checkCIF validation ALERTS: what they mean and how to respond.

Authors of a paper that includes a new crystal-structure determination are expected to not only report the structural results of inter-est and their inter-pretation, but are also expected to archive in computer-readable CIF format the experimental data on which the crystal-structure analysis is based. Additionally, an IUCr/checkCIF validation report will be required for the review of a submitted paper. Such a validation report, automatically created from the deposited CIF file, lists as ALERTS not only potential errors or unusual findings, but also suggestions for improvement along with inter-esting information on the structure at hand. Major ALERTS for issues are expected to have been acted on already before the submission for publication or discussed in the associated paper and/or commented on in the CIF file. In addition, referees, readers and users of the data should be able to make their own judgment and inter-pretation of the underlying experimental data or perform their own calculations with the archived data. All the above is consistent with the FAIR (findable, accessible, inter-operable, and reusable) initiative [Helliwell (2019 ▸). Struct. Dyn. 6, 05430]. Validation can also be helpful for less experienced authors in pointing to and avoiding of crystal-structure determination and inter-pretation pitfalls. The IUCr web-based checkCIF server provides such a validation report, based on data uploaded in CIF format. Alternatively, a locally installable checkCIF version is available to be used iteratively during the structure-determination process. ALERTS come mostly as short single-line messages. There is also a short explanation of the ALERTS available through the IUCr web server or with the locally installed PLATON/checkCIF version. This paper provides additional background information on the checkCIF procedure and additional details for a number of ALERTS along with options for how to act on them.

PLATON SQUEEZE: a tool for the calculation of the disordered solvent contribution to the calculated structure factors.

The completion of a crystal structure determination is often hampered by the presence of embedded solvent molecules or ions that are seriously disordered. Their contribution to the calculated structure factors in the least-squares refinement of a crystal structure has to be included in some way. Traditionally, an atomistic solvent disorder model is attempted. Such an approach is generally to be preferred, but it does not always lead to a satisfactory result and may even be impossible in cases where channels in the structure are filled with continuous electron density. This paper documents the SQUEEZE method as an alternative means of addressing the solvent disorder issue. It conveniently interfaces with the 2014 version of the least-squares refinement program SHELXL [Sheldrick (2015). Acta Cryst. C71. In the press] and other refinement programs that accept externally provided fixed contributions to the calculated structure factors. The PLATON SQUEEZE tool calculates the solvent contribution to the structure factors by back-Fourier transformation of the electron density found in the solvent-accessible region of a phase-optimized difference electron-density map. The actual least-squares structure refinement is delegated to, for example, SHELXL. The current versions of PLATON SQUEEZE and SHELXL now address several of the unnecessary complications with the earlier implementation of the SQUEEZE procedure that were a necessity because least-squares refinement with the now superseded SHELXL97 program did not allow for the input of fixed externally provided contributions to the structure-factor calculation. It is no longer necessary to subtract the solvent contribution temporarily from the observed intensities to be able to use SHELXL for the least-squares refinement, since that program now accepts the solvent contribution from an external file (.fab file) if the ABIN instruction is used. In addition, many twinned structures containing disordered solvents are now also treatable by SQUEEZE. The details of a SQUEEZE calculation are now automatically included in the CIF archive file, along with the unmerged reflection data. The current implementation of the SQUEEZE procedure is described, and discussed and illustrated with three examples. Two of them are based on the reflection data of published structures and one on synthetic reflection data generated for a published structure.

Organometallic benzylidene anilines: donor-acceptor features in NCN-pincer Pt(ii) complexes with a 4-(E)-[(4-R-phenyl)imino]methyl substituent.

