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We introduce in this paper a new definition for the overall system efficiency in network DEA, which is inspired by the “weak link” notion in supply chains and the maximum-flow/minimum- cut problem in networks. We use a two-phase max-min optimization technique in a multi-objective programming framework to estimate the individual stage efficiencies and the overall system efficiency in two-stage processes of varying complexity. This enables us to estimate unique and unbiased efficiency scores and, if required, to drive the efficiency assessments effectively in line with specific priorities given to the stages. A comparison with the multiplicative decomposition approach on data drawn from the literature brings into light the advantages of our method.

A new class of homoligated palladium(II) weak-link approach (WLA) complexes bearing hemilabile N-heterocyclic carbene (NHC)–thioether ligands is reported that, unlike previous tweezer-like WLA complexes, expand and contract in a linear fashion when switching between configurational states. These complexes can be chemically switched between a trans open state and a trans closed state via the addition or subsequent extraction of Cl–. These bis(NHC) complexes also display unusual isomerization behavior. For example, an NMR spectroscopic investigation into the solution-state configuration of the open complex reveals the presence of interconverting syn,trans and anti,trans isomers, and a kinetic study shows that the barrier is large enough to isolate, store, and study the anti,trans isomer at room temperature. Notably, the linker length between the NHC and thioether moieties can be tailored with additional −CH2– groups, which affords considerable control over the geometric changes imposed by switching. Therefo...

