Big Ligands for Stabilization of Small Functionalities in Calcium Chemistry

Ruspic, Christian; Harder, Sjoerd

doi:10.1021/ic701479r

Cited by 69 publications

(47 citation statements)

References 67 publications

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“…• amide complexes undergo facile external amine/amide exchange along with intramolecular site exchange between amide and amine ligands (Ruspic & Harder 2007;Crimmin et al 2009).…”

Section: (B) the Schlenk Equilibriummentioning

confidence: 99%

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

et al. 2010

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Despite the routine employment of Grignard reagents and Hauser bases as stoichiometric carbanion reagents in organic and inorganic synthesis, a defined reaction chemistry encompassing the heavier elements of Group II (M = Ca, Sr and Ba) has, until recently, remained unreported. This article provides details of the recent progress in heavier Group II catalysed small molecule transformations mediated by well-defined heteroleptic and homoleptic complexes of the form LMX or MX 2 ; where L is a mono-anionic ligand and X is a reactive s-bonded substituent. The intra-and intermolecular heterofunctionalization (hydroamination, hydrophosphination, hydrosilylation and hydrogenation) of alkenes, alkynes, dienes, carbodiimides, isocyanates and ketones is discussed.

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“…• amide complexes undergo facile external amine/amide exchange along with intramolecular site exchange between amide and amine ligands (Ruspic & Harder 2007;Crimmin et al 2009).…”

Section: (B) the Schlenk Equilibriummentioning

confidence: 99%

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

et al. 2010

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“…The presence of a sterically demanding spectator ligand helps to stabilise the Ae metal centre against lability and brings to the fore the importance of Ae···π, Ae···H-X and CH···π interactions. 16,38,39,[40][41][42] Such interactions have previously been overlooked due to difficulties in synthetic procedures as a consequence of high reactivity. 43 As a corollary, these interactions have also been largely ignored computationally.…”

Section: Resultsmentioning

confidence: 99%

Hydrophosphination of Styrene and Polymerization of Vinylpyridine: A Computational Investigation of Calcium-Catalyzed Reactions and the Role of Fluxional Noncovalent Interactions

Ward

Hunt

2016

ACS Catal.

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A computational investigation of the intermolecular hydrophosphination of styrene and 2-vinylpyridine, catalysed by the heteroleptic b-diketiminato-stabilised calcium complex [(PhNC(Me)CHC(Me)NPh)CaPPh2], is presented. Alkene insertion does not proceed via the traditional route as proposed by experimental and theoretical research related to intermolecular hydroamination catalysed by alkaline earth or lanthanide complexes. In contrast, for the hydrophosphination mechanism, insertion proceeds via an outer sphere, conjugative addition where there is no direct interaction of Ca with the vinyl functionality. Following the initial rate determining alkene insertion, two distinct mechanisms emerge, protonolysis or polymerisation. Polymerisation of styrene is energetically less favourable than protonolysis whereas the reverse is determined for 2-vinylpyridine, thereby providing strong evidence for outcomes observed experimentally. The vinylarene ring is important as it allows for preferential coordination of the unsaturated substrate through numerous non-covalent Ca···π, CH···π and CaE (E=P, N) interactions, moreover the vinylarene ring counteracts unfavourable charge localisation within the activated transition state. The additional stability of the CaN over CaP dative interaction in vinylpyridine provides a rationalisation for the experimentally observed enhanced reactivity of vinylpyridine, particularly in the context of the almost identical local alkene insertion barriers. Previously, little emphasis has been placed on the involvement of non-covalent interactions however, our calculations reveal that Ca···π, CH···π and Cadonor interactions are critical; stabilising key intermediates and transition states, while also introducing numerous competitive pathways.

