Square-planar Coordination Geometry Research Articles

Dicarbonyl[10,10-dimethyl-5,15-bis(pentafluorophenyl)biladiene]ruthenium(II): discovery of the first ruthenium tetrapyrrole cis-dicarbonyl complex by X-ray and electron diffraction.

Dicarbonyl[10,10-dimethyl-5,15-bis(pentafluorophenyl)biladiene]ruthenium(II), [Ru(C33H16F10N4)(CO)2] or Ru(CO)2[DMBil1], is the first reported ruthenium(II) cis-dicarbonyl tetrapyrrole complex. The neutral complex sports two carbonyls and an oligotetrapyrrolic biladiene ligand. Notably, the biladiene adopts a coordination geometry that is well distorted from square planar and much more closely approximates a seesaw arrangement. Accordingly, Ru(CO)2[DMBil1] is not only the first ruthenium cis-dicarbonyl with a tetrapyrrole ligand, but also the first metal biladiene complex in which the tetrapyrrole does not adopt a (pseudo-)square-planar coordination geometry. Ru(CO)2[DMBil1] is weakly luminescent, displaying λem= 552 nm upon excitation at λex= 500 nm, supports two reversible 1 e- reductions at -1.45 and -1.73 V (versus Fc+/Fc), and has significant absorption features at 481 and 531 nm, suggesting suitability for photocatalytic and photosensitization applications. While the structure of Ru(CO)2[DMBil1] was initially determined by X-ray diffraction, a traditionally acceptable quality structure could not be obtained (despite multiple attempts) because of consistently poor crystal quality. An independent structure obtained from electron diffraction experiments corroborates the structure of this unusual biladiene complex.

Iodonium cation stabilizes square-planar configuration of the silver(I) tetratriflate

In this work, we have experimentally and theoretically shown that halogen bonding can stabilize the rare example of square-planar configuration of the silver(I) center. The crystallographic analysis of tris-dibenziodolium silver(I) tetratriflate reveals two types of halogen bonding interactions between the triflate ligands and the dibenziodolium cation, which might stabilize the such square-planar coordination geometry. Theoretical calculations confirm the noncovalent nature of the I⋅⋅⋅O contacts and provide insights into their electronic properties.

Crystal structures of ten phosphane chalcogenide complexes of gold(III) chloride and bromide.

The structures of ten phosphane chalcogenide complexes of gold(III) halides, with general formula R 1 3-n R 2 nPEAuX 3 (R 1 = t-butyl; R 2 = i-propyl; n = 0 to 3; E = S or Se; X = Cl or Br) are presented. The eight possible chlorido derivatives are: 9a, n = 3, E = S; 10a, n = 2, E = S; 11a, n = 1, E = S; 12a, n = 0, E = S; 13a, n = 3, E = Se; 14a, n = 2, E = Se; 15a, n = 1, E = Se; and 16a, n = 0, E = Se, and the corresponding bromido derivatives are 9b-16b in the same order. Structures were obtained for 9a, 10a (and a second polymorph 10aa), 11a (and its deutero-chloro-form monosolvate 11aa), 12a (as its di-chloro-methane monosolvate), 14a, 15a (as its deutero-chloro-form monosolvate 15aa, in which the solvent mol-ecule is disordered over two positions), 9b, 11b, 13b and 15b. The structures of 11a, 15a, 11b and 15b form an isotypic set, and those of compounds 10aa and 14a form an isotypic pair. All structures have Z' = 1. The gold(III) centres show square-planar coordination geometry and the chalcogenide atoms show approximately tetra-hedral angles (except for the very wide angle in 12a, probably associated with the bulky t-butyl groups). The bond lengths at the gold atoms are lengthened with respect to the known gold(I) derivatives, and demonstrate a considerable trans influence of S and Se donor atoms on a trans Au-Cl bond. Each compound with an isopropyl group shows a short intra-molecular contact of the type C-Hmethine⋯Xcis; these may be regarded as intra-molecular 'weak' hydrogen bonds, and they determine the orientation of the AuX 3 groups. The mol-ecular packing is analysed in terms of various short contacts such as weak hydrogen bonds C-H⋯X and contacts between the heavier atoms, such as X⋯X (9a, 10aa, 11aa, 15aa and 9b), S⋯S (10aa, 11a and 12a) and S⋯Cl (10a). The packing of the polymorphs 10a and 10aa is thus quite different. The solvent mol-ecules take part in C-H⋯Cl hydrogen bonds; for 15aa, a disordered solvent region at z ≃ 0 is observed. Structure 13b involves unusual inversion-symmetric dimers with Se⋯Au and Se⋯Br contacts, further connected by Br⋯Br contacts.