Η συστηματική αποτίμηση της αποδοτικότητας ενός οργανισμού και η οριοθέτηση επιτεύξιμων στόχων αποτελούν συμπληρωματικές θεμελιώδεις πτυχές για την εύρυθμη λειτουργία του και τη βιωσιμότητά του. Συνεπώς, είναι απαραίτητη η υιοθέτηση τεχνικών αξιολόγησης που λαμβάνουν υπόψη όλους τους παράγοντες από το περιβάλλον λειτουργίας του οργανισμού, ώστε να εντοπίζουν τις μη αποδοτικές παραγωγικές διαδικασίες και να προτείνουν επαρκείς τρόπους για την βελτίωσή τους. Μια τέτοια τεχνική είναι η Περιβάλλουσα Ανάλυση Δεδομένων – ΠΑΔ (Data Envelopment Analysis - DEA), η οποία αποτελεί πλέον τη δημοφιλέστερη μη παραμετρική τεχνική για την αποτίμηση της αποδοτικότητας ομοειδών μονάδων ενός συστήματος (μονάδες απόφασης) επί τη βάσει πολλαπλών εισροών και πολλαπλών εκροών. Οι κλασσικές μεθοδολογίες της ΠΑΔ θεωρούν τις μονάδες απόφασης ως «μαύρα κουτιά» (black boxes) που χρησιμοποιούν εισροές για την παραγωγή εκροών, αγνοώντας την εσωτερική τους δομή. Αυτό έχει ως συνέπεια τα κλασσικά μοντέλα της ΠΑΔ να μπορούν μερικώς μόνο να ανταποκριθούν στην αποτίμηση της αποδοτικότητας όταν η εσωτερική δομή είναι γνωστή και κρίσιμη για τη λειτουργία της μονάδας. Το κενό αυτό έρχεται να καλύψει η Περιβάλλουσα Ανάλυση Πολυσταδιακών Διεργασιών (Network DEA), η οποία αποτελεί πρόσφατη επέκταση της κλασσικής ΠΑΔ. Πρόκειται για μια μεθοδολογία που μπορεί να εφαρμοστεί για την αξιολόγηση μονάδων απόφασης, οι οποίες απαρτίζονται από πολλά μέλη (γνωστά και ως διεργασίες, υπο-διαδικασίες, υπο-μονάδες παραγωγής ή στάδια), διότι λαμβάνει υπόψη την εσωτερική τους δομή και τις σχέσεις αλληλεπίδρασης που τη συνοδεύουν. Η κάθε μονάδα απόφασης (σύστημα) λειτουργεί ως ένα δίκτυο από διατεταγμένες διεργασίες οι οποίες συνδέονται και αλληλεπιδρούν μέσω εσωτερικών ροών υποπροϊόντων (ενδιάμεσων μεγεθών), τα οποία έχουν διττό ρόλο διότι αποτελούν ταυτόχρονα εκροές μιας υπο-διαδικασίας και εισροές μιας άλλης. Ενδεικτικό παράδειγμα αποτελεί η εφοδιαστική αλυσίδα που περιέχει πολλά μέλη και η εύρυθμη ή η μη αποδοτική λειτουργία του κάθε μέλους αντανακλάται στη συνολική λειτουργία της. Συνεπώς, η εκτίμηση της συνολικής αποδοτικότητας της εφοδιαστικής αλυσίδας (συστήματος) πρέπει να γίνεται συντονισμένα λαμβάνοντας υπόψη τις αποδοτικότητες των μελών της. Στην παρούσα διδακτορική διατριβή διεξάγουμε μια λεπτομερή ανασκόπηση των μεθόδων που έχουν προταθεί στη βιβλιογραφία στο πλαίσιο της Περιβάλλουσας Ανάλυσης Πολυσταδιακών Διεργασιών. Μελετούμε τις ιδιότητες-χαρακτηριστικά τους, τις τεχνικές επίλυσης που χρησιμοποιούν καθώς και τις ομοιότητες και διαφορές τους ώστε να τις κατατάξουμε σε κατηγορίες. Αναδεικνύουμε τα μειονεκτήματα των πιο διαδεδομένων προσεγγίσεων, τα οποία αφορούν την κλίμακα αποδόσεων και την αδυναμία να αποδώσουν επαρκή πληροφορία ώστε να καταστήσουν αποδοτικές τις μη αποδοτικές μονάδες. Επίσης, οι προσεγγίσεις που προτείνονται στη βιβλιογραφία δεν διασφαλίζουν τη μοναδικότητα των τιμών αποδοτικότητας των υπο-διαδικασιών, συνεπώς θέτουν σε αμφισβήτηση την εγκυρότητα των παραγόμενων αποτελεσμάτων. Εμφανίζονται δηλαδή περιπτώσεις όπου το ίδιο επίπεδο συνολικής αποδοτικότητας του συστήματος μπορεί να προκύπτει από διαφορετικούς συνδυασμούς τιμών αποδοτικότητας των επιμέρους διαδικασιών. Επίσης, υπάρχουν προσεγγίσεις που συχνά μεροληπτούν κατά την αποτίμηση της συνολικής αποδοτικότητας του συστήματος. Αποδεικνύουμε ότι η αθροιστική μέθοδος μεροληπτεί κατά την αποτίμηση υπέρ κάποιων συγκεκριμένων σταδίων. Επιπροσθέτως, δείχνουμε ότι οι προτεινόμενες προσεγγίσεις δεν μπορούν να εφαρμοστούν σε γενικές δικτυακές δομές παραγωγικών μονάδων. Για την αντιμετώπιση των παραπάνω αδυναμιών, εισάγουμε νέες μεθοδολογίες που βασίζονται στην ενσωμάτωση τεχνικών πολυκριτήριου προγραμματισμού στην Περιβάλλουσα Ανάλυση Δεδομένων. Επικεντρώνουμε την έρευνά μας σε μονάδες απόφασης που περιλαμβάνουν δύο υπο-διαδικασίες διατεταγμένες σε σειρά και μοντελοποιούμε το πρόβλημα της μέτρησης της αποδοτικότητάς τους ως πρόβλημα πολυκριτήριου προγραμματισμού. Χρησιμοποιούμε πραγματικές συναρτήσεις επίτευξης (achievement scalarizing functions) ώστε να ενσωματώσουμε τις ιδέες μας αλλά και τις ιδιότητες της αμεροληψίας και της μοναδικότητας των αποτελεσμάτων που θα πρέπει να διέπουν οι μέθοδοι της Περιβάλλουσας Ανάλυσης Πολυσταδιακών Διεργασιών. Εισάγουμε τη συνθετική προσέγγιση (composition approach), αντιμετωπίζοντας με ουδετερότητα τις υπο-διαδικασίες και κατασκευάζουμε αρχικά ένα μοντέλο με μια προσθετική συνάρτηση επίτευξης βασιζόμενοι στην L1 μετρική. Αυτό το μοντέλο αποδίδει αμερόληπτα αποτελέσματα, τα οποία απεικονίζονται ως ακραία σημεία (κορυφές) στο σύνορο Pareto. Σχηματίζουμε επιπλέον μοντέλα χρησιμοποιώντας συναρτήσεις επίτευξης, για την κατασκευή των οποίων εφαρμόζουμε μεθοδολογίες πολυκριτήριας βελτιστοποίησης που βασίζονται σε σημεία αναφοράς (reference points). Ειδικότερα, χρησιμοποιούμε την μετρική Tchebycheff (L∞) για τον εντοπισμό μιας μοναδικής Pareto βέλτιστης λύσης ελαχιστοποιώντας τη μέγιστη απόκλιση από το ιδεώδες σημείο (ideal point). Ήτοι στοχεύει στον υπολογισμό των επιμέρους αποδοτικοτήτων των υπο-διαδικασιών όσο δύναται πλησιέστερα στα υψηλότερα επίπεδα αποδοτικοτήτων που μπορούν να επιτύχουν οι υπο-διαδικασίες ξεχωριστά. Το μοντέλο αυτό αποδίδει αμερόληπτα αποτελέσματα και διασφαλίζει τη μοναδικότητά τους. Έπειτα, αναπτύσσουμε δύο μεθόδους που παρέχουν την απαραίτητη πληροφορία για τον σχηματισμό των προβολών των μη αποδοτικών μονάδων στο σύνορο αποδοτικότητας. Η πρώτη προκύπτει απ’ ευθείας από την συνθετική προσέγγιση ενώ η δεύτερη είναι προσανατολισμένη στο να καταστήσει αποδοτικές τη μη αποδοτικές μονάδες επιφέροντας όσο το δυνατόν ελάχιστες αλλαγές στα αρχικά επίπεδα των ενδιάμεσων μεγεθών. Στη συνέχεια, διατυπώνουμε έναν νέο ορισμό της συνολικής αποδοτικότητας των μονάδων απόφασης που περιέχουν δύο υπο-διαδικασίες διατεταγμένες σε σειρά, εμπνευσμένοι από τον ρόλο του αδύναμου κρίκου στις εφοδιαστικές αλυσίδες και από το θεώρημα της μέγιστης ροής-ελάχιστης κοπής (max flow-min cut) στα δίκτυα. Για την αξιολόγηση των μονάδων που περιέχουν δύο υπο-διαδικασίες με ποικίλη σειριακή διάταξη εισάγουμε την προσέγγιση του «αδύναμου κρίκου» (weak-link approach). Αναπτύσσουμε μια νέα μέθοδο βελτιστοποίησης max-min δύο φάσεων με την οποία διασφαλίζεται ότι η προκύπτουσα λύση θα είναι μοναδική και βέλτιστη κατά Pareto. Πρωτίστως, μεγιστοποιούμε την ελάχιστη αποδοτικότητα (αποδοτικότητα του αδύναμου κρίκου) μεταξύ των υπο-διαδικασιών και στη συνέχεια διασφαλίζουμε ότι η προκύπτουσα λύση είναι μοναδική και βέλτιστη κατά Pareto. Για την καθοδήγηση της διαδικασίας βελτιστοποίησης χρησιμοποιήσαμε τις ιδεώδεις αποδοτικότητες των υπο-διαδικασιών, ωστόσο, διαφορετικές προτιμήσεις δύναται να ενσωματωθούν για τον εντοπισμό εναλλακτικών βέλτιστων κατά Pareto λύσεων. Τέλος, επανεξετάζουμε τη μεθοδολογία των Aviles-Sacoto et al (2015) και αποδεικνύουμε ότι είναι προβληματική. Προτείνουμε μια εναλλακτική μοντελοποίηση η οποία διορθώνει τα μεθοδολογικά προβλήματα που παρατηρούμε., The systematic performance evaluation of the organizations as well as the target