Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

• using metal complexes as switching units (Figure 20). This concept named “weak link approach” (WLA) [78] uses square planar d8-transition metal complexes with two hemilabile bidentate ligands composed of a strong binding site (phosphorus) and a weaker one (generally sulfur, oxygen, selenium, or nitrogen

• decoordinated and one arm is set loose, leading to the “semi-open” conformation. A second ancillary ligand needs to be added to decoordinate the labile binding site on the second ligand and fully open the system. Symmetrical tweezers can be obtained by using two identical hemilabile ligands. For example

• ligands. The reversibility of the opening/closing process was achieved in situ by the addition and removal of CO yielding one of the first examples of allosteric regulation in artificial systems. Dissymmetric molecular tweezers are also accessible with high selectivity using two different hemilabile

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• association/dissociation of hemilabile ligands bound to a metal center. Through the addition of secondary ligands, the weakly coordinated donor sites are substituted which allows an opening of the switch from a rigid-closed to a flexible semi-open form [117]. A common protocol used addition/removal of

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• coordination [12]. Thus, their use in catalysis is the basis of this review article with the main focus on the synthesis of N-heterocyclic phosphines. The presence of soft donor atoms such as phosphorus results in the formation of hemilabile ligands. These are multidentate ligands having hard P-donor and soft

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• precatalysts can be attributed to electronic and steric effects associated with the adjacent bulky phenyl groups. Keywords: Grubbs-type precatalyst; hemilabile; 1-octene metathesis; pyridinyl-alcoholato ligand; Introduction The alkene metathesis reaction is now well established as a powerful synthetic tool

• based on the design concepts illustrated in Scheme 1 [3]. The design concept C is of interest because of the potential hemilabile nature and latent metathesis activity of these complexes [4]. Of particular interest to us are the ruthenium alkylidene complexes containing the pyridinyl alcoholato

• Ru–N bond (2.181 Å) in the geometry-optimised structure (Figure 9) of precatalyst 9 compared to that of the Ru–N bond (2.166 Å) of 6. A longer bond suggests a weaker Ru–N chelation thus a more active hemilabile complex. The difference in the Ru–N bond length may be attributed to the electron

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions

• Stefan Mark,
• Hubert Wadepohl and
• Markus Enders

Beilstein J. Org. Chem. 2016, 12, 1372–1379, doi:10.3762/bjoc.12.131

• Stefan Mark Hubert Wadepohl Markus Enders Anorganisch-Chemisches Institut, Heidelberg University, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany 10.3762/bjoc.12.131 Abstract A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were

• polyethylene; Introduction Chelate ligands with both, a strongly coordinating moiety and a weakly coordinating donor function allow the stabilization of vacant coordination sites at metal centers and may act as placeholders for external substrates. The concept of hemilabile ligands has been introduced in 1979

• [1] and has been applied for the development of improved transition metal catalysts [2][3][4][5][6][7]. The donor–acceptor interaction of the hemilabile moiety with the metal center should be weak enough to allow the displacement by a substrate, which should itself be transformed during the catalytic

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• chelation effect wherein the o-methoxy group acts as a hemilabile ligand, changing the steric and electronic environment around the metal center. Since 20 displayed inferior conversions and yields, however, it was eschewed in favor of complex 1. Cyclohexyl 21 was also an excellent catalyst in terms of

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

• Matthieu Jouffroy,
• Rafael Gramage-Doria,
• David Sémeril,
• Dominique Armspach,
• Dominique Matt,
• Werner Oberhauser and
• Loïc Toupet

Beilstein J. Org. Chem. 2014, 10, 2388–2405, doi:10.3762/bjoc.10.249

• mono-ligated intermediates are also likely to be operative with HUGPHOS ligands (Scheme 9). The fact that the observed reaction rates are higher with HUGPHOS ligands than with other bulky phosphines may be related to the presence of hemilabile methoxy groups [83] able either to stabilise highly

Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative

• Bernd Schmidt and
• Sylvia Hauke

Beilstein J. Org. Chem. 2014, 10, 1023–1031, doi:10.3762/bjoc.10.102

• ), whereas a significant improvement could be observed in toluene at 80 °C (Table 1, entry 3). We thought that the yield could not be further increased with catalyst A and therefore decided to test the phosphine free catalyst B. This and related catalysts [56], comprising a hemilabile ortho-isopropoxy

• better results were obtained with two different phosphine free catalysts comprising a hemilabile alkoxy substituted benzylidene ligand, even at only moderately elevated temperatures. The acrolein cross metathesis product can be converted into the 4-benzoate of L-amicetose via benzoylation, Pd-catalyzed

Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C₂-symmetric building block: a strategy for the synthesis of decanolide natural products

• Bernd Schmidt and
• Oliver Kunz

Beilstein J. Org. Chem. 2013, 9, 2544–2555, doi:10.3762/bjoc.9.289

• carbene complex B [35] as precatalysts (Table 1). Phosphine-free precatalysts with a hemilabile alkoxy ligand are supposed to be well-suited for cross metathesis reactions [36][37]. With a moderate catalyst loading of 2.0 mol % of A, we isolated the expected cross metathesis product 11 in an acceptable

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• generation catalyst (3), where the catalytically active species is stabilized by a hemilabile benzylidene ligand. The activating effect of the allylic hydroxy group in RCM is further supported by the dramatic decrease in conversion when the free OH group was protected (i.e., R ≠ H, R′ = Me) in pathway B

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• robustness and tolerance towards several functional groups [19]. A third major topic in catalyst development has been the variation of the dissociating “placeholder”-ligand. In this respect, the introduction and further improvement of hemilabile benzylidene ligands by Hoveyda [20], Grela[21] and Blechert [22