Coordination of arenes and phosphines by charge separated alkaline earth cations

Garcı́a, Lucía; Anker, Mathew D.; Mahon, Mary F.; Maron, Laurent; Hill, Michael S.

doi:10.1039/c8dt03124j

Cited by 65 publications

(67 citation statements)

References 71 publications

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“…Figure shows the crystal structures of [(BDI)Mg + ⋅ PPh 3 ][B(C 6 F 5 ) 4 − ] ( 6 ), [(BDI)Mg + ⋅ (PCy 3 )(PhF)][B(C 6 F 5 ) 4 − ] ( 7 ), and [(BDI)Mg + ⋅ (P t Bu 3 )(PhF)][B(C 6 F 5 ) 4 − ] ( 8 ); selected geometric parameters are summarized in Table . Whereas the previously reported [(BDI)Mg + ⋅ PPh 3 ][Al{OC(CF 3 ) 3 } 4 − ] is a truly separated ion pair, the crystal structure of [(BDI)Mg + ⋅ PPh 3 ][B(C 6 F 5 ) 4 − ] ( 6 ) shows a single Mg ⋅⋅⋅ F interaction. Consequently, the Mg−P bond in 6 (2.6549(5) Å) is slightly longer than that in its aluminate salt (2.597(1) Å).…”

Section: Resultsmentioning

confidence: 71%

“…Addition of one equivalent of PPh 3 led to a complex with 1 H and 13 C NMR chemical shifts closely matching those of [(BDI)Mg + ⋅ PPh 3 ][Al{OC(CF 3 ) 3 } 4 − ], despite the use of a different solvent. The 31 P signal at δ =−5.0 ppm is basically identical to that reported by Hill and co‐workers ( δ =−4.9 ppm).…”

Section: Resultsmentioning

confidence: 82%

“…Evidence for unsupported interactions of magnesium complexes with neutral phosphine ligands is limited to the small phosphine PMe 3 or P , P ‐chelating ligands . The recent isolation of [(BDI)Mg + ⋅ PPh 3 ][Al{OC(CF 3 ) 3 } 4 − ] illustrates that there is ample space at the metal atom in (BDI)Mg + for complexation by a larger phosphine. Thus, we investigated the interaction of (BDI)Mg + with a series of phosphines of increasing bulk and/or donor properties.…”

Section: Resultsmentioning

confidence: 99%

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Complexation and Versatile Reactivity of a Highly Lewis Acidic Cationic Mg Complex with Alkynes and Phosphines

Pahl

Stennett

Volland

et al. 2019

Chemistry A European J

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[(BDI)Mg+][B(C6F5)4−] (1; BDI=CH[C(CH3)NDipp]2; Dipp=2,6‐diisopropylphenyl) was prepared by reaction of (BDI)MgnPr with [Ph3C+][B(C6F5)4−]. Addition of 3‐hexyne gave [(BDI)Mg+⋅(EtC≡CEt)][B(C6F5)4−]. Single‐crystal X‐ray analysis, NMR investigations, Raman spectra, and DFT calculations indicate a significant Mg‐alkyne interaction. Addition of the terminal alkynes PhC≡CH or Me3SiC≡CH led to alkyne deprotonation by the BDI ligand to give [(BDI‐H)Mg+(C≡CPh)]2⋅2 [B(C6F5)4−] (2, 70 %) and [(BDI‐H)Mg+(C≡CSiMe3)]2⋅2 [B(C6F5)4−] (3, 63 %). Addition of internal alkynes PhC≡CPh or PhC≡CMe led to [4+2] cycloadditions with the BDI ligand to give {Mg+C(Ph)=C(Ph)C[C(Me)=NDipp]2}2⋅ 2 [B(C6F5)4−] (4, 53 %) and {Mg+C(Ph)=C(Me)C[C(Me)=NDipp]2}2⋅2 [B(C6F5)4−] (5, 73 %), in which the Mg center is N,N,C‐chelated. The (BDI)Mg+ cation can be viewed as an intramolecular frustrated Lewis pair (FLP) with a Lewis acidic site (Mg) and a Lewis (or Brønsted) basic site (BDI). Reaction of [(BDI)Mg+][B(C6F5)4−] (1) with a range of phosphines varying in bulk and donor strength generated [(BDI)Mg+⋅PPh3][B(C6F5)4−] (6), [(BDI)Mg+⋅PCy3][B(C6F5)4−] (7), and [(BDI)Mg+⋅ PtBu3][B(C6F5)4−] (8). The bulkier phosphine PMes3 (Mes=mesityl) did not show any interaction. Combinations of [(BDI)Mg+][B(C6F5)4−] and phosphines did not result in addition to the triple bond in 3‐hexyne, but during the screening process it was discovered that the cationic magnesium complex catalyzes the hydrophosphination of PhC≡CH with HPPh2, for which an FLP‐type mechanism is tentatively proposed.