setting are key aspects for its proper operation and viability. Thus, the adoption of evaluation methods is necessary, which are capable of taking into account all the environmental factors of the organization, identifying the inefficient production processes and suggesting adequate ways to improve them. Such a method is Data Envelopment Analysis (DEA), which is the most popular non-parametric technique for assessing the efficiency of homogeneous decision making units (DMUs) that use multiple inputs to produce multiple outputs. The DMUs may consist of several sub-processes (also known as stages, sub-units, divisions etc.) that interact and perform various operations. However, the classical DEA models treat the DMU as a “black box”, i.e. a single stage production process that transforms some external inputs to final outputs. In such a setting, the internal structure of the DMU is not taken into consideration. Thus, the conventional DEA models fail to mathematically represent the internal characteristics of the DMUs, as well as they fall short to provide precise results and useful information regarding the sources that cause inefficiency. In order to take into account for the internal structure of the DMUs, recent methodological advancements are developed, which extend the standard DEA and constitute a new field, namely the network DEA. The network DEA methods are capable of reflecting accurately the DMUs’ internal operations as well as to incorporate their relationships and interdependences. In network DEA, the DMU is considered as a network of interconnected sub-units, with the connections indicating the flow of intermediate products (commonly called intermediate measures or links). An indicative example of such a DMU is a supply chain, which has a network structure and is composed of several members whose performances affect the overall performance of the supply chain. Therefore, the overall efficiency of the supply chain (DMU) should be evaluated by taking into account the individual efficiencies of its members in a coordinated manner. In this thesis, we conduct a critical survey and categorization of the state-of-the art network DEA methods and we classify a great volume of network DEA studies based on the assessment method they follow. We unveil the relations and the differences of the existing network DEA methods. Also, we uncover their defects concerning the returns to scale, the inconsistency between the multiplier and the envelopment models as well as the inadequate information that provide for the calculation of efficient projections. The most important network DEA methods do not secure the uniqueness of the efficiency scores, i.e. the same level of overall efficiency is obtained from different combinations of the efficiencies of the sub-processes. Also, we prove that the additive efficiency decomposition method unduly and implicitly assigns different priority to the sub-processes, hence provides biased efficiency assessments. Finally, we discuss about the inability of the existing approaches to be universally applied on every type of network structure. We develop two new approaches in network DEA that overcome effectively the deficiencies and provide unique and unbiased efficiency scores, based on a multiple objective framework. We focus our research to serial two-stage network structures and we formulate the problem of their efficiency assessment as a multi-objective mathematical programming problem. Initially, we introduce the composition approach to two-stage network DEA, which is based on a bi-objective mathematical program for the efficiency assessments. We employ two scalarization techniques, firstly based on the L1 norm we aggregate the two objective functions additively without giving any priority between them. The application of this scalarizing function yields an extreme (vertex) Pareto-optimal solution. Then, we employ a min-max scalarization technique, i.e. the Tchebycheff norm (L∞), which minimizes the distance between the ideal point and the feasible objective functions space so as to locate a point on the Pareto front not necessarily extreme. This model provides unique and unbiased efficiency scores. In the composition approach, we estimate first the stage efficiencies and then we aggregate them either additively or multiplicatively to obtain the overall efficiency. Next, we develop two methods to derive the efficient frontier in two-stage DEA and provide efficient projections. The first naturally stems from our composition approach, while the second seeks to provide efficient projections by altering the original levels of the intermediate measures at a minimum distortion. We build upon the composition approach and we introduce the “weak-link” approach to two-stage network DEA, which inherits the nice properties of the former, i.e. provides unique and unbiased efficiency scores. Also, the “weak-link” approach can be readily applied to various types of two-stage network structures. In this approach, we introduce a novel definition about the overall efficiency of the DMU, inspired by the “weak link” notion in supply chains and the maximum-flow/minimum-cut problem in networks. We incorporate this notion into the assessment by assuming that given the stage efficiencies, the system efficiency can be viewed as the maximum flow through the network and can be estimated as the min-cut of the network, i.e. the system efficiency derives as the lowest of the stage efficiencies. We mathematically represent this concept by employing a two-phase max-min optimization method in a multi-objective programming framework, which seeks to maximize the minimum weighted achievement from zero-level efficiency, i.e. maximizing the lowest of the stage efficiencies (weak link). The proposed two-phase procedure estimates the stage efficiencies and the overall efficiency simultaneously by providing a unique Pareto optimal solution. The search direction towards the Pareto front is driven by the assumption that the stage efficiencies are proportional to their independent counterparts. External priorities can be also introduced to our methodology so as to obtain alternative Pareto optimal solutions. We conduct a systematic investigation of the sensitivity of the weak link so as to identify the source of inefficiency in the two-stage processes. Finally, we revisit the work of Aviles-Sacoto et al (2015) who studied a peculiar situation of a two-stage process where some of the intermediate measures are inputs to the second stage and at the same time external outputs from that stage. We show that their modelling approach departs from the described setting and adapts a different situation, where the specific intermediate measure is viewed either as input to or as output from the second stage of the process. We alternatively propose a different modelling approach for the performance assessment of the two-stage process under examination, which rectifies the methodological problems that we observe.

