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The crystal structure of the cis isomer of cis-bis(L-DOPA-κ2 N,O)copper(II) monohydrate (L-DOPA is 3,4-dihydroxy-L-phenylalanine) (CuLD), [Cu(C9H10NO4)2]·H2O, is a singular example of a structurally characterized, homoleptic, crystalline metal L-DOPA complex. CuLD crystallizes in the space group P21, with Z′ = 2. The two independent molecules are square planar, and are interconnected by a linear hydrogen-bonded chain containing 12 independent hydrogen bonds. The copper ions in both molecules have weak apical intermolecular Cu...O interactions [2.739 (2) and 2.973 (2) Å] with catechol –OH groups. A survey of the Cambridge Structural Database suggested that cis and trans isomers of Cu(NH2–C–CO2)2 amino acid complexes are equally likely to occur. 12 strong O—H...O and N—H...O hydrogen bonds stabilize an unusual linear arrangement of the Cu complexes. The Cu...Cu′ distances along the chain are nearly equal [5.0739 (3) and 5.1107 (3) Å] and the Cu...Cu′...Cu angles are nearly linear [176.75 (1)°]. The MATCH procedure available in the Oxford University Crystals for Windows package was used to carry out a detailed analysis of the relationship between the two independent molecules. MATCH has some particular advantages in studying the details of pseudosymmetry, which include: (i) no atomic-order requirements; (ii) the pseudosymmetry matrix is readily available, which allows quick insight into the symmetry elements involved and their location; and (iii) the differences between molecular centroids, as well as between all atomic positions and torsion angles, are listed. A tutorial presentation is designed to attract new users to the technique. In the present case, a search for a pseudosymmetric relationship between the two independent molecules showed that they are related by a pseudo-42 axis along the crystallographic c direction. A detailed analysis shows that the pseudo-42 symmetry is disrupted by torsions about the CH2—C(ipso) bonds, and that there is no supergroup that can be used to describe the crystal structure.

While Δ9-tetrahydrocannabinolic acid A (THCA-A) has been reported to be difficult to crystallize and/or amorphous, we have obtained THCA-A in a pure crystalline form by extraction of marijuana and selective fractionation with liquid CO2. THCA-A (systematic name: 1-hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]isochromene-2-carboxylic acid, C22H30O4) crystallizes in the orthorhombic space group P212121, with Z = 8 and Z′ = 2. The two independent molecules are related by a pseudo-twofold axis centered between the two –CO2H groups, but the conformations of the two –C5H11 chains are quite different (tgt and ttg; t is trans and g is gauche). The carboxylate groups form an intermolecular R 2 2(8) hydrogen-bonded ring; the two C2O2 carboxylate planes are twisted out of the planes of the attached arene rings in opposite directions by 13.59 (8) and 18.92 (8)°, respectively, with a resultant interplanar angle of 28.89 (8)°. Each molecule also has an intramolecular S(6) hydrogen-bond motif between the ortho –OH group and the dihydropyran-ring O atom. Other conformational aspects of the two independent molecules are quite similar to those found in the previously determined structure of THCA-B. THCA-A has shown promise in a number of medical applications. Demonstration of the crystallinity and details of the crystal structure are expected to provide a standard point of departure for chemical and medical experiments.

γ-Irradiation of crystalline hexaaquamagnesium trans-2-butenoate dihydrate affords rel-(3S,4R)-1-hexene-3,4-dicarboxylate by a single-crystal-to-single-crystal reaction. The reaction proceeds by a ...

Solid solutions of aripiprazole (APZ) and its active metabolite, dehydro-aripiprazole (dAPZ), have been prepared as free form (neat or nonsolvated), hydrated, or alcohol- solvated modifications wit...

A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multielectron redox processes that are both metal- and ligand-centered. Reduction of (PPClP)CoCl2 (1) with excess magnesium affords the CoICoI N-heterocyclic phosphido (NHP-)-bridged symmetric dimer [(μ-PPP)Co]2 (2). Two-electron oxidation of 2 with FcPF6 generates an asymmetrically bridged dication [(μ-PPP)Co]2[PF6]2 (3) in which the oxidation has occurred in a delocalized fashion throughout the Co2P2 core. In contrast, [(μ-PPP)Co]2+ (5), which can be generated either by one-electron oxidation of 2 with FcPF6 or comportionation of 2 and 3, features an asymmetric geometry and localized mixed valence. Treatment of 1 with the milder reductants CoCp2 and KBEt3H does not lead to formation of 2, 3, or 5 but instead generates dimeric species [(PPP)CoCl]2 (6) and [(PPP)CoH]2 (7). Unlike 2-5, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex 6 and 7 are connected solely by NHP- ligands that bridge the two (PPP)Co fragments.

Enynes are important synthetic intermediates that are also found in a variety of natural products and other biologically relevant molecules. The most atom economical synthetic route to enynes is via the direct coupling of readily available terminal alkyne precursors. Towards this goal, we demonstrate the formation of 1,3-enynes from terminal alkynes facilitated by a reduced ZrIV/Co-I heterobimetallic complex. An intermediate is trapped as a tBuNC adduct, revealing that bimetallic activation of the terminal C-H bond of the alkyne is an essential mechanistic step.