A series of organometallic 4,4'-substituted benzylidene aniline complexes 4-ClPt-3,5-(CH2NMe2)2C6H2CH[double bond, length as m-dash]NC6H4R'-4', abbreviated as PtCl[NCN(CH[double bond, length as m-dash]NC6H4R'-4')-4], with R' = NMe2, Me, H, Cl, CN (, respectively), was synthesized via a Schiff-base condensation reaction involving reaction of PtCl[NCN(CH[double bond, length as m-dash]O)-4] () with the appropriate 4-R'-substituted aniline derivative () in toluene. The resulting arylplatinum(ii) products were obtained in 75-88% yield. Notably, product was also obtained in 68% yield from a reaction in the solid state by grinding solid with aniline . The structures of , , and in the solid state (single crystal X-ray diffraction) showed a non-planar geometry, in particular for compound . The electronic interaction between the donor benzylidene fragment PtCl(NCN-CH) and the para-R' aniline substituent through the azomethine bridge was studied with NMR and UV/Vis spectroscopy. Linear correlations were found between the azomethine (1)H, the (195)Pt NMR and various (13)C NMR chemical shifts, and the substituent parameters σF and σR of R' at the aniline site. In common with organic benzylidene anilines, the azomethine (1)H NMR chemical shift showed anomalous substituent behavior. The (195)Pt NMR chemical shift of the platinum center can be used as a probe for the electronic properties of the delocalized π-system of the benzylidene aniline framework, to which it is connected. The dual substituent parameter treatment of the azomethine (13)C NMR shift gave important insight into the unique behaviour of the Pt-pincer group as a substituent. Inductively, it is a very strong electron-withdrawing group, whereas mesomerically it behaves like a very strong electron donating group.

Facial triad modelling using ferrous pyridinyl prolinate complexes: synthesis and catalytic applications.

A series of new chiral pyridinyl prolinate (RPyProR) ligands and their corresponding Fe(II) triflate and chloride complexes are reported. The ligands possess an NN'O coordination motif, as found in the active site of non-heme iron enzymes with the so-called 2-His-1-carboxylate facial triad. The coordination behaviour of these ligands towards iron turned out to be dependent on the counter ion (chloride or triflate), the crystallization conditions (coordinating or non-coordinating solvents) and the presence of substituents on the ligand. In combination with Fe(II)(OTf)2, coordinatively saturated complexes of the type [Fe(L)2](OTf)2 are formed, in which the ligands adopt a meridional coordination mode. The use of FeCl2 in a non-coordinating solvent leads to 5-coordinated complexes [Fe(L)(Cl)2] with a meridional N,N',O ligand. Crystallization of these complexes from a coordinating solvent leads to 6-coordinated [Fe(L)(solv)(Cl)2] complexes (solv = methanol or acetonitrile), in which the N,N',O ligand is coordinated in a facial manner. For RPyProR ligands bearing a 6-Me substituent on the pyridine ring, solvent coordination and, accordingly, ligand rearrangement are prevented by steric constraints. The complexes were tested as oxidation catalysts in the epoxidation of alkene substrates in acetonitrile with hydrogen peroxide as the oxidant under oxidant limiting conditions. The complexes were shown to be especially active in the epoxidation of styrene type substrates (styrene and trans-beta-methylstyrene). In the best case, complex [Fe(6-Me-PyProNH2)Cl2] (15) allowed for 65% productive consumption of hydrogen peroxide toward epoxide and benzaldehyde products.

Capsule-controlled selectivity of a rhodium hydroformylation catalyst.

Chemical processes proceed much faster and more selectively in the presence of appropriate catalysts, and as such the field of catalysis is of key importance for the chemical industry, especially in light of sustainable chemistry. Enzymes, the natural catalysts, are generally orders of magnitude more selective than synthetic catalysts and a major difference is that they take advantage of well-defined cavities around the active site to steer the selectivity of a reaction via the second coordination sphere. Here we demonstrate that such a strategy also applies for a rhodium catalyst; when used in the hydroformylation of internal alkenes, the selectivity of the product formed is steered solely by changing the cavity surrounding the metal complex. Detailed studies reveal that the origin of the capsule-controlled selectivity is the capsule reorganization energy, that is, the high energy required to accommodate the hydride migration transition state, which leads to the minor product.

Directed ortho-lithiation: observation of an unexpected 1-lithio to 3-lithio conversion of 1-lithio-naphthyllithium compounds with an ortho-directing 2-(dimethylamino)methyl group.