The anionic hemilabile phosphinothioether ligand, [1-(Ph2PCH2CH2S)-closo-1-CB11H11 ](-), which is functionalized with an anionic icosahedral monocarbaborane anion, was synthesized in three steps from [HNMe3][closo-CB11H12]. The ligand was used to synthesize a family of zwitterionic Weak-Link Approach (WLA) complexes that contain platinum(II), palladium(II), and rhodium(I). These complexes were characterized using multinuclear NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction analyses. Although the C-bound [closo-CB11H11](-) anion behaves as an electron-withdrawing moiety, hemilabile phosphinothioether ligands that are based on this unit are strongly chelating, as determined via the measurement of the chloride association constant. The chelating strength is comparable to that of hemilabile ligands that are functionalized with the very electron-rich B-bound closo-1,7-C2B10H11 moiety, thus demonstrating the use of charge to influence ligand coordination strength. The anionic Rh(I) WLA complex that is synthesized using this ligand can act as the noncoordinating anion of a regular cationic Rh(I) WLA complex. Thus, an unprecedented type of salt, in which the anion and cation are mutually isostructural and isoelectronic WLA complexes, has been synthesized and characterized crystallographically.

A series of d(8) transition-metal (Pt(II) and Pd(II)) coordination complexes incorporating phosphine-functionalized aminoazobenzene derivatives as hemilabile phosphino-amine (P,N) ligands were synthesized and studied as model weak-link approach (WLA) photoresponsive constructs. The optical and photochemical properties of these complexes were found to be highly influenced by various tunable parameters in WLA systems, which include type of metal, coordination mode, type of ancillary ligand, solvent, and outer-sphere counteranions. In dichloromethane, reversible chelation and partial displacement of the P,N coordinating moieties allow for toggling between aminoazobenzene- or pseudostilbene- and azobenzene-type derivatives. The reversible switching between electronic states of azobenzene can be controlled through either addition or extraction of chloride counterions and is readily visualized in the separation between π-π* and n-π* bands in the complexes' electronic spectra. In acetonitrile solution, the WLA variables inherent to semiopen complexes have a significant impact on the half-lives of the corresponding cis isomers, allowing one to tune their half-lives from 20 to 21000 s, while maintaining photoisomerization behaviors with visible light. Therefore, one can significantly increase the thermal stability of a cis-aminoazobenzene derivative to the extent that single crystals for X-ray diffraction analysis can be grown for the first time, uncovering an unprecedented edge-to-face arrangement of the phenyl rings in the cis isomer. Overall, the azobenzene-functionalized model complexes shed light on the design parameters relevant for photocontrolled WLA molecular switches, as well as offer new ways of tuning the properties of azobenzene-based, photoresponsive materials.