The crystal structures of potassium acrylate and related compounds studied by the group of Herbert Morawetz (1915-2017) have remained unknown for 60 years. 60Co γ-irradiation of potassium acrylate, the most reactive of all materials studied, affords high yields of polyacrylate, with molecular weights in the range 120,000 – 400,000. At the present time, the only alkali metal salts of acrylic and methacrylic acid whose structures appear in the Cambridge Structural Database are those of lithium. We report five new crystal structures: potassium acrylate (1), potassium methacrylate (2), potassium hydrogen dimethacrylate (3), rubidium hydrogen dimethacrylate (4), and sodium dihydrogen trimethacrylate (5). The discussion focuses on metal coordination, proposed reaction pathways for radical polymerization in the solid state, and possible reasons for differences in acrylate vs. methacrylate reactivity.

Oxygen reduction is a critical half reaction in renewable fuel cell development and a key step in the development of aerobic oxidation reactions. Herein, we report rapid two-electron O2 reduction by a d0 ZrIV center with an appended redox-active Co-I site serving as an electron reservoir. The early/late heterobimetallic Zr/Co complex (THF)Zr(MesNP iPr2)3CoCN tBu (1) reacts readily with O2 and O atom transfer reagents to generate reactive oxygenated species including terminal peroxo and oxo complexes, (O2)Zr(MesNP iPr2)3CoCN tBu (2) and O≡Zr(MesNP iPr2)3CoCN tBu (3). The bimetallic Zr/Co complex provides a new cooperative synthetic pathway to promote multielectron redox processes such as oxygen reduction, with each metal playing a distinct role as a substrate binding site or redox mediator.

Metal-ligand cooperation has proven to be a viable concept for σ bond activation and catalysis, however there are few examples involving phosphorus as an active participant in bond cleavage. The reactivity of E-H bonds (E = S, O) across a metal-phosphorus bond of a cobalt(i) center ligated by a tridenate N-heterocyclic phosphido (NHP-) ligand with diphosphine sidearms, (PPP)-, has been explored. Addition of PhOH to (PPP)CoPMe3 (1) cleanly affords (PPOPhP)Co(H)PMe3 (2), in which the O-H bond was heterolytically cleaved across the M-PNHP bond. Addition of PhSH to 1 first generates (PPHP)Co(SPh)PMe3 (3), which undergoes an intermolecular rearrangement to generate (PPSPhP)Co(H)PMe3 (4) as the thermodynamic product. A comparison with a related platinum(ii) system reveals the subtle effects that variations in metal intrinsic properties can have on metal-ligand bifunctional σ bond activation processes.

Although l-DOPA is a major drug that has been used for more than 50 years to treat the motor symptoms of Parkinson’s disease, the Cambridge Structural Database contains only two structures in which it is coordinated to a metal. Why are there not more? The new structure is also notable for an approximate 42 axis.

While Δ

A one-pot synthetic procedure for a series of bimetallic Nb/M complexes, Cl–Nb(iPrNPPh2)3M–X (M = Fe (2), Ni (4), Cu (5)), is described. A similar procedure aimed at synthesizing a Nb/Co analogue instead affords iPrN═Nb(iPrNPPh2)2(μ-PPh2)Co–I (3) through cleavage of one phosphinoamide P–N bond under reducing conditions. Complexes 4 and 5 are found to have short Nb-M distances, corresponding to unusual metal–metal bonds between Nb and these first row transition metals. For comparison, a series of heterobimetallic O≡Nb(iPrNPPh2)3M–X complexes (M = Fe (7), Co (8), Ni (9), Cu (10)) was synthesized. In these complexes, the NbV center is engaged in sufficient π-bonding to the terminal oxo ligand to remove the driving force for direct metal–metal interactions. A comparison of the cyclic voltammograms of 2 and 4–10 reveals that the presence of a second metal shifts the redox potentials of both Nb and the late metal center anodically, even when direct metal–metal interactions are not present.

The phase behavior and characterization of two forms of naltrexone hydrochloride dihydrate are presented. A metastable form was isolated first in the solid state under kinetically controlled conditions, namely dehydration of a higher hydrate followed by exposure to ∼38% relative humidity. The second, more thermodynamically stable polymorph was isolated from an aqueous slurry at an elevated temperature. The phase transition boundaries between naltrexone hydrochloride anhydrate and the metastable hydrate species are established through a combination of slurry and moisture sorption experiments to provide a detailed mechanistic understanding of the hydration/dehydration behavior.