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“…[11] Deprotonation of a range of N-substituted ammonia boranes in toluene gave moderate yields of pure crystalline calciumamidoborane complexes that contained between one and three neutral NH 3 ligands per calcium atom. The complexes with the smaller substituents (R = H, Me, iPr) crystallized as bis-ammine adducts whereas the amidoborane complex with the larger DIPP-substituent crystallized with only one NH 3 ligand.…”

Section: Resultsmentioning

confidence: 99%

“…The following starting materials have been prepared according to literature procedures: [11] NH 3 BH 3 , [28] MeNH 2 BH 3 , [28] iPrNH 2 BH 3 , [9] and DIPPNH 2 BH 3 .…”

Section: Methodsmentioning

confidence: 99%

“…The fate of the concomitantly formed NH(R)BH 2 is unknown but it likely polymerizes and is part of the insoluble precipitate. After complete decomposition, the solution only contained DIPP-nacnacH and [Ca(DIPP-nacnac)A C H T U N G T R E N N U N G (NH 2 )] 2 and, as deter- www.chemeurj.org mined by 11 B NMR spectroscopy, there were no major boron-containing compounds in solution.…”

Section: + Bonding Interactions In Ca(dipp-nacnac)-a C H T U N G T mentioning

confidence: 99%

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Calcium–Amidoborane–Ammine Complexes: Thermal Decomposition of Model Systems

Harder¹,

Spielmann

Tobey

2012

Chemistry A European J

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Hydrocarbon-soluble model systems for the calcium-amidoborane-ammine complex Ca(NH(2)BH(3))(2)⋅(NH(3))(2) were prepared and structurally characterized. The following complexes were obtained by the reaction of RNH(2)BH(3) (R = H, Me, iPr, DIPP; DIPP = 2,6-diisopropylphenyl) with Ca(DIPP-nacnac)(NH(2))⋅(NH(3))(2) (DIPP-nacnac = DIPP-NC(Me)CHC(Me)N-DIPP): Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))(2), Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))(3), Ca(DIPP-nacnac)[NH(Me)BH(3)]⋅(NH(3))(2), Ca(DIPP-nacnac)[NH(iPr)BH(3)]⋅(NH(3))(2), and Ca(DIPP-nacnac)[NH(DIPP)BH(3)]⋅NH(3). The crystal structure of Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3)(3) showed a NH(2)BH(3)(-) unit that was fully embedded in a network of BH⋅⋅⋅HN interactions (range: 1.97(4)-2.39(4) Å) that were mainly found between NH(3) ligands and BH(3) groups. In addition, there were N-H⋅⋅⋅C interactions between NH(3) ligands and the central carbon atom in the ligand. Solutions of these calcium-amidoborane-ammine complexes in benzene were heated stepwise to 60 °C and thermally decomposed. The following main conclusions can be drawn: 1) Competing protonation of the DIPP-nacnac anion by NH(3) was observed; 2) The NH(3) ligands were bound loosely to the Ca(2+) ions and were partially eliminated upon heating. Crystal structures of [Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))](∞), Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))⋅(THF), and [Ca(DIPP-nacnac){NH(iPr)BH(3)}](2) were obtained. 3) Independent of the nature of the substituent R in NH(R)BH(3), the formation of H(2) was observed at around 50 °C. 4) In all cases, the complex [Ca(DIPP-nacnac)(NH(2))](2) was formed as a major product of thermal decomposition, and its dimeric nature was confirmed by single-crystal analysis. We proposed that thermal decomposition of calcium-amidoborane-ammine complexes goes through an intermediate calcium-hydride-ammine complex which eliminates hydrogen and [Ca(DIPP-nacnac)(NH(2))](2). It is likely that the formation of metal amides is also an important reaction pathway for the decomposition of metal-amidoborane-ammine complexes in the solid state.

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Big Ligands for Stabilization of Small Functionalities in Calcium Chemistry

Cited by 69 publications

References 67 publications

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

Hydrophosphination of Styrene and Polymerization of Vinylpyridine: A Computational Investigation of Calcium-Catalyzed Reactions and the Role of Fluxional Noncovalent Interactions

Calcium–Amidoborane–Ammine Complexes: Thermal Decomposition of Model Systems

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