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy's meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence "turn-on" fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases. The Pt(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation suggest that the heavy Pt(II) center also influences Bodipy's emission efficiency by affecting intersystem crossing from the Bodipy excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode and potentially will enable the design of new molecular systems for sensing and signal amplification.

An allosterically regulated, asymmetric receptor featuring a binding cavity large enough to accommodate three-dimensional pharmaceutical guest molecules as opposed to planar, rigid aromatics, was synthesized via the Weak-Link Approach. This architecture is capable of switching between an expanded, flexible “open” configuration and a collapsed, rigid “closed” one. The structure of the molecular receptor can be completely modulated in situ through the use of simple ionic effectors, which reversibly control the coordination state of the Pt(II) metal hinges to open and close the molecular receptor. The substantial change in binding cavity size and electrostatic charge between the two configurations is used to explore the capture and release of two guest molecules, dextromethorphan and β-estradiol, which are widely found as pollutants in groundwater.

The reaction of a macrocyclic Rh(I) complex having hemilabile PO ligands with Cl− results in Rh−O bond breakage and yields a Cl-bridged tetranuclear Rh(I) complex, which was characterized by a single-crystal X-ray diffraction study. Reactivity of the complex with CO and halide abstracting agents is described.

Through the weak link approach and a halide-induced ligand rearrangement process, semi-open and condensed triple-decker complexes (TDCs) were prepared and fully characterized. These triple-decker structures with tailorable layers through choice of hemilabile ligand starting materials can be chemically opened and closed to expose the interior layer in a reversible fashion using small-molecule and elemental anion ligand substitution reactions.

Tröger's base, a chiral molecule with a rigid 90 degrees backbone, has been incorporated into a novel hemilabile phosphinoalkyl thioether ligand. Using the Weak Link Approach, this ligand has been reacted with Cu(CH3CN)4PF6 and [Rh(COE)2Cl]x (COE = cyclooctene) to form metallomacrocycles. Upon reaction of the ligand with Cu(I), which prefers a tetrahedral coordination geometry, a bimetallic macrocycle was formed. Alternatively, owing to the steric restrictions imposed by the 90 degrees backbone of the ligand and the square-planar geometry of Rh(I), when the ligand was reacted with [Rh(COE)2Cl]x, the formation of bimetallic closed macrocycles was not observed, and instead a mixture of tri- and tetrametallic closed macrocycles is formed. Introducing pyridine to the Cu(I) complex causes the weak thioether-Cu bonds to break, generating a large bimetallic open macrocycle. Upon reaction of the mixture of Rh(I) metallomacrocycles with CO and Cl-, the cyclic structure of these complexes becomes flexible enough that the dimeric bimetallic macrocycle forms, along with tri- and tetrameric open complexes. The mixture of differently sized Rh(I) macrocyclic complexes has been analyzed using gel permeation chromatography, and the tetramer has been characterized by a single-crystal X-ray diffraction study. These are the first examples of metallomacrocycles containing a Tröger's base derivative.