Computational Structural Assessment on the Stereochemistry of the Transition Metal Complex Formed by a Naphthalene-1,4-dione Based Ligand with Divalent Nickel

The purpose of this paper is elucidating the stereochemistry of a complex obtained by coordinating to divalent nickel a naphthalene-1,4-dione based chemical compound, namely N-(3-mercapto-naphthalene-1,4-dione-2-yl)nicotinamide. As this particular transition metal ion may lead to different coordination geometries and also tacking into account the fact that the organic ligand contains six heteroatoms, it seem to be worth clarifying denticity of the ligand, the coordination geometry (including stereoisomerism) and, of course, what are the atoms involved into the coordination process. The study has been conducted by computational means, followed by quantum-chemical calculations and comparative interpretation of the UV-Vis spectra of both the ligand and the complex compound, in order to find out in which case the structural assessment is consistent with the electronic transitions exhibited whithin the spectra, i.e. which of the several theoretical coordination posibilities is the actual one. This investigation leads to the conclusion that the organic compound acts as a bidentate ligand and, moreover, the complex compound has a square-planar coordination geometry, the two heteroatoms through which the coordination is realized being the sulfur atom and the nitrogen atom directly bonded to the naphthalene-1,4-dione heterocycle. This is an important achievement, as the properties of the complex compound � including its biologic activity - are obviously related to the coordination manner.

(4-Butyl-1-ethyl-1,2,4-triazol-5-yl-idene)[(1,2,5,6-η)-cyclo-octa-1,5-diene](tri-phenyl-phosphane)rhodium(I) tetra-fluorido-borate.

In the title triazole-based N-heterocyclic carbene rhodium(I) cationic complex with a tetra-fluorido-borate counter-anion, [Rh(C8H12)(C8H15N3)(C18H15P)]BF4, which crystallizes with two cations and two anions in the asymmetric unit, the Rh center has a distorted square-planar coordination geometry with expected bond distances. Several nonclassical C-H⋯F hydrogen-bonding inter-actions help to consolidate the packing. Two of the F atoms of one of the anions are disordered over adjacent sites in a 0.814 (4):0.186 (4) ratio.

Helicity control of a polyaromatic coordination capsule through stereoselective CH-π interactions.

Although square-planar ML4 units are essential building blocks for coordination cages and capsules, the non-covalent control of the chirality and helicity of the resultant nanostructures is quite difficult. Here we report the helicity control of an M2L4 polyaromatic capsule, formed from metal ions with square-planar coordination geometry and bent bispyridine ligands, through stereoselective CH-π interactions with monosaccharide derivatives. Thanks to host-guest CH-π multi-interactions, one molecule of various permethylated monosaccharides is quantitatively bound by the capsule in water (K a up to >108 M-1). In the polyaromatic cavity, among them, the selective binding of a β-glucose derivative (>80 : 20 ratio) is demonstrated from a mixture of the α/β-glucoses, through the equatorial-selective recognition of the anomeric (C1) group. A similar stereoselective binding is accomplished from an α/β-galactose mixture. Interestingly, single equatorial/axial configurations on the bound monosaccharides can regulate the helical conformation of the capsule in water, confirmed by CD, NMR, and theoretical analyses. An intense capsule-based Cotton effect is exclusively observed upon encapsulation of the permethylated α-glucose (>20-fold enhancement as compared to the β-glucose derivative), via the induction of a single-handed host helicity to a large extent. Inverse capsule helicity is induced by the binding of a β-galactose derivative under the same conditions.

Nickel(II) complexes with 14-membered bis-thiosemicarbazide and bis-isothiosemicarbazide ligands: synthesis, characterization and catalysis of oxygen evolution reaction.

