Hydrogen bonds involving transition metal centres – a brief review

Brammer, Lee; Zhao, Dong; Ladipo, Folami T.; Braddock‐Wilking, Janet

doi:10.1107/s0108768195003673

Cited by 143 publications

(76 citation statements)

References 11 publications

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“…Interactions between protons bound to oxygen or nitrogen and late transition metals in low oxidation states have lately been observed in several cases (22)(23)(24)(25)(26). The interaction exhibits features similar to those of the classical hydrogen bond (27), with elongated OOH bonds, short MOH distances, and large OOHOM bond angles.…”

Section: Resultsmentioning

confidence: 83%

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

Hallman

Frölander²,

Wondimagegn³

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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In palladium-catalyzed alkylations of allylic acetates with malonate as nucleophile, catalysts with oxazoline ligands bearing hydroxymethyl substituents in 4-position have been shown by density functional theory computations to undergo a conformational change on nucleophilic attack, which is accompanied by reduction of Pd(II) to Pd(0). The conformations of the Pd(0) complexes were shown to be governed by the presence of a hydrogen bond with the metal center acting as a hydrogen bond acceptor. The conformational change, which is absent in catalysts with O-alkylated analogs, largely affects the enantioselectivity of the catalytic process. This process is a previously uninvestigated example of where this type of weak hydrogen bond has been shown to influence the stereochemistry of a chemical reaction.A symmetric metal catalysis constitutes a powerful method for the preparation of enantiopure chiral compounds (1-3). To achieve high selectivity in the catalytic reactions, proper design of chiral ligands having the ability to transfer the chiral information to the reacting substrates is required. Proper design is usually accomplished by consideration of the steric and electronic demands of the catalytic process under study. Secondary interactions between the chiral ligand and the reacting species may influence the conformation of the catalyst, thereby affecting the stereoselectivity (4). At the same time, such interactions may be used to tune the electronic properties, resulting in increased reactivity of the catalytic system. Several examples of increased stereoselectivity and͞or acceleration of catalytic processes by ligands containing properly situated hydroxy groups have been reported. In rhodium-catalyzed hydrogenations of olefins, hydroxy substituents in the ligands have been shown to have remarkable effects. Thus, Knowles et al. (5) observed that a (R,R)-1,2-ethanediylbis[(2-methoxyphenyl)-phenylphosphine] derivative with the methoxy groups replaced by hydroxy groups provided high enantioselectivity, although it was at the expense of the high reactivity. Later, Börner (ref. 6 and references cited therein) noted similar effects for other types of ligands and provided evidence that properly situated hydroxy groups in the ligands coordinate to the cationic rhodium center by their oxygen lone pairs. Hayashi and coworkers (7-9) observed an accelerating effect by hydroxy groups in palladium-catalyzed allylic alkylations by using ferrocenylphosphine ligands. The effect was believed to be caused by an attractive interaction involving hydrogen bonding between a hydroxy group in the ligand and the nucleophile.We recently found that use of 2-(1-hydroxyalkyl)-(1a) and 2-(1-alkoxyalkyl)pyridinooxazolines (1b) as ligands in palladium-catalyzed allylic alkylations with malonate resulted in profoundly different enantioselectivities, ligands with (R*,R*)-configuration of the former type and those with (R*,S*)-configuration of the latter type, resulting in higher enantioselectivity than their diastereomers (10). This difference...

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Section: Resultsmentioning

confidence: 83%

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

Hallman

Frölander²,

Wondimagegn³

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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“…Other compounds containing NÀH´´´M interactions have previously been reported, and in most of them the interactions are intra-rather than intermolecular. [85,86] Intermolecular NÀH´´´M interactions with quaternary amino cations as hydrogen-bond donors [87] or with [PtCl 4 ] 2À as hydrogen-bond acceptor [88] have been reported. are in contact with atmospheric oxygen.…”

Section: Discussionmentioning

confidence: 98%

Synthesis and Reactivity of 2-Aminophenylpalladium(II) Complexes: Insertion Reactions of Oxygen and Carbon Monoxide into Carbon−Palladium Bonds—New Examples of “Transphobia”

et al. 1999

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“…[12] Hence, as early as 1972 a distinction had been made between agostic interactions and so-called three-center, four-electron (3c-4e) M···HX bonds. [13] By the early 1980s an irrefutable body of evidence had been gathered showing that alkyl ligands can coordinate to a transition-metal center M in an h 2 -fashion, with the primary MÀC bond being augmented by a significant secondary interaction involving an unusually short M···HC contact. In 1982, Green et al reported what are now the textbook examples of M···HC-a and -b interactions in the transitionmetal alkyl complexes [RTiCl 3 (dmpe)] (dmpe = Me 2 PCH 2 CH 2 PMe 2 ; R = Me 10 or Et 11).…”

Section: Introductionmentioning

confidence: 99%

Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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The phenomenon of agostic interactions is reviewed and the nature of the interaction is revisited. A historical perspective is followed by an overview of experimental techniques used to diagnose agostic behavior, and previous interpretations of agostic bonding are presented. A series of simple metal alkyl complexes is considered and a new model for the phenomenon in d(0) systems is developed which sets them apart from agostic late-transition-metal complexes. Factors such as the valence electron count and coordination number of the metal center are revealed to be unimportant in facilitating the interaction in most d(0) systems. The charge density distribution in several transition-metal alkyl complexes is explored by experimental and theoretical techniques, including the powerful "Atoms in Molecules" approach. Local charge concentrations are shown to play an important role in the agostic interaction. Finally, we demonstrate for the first time a way to manipulate and control the magnitude and disposition of such local charge concentrations, and hence the strength of agostic interactions in d(0) metal alkyl complexes.

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Hydrogen bonds involving transition metal centres – a brief review

Cited by 143 publications

References 11 publications

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

Synthesis and Reactivity of 2-Aminophenylpalladium(II) Complexes: Insertion Reactions of Oxygen and Carbon Monoxide into Carbon−Palladium Bonds—New Examples of “Transphobia”

Agostic Interactions in d⁰Metal Alkyl Complexes

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Hydrogen bonds involving transition metal centres – a brief review

Cited by 143 publications

References 11 publications

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

OH–Pd(0) interaction as a stabilizing factor in palladium-catalyzed allylic alkylations

Synthesis and Reactivity of 2-Aminophenylpalladium(II) Complexes: Insertion Reactions of Oxygen and Carbon Monoxide into Carbon−Palladium Bonds—New Examples of “Transphobia”

Agostic Interactions in d0Metal Alkyl Complexes

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Agostic Interactions in d⁰Metal Alkyl Complexes