The weak-link approach has been employed to synthesize a series of bimetallic Cu(I) macrocycles in high yield. Addition of phosphinoalkylether or -thioether ligands to [Cu(MeCN)4]PF6 produces "condensed" intermediates, [mu-(1,4-(PPh2CH2CH2X)2Y)2Cu2][PF6]2 (X = S, O; Y = C6H4, C6F4), containing strong P-Cu bonds and weaker O-Cu or S-Cu bonds. The weak bonds of these intermediates can be cleaved through ligand substitution reactions to generate macrocyclic structures, [mu-(1,4-(PPh2CH2CH2X)2Y)2(Z)nCu2][PF6]2 (X = S, O; Y = C6H4, C6F4; Z = pyridine, acetonitrile, diimines, isocyanide) in nearly quantitative yields. The incorporation of tetrahedral Cu(I) metal centers into these macrocycles provides a pathway to complexes that differ from analogous d8 square planar macrocycles generated via this approach in their increased air stability, small molecule reactivity, and ability to form multiple structural isomers. Solid-state structures, as determined by single-crystal X-ray diffraction studies, are presented for condensed intermediates and an open macrocycle

A series of new bis-1,4-phosphinoethoxyaryl hemilabile ligands of the form (1,4-(Ph2PCH2CH2O)2-arene), where the nature and substituent pattern of the central arene ring have been systematically va...

Gradient-corrected density functional theory calculations have resulted in geometry-optimized structures for a series of six large dirhodium complexes that are important synthetic intermediates in the weak-link synthetic approach. Analysis of these computed structures and their electronic makeup (including natural localized molecular orbital (NLMO) bond order analysis, natural population analysis (NPA) atomic charges, atoms-in-molecules (AIM) calculations, single-point energy analysis, and calculated vibrational frequency analysis) has provided insight into subtle secondary ligand−ligand effects, which lead to product selection in the first step of this synthetic strategy toward supramolecular coordination complexes.

Through the Weak-Link Synthetic Approach, the unsymmetric hemilabile ligand, 1,4-bis(2-diphenylphosphinoethoxy)naphthalene (7), has been used to prepare binuclear Rh(I) macrocycles in a two-step fashion. The intermediate structure, [(μ2,η1:η4:η1-(1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene))2Rh2][BF4]2 (8), and several macrocyclic complexes, [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2Rh2(CH3CN)4][BF4]2 (9), [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2Rh2(CO)6][BF4]2 (10), and [(μ2-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)2(CO)2Rh2(CH3CN)2][BF4]2 (11), are reported herein. Additionally, the mononuclear Rh(I) complexes, [(η1:η4:η1-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)Rh][BF4] (12) and [(η1:η1-1,4-bis(2-(diphenylphosphino)ethoxy)naphthalene)(CO)Rh(CH3CN)][BF4] (13), were isolated and fully characterized. Single-crystal X-ray diffraction structures of 8, 9 (cis-, anti-), 11, and 12 were determined. 2-D solution NMR studies and the solid-state crystal structures of 8 ...

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

The “weak-link approach” to metallomacrocycle synthesis has been employed to synthesize a series of Pd(II) macrocycles in high yield. Although this approach has been used to construct several Rh(I) complexes with a variety of ligands, the generality of this methodology with respect to transition metals has not been demonstrated. When added to [Pd(NCCH3)4][BF4]2, the phosphinoalkyl ether or thioether ligands produce “condensed intermediates”, [(μ-(1,4-(PPh2CH2CH2X)2−Y)2Pd2)][BF4]4 (4, X = O, Y = 2,3,5,6-((CH3)4C6); 5, X = O, Y = C6H4; 6, X = S, Y = C6H4), containing strong P−Pd bonds and weaker O−Pd or S−Pd bonds. The weak bonds of these intermediates can be quantitatively broken through simple ligand substitution reactions to generate the macrocyclic structures [(μ-(1,4-(PPh2CH2CH2X)2−Y)2(Z)4Pd2)][BF4]n (7, X = O, Y = 2,3,5,6-((CH3)4C6), Z = CH3CN, n = 4; 8, X = O, Y = C6H4, Z = CH3CN, n = 4; 9, X = O, Y = 2,3,5,6-((CH3)4C6), Z = CN, n = 0; 10, X = O, Y = C6H4, Z = CN, n = 0; 11, X = S, Y = C6H4, Z = CN, ...

We report a general, high-yielding method for the synthesis of water-soluble complexes, which is based upon the weak-link approach to supramolecular coordination chemistry. Specifically, we have utilized oligomeric ethylene glycol functional groups appended to the aryl groups of the diphenylphosphine moieties to achieve solubility. Small molecules or halide ions can be used to expand these complexes into larger, more flexible macrocyclic structures. The realization of this approach should allow for the preparation of allosteric biomimetic structures which can be used in aqueous media.

