The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1‐BR2‐2‐[(Me2N)2C=N]‐C6H4(
Reactions of (O=)PH(OCH2CH3)2and BrMg(CH2)
- NSF-PAR ID:
- 10067338
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – An Asian Journal
- Volume:
- 13
- Issue:
- 18
- ISSN:
- 1861-4728
- Page Range / eLocation ID:
- p. 2632-2640
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 3 –6 ) [BR2=BMes2(3 ), BC12H8, (4 ), BBN (5 ), BBNO (6 )] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X‐ray analysis. These novel types of pre‐organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via anortho ‐phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds.4 and5 deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1‐(RC≡C‐BR2)‐2‐[(Me2N)2C=NH]‐C6H4(R=Ph, H) and reacted with ammonia, BnNH2and pyrrolidine, to generate the FLP adducts 1‐(R2HN→BR2)‐2‐[(Me2N)2C=NH]‐C6H4, where the N‐H functionality is activated by intramolecular H‐bond interactions. In addition,5 was found to rapidly add across the double bond of H2CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise,5 is capable of cleaving H2, HBPin and PhSiH3to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules. -
Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH 2 Cl 2 solution of H 3 B·P((CH 2 ) 6 CH=CH 2 ) 3 ( 1 ·BH 3 ) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H 2 (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H 3 B·P( n- C 8 H 17 ) 3 (1%), H 3 B· P ((CH 2 ) 13 C H 2 )( n -C 8 H 17 ) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H 3 B· P ((CH 2 ) 13 C H 2 )((CH 2 ) 14 ) P ((CH 2 ) 13 C H 2 )·BH 3 ( 6 ·2BH 3 , 10%), in,out -H 3 B·P((CH 2 ) 14 ) 3 P·BH 3 ( in,out - 2 ·2BH 3 , 4%) and the stereoisomer ( in,in / out,out )- 2 ·2BH 3 (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH 4 ) to H 2 P((CH 2 ) 14 )PH 2 ( 10 ; 76% overall yield). The reaction with H 3 B·SMe 2 gives 10 ·2BH 3 , which is treated with n -BuLi (4.4 equiv) and Br(CH 2 ) 6 CH=CH 2 (4.0 equiv) to afford the tetraalkenyl precursor (H 2 C=CH(CH 2 ) 6 ) 2 (H 3 B)P((CH 2 ) 14 )P(BH 3 )((CH 2 ) 6 CH=CH 2 ) 2 ( 11 ·2BH 3 ; 18%). Alternative approaches to 11 ·2BH 3 (e.g., via 11 ) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11 ·2BH 3 (0.0010 M in CH 2 Cl 2 ) gives 6 ·2BH 3 (5%), in,out - 2 ·2BH 3 (6%), and ( in,in / out,out )- 2 ·2BH 3 (7%). Despite the doubled yield of 2 ·2BH 3 , the longer synthesis of 11 ·2BH 3 vs 1 ·BH 3 renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.more » « less
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The model reactions CH3X + (NH—CH=O)M ➔ CH3—NH—NH═O or NH═CH—O—CH3 + MX (M = none, Li, Na, K, Ag, Cu; X = F, Cl, Br) are investigated to demonstrate the feasibility of Marcus theory and the hard and soft acids and bases (HSAB) principle in predicting the reactivity of ambident nucleophiles. The delocalization indices (DI) are defined in the framework of the quantum theory of atoms in molecules (QT‐AIM), and are used as the scale of softness in the HSAB principle. To react with the ambident nucleophile NH═CH—O−, the carbocation H3C+from CH3X (F, Cl, Br) is actually a borderline acid according to the DI values of the forming C…N and C…O bonds in the transition states (between 0.25 and 0.49), while the counter ions are divided into three groups according to the DI values of weak interactions involving M (M…X, M…N, and M…O): group I (M = none, and Me4N) basically show zero DI values; group II species (M = Li, Na, and K) have noticeable DI values but the magnitudes are usually less than 0.15; and group III species (M = Ag and Cu(I)) have significant DI values (0.30–0.61). On a relative basis, H3C+is a soft acid with respect to group I and group II counter ions, and a hard acid with respect to group III counter ions. Therefore, N‐regioselectivity is found in the presence of group I and group II counter ions (M = Me4N, Li, Na, K), while O‐regioselectivity is observed in the presence of the group III counter ions (M = Ag, and Cu(I)). The hardness of atoms, groups, and molecules is also calculated with new functions that depend on ionization potential (
I ) and electron affinity (A ) and use the atomic charges obtained from localization indices (LI), so that the regioselectivity is explained by the atomic hardness of reactive nitrogen atoms in the transition states according to the maximum hardness principle (MHP). The exact Marcus equation is derived from the simple harmonic potential energy parabola, so that the concepts of activation free energy, intrinsic activation barrier, and reaction energy are completely connected. The required intrinsic activation barriers can be either estimated fromab initio calculations on reactant, transition state, and product of the model reactions, or calculated from identity reactions. The counter ions stabilize the reactant through bridging N‐ and O‐site of reactant of identity reactions, so that the intrinsic barriers for the salts are higher than those for free ambident anions, which is explained by the increased reorganization parameter Δr . The proper application of Marcus theory should quantitatively consider all three terms of Marcus equation, and reliably represent the results with potential energy parabolas for reactants and all products. For the model reactions, both Marcus theory and HSAB principle/MHP principle predict the N‐regioselectivity when M = none, Me4N, Li, Na, K, and the O‐regioselectivity when M = Ag and Cu(I). © 2019 Wiley Periodicals, Inc. -
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Abstract With the goal of generating anionic analogues to MN2S2
⋅ Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22−prepared from the Cys‐X‐Cys biomimetic, ema4−ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2resulted from loss of M originally residing in the N2S24−pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24−cavity holding a single metal, to a binucleating H2ema2−with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2product. By computational studies we compared the conformations of “linear” ema4−to ema4−frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2−that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. -
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Abstract With the goal of generating anionic analogues to MN2S2
⋅ Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22−prepared from the Cys‐X‐Cys biomimetic, ema4−ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2resulted from loss of M originally residing in the N2S24−pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24−cavity holding a single metal, to a binucleating H2ema2−with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2product. By computational studies we compared the conformations of “linear” ema4−to ema4−frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2−that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state.
