Boron Functionalization of Bis(pyrazolyl)borate Ligands: Molecular Structures of [RuX(PPh3)2{(MeO)2B(pz)2}] (X = H, Cl; pz = pyrazol-1-yl)

Abernethy, Robyn J.; Hill, Anthony F.; Smith, Matthew K.; Willis, Anthony C.

doi:10.1021/om9006592

Cited by 18 publications

(12 citation statements)

References 94 publications

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“…Here we report for the first time, the characterization of novel trimethylplatinum(IV) complexes supported by Bp and Bp* ligands. Finally, we report selective reactivity of the endo B–H fragment of Bp*Pt IV Me 3 towards methanol and acetonitrile, and rationalize our findings of enhancement of reactivity through density functional theory (DFT) calculations…”

Section: Introductionsupporting

confidence: 68%

“…Since neither potassium salts of Bp or Bp* ligands or 3 underwent similar fast protonolysis in methanol, we presume coordination of methanol to the Pt IV center of 4 enhances the reactivity by forcing the B–H and OH fragments in close proximity, which leads to immediate hydrogen evolution. Unselective and complete B–H protonolysis of Bp to form bis(pyrazolyl)dimethoxyborate has been reported for Ru, but to the best of our knowledge, this is the first example of selective enhancement of reactivity of BH fragments towards protonolysis through conformational rigidity.…”

Section: Resultsmentioning

confidence: 86%

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Enhancing Reactivity of Directly íObservable B–H–Pt Interactions through Conformational Rigidity

et al. 2016

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We report for the first time the direct syntheses of trimethylplatinum(IV) complexes supported by bis(pyrazolyl)dihydridoborate (Bp) and bis(3,5-dimethylpyrazolyl)dihydridoborate (Bp*) ligands from the corresponding dimethylplatinum(II) complexes. X-ray crystallographic and multinuclear NMR characterization of the trimethylplatinum(IV) complexes reveal agostic B-H-Pt interactions. Solid-state analysis reveals that BpPt IV Me 3 adopts a dinuclear structure featuring an intermolecular B-H-Pt bridge, whereas Bp*Pt IV Me 3 adopts a mononuclear structure [a]

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Section: Introductionsupporting

confidence: 68%

Section: Resultsmentioning

confidence: 86%

Enhancing Reactivity of Directly íObservable B–H–Pt Interactions through Conformational Rigidity

et al. 2016

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“…The synthesis of 3 (Scheme 1) proceeds from potassium di(pyrazolyl)borohydride v, vi, vii and commercially-available (cymene)ruthenium dichloride dimer to give intermediate chloride 4 . Although 4 can be isolated, it is easily converted in situ to 3 by treatment with 1 equiv.…”

mentioning

confidence: 99%

“…The crystal structure of 3 shows the borate ligand in a tetrahedral geometry at boron, which has analogy to the popular tris(pyrazolyl)borohydride (Tp) ligand series. vi, vii, viii …”

mentioning

confidence: 99%

A dual site catalyst for mild, selective nitrile reduction

Lü

Williams

2014

Chem. Commun.

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We report a novel ruthenium bis(pyrazolyl)borate scaffold that enables cooperative reduction reactivity in which boron and ruthenium centers work in concert to effect selective nitrile reduction. The pre-catalyst compound {[κ 3 -(1-pz) 2 HB(N=CHCH 3 )]Ru(cymene)} + TfO − (pz = pyrazolyl) was synthesized from readily-available materials through a straightforward route, thus making it an appealing catalyst for a number of reactions.As part of our ongoing studies of dual site ruthenium, boron-containing catalysts for the manipulation of hydride groups, we have recently reported a series of [di(pyridyl)borate]ruthenium complexes (1, 2) i that exhibit remarkable reactivity in a number of applications, ii notably including dehydrogenation of ammonia borane. iii Although they are successful catalysts, these di(pyridyl)dimethylborate-derived complexes are cumbersome to prepare, due largely to dependence on an expensive and reactive BrBMe 2 starting material and high water and oxygen sensitivity of intermediate complexes in their syntheses. Further, despite their catalytic utility, no direct evidence has been collected to show a mechanistic account of the cooperative role, if any, that boron and ruthenium are playing in the reactive mechanisms of 1 or 2. iv We suspect this is partially due to the robustness of the bridging μ-OH ligand between the boron and ruthenium centers, which inhibits access to a free borane in catalytic reactions.We show here a conveniently prepared, borate-pendant ruthenium complex (3) that retains much of the reactivity of the original di(pyridyl)borate complexes (see ESI), show that it is an efficient and selective catalyst for nitrile reduction, and provide evidence for the cooperative role that boron and ruthenium play in the reaction, as hydride donor and activating group, respectively. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript steps without the need for materials that are cost-prohibitive or difficult to manipulate: all materials are amenable to handling using standard Schlenk techniques and/or a glove box. 3 can be crystallized from isopropanol and hexanes; its molecular structure was determined by single crystal X-ray diffraction (Scheme 1). The crystal structure of 3 shows the borate ligand in a tetrahedral geometry at boron, which has analogy to the popular tris(pyrazolyl)borohydride (Tp) ligand series. vi, vii, viii The synthesis of 3 revealed an important insight into the mechanism of its catalytic reactivity. In the conversion of 4 to 3, a hydride is transferred from a ligand B-H group to 5's coordinated nitrile in >90% NMR yield (Scheme 1). This reaction is the first example of our envisioned cooperative reactivity of ruthenium and boron. Contrary to the design concept from which we originally prepared 2, ii boron in 3 is not behaving as a Lewis acid. The structure of 3 shows that B-H addition to the nitrile proceeds in a cis fashion, and NMR evidence reveals that the selectivity for this geometry is exclusive. Thus we believe that the mech...

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“…Heteroscorpionates, defined simply as any bispyrazolylborate (see Figure , A),, have found widespread utility in a number of arenas, from coordination polymers to catalysis Asymmetric substitution of one or both of the pendant (R) groups has led a whole new generation of tridentate ligands with heterogeneous donor sets . Homoleptic four‐coordinate complexes similar to those formed by the original heteroscorpionate, dihyrobis(1‐pyrazolyl)borate (Bp, Figure , A), are far less common.…”

Section: Introductionmentioning

confidence: 99%

The Original CoII Heteroscorpionates Revisited: On the EPR of Pseudotetrahedral CoII

et al. 2016

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An examination of the solution spectroscopy of a series of tetrahedral bis-bispyrazolylborate complexes of Co II is presented. This includes a re-examination of the UV/Vis-NIR of the three stable derivatives, Bp 2 Co, Bp 3,5Me 2 Co and (Ph 2 Bp) 2 Co, which showed two transitions previously unobserved, one arising from splitting of the near-infrared d-d transition and one arising from a ligand-based or charge-transfer mechanism; a reevaluation of Δ and B led to values more in line with similar complexes. Frozen solution EPR of the series of complexes suggests all are under the influence of a non-negligible, negative [a]

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Boron Functionalization of Bis(pyrazolyl)borate Ligands: Molecular Structures of [RuX(PPh₃)₂{(MeO)₂B(pz)₂}] (X = H, Cl; pz = pyrazol-1-yl)

Cited by 18 publications

References 94 publications

Enhancing Reactivity of Directly íObservable B–H–Pt Interactions through Conformational Rigidity

Enhancing Reactivity of Directly íObservable B–H–Pt Interactions through Conformational Rigidity

A dual site catalyst for mild, selective nitrile reduction

The Original CoII Heteroscorpionates Revisited: On the EPR of Pseudotetrahedral CoII

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