Regioselectivity is an important aspect in the design of organic protocols involving Directed ortho-Lithiation (DoL) of arenes, in particular with those arenes containing heteroatom substituents as directing groups. The DoL of 2-[(dimethylamino)methyl]naphthalene (dman) that proceeds with low regioselectivity was revisited by varying both the nature of the lithiating reagent (either n-BuLi or t-BuLi) and/or the solvent (pentane or diethyl ether); the 3-deuterated substrate, 3-Ddman, was also investigated as a substrate to compare to that of dman. The 3-lithio regioisomer exists as tetranuclear [2-(Me2NCH2)C10H6Li-3]4, 1, both in the solid state (X-ray) and in solution (NMR). The 1-lithio regioisomer, 2a, is insoluble; in the presence of additional coordinating solvents (Et2O) or ligands (dman), it exists as dinuclear [2-(Me2NCH2)C10H6Li-1]2·L (coordinated L = Et2O: 2b, dman: 2c) in apolar solvents. Heating solutions of 2c in toluene-d8 (to 90 °C) induced a surprisingly clean and quantitative 1-lithio to 3-lithio conversion of the 1-lithio-naphthalene isomer. This type of reaction is rare in organolithium chemistry and has obvious significant implications for the design of regioselective DoL protocols; this thus represents the synthetically useful protocol for the DoL of dman in a one-pot/two-step process in toluene solution. The results of the use of 3-Ddman in these reactions gives strong credence to a mechanism involving formation of the heteroleptic species [(2-(Me2NCH2)C10H6-1)(2-(Me2NCH2)C10H6-3)Li2]·[dman], A, as the key intermediate. Intramolecular trans-lithiation takes place with A; dman becomes selectively lithiated at its 3-position, while the formerly 1-lithio-naphthalene fragment, acting as a highly unusual ortho-lithiating reagent, is converted into the N-coordinated amine, dman. In this intramolecular DoL process, free dman can be considered to act as a catalyst.

Triphenylsilanol-4,4'-bipyridyl (4/1): the Z' = 4 polymorph revisited.

A fully ordered structure is reported for the polymorph of triphenylsilanol-4,4'-bipyridyl (4/1), 4C18H16OSi·C10H8N2, having Z' = 4. The asymmetric unit contains four similar but distinct five-molecule aggregates, in which the central bipyridyl unit is linked to two molecules of triphenylsilanol via O-H···N hydrogen bonds, with a further pair of triphenylsilanol molecules linked to the first pair via O-H···O hydrogen bonds. An extensive series of C-H···π(arene) hydrogen bonds links these aggregates into complex sheets. This structure is compared with a previously reported structure [Bowes, Ferguson, Lough & Glidewell (2003). Acta Cryst. B59, 277-286], which was based on an erroneous disordered structural model arising from a false direct-methods solution with reference to a strong pseudo-inversion centre.

Bioinspired nonheme iron complexes derived from an extended series of N,N,O-ligated BAIP ligands.

A series of mononuclear Fe(II) triflate complexes based on the 3,3-bis(1-alkylimidazole-2-yl)propionate ester (BAIP) ligand scaffold are reported. In these complexes, the tripodal N,N,O-BAIP ester ligand is varied by (i) changing the ester moiety (i.e., n-Pr, tert-Bu esters, n-Pr amide), (ii) changing the methylimidazole moieties to methylbenzimidazole moieties, and (iii) changing the methylimidazole moieties to 1-ethyl-4-isopropylimidazole moieties. The general structure of the resulting complexes comprises two facially capping BAIP ligands around a coordinatively saturated octahedral Fe(II) center, with either a transoid or cisoid orientation of the N,N,O-donor manifold that depends on the combined steric and electronic demand of the ligands. In the case of the sterically most encumbered ligand, a four-coordinate all N-coordinate complex is formed as well, which cocrystallizes with the six-coordinate complex. In combination with the catalytic properties of the new complexes in the epoxidation/cis-dihydroxylation of cyclooctene with H2O2, in terms of turnover number and cis-diol formation, these studies provide a number of insights for further ligand design and catalyst development aimed at Fe-mediated cis-dihydroxylation.

Heterolytic activation of dihydrogen by platinum and palladium complexes.