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Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Complexation and Versatile Reactivity of a Highly Lewis Acidic Cationic Mg Complex with Alkynes and Phosphines

Pahl

Stennett

Volland

et al. 2019

Chemistry A European J

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“…Theh ydrogenation transition states are particularly notable and display features which discriminate them from ac lassical s-bond metathesis.E xamination of the relevant molecular orbitals and the NBO analysis of the hydrogenation of the n-hexyl-hydride species C (6)i sc learly indicative of aheterolytic cleavage of the H 2 molecule.T he HOMOÀ2 ( Figure S22) involves the filled sp 3 orbital of the n-hexyl chain, the H 2 s*a nd a3 d orbital of both Ca centers.T he involvement of 3d orbitals on Ca has recently been invoked as ap otentially significant factor in the structural and reaction chemistry of organocalcium species. [26][27][28] This analysis indicates,t herefore,t hat the hydrogen atom interacting with the n-hexyl unit is better viewed as ap roton, whereas the hydrogen atom interacting with the two Ca centers is much more hydridic in nature.T his interpretation is further corroborated by the corresponding NBO analysis in which as trong second order interaction is observed between the filled a-methylene sp 3 orbital of the n-hexyl chain and the s* orbital of the H 2 molecule,s ignifying that the HÀHb ond is broken by what is effectively the nucleophilic displacement of hydride by the organic substituent. This electron density is then redistributed via by al ess strong second order interaction between the s* HÀH orbital and the two Ca atoms.T he highly polarized nature of this process is underscored by the NPAcharge analysis,which indicates acharge of À1.0 on the a-methylene carbon of the n-hexyl chain, charges of + 1.50 and + 1.43 for the two Ca centers and charges of À0.23 and + 0.03 for the two H 2 hydrogen atoms.A ne ffectively identical interpretation also emerges for the hydrogenation TS from the dicalcium di-n-hexyl species F (9)( Figure S23).…”

Section: Angewandte Chemiementioning

confidence: 98%

Heterolysis of Dihydrogen by Nucleophilic Calcium Alkyls

et al. 2018

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Abstractβ‐Diketiminato (BDI) calcium alkyl derivatives undergo hydrogenolysis with H2 to regenerate [(BDI)CaH]2, allowing the catalytic hydrogenation of a wide range of 1‐alkenes and norbornene under very mild conditions (2 bar H2, 298 K). The reactions are deduced to take place with the retention of the dimeric structures of the calcium hydrido‐alkyl and alkyl intermediates via a well‐defined sequence of Ca−H/C=C insertion and Ca−C hydrogenation events. This latter deduction is strongly supported by DFT calculations (B3PW91) performed on the 1‐hexene/H2 system, which also indicates that the hydrogenation transition states display features which discriminate them from a classical σ‐bond metathesis mechanism. In particular, NBO analysis identifies a strong second order interaction between the filled α‐methylene sp3 orbital of the n‐hexyl chain and the σ* orbital of the H2 molecule, signifying that the H−H bond is broken by what is effectively the nucleophilic displacement of hydride by the organic substituent.

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“…Reactions of 2 with naphthalene,a nthracene and tetracene performed at 350 Kw ithin the cavity of aC WE PR spectrometer provided no evidence for the production of short lived hydrogen radicals.I ne ach case,h owever, signals (17), Ca1-C88 2.651(2), Ca1-C89 2.923(2), Ca1-C94 2.838(2), Ca1-C95 2.624(2), Ca1-C96 3.019(2), Ca2-N3 2.3492 (17),C a2-N4 2.4179(18), Ca2-C96 3.071(2), Ca2-C97 2.981(2), Ca2-C98 2.858(2), Ca2-C99 2.748(2), Ca2-C1002 .712(2), Ca2-C101 2.868(2), Ca3-N5 2.3902(18), Ca3-N6 2.4405 (19),C a3-C89 3.138(2), Ca3-C90 2.995(2), Ca3-C91, 2.875(2) Ca3-C92 2.804(2), Ca3-C93 2.801(2), Ca3-C94 2.964(2); N1-Ca1-N2 78.05 (6), N3-Ca2-N4 77.51(6), N5-Ca3-N6 78.73(6);(11)C a1-N1 2.3290(12), Ca1-N2 2.3412(12), Ca1-C30 2.7127(15), Ca1-C31 2.8973(15), Ca1-C32 2.7097 (14), Ca1-C33 2.7711 (14),C a1-C34 2.7660 (15);N1-Ca1-N2 76.92 (4). Symmetry operations to generate equivalent atoms 1Àx,1 Ày,1 Àz.…”

Section: Angewandte Chemiementioning

confidence: 99%