Design and development of novel, low-cost and efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media is crucial for lowering the reaction overpotential and thus decreasing the energy input during the water electrolysis process. Herein, we present the synthesis of new 14-membered bis-thiosemicarbazide and bis-isothiosemicarbazide macrocycles and their nickel(II) complexes characterized by spectroscopic techniques (1H and 13C NMR, IR, UV-vis), electrospray ionization mass spectrometry, single crystal X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and cyclic voltammetry. Finally, the activity of nickel(II) complexes towards OER is reported. NiIILSEt delivered a current density of 10 mA cm-2 at the lowest overpotential of 350 mV with the lowest Tafel slope of 93 mV dec-1. The high performance of NiIILSEt might be attributed to its high surface area and thus abundant active sites with the observed low charge-transfer resistance enabling the effective current flow through the electrocatalyst. Square-planar coordination geometry and increment in Ni oxidation state are believed to favor its OER performance. Beside high activity towards OER, NiIILSEt demonstrated excellent long-term stability with continuous operation, advocating its possible application in commercial systems.

Copper(II) complexes with N,O-coordinating thiopseudoureas: syntheses, structures, and properties

Syntheses, characterization, and physical properties of two complexes of copper(II) having the general molecular formula [Cu(L n )2] (1 and 2) with benzyl-N′-(4-R-benzoyl)-N-(2,6-diisopropylphenyl)carbamimidothioates (HL n , where n = 1 and 2 for R = H and Cl, respectively) are reported. Both complexes were characterized by mass spectrometric, magnetic susceptibility, and various spectroscopic (IR, UV–Vis, and EPR) measurements. The molecular structures of 1 and 2 were established by single crystal X-ray crystallographic studies. In each complex, the bivalent metal center is in a near perfect square-planar trans-N2O2 coordination environment assembled by two bidentate six-membered chelate rings forming iminolate-O and azomethine-N donor (L n )− ligands. In the crystal lattice, the packing of 1 is according to the symmetry operations, while intermolecular π⋯π and C–H⋯π interactions assisted self-assembly of 2 leads to a two-dimensional sheet-like structure. Mass spectrometric and infrared and electronic spectroscopic data are in agreement with their molecular formulas and similar structures. The room temperature magnetic moments and EPR spectra of both complexes are consistent with the S = ½ ground state and the square-planar coordination geometry of the metal ion in each complex.

Cyclopalladated complexes with pincer-like ONC-donor N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines: Regioselective peri‑palladation of the 9-phenanthryl group

Two series of cyclopalladates [Pd(HL1–5)Cl] (1–5) and [Pd(L1–5)(PPh3)] (6–10) with the Schiff bases N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines (H2Ln, where n = 1–5 for R = H, Cl, OMe, NO2 and NMe2, respectively and 2 Hs represent the amide and the ortho or peri H-atom of the 9-phenanthryl group) are reported. All the complexes were characterized by mass spectrometric and spectroscopic (IR, UV–Vis and fluorescence) measurements. Molecular structures of two Schiff bases (H2L1 and H2L4) and three representative complexes from each series [Pd(HL1,3,5)Cl] (1, 3 and 5) and [Pd(L1,2,4)(PPh3)] (6, 7 and 9) were confirmed by single crystal X-ray crystallographic studies. In each of the two types of complexes (HLn)– or (Ln)2– acts as ONC-donor pincer-like ligand. In [Pd(HL1,3,5)Cl], the metal center is in square-planar ONCCl environment assembled by amide-O, azomethine-N and 9-phenanthryl peri‑C coordinating (HL1,3,5)– and the Cl-atom. On the other hand, in [Pd(L1,2,4)(PPh3)], (L1,2,4)2– coordinate through amidate-O, azomethine-N and 9-phenanthryl peri‑C and the P-atom of PPh3 satisfies the fourth coordination site to form a square-planar ONCP coordination geometry around the metal center. The mass spectrometric and infrared and electronic spectroscopic characteristics of all the complexes are complementary to their molecular structures. All the Schiff bases and the complexes are emissive in solution. Theoretical calculations were carried out with a representative complex to comprehend the regioselective peri‑palladation of the 9-phenanthryl fragment of the tridentate ligand.