Carboxylic acid-functionalized Pd and Pt PNNNP pincer complexes were used for the assembly of two porous Zr metal-organic frameworks (MOFs), 2-PdX and 2-PtX. Powder X-ray diffraction analysis shows that the new MOFs adopt cubic framework structures similar to the previously reported Zr6O4(OH)4[(POCOP)PdX]3, [POCOP = 2,6-(OPAr2)2C6H3); Ar = p-C6H4CO2-, X = Cl-, I-] (1-PdX). Elemental analysis and spectroscopic characterization indicate the presence of missing linker defects, and 2-PdX and 2-PtX were formulated as Zr6O4(OH)4(OAc)2.4[M(PNNNP)X]2.4 [M = Pd, Pt; PNNNP = 2,6-(HNPAr2)2C5H3N; Ar = p-C6H4CO2-; X = Cl-, I-]. Postsynthetic halide ligand exchange reactions were carried out by treating 2-PdX with Ag(O3SCF3) or NaI followed by PhI(O2CCF3)2. The latter strategy proved to be more effective at activating the MOF for the catalytic intramolecular hydroamination of an o-substituted alkynyl aniline, underscoring the advantage of using halide exchange reagents that produce soluble byproducts.

Addition of H2 across the cobalt-phosphorus bond of (PPP)CoPMe3 (3) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N-heterocyclic phosphido (NHP- ) donor. The chlorophosphine CoII complex (PPCl P)CoCl2 (2) can be generated through coordination of the chlorophosphine ligand (PPCl P, 1) to CoCl2 . Subsequent reduction of 2 with KC8 in the presence of PMe3 generates (PPP)CoPMe3 (3), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H2 to complex 3 cleanly affords (PPH P)Co(H)PMe3 (4), in which H2 has ultimately been added across the metal-phosphorus bond. Complex 4 was characterized spectroscopically and using computational methods to predict its geometry.

A straightforward procedure is outlined for prediction of the complete three-dimensional coordinate set for a highly disordered phase. For a mother and daughter phase, where one of the pair has an “unsolvable” structure, one needs only to (a) establish the topotaxy using previously published techniques, (b) obtain the topotactic transformation matrix, φ, between the ordered and highly disordered phase, and (c) apply the transpose of φ–1 to obtain a trial set of coordinates for refinement using the reflection data set of the highly disordered phase. For the inclusion compound [Fe(η-C5H5)]·3(NH2)2CS (1), which contains highly disordered ferrocene molecules above 160 K (polymorph 1_I), we found a more ordered structure at low temperature. At 135 K (polymorph 1_II), two ferrocene moieties are present in the thiourea channel in an approximately 1:1 ratio. One is nearly orthogonal (87.0°) to the channel axis, while the other is tipped 16.2° from that direction. Using steps (a–c) outlined above, a trial structur...

The reactivity of the reduced Zr/Co and Ti/Co complexes (THF)Zr(MesNPiPr2)3CoN2 (1, Mes = 2,4,6-trimethylphenyl) and (THF)Ti(XylNPiPr2)3CoN2 (7, Xyl = 3,5-dimethylphenyl) toward diaryl ketones is explored in an effort to gain mechanistic insight into C═O bond cleavage processes. Complex 1 reacts with 4,4′-dimethoxybenzophenone to generate ((p-OMeC6H4)2CO)Zr(MesNPiPr2)3CoN2 (2), which exists as a mixture of valence tautomers in solution that interconvert via electron transfer from Co–I to the Zr-bound ketone in 2S to form a Zr-bound ketyl radical in 2T. The geometry of 2 in the solid state is most consistent with the singlet ketone adduct tautomer 2S. Upon removal of the Co-bound N2 under vacuum, complex 2 cleanly coverts to the μ-oxo carbene product (η2-MesNPiPr2)Zr(MesNPiPr2)2(μ-O)Co═C(C6H4p-OMe)2 (5) at room temperature in solution. A diamagnetic intermediate, tentatively assigned as ketone-bridged species (η2-MesNPiPr2)Zr(MesNPiPr2)2Co(μ2,η1η2-OC(p-OMeC6H4)2) (6), is observed spectroscopically during t...

Heterometallic multiple bonds between niobium and other transition metals have not been reported to date, likely owing to the highly reactive nature of low-valent niobium centers. Herein, a C3-symmetric tris(phosphinoamide) ligand framework is used to construct a Nb/Fe heterobimetallic complex Cl–Nb(iPrNPPh2)3Fe−Br (2), which features a Fe→Nb dative bond with a metal–metal distance of 2.4269(4) A. Reduction of 2 in the presence of PMe3 affords Nb(iPrNPPh2)3Fe–PMe3 (6), a compound with an unusual trigonal pyramidal geometry at a NbIII center, a Nb≡Fe triple bond, and the shortest bond distance (2.1446(8) A) ever reported between Nb and any other transition metal. Complex 6 is thermally unstable and degrades via P–N bond cleavage to form a NbV═NR imide complex, iPrN═Nb(iPrNPPh2)3Fe−PMe3 (9). The heterobimetallic complexes iPrN═Nb(iPrNPPh2)3Fe−Br (8) and 9 are independently synthesized, revealing that the strongly π-bonding imido functionality prevents significant metal–metal interactions. The 57Fe Mossbauer...

