Activation of organic substrates with transition metal cluster complexes

The olefin metathesis reaction induces the mild cleavage and redistribution of carbon-carbon double bonds, and ever since its discovery has been highly utilized in polymer science and organic synthesis (basic chemicals, pharmaceuticals). The reaction is catalyzed by a broad range of uni-, bi-, ternary and multicomponent systems based mainly on mononuclear transition metal complexes along the periodic table (Ti, Nb, Ta, Cr, Mo, W, Re, Co, Ru, Os). Despite the abundance of mononuclear catalytic systems, there is a limited number of bimetallic multiply bonded complexes inducing the metathetical polymerization of alkynes and the ROMP of cycloolefins. Within the latter, salts of the anions [W2Cl8]4- [(W4W)4+, σ2π4δ2] and [W2Cl7(THF)2]- [(W3W)6+ , a’2e’4] have been proved to be very effective initiators for the above reactions. In this context, scope of this thesis has been the synthesis and study of the catalytic properties of various salts of the analogous anions [M2Cl8]n- [(M4M)n+, σ2π4δ2; M=Mo, n=4, (1), M=Re, n=6, (2)] and [Mo2X9]3- [(Mo3Mo)6+, a’2e’4 , X=Cl (3a), X=Br (3b), X=I (3c)].Complexes 1, 2, 3a have been prepared by literature methods. Attempts to isolate the novel 3b,c produced mixtures from which the trinuclear [nBu4N]2[Mo3Br11] (4) and tetranuclear [nBu4N]2[Mo4OI12] (5) clusters have been isolated and characterized by spectroscopic methods (IR, UV-Vis, CV, ES-MS) and X-Ray crystallography.Compounds 1-4 fail to act as unicomponent initiators under a variety of experimental conditions, but upon activation with cocatalysts induce the polymerization and cyclotrimerization of PhC≡CH (PA) and the ROMP of selected mono- and bicycloolefins [norbornene (NBE), norbornadiene (NBD), dicyclopentadiene (DCPD), cyclopentene (CPE)], albeit in small yields. The cyclotrimers and polymers have been characterised by IR, and NMR techniques.Η αντίδραση ολεφινικής μετάθεσης επάγει την ήπια σχάση και επανασχηματισμό των διπλών δεσμών άνθρακα-άνθρακα ενώ, από την ανακάλυψή της, έχει βρει εφαρμογές στην οργανική σύνθεση (βασικές χημικές ουσίες, φαρμακευτικά προϊόντα). Η αντίδραση καταλύεται από πληθώρα συστημάτων, τα οποία βασίζονται κυρίως σε μονοπυρηνικά σύμπλοκα στοιχείων μετάλλων μεταπτώσεως (Ti, Nb, Ta, Cr, Mo, W, Re, Co, Ru, Os). Παρ’όλα αυτά, υπάρχει επίσης ένας περιορισμένος αριθμός διμεταλλικών συμπλόκων με πολλαπλό δεσμό μετάλλου-μετάλλου που επάγουν τον μεταθετικό πολυμερισμό αλκινίων και τον ROMP κυκλοολεφινών. Στο πλαίσιο αυτό, άλατα των ανιόντων [W2Cl8]4- [(W4W)4+, σ2π4δ2] και [W2Cl7(THF)2]- [(W3W)6+ , a’2e’4] έχει αποδειχθεί ότι είναι πολύ αποτελεσματικοί απαρχητές για τις παραπάνω αντιδράσεις. Σκοπός της παρούσας διατριβής είναι η σύνθεση και η μελέτη των καταλυτικών ιδιοτήτων μιας σειράς αλάτων των ανάλογων ανιόντων [M2Cl8]n- [(M4M)n+, σ2π4δ2; M=Mo, n=4, (1), M=Re, n=6, (2)] και [Mo2X9]3- [(Mo3Mo)6+, a’2e’4 , X=Cl (3a), X=Br (3b), X=I (3c)].Τα σύμπλοκα 1, 2, 3a παρασκευάστηκαν σύμφωνα με γνωστές βιβλιογραφικές μεθόδους. Προσπάθειες να απομονωθούν τα καινούργια 3b,c είχαν ως αποτέλεσμα το σχηματισμό μιγμάτων, από τα οποία το τριπυρηνικό [nBu4N]2[Mo3Br11] (4) και το τετραπυρηνικό [nBu4N]2[Mo4OI12] (5) σύμπλοκο απομονώθηκαν και χαρακτηρίστηκαν φασματοσκοπικά (IR, UV-Vis, CV, ES-MS) και κρυσταλλογραφικά.Οι ενώσεις 1-4 δεν δρουν από μόνες τους ως απαρχητές, υπό διάφορες πειραματικές συνθήκες. Κατά την ενεργοποίησή τους όμως με συγκαταλύτες επάγουν σε μικρή απόδοση τον πολυμερισμό και κυκλοτριμερισμό φαινυλακετυλενίου (PA), καθώς και τον ROMP συγκεκριμένων μονο- και δι- κυκλοολεφινών [νορβορνένιο (NBE), νορβορναδιένιο (NBD), δικυκλοπενταδιένιο (DCPD), κυκλοπεντένιο (CPE)]. Τα κυκλοτριμερή και πολυμερή χαρακτηρίστηκαν με τεχνικές IR και NMR

Isolation, Characterization, and Computational Studies of the Novel [Mo-3(mu(3)-Br)(2)(mu-Br)(3)Br-6](2-) Cluster Anion

The novel trimolybdenum cluster [Mo-3(mu(3)-Br)(2)(mu-Br)(3)Br-6](2-) (1, Mo-3(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C2H4Br2 in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N+ (1), Et4N+, Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N+ salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) angstrom, b = 11.8638(11) angstrom, c = 22.521(2) angstrom, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) angstrom(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided

Isolation, Characterization, and Computational Studies of the Novel [Mo₃(μ₃-Br)₂(μ-Br)₃Br ₆]²⁻ Cluster Anion

The novel trimolybdenum cluster [Mo3(μ 3-Br)2(μ -Br)3Br6]2- (1, {Mo3}9+, 9 d-electrons) has been isolated from the reaction of [Mo(CO)6] with 1,2-C2H4Br2 in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)4N+ (1), Et4N+, Et3BzN+), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)4N+ salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) Å, b = 11.8638(11) Å, c = 22.521(2) Å, α = 90 deg, β = 109.348(4) deg, γ = 90 deg, V = 5061.3(9) Å3, Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (μ eff, 1.55 μ B, r.t.) is lower than the spin-only value (1.73 μ B) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm-1). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided