅⋅⋅P hydrogen bonds are surprisingly scarce, with few displaying the favourable close‐to‐linear alignment of the three atoms seen in 4 a – c [38,41,44–47] . The xanthene backbone in all three cases displays a near planar geometry (xanthene fold angles of 4 a : 5.67(6) °; 4 b : 4.97(7) °; 4 c : 0.45(10) °), rather than being puckered, thereby increasing the distance between the P and B substituents, and allowing for accommodation of the close‐to‐linear NH⋅⋅⋅P unit.…”

Section: Resultsmentioning

confidence: 99%

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

Crumpton,

Heilmann,

Aldridge

2024

Angewandte Chemie

0

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Xanthene‐backbone FLPs featuring secondary borane functions –B(ArX)H (where ArX = C6F5 (ArF) or C6Cl5 (ArCl)) have been targeted through reactions of the dihydroboranes Me2S·BArXH2 with [4,5‐xanth(PR2)Li]2 (R = Ph, iPr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N–H bond ‘activation.’ We find that in the case of four‐coordinate boron systems (cationic or change neutral), the N–H linkage remains intact, supported by a NH···P hydrogen bond which is worth up to 17 kcal mol‐1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N‐to‐P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH2]‐ conjugate base through N‐to‐B p bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B‐bound ArX group. It is viable in the case of C6F5 substituents, but is prevented by the more sterically encumbering and secondary donor‐stabilising capabilities of the C6Cl5 substituent.

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“…47 To our knowledge, the use of the amide moiety in the chelating ligands (N, as a monoanionic coordinating atom) has only been reported by Durran et al in 2010 (R, Figure 1.12). 48 The synthesis and complexation of the tetradentate ligands and their complexes with Pt(II), Pd(II) and Ni(II) were studied. 48…”

mentioning

confidence: 99%

Low symmetry Pincer Ligands designed for applications in coordination chemistry and catalysis

Herasymchuk¹

2021

Preprint

0

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Pincer ligands are monoanionic, tridentate binding molecules that have been used in coordination chemistry as efficient homogeneous and heterogeneous catalysts (i.e. as transition metal complexes). The focus of this work lies in the synthesis, characterization and coordination chemistry of a series of novel asymmetric potentially monoanionic NN'N", NN'C and NN'P type pincer ligands with amide functionality derived from the skeleton of 2-(2'-anilinyl)-4,4-dimethyl-2-oxazoline. Modular approach to this synthesis has been developed through an alkyl halide intermediate, in addition to the substrate-dependent alternative pincer syntheses, which are also described. The coordination chemistries of Pd and Ni, as well as the potential application of these pincer complexes in metal mediated catalysis of aldehyde allylation reactions will be explored. Moreover, a number of Pd(II) pincer complexes have been successfully synthesized and structurally characterized and these results are likewise described.

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Flexible κ4-PNN′O-tetradentate ligands: synthesis, complexation and structural studies

Cited by 19 publications

References 96 publications

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

Modulating Hydrogen Shuttling in Ammonia by Neutral and Cationic Boron‐Containing Frustrated Lewis Pairs (FLPs)

Low symmetry Pincer Ligands designed for applications in coordination chemistry and catalysis

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