Synthesis, characterization and antiproliferative activity of platinum(II) complexes with 3-(2-pyridyl)-N1,2-methyl-1,2,4-triazoles

The present work describes the synthesis, investigation and in vitro cytotoxicity of Pt(II) complexes with 3-(2-pyridyl)-N1-methyl-1,2,4-triazole (L1) and 3-(2-pyridyl)–N2-methyl-1,2,4-triazole (L2). The crystal structures of PtL1Cl2 and PtL2Cl2 were established using X-Ray analysis, which revealed the square-planar PtN2Cl2 coordination geometry for the central metal ion. High-resolution mass spectrometry (HRMS), as well as one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy showed stability of the investigated complexes in DMF solution, in contrast to DMSO, where species were shown to partially dissociate. The cytotoxicity of the investigated compounds was determined by the colorimetric MTT assay against two human cancer cell lines, including cisplatin-sensitive human ovarian adenocarcinoma A2780 cells (IC50 = 26 ± 5 and 6.1 ± 0.6 for PtL1Cl2 and PtL2Cl2 correspondingly) and their cisplatin-resistant A2780cis analogue (IC50 = 24 ± 2 and 20 ± 3 for PtL1Cl2 and PtL2Cl2 correspondingly).

Synthesis and structure of two novel trans-platinum complexes.

Here for the first time the synthesis and characterization of two new trans-platinum complexes, trans-[PtCl2{HN=C(OH)C6H5}2] (compound 1) and trans-[PtCl4(NH3){HN=C(OH)tBu}] (compound 2) [with tBu = C(CH3)3] are described. The structures have been characterized using nuclear magnetic resonance spectroscopy and X-ray single-crystal diffraction. In compound 1 the platinum cation, at the inversion center, is in the expected square-planar coordination geometry. It is coordinated to two chloride anions, trans to each other, and two nitrogen atoms from the benzamide ligands. The van der Waals interactions between the molecules produce extended two-dimensional layers that are linked into a three-dimensional structure through π...π intermolecular interactions. In compound 2 the platinum cation is octahedrally coordinated by four chloride anions and two nitrogen atoms from the pivalamide and ammine ligands, in trans configuration. The molecular packing is governed by intermolecular hydrogen bonds and van der Waals interactions.

Crystal structure of bis-[4-(all-yloxy)-N'-(but-2-en-1-yl-idene)benzohydrazidato]nickel(II).

In the title complex, [Ni(C14H15N2O2)2], the nickel(II) atom exhibits a square-planar coordination geometry, being coordinated by two negatively charged N,O chelating ligands in a trans configuration, with the metal located on a crystallographic center of symmetry. The X-ray structural characterization showed the complex to be disordered over two orientations with refined occupancies of 0.898 (2) and 0.102 (2). The whole mol-ecule is close to planar, the five- and six-membered rings subtending a dihedral angle of 7.5 (2)°. The crystal packing is supported by C-H⋯π and C-H⋯O inter-actions that form a di-periodic layered network.

Discovery of Polythioplatinate(II) [Pt3S2(SO3)6]10- and Study of Its Solution and Catalytic Properties.

We have discovered the first polythioplatinate(II), [PtII3S2(SO3)6]10- (1), which was synthesized in aqueous basic medium (pH 11) by hydrothermal heating at 150 °C. Polyanion 1 comprises a discrete, triangular assembly of three Pt2+ ions linked by two μ3-sulfido ligands, and their square-planar coordination geometry is completed by two terminal S-bound sulfito ligands. Polyanion 1 was isolated as a hydrated sodium salt, Na10[PtII3(μ3-S)2(SO3)6]·22H2O (Na-1), which was characterized in the solid state by single-crystal X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectra, and elemental analysis, in solution by 195Pt NMR and atomic absorption spectroscopy, and in the gas phase by electrospray ionization mass spectrometry. Density functional theory calculations were performed, and the 195Pt NMR chemical shifts of 1 were computed theoretically and shown to match well with the experimental data. Furthermore, the discrete title polyanion 1 was immobilized on mesoporous SBA-15 support and used as a precatalyst for the hydrogenation of o-xylene.

Nonaromatic Organonickel(II) Phototheranostics.