Treatment of the N-heterocyclic chlorophosphine precursor (PPP)Cl (1) with two equivalents of nickelocene (NiCp2) affords the phosphorus-bridged dimer [(μ-PPP)Ni2Cp2]Cl (2). In contrast, an equimolar mixture of 1 and NiCp2 in the presence of PPh3 generates a different product, (PP(C5H5)P)NiCl2 (3), in which a cyclopentadienyl anion has migrated to the N-heterocyclic phosphenium center. The phosphorus-bound Cp ring in complex 3 has undergone a [1,5]-hydride shift to afford a vinylic C5H5− ring, and can be subsequently deprotonated to produce [(PP(C5H4)P)NiCl] (4).

The effects of Li+ and Mg2+ on the electrochemical behaviour and photoreduction of N,N′-bis(2,6-diisopropylphenyl)naphthalene diimide (Dipp2NDI) have been investigated using cyclic voltammetry and UV-vis spectroscopy. Strong cation–anion interactions between Li+ or Mg2+ and [Dipp2NDI]2− result in solvent-dependent anodic shifts of the NDI˙−/2− redox couple. In organic solvents of moderate dielectric constant and donor ability, the two, one-electron redox processes typically observed for Dipp2NDI merge into a single, two-electron process. This strong metal cation effect has been leveraged for the photoreduction of Dipp2NDI to [Dipp2NDI]2−via a disproportionation process. Chemical reduction of Dipp2NDI with iPrMgCl has allowed the isolation of Mg2+ complexes of [Dipp2NDI]2−. Single crystal X-ray diffraction was used to determine the structure of a dimeric complex, [(Dipp2NDI)Mg2(THF)3]2, that features strong coordination of Mg2+ by the oxygen atoms of the reduced NDI.

Oxygen reduction is a critical half reaction in renewable fuel cell development and a key step in the development of aerobic oxidation reactions. Herein, we report rapid two-electron O

To understand the metal–metal bonding and conformational flexibility of first-row transition metal heterobimetallic complexes, a series of heterobimetallic Ti/M and V/M complexes (M = Fe, Co, Ni, and Cu) have been investigated. The titanium tris(phosphinoamide) precursors ClTi(XylNPiPr2)3 (1) and Ti(XylNPiPr2)3 (2) have been used to synthesize Ti/Fe (3), Ti/Ni (4, 4THF), and Ti/Cu (5) heterobimetallic complexes. A series of V/M (M = Fe (7), Co (8), Ni (9), and Cu (10)) complexes have been generated starting from the vanadium tris(phosphinoamide) precursor V(XylNPiPr2)3 (6). The new heterobimetallic complexes were characterized and studied by NMR spectroscopy, X-ray crystallography, electron paramagnetic resonance, and Mossbauer spectroscopy, where applicable, and computational methods (DFT). Compounds 3, 4THF, 7, and 8 are C3-symmetric with three bridging phosphinoamide ligands, while compounds 9 and 10 adopt an asymmetric geometry with two bridging phosphinoamides and one phosphinoamide ligand bound η2 t...

The dinuclear gold(II,II) and gold(III,III) complexes [Au2(μ-PY)2(MeCN)2]OTf2 (2-OTf2) and [Au2(μ-PY)2(μ-CH2)(MeCN)2]OTf2 (3-OTf2) (PY = [(CH2)2PPh2]−) have been synthesized and evaluated as Lewis acid catalysts for Mukaiyama addition and alkyne hydroamination reactions. 2-OTf2 and 3-OTf2 provide similar or improved catalytic activity for these reactions compared to the commonly used gold(I) Lewis acids Ph3PAuOTf and IPrAuOTf. The versatile Lewis acidity of 2-OTf2 was further demonstrated by its superior performance in a cascade reaction involving intramolecular hydroamination followed by intermolecular conjugate addition to generate a 2,3-substituted indole.

A chelating diphosphine ligand with a central N-heterocyclic phosphenium cation (NHP(+)) has been used to explore the coordination chemistry of NHPs with nickel. Treatment of the chlorophosphine precursor [PPP]Cl (1) with stoichiometric Ni(COD)2 affords (PPP)NiCl (8), which is best described as a Ni(II)/NHP(-) phosphido complex formed via oxidative addition of the P-Cl bond. In contrast, treating [PPP]Cl (1) with excess Ni(COD)2 results in a mixture of the trimetallic complex (PPP)2Ni3Cl2 (9) and the reduced NHP-bridged dimer [(PPP)Ni]2 (10). Compound 9 is found to be a Ni(II)Ni(II)Ni(0) complex in which the two NHP ligands act as bridging NHP(-) phosphidos, while complex 10 is a Ni(I)Ni(I) complex that is highly delocalized throughout the symmetric Ni2P2 core. In contrast, the reaction of [PPP][PF6] (11) with Ni(COD)2 affords an asymmetrically-bridged dication [(PPP)Ni]2[PF6]2 (12), which is found to contain two bridging NHP(+) cations bridging two Ni(0) centers. Comproportionation of 10 and 12 affords monocationic [(PPP)Ni]2[PF6] (13), completing the redox series. Nickel complexes 8-10 and 12 are largely similar to their Pd and Pt analogues, but a paramagnetic monocation such as 13 was not observed in the Pd and Pt case. Computational studies lend further insight into the electronic structure and bonding in complexes 8-10 and 12-13, and further support the potential redox non-innocent properties of NHP ligands.