A new approach to synthesizing binuclear metallomacrocycles is reported. This approach utilizes flexible bisphosphine alkyl−aryl ether hemilabile ligands which complex Rh(I) to form “condensed” mac...

Air-stable, heteroligated platinum(II) weak-link approach (WLA) tweezer and triple-layer complexes that possess P,X-Aryl hemilabile ligands (P^ = Ph2PCH2CH2-, X = chalcoethers or amines) have been synthesized via the halide-induced ligand rearrangement (HILR) reaction, using a one-pot, partial chloride-abstraction method. The approach is general and works with a variety of phosphine-based hemilabile ligands; when a P,S-Ph ligand is used as the relatively strongly chelating ligand, heteroligated complexes are formed cleanly when an ether- (P,O-Ph), amine- (P,N-Ph2), or fluorinated thioether-based (P,S-C6F4H) hemilabile ligand is used as the weakly chelating counterpart. The HILR reaction has also been used to synthesize bisplatinum(II) macrocycles free of oligomeric material without having to resort to the high-dilution conditions typical for macrocycle synthesis. This approach is complementary to the traditional WLA to the synthesis of macrocyclic complexes which typically proceeds via fully closed, chloride-free intermediates. The structures of the complexes may be toggled between semiopen (with only one chelating ligand) and fully closed (with both ligands chelating) via the abstraction and addition of chloride.

Sequential reaction of two different hemilabile ligands (Ph(2)PCH(2)CH(2)X)(2)Ar (X = S, Ar = C(6)H(4) or C(6)(CH(3))(4); X = NCH(3), Ar = C(6)H(4); X = O, Ar = 9,10-C(14)H(8)) with a Rh(I) metal center resulted in the formation of heteroligated metallomacrocycles in high yield. The specific reaction conditions for each pair of hemilabile ligands are discussed. The solid-state structure of [[1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)H(4)]-[1,4-(Ph(2)PCH(2)CH(2)S)(2)C(6)(CH(3))(4)]Rh(2)](BF(4))(2), as determined by X-ray crystallography, is presented.

Classification of O,P ligands: ether-phosphines and furylphosphines, β-ketophosphines, phosphinocarboxylates, α-phosphinosulphoxides and their complexes of chromium group, of ruthenium, of cobalt group, of nickel group. Reactivity: oxidative additions, insertion reactions, metallation and catalytic applications

Through the Weak-Link Approach, fluorescent condensed and open Cu(I) tweezer complexes were prepared and characterized. These complexes exhibit fluorescence-sensitive binding properties for halide anions. The solid-state structure of a non-fluorescent Rh(I) tweezer analogue, determined by X-ray crystallography, shows that the counter anion, Cl−, is trapped inbetween the two amide groups of the tweezer arms through hydrogen bonds. Although the tweezer binds Cl−, the open complex also binds Cl−, showing that the main role of the metal is to increase the local concentration of the pyrenyl amide moieties so that 2:1 binding can take place.

Through the Weak-Link Approach, fluorescent condensed and open Cu(I) tweezer complexes were prepared and characterized. These complexes exhibit fluorescence-sensitive binding properties for halide anions. The solid-state structure of a non-fluorescent Rh(I) tweezer analogue, determined by X-ray crystallography, shows that the counter anion, Cl−, is trapped inbetween the two amide groups of the tweezer arms through hydrogen bonds. Although the tweezer binds Cl−, the open complex also binds Cl−, showing that the main role of the metal is to increase the local concentration of the pyrenyl amide moieties so that 2:1 binding can take place.

Homobimetallic macrocycles are prepared from flexible ligands in high yield by means of a new and general synthetic strategy called the "weak-link approach" [Eq. (a)]. Small aromatic molecules can be aligned inside the cage based on their interactions with the two Rh centers of the macrocycle.

The weak-link approach (WLA) to supramolecular assemblies allows for the design of multimetallic two- and three-dimensional arrays, host-guest architectures, sensors, catalysts, switches, and signal amplification devices. This Account describes the course of our investigations in this area beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands. These building blocks can be rationally mixed and matched to provide structures with a wide range of properties that have been used to develop functional supramolecular architectures, including chemical sensors and allosteric catalysts.

The "weak-link approach" for the synthesis of metallomacrocycles has been used to synthesize a series of novel Ru(II) macrocycles in high yield. RuCl 2 (PPh 3 ) 3 has been reacted with two different phosphino-alkyl-ether hemilabile ligands, 1,4-(PPh 2 (CH 2 ) 2 O) 2 C 6 H 4 and 1,4-(PPh 2 (CH 2 ) 2 OCH 2 ) 2 C 6 H 4 . The hemilabile bidentate ligand coordinates to Ru(II) centers through both the P and O atoms to form bimetallic "condensed intermediates". The weak Ru-O bonds have been selectively cleaved with CO, 1,2-diaminopropane, and pyridine to yield large open macrocycles. This is the first example of the weak-link approach employed to synthesize macrocycles with Ru, and metal centers in general that have more than four coordination sites.