Wide bite angle diphosphine ligands were used to prepare [(diphosphine)M(2-(diphenylphosphino)pyridine)](2+) complexes (M = Pd, Pt). Except for the ligand with the largest bite angle, 2-(diphenylphosphino)pyridine coordinates in a bidentate mode leading to bis-chelate complexes. In the case of Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene, ßn = 111°) two types of complexes are formed, in which 2-(diphenylphosphino)pyridine coordinates in a mono- or bidentate fashion, respectively. The crystal structures of three of the Pt complexes were determined. The X-ray crystal structure of [(Xantphos)-Pt(2-(diphenylphosphino)pyridine)](2+) shows that Xantphos coordinates in a tridentate P,O,P fashion. Under dihydrogen pressure, the pyridyl moiety in the platinum complexes can de-coordinate to provide a vacant coordination site at the metal center. Furthermore it can act as an internal base to assist the heterolytic cleavage of dihydrogen. The reaction yields a platinum hydride with a protonated pyridine moiety in close proximity to one another. The structure as well as the reactivity of the complexes towards dihydrogen is governed by the steric requirements of the diphosphines. The crystal structure of [(dppf)PtH(2-(diphenylphosphino)pyridinium)](OTf)2 has been determined. Palladium complexes containing DPEphos or Xantphos decompose under dihydrogen pressure. In the case of dppf slow heterolytic splitting of dihydrogen occurs to form the hydride complex [(dppf)PdH(2-(diphenylphosphino)pyridinium)](OTf)2 which contains a protonated 2-(diphenylphosphino)pyridine ligand. In solution, this compound slowly undergoes P-C bond cleavage of the 2-(diphenylphosphino)pyridine ligand to form [(dppf)Pd(PHPh2)(η(1)-C5H4NH)](OTf)2. When the 6-methyl-2-pyridyldiphenylphosphine ligand is used, the reaction of the palladium complex with dihydrogen is very fast and the hydride complex immediately rearranges to the diphenylphosphino compound resulting from P-C bond cleavage.

Bis-(thiosemicarbazonato) Zn(II) complexes as building blocks for construction of supramolecular catalysts.

In this paper we report the application of bis-(thiosemicarbazonato) Zn(II) complexes as building blocks in the construction of supramolecular transition metal assemblies. We investigated their coordination behaviour towards pyridylphosphine molecules and found these systems comparable to those based on Zn(porphyrin) and Zn(salphen) complexes. Additionally, catalytic experiments and an in situ high-pressure FTIR study of the supramolecular rhodium hydroformylation catalysts, assembled using the bis-(thiosemicarbazonato) Zn(II) complexes, demonstrate their applicability in supramolecular catalysis and their potential for application in other areas of supramolecular chemistry.

Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies.

The newly synthesized dinuclear complex [Fe(III)(2)(µ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) Å) and Fe-O distances (1.941(2)/1.949(2) Å) compared to other unsupported Fe(III)(2)(µ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mössbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 Å, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 Å) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.

Mono N,C,N-pincer complexes of titanium, vanadium and niobium. Synthesis, structure and catalytic activity in olefin polymerisation.

Transmetallation of 4,4'-bis{(2,6-bis[(dimethylamino)methyl]phenylgold)diphenyl-phosphino}biphenyl (3) with MCl(4) (M = Ti, NbCl, V) in benzene gave the corresponding transition metal pincer complexes (4) and insoluble 4,4'-bis[P-(chloro gold(I))diphenylphosphino]biphenyl (2), which can be quantitatively recovered and recycled. Interestingly, 3 did not react with TiCl(3). However, reaction of 2,6-bis[(dimethylamino)methyl]phenyllithium (1) with TiCl(3) resulted in formation of the novel diaryltitanium(IV) compound 5 (16% yield), comprising one N,C,N-mer bound NCN-pincer ligand and a second NCN-pincer ligand that is rearranged from a 1,2,6-isomer to a 1,2,4 one. The latter NCN-ligand is dianionic and is bidentate bonded; one of the CH(2)NMe(2) substituents (para to C'(ipso)) is non-coordinated, while the second CH(2)NMe(2) group, after C-H activation of one of the Me groups, is η(2)-C,N-bonded to the titanium centre trans to C(ipso) of the mer-NCN ligand. The new NCN-pincer metal complexes 2,6-bis[(dimethylamino)methyl]phenylTiCl(3) (4a) and 2,6-bis[(dimethylamino)methyl]-phenylVCl(2) (4d) gave, after immobilization on MgCl(2)-based supports, very high activity in ethene polymerisation.

Coulombic inter-ligand repulsion effects on the Pt(II) coordination chemistry of oligocationic, ammonium-functionalized triarylphosphines.

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX(2)(L)(2) (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1](6+) and [2](6+), two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX(2)(L)(2), while for the tri-para-ammoniomethyl-substituted ligand [7](3+), the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI(2)(1)(2)]I(12), the geometrical parameters of the phosphine ligand [1](6+) are very similar to those found in the analogous complex of the benchmark ligand PPh(3), i.e. trans-PtI(2)(PPh(3))(2), indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.

Homoleptic diphosphacyclobutadiene complexes [M(η(4)-P2C2R2)2]x- (M = Fe, Co; x = 0, 1).