Cinchona alkaloid-derived chiral catalysts represent one of the most widely applied classes of organocatalysts, which have been successfully utilized in the promotion of a wide variety of asymmetric reactions. Cinchona alkaloids exist in nature as pseudoenantiomers, which allow cinchona alkaloid-catalyzed reactions to provide high enantioselectivities and yields toward both enantiomers of interest in many reactions. On the other hand, the subtle structural difference between pseudoenantiomeric cinchona alkaloids could also lead to uneven efficiency that severely limits the applicability of some cinchona alkaloid-catalyzed reactions. We describe here the elucidation of the origin of and the consequent development of novel modified cinchona alkaloids to address such a problem in asymmetric imine umpolung reactions by cinchonium salts.

Carboxylic acid-functionalized Pd and Pt P

Treatment of the tris(phosphinoamide) titanium precursor ClTi(XylNP(i)Pr2)3 (1) with CoI2 leads to the heterobimetallic complex (η(2)-(i)Pr2PNXyl)Ti(XylNP(i)Pr2)2(μ-Cl)CoI (2). One-electron reduction of 2 affords (η(2)-(i)Pr2PNXyl)Ti(XylNP(i)Pr2)2CoI (3), which can be reduced by another electron under dinitrogen to generate the reduced diamagnetic complex (THF)Ti(XylNP(i)Pr2)3CoN2 (4). The removal of the dinitrogen ligand from 4 under vacuum affords (THF)Ti(XylNP(i)Pr2)3Co (5), which features a Ti-Co triple bond. Treatment of 4 with hydrazine or methyl hydrazine results in N-N bond cleavage and affords the new diamagnetic complexes (L)Ti(XylNP(i)Pr2)3CoN2 (L = NH3 (6), MeNH2 (7)). Complexes 4, 5, and 6 have been shown to catalyze the disproportionation of hydrazine into ammonia and dinitrogen gas through a mechanism involving a diazene intermediate.

A novel bidentate ligand featuring an N-heterocyclic phosphenium cation (NHP(+)) linked to a phosphine side arm is used to explore the coordination chemistry of NHP(+) ligands with nickel. Direct P-Cl bond cleavage from a chlorophosphine precursor [PP]-Cl (1) by Ni(COD)2 affords the asymmetric bimetallic complex [Cl2Ni(μ-PP)2Ni] (2) via a nonoxidative process. Abstraction of the halide with either NaBPh4 or K[B(C6F5)4] prior to metal coordination to form the free phosphenium ligand [PP](+) in situ, followed by coordination to Ni(COD)2, afforded the halide-free Ni(0) complexes [(PP)Ni(COD)] [B(C6F5)4] (4) and [(PP)Ni(COD)][BPh4] (5). Chloride abstraction from 1 is problematic in the presence of a PF6(-) counterion, however, as evident by the formation of [(PP)Ni(PP-F)][PF6] (3). The COD ligand in 5 can be readily displaced with PMe3 or PPh3 to afford [(PP)NiL2][BPh4] (L = PMe3 (6), PPh3 (7)). Complexes 2-7 feature planar geometries about the NHP(+) phosphorus atom and unusually short Ni-P distances, indicative of multiple bonding resulting from both P → Ni σ donation and Ni → P π backbonding. This bonding description is supported by theoretical studies using natural bond orbital analysis.

The reduced heterobimetallic Co/Zr complex N2Co(iPr2PNMes)3Zr(THF) (1) has been previously reported to react with the C═O bonds of CO2 and benzophenone to generate Zr/Co μ-oxo complexes OC-Co(iPr2PNMes)2(μ-O)Zr(iPr2PNMes) (1-CO2) and Ph2C═Co(iPr2PNMes)2(μ-O)Zr(iPr2PNMes) (1-Ph2CO), respectively. Herein, we report a similar reaction of 1 with pyridine-N-oxide to form an analogous complex (pyridine)Co(iPr2PNMes)2(μ-O)Zr(iPr2PNMes) (2) with a more labile ligand bound to cobalt. Much like 1-CO2 and 1-Ph2CO, compound 2 reacts with Ph3SiH via formation of a Si–O linkage to form (N2)(H)Co(iPr2PNMes)3ZrOSiPh3 (5). The dinitrogen ligand in 5 is weakly bound and can be readily removed in vacuo or displaced by other L-type ligands. This allows complex 5 to undergo insertion reactions with unsaturated substrates, including diphenyldiazomethane, CO2, benzonitrile, and phenylacetylene to give hydrazonato (Ph2C═NNH)Co(iPr2PNMes)3ZrOSiPh3 (7), formate (OC(H)O)Co(iPr2PNMes)3ZrOSiPh3 (8), ketimide (PhHC═N)Co(iPr2PNMes)3ZrO...