Earth-abundant metal-based theranostics, agents that integrate diagnostic and therapeutic functions within the same molecule, may hold the key to the development of low-cost personalized medicines. Here, we report a set of O-linked nonaromatic benzitripyrrin (C^N^N^N) macrocyclic organonickel(II) complexes, Ni-1-4, containing strong σ-donating M-C bonds. Complexes Ni-1-4 are characterized by a square-planar coordination geometry as inferred from the structural studies of Ni-1. They integrate photothermal therapy, photothermal imaging, and photoacoustic imaging (PAI) within one system. This makes them attractive as potential phototheranostics. Relative to traditional Ni(II) porphyrins, such as F20TPP (tetrapentafluorophenylporphyrin), the lowest energy absorption of Ni-1 is shifted into the near infrared region, presumably as a consequence of Ni-C bonding. Ultrafast transient absorption spectroscopy combined with theoretical calculations revealed that, upon photoexcitation, a higher population of ligand-centered and 3MLCT states is seen in Ni-1 relative to NiTPBP (TPBP = 6,11,16,21-tetraphenylbenziporphyrin). Encapsulating Ni-1 in 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG2000) afforded nanoparticles, Ni-1@DSPE, displaying red-shifted absorption features, as well as good photothermal conversion efficiency (∼45%) in aqueous media. Proof-of-principle experiments involving thrombus treatment were carried out both in vitro and in vivo. It was found that Ni-1@DSPE in combination with 785 nm photo-irradiation for 3 min (0.3 W/cm2) proved successful in removing blood clots from a mouse thrombus model as monitored by photoacoustic imaging (PAI). The present work highlights the promise of organonickel(II) complexes as potential theranostics and the benefits that can accrue from manipulating the excited-state features of early transition-metal complexes via, for example, interrupting π-conjugation pathways.

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Photolytic Activation of Late-Transition-Metal–Carbon Bonds and Their Reactivity toward Oxygen

The photolytic activation of palladium(II) and platinum(II) complexes [M(BPI)(R)] (R = alkyl, aryl) featuring the 1,3-bis(2-pyridylimino)isoindole (BPI) ligand has been investigated in various solvents. In the absence of oxygen, the formation of chloro complexes [M(BPI)Cl] is observed in chlorinated solvents, most likely due to the photolytic degradation of the solvent and formation of HCl. The reactivity of the complexes toward oxygen has been studied both experimentally and computationally. Excitation by UV irradiation (365 nm) of the metal complexes [Pt(BPI)Me] and [Pd(BPI)Me] leads to distortion of the square-planar coordination geometry in the excited triplet state and a change in the electronic structure of the complexes that allows the interaction with oxygen. TD-DFT computational studies suggest that, in the case of palladium, the Pd(III) superoxide intermediate [Pd(BPI)(κ1-O2)Me] is formed and, in the case of platinum, the Pt(IV) peroxide intermediate [Pt(BPI)(κ2-O2)Me]. For alkyl complexes where metal–carbon bonds are sufficiently weak, the photoactivation leads to the insertion of oxygen into the metal–carbon bond to generate alkylperoxo complexes: for example [Pd(BPI)OOMe], which has been isolated and structurally characterized. For stronger M–C(aryl) bonds, the reaction of [Pt(BPI)Ph] with O2 and light results in a Pt(IV) complex, tentatively assigned as the peroxo complex [Pt(BPI)(κ2-O2)Ph], which in chlorinated solvents reacts further to give [Pt(BPI)Cl2Ph], which has been isolated and characterized by scXRD. In addition to the facilitation of oxygen insertion reactions, UV irradiation can also affect the reactivity of other components in the reaction mixture, such as the solvent or other reaction products, which can result in further reactions. Labeling studies using [Pt(BPI)(CD3)] in chloroform have shown that photolytic reactions with oxygen involve degradation of the solvent.

Bis(pyridine-2-carboxyl-ato-κ2 N,O)copper(II)]-benzene-1,3,5-tri-carb-oxy-lic acid-water (1/2/2).

In the title complex, [Cu(C6H4O2N)2]·2C9H6O6·2H2O, the Cu2+ ion lies on a center of inversion and coordinates with symmetry related pyridine nitro-gen and carboxyl oxygen atoms from two pyridine-2-carb-oxy-lic acid anions, giving rise to a square-planar coordination geometry. There are weak axial bonds between Cu and an O atom of a symmetry-related trimesic acid moieties [Cu⋯O = 2.837 (2) Å] The Cu⋯O weak inter-actions and hydrogen bonds stabilize the whole structure.