The design and synthesis of a novel, supramolecular allosteric catalyst system, assembled via the weak-link approach, is presented. The catalyst contains two structural Rh(I) centers in thioether- and phosphine-rich hemilabile pockets, and two functional Cr(III) centers bound within salen-based moieties. The catalytic properties of the supramolecular catalyst are compared to those of a Cr(III)-salen monomeric analogue in the context of the asymmetric ring opening of cyclohexene oxide by TMSN3. Allosteric control is afforded via reactions that occur at distal sites which open the macrocyclic cavity and facilitate the catalytic reaction. Kinetic data show a significant rate increase upon opening of the catalyst's flexible macrocyclic cavity and enhanced selectivity and reactivity with respect to the monomeric Cr(III)-salen analogue. The work presented represents a new approach to the construction of abiotic allosteric catalysts.

A new dissymmetric bis-hemilabile ligand with strong binding phosphorus moieties, weak binding thioether moieties, and weaker binding ether moieties has been synthesized to construct heterobimetallic Rh(I)- and Pd(II)-containing macrocycles. The metals are placed in either the phosphorus/thioether or the phosphorus/ether coordination pocket of the dissymmetric ligand by taking advantage of the stepwise synthetic control offered by the weak-link approach. The weak bonds of these isomeric intermediates are systematically broken through ligand substitution reactions to cleanly and selectively generate a variety of open, macrocyclic architectures.

The synthesis and characterization of a new threefold symmetric hemilabile phosphino-alkylthioether ligand are described. This ligand can be used in combination with Rh(I) and Ir(I) precursor complexes to prepare 40-membered macrocyles with threefold symmetry via the Weak-Link Approach. Synthesis and characterization of two such structures are reported along with a single crystal x-ray diffraction analysis of one of the key intermediates in the case of Rh(I). This is a demonstration of the viability of the Weak-Link Approach for preparing structures other than bimetallic macrocycles and suggests that it could be generalized for a wide range of higher symmetry structures through appropriate hemilabile ligand design.

The design of a supramolecular allosteric catalyst system for catalytic signal amplification and detection is presented. The catalyst was switched "on" by the introduction of an analyte that also behaves as an allosteric activator. Concentrations of Cl- ions as low as 800 nM were catalytically amplified and detected. The signal was transduced via a pH-sensitive fluorescent probe and observed visually using a laboratory, handheld UV lamp and by spectrophotometry. Furthermore, the allosteric effect was quantified using gas chromatography for a range of Cl- concentrations. This three-part detection scheme involving analyte binding, allosteric catalyst activation, and signal transduction represents a new approach to small-molecule detection.

Herein we demonstrate a stepwise synthesis of heteroligated PtII Weak-Link Approach complexes with hemilabile N-heterocyclic carbene–thioether (NHC,S) and phosphino-thioether (P,S) ligands. These complexes, with both tweezer and triple-layer geometries, can be toggled between open, semiopen, and condensed states through the abstraction or introduction of Cl−. All species were fully characterized by multinuclear NMR spectroscopy and, in many cases, by single-crystal X-ray diffraction studies. Because the condensed tweezer and triple-layer species exhibit dynamic behavior at room temperature, the tweezer complex was studied by variable temperature NMR spectroscopy, revealing two species at low temperatures thought to be diastereomers resulting from thioether inversion. The relevant thermodynamic parameters for this exchange were determined. Competition experiments were performed to probe the lability of the P,S ligand, and the ligand scrambling that occurs in WLA systems with entirely P,S ligands was not observed in these NHC,S/P,S heteroligated complexes. In contrast to the halide-induced ligand rearrangement reaction, in which heteroligated complexes form when the electron donating abilities of the “weak links” are different, the stepwise assembly strategy described here does not require different electron-donating abilities of the “weak links”, as it makes use of a non-labile N-heterocyclic carbene–metal interaction instead.

A method that utilizes the “weak-link synthetic approach” to binuclear macrocycles and a hemilabile ligand derived from Wurster's reagent (N,N,N‘,N‘-tetramethyl-1,4-phenylenediamine (TMPD)) to prep...

A novel halide-assisted approach for opening RhI−thioether-based condensed intermediates into binuclear macrocycles is reported. This novel ring-opening reaction provides entry into a class of neutral binuclear macrocycles prepared via the “weak-link” synthetic strategy.