A simple procedure, with an available program, may readily be used to establish the three-dimensional relationships between a mother and daughter phase, where mother and daughter are either two different phases of a material or a reactant and product in a solid-state transformation. The only requirements are that (i) the process involves a crystal-to-crystal transformation, and (ii) the experiment must be carried out without changing the alignment of the mother crystal. Application of the method supports the inferred alignment of mother and daughter phases in the published structures of two polymorphs of 4-cyanopyridinium perchlorate monohydrate 1. A new low-temperature, monoclinic polymorph of ferrocenium tetrafluoroborate 2 is produced when the known orthorhombic polymorph is cooled from 173 to 120 K. The major features of the transformation include “conservative twinning” and a modulation of the structure along the crystallographic b direction upon cooling. Redetermination of the structure of the low-t...

This paper presents the synthesis and characterization of a series of pincer ligands and their Ni, Pd, Pt, and Rh complexes. The ligands under examination are based on a diarylamine which is modified either by two phosphino (-PR2) substituents in the ortho-positions (PNP ligands) or by a combination of a phosphino and an iminyl (-CH═NX) substituent (PNN ligands). The ligands can be broken down into three groups: (a) C2v-symmetric PNP ligands with identical side -PR2 donors, (b) Cs-symmetric PNP' ligands with different -PR2 side donors, and (c) PNN ligands containing a -P(i)Pr2 side donor. All of the ligands under study readily formed square-planar complexes of the types (PNZ)PdCl, (PNZ)Pd(OAc), and (PNZ)RhCO, where PNZ is the corresponding anionic tridentate pincer ligand. For select PNP ligands, (PNP)NiCl and (PNP)PtCl were also studied. The (PNZ)MCl complexes (M = Ni, Pd, Pt) underwent quasireversible oxidation in cyclic voltammetry experiments. Based on the close similarity of formal potentials for Ni, Pd, and Pt analogs, and based on the previous literature evidence, these oxidation events are ascribed primarily to the PNZ ligand, and the E1/2 values can be used to compare the ease of oxidation of different ligands. A (PNP)PdCl complex containing methoxy substituents para- to the central nitrogen underwent two quasireversible oxidations. Two mono-oxidized complexes were isolated and structurally characterized in comparison to their neutral analog, revealing minimal changes in the bond distances and angles. Several other neutral complexes were also structurally characterized. The carbonyl stretching frequency in (PNZ)RhCO complexes was used to gauge the donating ability of the various pincer ligands toward the metal. Comparison of E1/2 values for (PNZ)PdCl and νCO values for (PNZ)RhCO revealed that the two are not consistently correlated across all the studied ligands and can be tuned to different degrees through judicious ligand alteration.

Recent work has revealed substantial differences in the structure, spectroscopic properties, and reactivity of heterobimetallic Zr/Co complexes of the general form XZr(R′NPR2)3CoY (R′ = iPr, 2,4,6-trimethylphenyl, 3,5-dimethylphenyl; R = Ph, iPr; X, Y = halides or neutral donor ligands) as a function of nitrogen and phosphorus donor atom substituents. To probe the electronic differences between these ligands, a series of Mo(CO)5(R2PNHR′) complexes has been synthesized (R = Ph, R′ = iPr (2a); R = iPr, R′ = iPr (2b), 2,4,6-trimethylphenyl (2c), 3,5-dimethylphenyl (2d), 4-methylphenyl (2e), 4-trifluoromethylphenyl (2f), 4-methoxyphenyl (2g)). Thermolysis of Mo(CO)6 with the corresponding phosphinoamine ligands 1a–1g affords 2a–2g. The infrared carbonyl stretching frequencies of these complexes have been compared to probe the effects of phosphorus and nitrogen substituents on the electronic properties of the phosphinoamine ligands.

New carborane anions carrying one or three triflyloxy substituents are described. The mono-triflyloxy substituted carborane can be halogenated to give pentabromo and decachloro derivatives with preservation of the B-OTf linkage. The use of [HCB11Cl10OTf](-) as a weakly coordinating anion is demonstrated.

The chromium(III) tris(phosphinoamide) precursor Cr(iPrNPiPr2)3 (1) has been used to synthesize Cr/Rh and Cr/Ir heterobimetallic complexes. Treatment of [MCl(COD)]2 with 1 affords the open shell S = 3/2 complexes ClCr(μ-iPrNPiPr2)2M(η2-iPrNPiPr2) (M = Rh (2), Ir (3)). Instead of simple coordination of the late transition metal fragment to the C3-symmetric tris(phosphinoamide) binding pocket, the preference of RhI and IrI for a square planar environment leads to a chloride/amide ligand exchange process. Complexes 1–3 have been structurally characterized using X-ray crystallography, revealing short Cr–Rh and Cr–Ir distances (2.6095(3) A (2); 2.6064(4) A (3)) indicative of metal–metal bonds. A computational investigation of the electronic structures of 2 and 3 reveals substantial metal–metal orbital overlap, but the high spin nature of the CrIII center leads to population of metal–metal antibonding orbitals and relatively weak metal–metal bonding. The effects of the metal–metal interaction on the redox properties of the CrIII center are investigated using cyclic voltammetry.

A new polymorph of aripiprazole has been discovered, making it the most polymorphic drug to date with twelve reported anhydrous forms, and a record-breaking ninth solved crystal structure. The new form was induced by seeding with crystals of the active metabolite dehydro-aripiprazole.