(Nitrato-κO)(2,2':6',2''-terpyridine-κ3 N,N',N'')palladium(II) nitrate.

The title complex, [Pd(NO3)(C15H11N3)]NO3, comprises a cationic PdII complex and a nitrate anion. In the complex, the PdII cation is four-coordinated in a distorted square-planar coordination geometry defined by the three N atoms of the tridentate 2,2':6',2''-terpyridine ligand and one O atom from the NO3 - anion. In the crystal, the complex mol-ecules are stacked in columns along the a axis being connected by π-π stacking [closest inter-centroid separation between pyridyl rings = 3.878 (3) Å]. The connections between columns and anions to sustain a three-dimensional architecture are C-H⋯O hydrogen bonds.

{4,4'-Di-bromo-2,2'-[cyclo-hexane-1,2-diylbis(nitrilo-methanylyl-idene)]diphenolato-κ4 O,N,N',O'}nickel(II).

In the title compound, [Ni(C20H18Br2N2O2)], the NiII ion is four-coordinated in a slightly distorted square-planar coordination geometry defined by two N atoms and two O atoms of the tetra-dentate dianionic 4,4'-di-bromo-2,2'-[cyclo-hexane-1,2-diylbis(nitrilo-methanylyl-idene)]diphenolato ligand. Pairs of complex mol-ecules are assembled by inter-molecular C-H⋯O hydrogen bonds with d(C⋯O) = 3.247 (4) Å.

A Type of Structurally Adaptable Aromatic Spiroketal Based Chiral Diphosphine Ligands in Asymmetric Catalysis.

ConspectusWhile spectacular successes have been achieved in homogeneous catalysis with the use of achiral diphosphine ligands featuring a wide natural bite angle, such as XantPhos, chiral diphosphines that can induce a large P-M-P bite angle in their transition metal complexes are conspicuously less explored in asymmetric catalysis, probably due to the challenges in the identification and efficient construction of a suitable chiral backbone. In the past decade, a highly efficient synthesis of chiral aromatic spiroketals and the corresponding diphosphine ligands (SKPs) has been developed in this group.Based on a one-pot catalytic tandem double asymmetric hydrogenation-spiroketalization ring-closure reaction sequence, these SKP ligands featuring an extraordinarily long P···P distance and a flexible backbone have been readily prepared in large scale. Remarkably versatile coordination modes have been found in the complexes of SKP with some catalysis-relevant transition metals, for example, Pd, Cu, Au, and Rh. Whereas SKP enforces an unusually large bite angle in [Pd(SKP)Cl2] and [Cu(SKP)Cl] complexes (160.1° and 132.8°, respectively), it also allows for a bimetallic Au-Au interaction (3.254 Å) in the complex of [Au2(SKP)Cl2] or a square-planar coordination geometry for the [Rh(SKP)(cod)]SbF6 complex. Such an adaptable nature of SKP ligands for transition metal coordination has profound consequences in homogeneous asymmetric catalysis, as demonstrated by their unique performance in several types of catalytic asymmetric reactions. One of the most exciting examples is SKP/Pd-catalyzed asymmetric allylic amination of Morita-Baylis-Hillman (MBH) adducts, in which SKP/Pd complexes demonstrated excellent control of regio- and enantioselectivities and exhibited exceptionally high efficiency (with a TON up to 4750) in the catalysis. SKP ligands have also found a diversity of successful applications in Cu-, Au-, or Rh-catalyzed asymmetric reactions, further attesting their wide utilities in asymmetric catalysis. Overall, this class of readily accessible SKP ligands featuring a chiral aromatic spiroketal skeleton have demonstrated unique adaptable structures in a variety of transition metal complexes and provided outstanding performance in some difficult asymmetric transformations. The works delineated herein would be expected to stimulate further research efforts on the application of this type of chiral ligand and to provide useful clues in the design of new chiral diphosphine ligands with adaptable bite angles for transition metal catalyzed asymmetric reactions.