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K([18]crown-6)(thf)(2)][Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K([18]crown-6)(thf)(2)][M(η(4)-C(14)H(10))(2)] (M = Fe, Co) with tBuC[triple bond]P (1, 2), or with AdC[triple bond]P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(2)] (4: M = Fe 5: M = Co) were obtained by oxidizing 1 and 2 with [Cp(2)Fe]PF(6). Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(2)] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and Mössbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). The molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D(2d)-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed.

Structure elucidation of the unprecedented asymmetric bis-chelate complex [Pd(1,3-bis(di(o-methoxy-m-methylphenyl)phosphino)propane)2]2+ in the solid state and in solution.

Complexes of the type [Pd(ligand)(2)](anion)(2) were prepared with a series of bidentate di(o-methoxyphenyl)phosphine ligands with increasing steric bulk on the meta position of the phenyl groups: m-H (L1); m-MeO (L2); and m-Me (L3). The solid-state structure of [Pd(L2)(2)](OTs)(2) revealed that the two ligands are symmetrically coordinated to Pd(2+). In the solid state structure of [Pd(L3)(2)](OTs)(2) however, the two ligands are unsymmetrically coordinated to Pd(2+), yielding an unprecedented conformation of this bis-chelate P(4)Pd(2+) complex. (1)H-(1)H-COSY and NOESY analysis and a (31)P-NMR simulation showed that the asymmetric structure of [Pd(L3)(2)](OTs)(2) is retained in solution.

Mono(NCN-pincer palladium)-metalloporphyrin catalysts: evidence for supramolecular bimetallic catalysis.

The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB(3)-type tetraphenylporphyrin, containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest yielding alternative, giving pincer-porphyrin hybrids of general formula [M(1)(M(2)X)] (M(1) = 2H, Mg, Co, Ni, Zn; M(2) = Pd, Br; X = Cl, Br). (195)Pt NMR spectroscopy revealed that the porphyrin metal has a modest influence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl ketone and ethyl alpha-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M(1) = 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was conducted with a mixture of the two constituents of [Mg(PdOH(2))]BF(4) (i.e. MgTTP and [PdOH(2)(NCN)]BF(4)) this could not fully account for the rate enhancement. We believe that the rationale for this behaviour is dual, consisting of "cooperative dual catalysis" and supramolecular aggregation of two or more catalyst-substrate complexes.

Versatile new C(3)-symmetric tripodal tetraphosphine ligands; structural flexibility to stabilize Cu(I) and Rh(I) species and tune their reactivity.

The high-yielding synthesis and detailed characterization of two well-defined, linkage isomeric tripodal, tetradentate all-phosphorus ligands 1-3 is described. Coordination to Cu(I) resulted in formation of complexes 4-6, for which the molecular structures indicate overall tridentate coordination to the copper atom in the solid state, with one dangling peripheral phosphine. The solution studies suggest fast exchange between the three phosphine side-arms. For these new Cu(I) complexes, preliminary catalytic activity in the cyclopropanation of styrene with ethyldiazoacetate (EDA) is disclosed. The anticipated well-defined tetradentate coordination in a C(3)-symmetric fashion was achieved with Rh(I) and Ir(I), leading to the overall five-coordinated complexes 7-12. Complex 11 has the norbornadiene (nbd) ligand coordinated in an unprecedented monodentate 2,3-eta(2) mode to Rh. Furthermore, unexpected but very interesting redox-chemistry and reactivity was displayed by the Rh(Cl)-complexes 7 and 8. Oxidation resulted in the formation of stable Rh(II) metalloradicals [7]PF(6) and [8]PF(6) that were characterized by X-ray crystallography, magnetic susceptibility measurements, cyclic voltammetry, and electron paramagnetic resonance (EPR) spectroscopy. Subsequent redox-reactivity of these metalloradicals toward molecular hydrogen is described, resulting in the formation of Rh(III) hydride compounds.

Heterotopic silver-NHC complexes: from coordination polymers to supramolecular assemblies.

New coordination polymers based on different combinations of silver atoms and pyridyl-substituted N-heterocyclic carbene moieties are described. The addition of Zn(ii) templates leads to Ag-Zn supramolecular assemblies via selective ZnN interactions; a process that can be reverted.

Activation of H2 by a highly distorted Rh(II) complex with a new C3-symmetric tripodal tetraphosphine ligand.

Facile oxidation of a sterically encumbered Rh(I) complex generates a stable Rh(II) metalloradical species; the latter is able to activate H(2) under formation of the corresponding Rh(III) complex.