Addition of H

Heterometallic multiple bonds between niobium and other transition metals have not been reported to date, likely owing to the highly reactive nature of low-valent niobium centers. Herein, a C

This manuscript describes the preparation of a new PN(H)SiO(H) pincer-type ligand that is based on the diarylamine backbone and links together phosphine, amine, and silanol donor sites. Treatment of PN(H)SiO(H) with Pd(acac)2, (COD)PdCl2, or Pd(OAc)2 resulted in the formation of (κ2-PNSiO(H))Pd(acac) (3), (κ2-PN(H)SiO(H))PdCl2 (4), and (κ3-PNSiO(H))PdOAc (5), in which the supporting ligand displays different degrees of coordination and protonation. In complex 5, the PNSiO(H) ligand functions as a tridentate phosphine-amido-silanol pincer ligand, with additional strong hydrogen bonding between the silanol OH and one of the oxygens of the Pd-bound acetate. Complex 5 cleanly exchanged acetate for a triflate upon treatment with Me3SiOTf, yielding (κ3-PNSiO(H))PdOTf (6). Analogous treatment with Me3SiCl did not lead cleanly to the expected (κ3-PNSiO(H))PdCl (7), but instead ultimately to (κ2-PN(H)SiO(SiMe3))PdCl2 (8). The dianionic PNSiO ligand was accessed by reactions of 5 with base in the presence of pyridine or PMe3 to give (κ3-PNSiO)Pd(py) (9) and (κ3-PNSiO)Pd(PMe3) (10), respectively. Solid-state structures of 5 and 9 were established by single-crystal X-ray diffractometry and revealed square-planar geometry about Pd with tridentate coordination of the pincer ligand.

The coordination chemistry of a diphosphine pincer ligand incorporating an N-heterocyclic phosphenium cation (PPP+) and its halophosphine precursors [PP(X)P] has been explored using copper(I) reagents. In contrast to the P–X bond cleavage observed when other low valent transition metals are used, simple coordination compounds [PP(X)P]CuY (X = Y = Cl (1); X = Cl, Y = I (2); X = Y = I (3)) are formed when halophosphine precursors are treated with CuY starting materials. Exposure of the N-heterocyclic iodophosphine complex 3 to THF results in ring-opening insertion to form the alkoxyphosphine complex [PP(O-CH2CH2CH2CH2-I)P]CuI (4). Since this reaction does not occur with the chlorophosphine compounds 1 and 2, it is proposed that iodide dissociation exposes the electrophilic metal-bound phosphenium cation to allow THF coordination and subsequent ring-opening. The electrophilicity of the N-heterocyclic phosphenium is also apparent when the halide-free ligand precursor [PPP][BPh4] is employed: CuCl reacts with [PPP][BPh4] to form [PP(Ph)P]CuCl (5), the product of phenyl group abstraction from [BPh4]−. A similar arylphosphine product [PP(Mes)P]CuCl (6, Mes = 2,4,6-trimethylphenyl) is obtained via transmetallation between [PP(Cl)P] and mesitylcopper(I). The isolation of complexes 4–6 provide indirect evidence for the formation of an electrophilic copper–phosphenium intermediate {[PPP]CuCl}+.

The chemical oxidation and subsequent group transfer activity of the unusual diiron imido complexes Fe((i)PrNPPh2)3Fe≡NR (R = tert-butyl ((t)Bu), 1; adamantyl, 2) was examined. Bulk chemical oxidation of 1 and 2 with Fc[PF6] (Fc = ferrocene) is accompanied by fluoride ion abstraction from PF6(-) by the iron center trans to the Fe≡NR functionality, forming F-Fe((i)PrNPPh2)3Fe≡NR ((i)Pr = isopropyl) (R = (t)Bu, 3; adamantyl, 4). Axial halide ligation in 3 and 4 significantly disrupts the Fe-Fe interaction in these complexes, as is evident by the0.3 Å increase in the intermetallic distance in 3 and 4 compared to 1 and 2. Mössbauer spectroscopy suggests that each of the two pseudotetrahedral iron centers in 3 and 4 is best described as Fe(III) and that one-electron oxidation has occurred at the tris(amido)-ligated iron center. The absence of electron delocalization across the Fe-Fe≡NR chain in 3 and 4 allows these complexes to readily react with CO and (t)BuNC to generate the Fe(III)Fe(I) complexes F-Fe((i)PrNPPh2)3Fe(CO)2 (5) and F-Fe((i)PrNPPh2)3Fe((t)BuNC)2 (6), respectively. Computational methods are utilized to better understand the electronic structure and reactivity of oxidized complexes 3 and 4.

Single-electron transfer from the ZrIVCo–I heterobimetallic complex (THF)Zr(MesNPiPr2)3Co-N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)Zr(MesNPiPr2)3Co-N2]2 (4) via coupling of two ketyl radicals. Thermolysis of 4 led to cleavage of the C═O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co═CPh2 carbene linkage (3). In this work monomeric ketyl radical complexes have been synthesized, and the reactivity of these compounds has been explored. The electronic preference for the formation of a ketyl radical complex or a coordination complex has been investigated computationally. Furthermore, thione substrates were allowed to react with 1, generating new complexes that bind the thione to the Co rather than undergoing single-electron transfer (12, 14). The preference of thiones to coordinate to Co can be overridden if the Co is ligated by CO, in which case a thioketyl radical complex forms (13) analogous to 4. The reaction between 1 and imines ...

A series of copper halide complexes have been prepared employing 2-pyridone as a ligand. The compounds [CuBr 2 (2-pyridone) 2 ] 2 ( 1 ), [CuCl 2 (2-pyridone) 2 ] 2 ( 2 ), [CuCl 2 (2-pyridone)] 2 ( 3 ), [CuCl 2 (2-pyridone) 3 ] ( 4 ), and [CuCl 2 ·2H 2 O] 2 [(2-pyridone) 2 ] ( 5 ) were prepared and their structures and magnetic properties studied. Compounds 1 and 2 are dimeric species with the Cu(II) ions bridged by a pair of O-atoms from 2-pyridone molecules. Compound 3 is also a dimer, but in this case bridged by a pair of chloride ions. Only compound 4 is monomeric with fairly well isolated copper(II) ions, while compound 5 is a coordination polymer with the Cu(II) ions linked into chains via pairs of bridging chloride ions. Analysis of the magnetic data reveals that 1 and 2 exhibit significant antiferromagnetic interactions, while 4 is very weakly antiferromagnetic. Compounds 3 and 5 show weak ferromagnetic interactions. Data for 1 and 2 were fit to the antiferromagnetic dimer model with a Curie–Weiss correction to account for interdimer interactions: 1 , J = −41.7(1) K, θ = −0.8(1) K; 2 , J = −38.2(1) K, θ = −0.7(1) K. Data for 3 were fit to the ferromagnetic dimer model with a Curie–Weiss correction for interdimer interactions:); 2 , J = 9.4(6), θ = −3.2(3). Interactions in both 4 and 5 were sufficiently weak that data were fit only to the Curie–Weiss expression resulting in θ -values of −0.50(7) and 0.58(4) K respectively.

By incorporating an N-heterocyclic phosphenium/phosphide (NHP) ligand into a chelating pincer ligand framework (PPP(+)/PPP(-)), we have elucidated several different and unprecedented binding modes of NHP ligands in homobimetallic, heterobimetallic, and trimetallic metal complexes. One-electron reduction of the previously reported (PPP)(-)/M(II) complexes (PPP)M-Cl (M = Pd (1), Pt (2)) results in clean formation of the symmetric homobimetallic M(I)/M(I) complexes [(μ-PPP)Pd]2 (5) and [(μ-PPP)Pt]2 (6). The tridentate NHP ligand has also been utilized as a bridging linker in the M/Co heterobimetallic compounds (OC)3Co(u-PPP)M(CO) (M = Pd (7), Pt (8)), synthesized via salt elimination from mixtures of 1 and 2 and Na[Co(CO)4]. Furthermore, an NHP-bridged trimetallic complex (PPP)2Pd3Cl2 (9) can be synthesized in a manner similar to precursor 1 (Pd(PPh3)4 + (PPP)Cl) via careful adjustment of reaction stoichiometry. Examination of the interatomic distances and angles in complexes 5-9, in tandem with density functional theory calculations have been used to evaluate and characterize the bonding interactions in these complexes.

The crystal structure of a fifth polymorph of malonic acid has been determined by single crystal X-ray diffraction. The unit cell parameters, crystal structure and calculated powder diffraction lines for the new polymorph (monoclinic, Z ′ = 3) are distinctly different from those of the reported forms. There are both similarities as well as differences in the arrangement of molecules in the crystal lattice in all the forms. The molecules, in all the polymorphs, interact through the formation of O–H⋯O hydrogen bonded dimers by –COOH group with significant differences between the forms within this packing pattern.

The reactivity of the reduced ZrIIICo0 heterobimetallic complex [(thf)Zr(MesNPiPr2)3CoN2] (1a) towards O–H, S–H, S–S, and O–O bonds has been investigated. Complex 1a reacts readily with PhOH, EtOH, and H2O to generate the one-electron-oxidized complexes [(RO)Zr(MesNPiPr2)3CoN2] [R = Et (2), Ph (3), H (4)]. In contrast, PhSH and PhS–SPh react by means of overall two-electron processes to form [(η2-MesNPiPr2)Zr(μ-SPh)(MesNPiPr2)2Co(SPh)] (5a). Addition of stoichiometric diethyl peroxide to 1a generates 2, but further equivalents lead to the two-electron oxidized product [(EtO)Zr(MesNPiPr2)3Co(OEt)] (6). More sterically hindered peroxides such as dicumyl peroxide or di-tert-butyl peroxide do not react with 1a under ambient conditions, but upon photolysis, di-tert-butyl peroxide reacts with 1a to form [(tBuO)Zr(MesNPiPr2)3CoN2] (7). These results imply that an inner-sphere electron-transfer process is occurring at the Zr site of 1a upon treatment with these chalcogen-based substrates, and a dissociative electron-transfer mechanism is proposed.