AB initio και ημιεμπειρική κβαντοχημική μελέτη της ηλεκτρονικής δομής και της γεωμετρικής ισομερείας ενώσεων συναρμογής του τύπου d1 °-Pd(PR3)2(RP=PR) και d6-8-M(PR3)2L3J (Μ = Os, Ir)

Abstract

The results of the theoretical studies of this Thesis are summarized as follows. (i) The optimization of the molecular structure of the unsubstituded diphosphene (HP=PH) by means of ab initio HF and MP2 calculations, as well as DFT calculations, showed that the trans structure is more stable than cis by 3-4 kcal/mol, depending upon the method and the basis set used. The calculated geometrical parameters of both isomers are very close to those calculated with methods beyond HF and to experimental values for the trans isomer. This agreement is even better when polarization functions were added in the basis set. Both structures have a low energy LUMO of n*pp character,whereas the HOMO and NHOMO are close to each other and have npp and n+ character respectively. (ii) The ab initio study of the two possible structures of diphosphene (HP=PH) complexes with the metal fragment Pd(PH3)2, at the HF, MP2 and DFT levels of theory, showed that the structure 77 2-(HP=PH)Pd(PH3)2, where diphosphene acts as a π-ligand, is 20 - 25 kcal/mol more stable than the structure r]1-(HP=PH)Pd(PH3)2, in which diphosphene coordinates as a monodentate ligand. The optimized geometry of the η2 structure is in good agreement withthe experimental structure of the complex (i72-F3CP=PCF3)Pd(PPh3)2, whereas this of the T]1 structure with experimental data for rj'-diphosphene complexes with other transition metals.The energies of the frontier orbitals as well as the results of the Mulliken population analysis for both structures showed that the elongation of the P=P bond upon coordination is due to the π-back bonding interaction, that is the transfer of electron density from an occupied d orbital of the metal to the n*pp orbital of diphosphene. This interaction is stronger in the case of the η2 structure, a fact that has been also proved by the energy decomposition analysis of the metal - diphosphene interaction energy according to the scheme of Kitaura and Morokuma. The barriers to rotation of both structures have been calcu­ lated at the MP2 και DFT level. The barrier is larger in the f]2 structure due to the more extensive π-back bonding interaction found in this case. (iii) The analysis of the interactions of the frontier orbitals of diphosphene (HP=PH) and d10-M(PR3)2 metal fragment, based on EHT calculations, showed that the electron rich d10-M(PR3)2 metal fragment prefers to coordinate in a dihapto (η2) mode with HP=PH to maximize the stabilization of its HOMO through a π-back bonding interaction. Furthermore, this analysis elucidates the conformation preferences of both T]1- and T]2-(HP=PH)Pd(PH3)2 complexes. (iv) A series of ab initio HF and MP2 calculations showed that the 16 electron OsHCl(CO)(PH3)2 complex adopts a distorted square pyramidal structure with H' ligand in the apical position and CL" and CO ligands in trans positions in the base. The calculated values of some crucial geometrical parameters of this complex are in good agreement with those found experimentaly for the isoelectronic OsHCl(CO)(P(i-Pr)3)2 and RuH(OSiPh3)(CO)(P(tBu2Me)3)2 complexes. An analogous structure has been also calculated for the isoelectronic complex Os(CH=CH2)C1(CO)(PH3)2 at both HF and MP2 levels. The CCH=CH2) ligand occupies the apical position of a square pyramidal structure and lies in the plane of Cl and CO ligands. A second local minimum with the vinyl ligand in the plane of the phosphines has been found 5-6 kcal/mol higher. (v) The analysis of the interactions of the frontier orbitals of the fragments consisting the OsHCl(CO)(PH3)2 complex, based on EHT calculations, showed that the π-donor (Cl ) and the π-acceptor (CO) prefer the trans position to each other, in order to achieve a push - pull mechanism. In this mechanism the donor and acceptor orbitals of the ligands interact with the same d orbital of the metal. Furthermore, this analysis elucidates the conformation preference of the Os(CH=CH2)C1(CO)(PH3)2 complex. (vi) The analysis of the interactions of the frontier orbitals of (NO) and ML4 fragments showed that 18 electron ML4(NO) complexes with strong nacceptors ligands L prefer the trigonal bipyramidal structure (TB) with linear coordination of NO, whereas in the case of strong π-donor ligands L the square pyramidal (SP) structure with a bent NO is also possible. In any case the crucial factor is the relative energy of the d orbitals of the ML4 metal fragment and the n*NO orbitals of the NO ligand. The potential energy surfaces of the 18 electron complexes OsCl(CO)(NO)(PH3)2 and [IrCl(CO)(NO)(PH3)2]+ have been calculated at the EHT level. Although their close analogy the two complexes adopt different geometry (TB and SP respectively) in full agreement with experimental data. According to the frontier orbital analysis this difference is due to the different nature of the two transition metals and in particular the energy of their d orbitals, which affects the relative position of the dz2 orbital and gives a SP structure for Ir complex. (vii) In the ab initio potential energy surfaces of both OsC1(CO)(NO)(PH3)2 and [IrCl(CO)(NO)(PH3)2]+ complexes there are two minima. Both global and local minima have been fully optimized at the HF and MP2 level of theory. For the osmium complex the TB structure with linear NO is 2 - 6 kcal/mol lower than the SP structure with bent NO, whereas forthe iridium complex the SP structure with bent NO is 4 - 7 kcal/mol lower than the TB structure with linear NO. Finally, the molecular structure of the OsC1(CH2)(NO)(PR3)2 complex has been optimized at the HF and MP2 level. It is also a TB structure with linear NO and with the carbene ligand vertical to the equatorial plane, in full agreement with experimental data. A local minimum with distorted SP structure has been also found (18 - 45 kcal/mol higher), in which the carbene ligand occupies the apical position.

ΣΤΗΝ ΠΑΡΟΥΣΑ ΔΙΑΤΡΙΒΗ ΓΙΝΕΤΑΙ ΧΡΗΣΗ AB INITIO ΚΑΙ ΗΜΙΕΜΠΕΙΡΙΚΩΝ ΥΠΟΛΟΓΙΣΜΩΝ ΜΕ ΣΤΟΧΟ ΤΗΝ ΕΡΜΗΝΕΙΑ ΤΗΣ ΗΛΕΚΤΡΟΝΙΚΗΣ ΚΑΙ ΤΗΣ ΜΟΡΙΑΚΗΣ ΔΟΜΗΣ ΔΥΟ ΤΑΞΕΩΝ ΣΥΜΠΛΟΚΩΝ ΕΝΩΣΕΩΝ ΚΑΙ ΣΥΓΚΕΚΡΙΜΕΝΑ ΤΩΝ ΕΝΩΣΕΩΝ ΣΥΝΑΡΜΙΓΗΣ ΤΟΥ ΔΙΦΩΣΦΕΝΙΟΥ (ΗΡ=ΡΗ) ΜΕ ΘΡΑΥΣΜΑΤΑ ΜΕΤΑΒΑΤΙΚΩΝ ΜΕΤΑΛΛΩΝ ΤΟΥ ΤΥΠΟΥ D^10-M(PR3)2 ΚΑΙ ΟΡΙΣΜΕΝΩΝ ΣΥΣΤΗΜΑΤΩΝ ΕΝΩΣΕΩΝ ΣΥΝΑΡΜΟΓΗΣ ΤΟΥ ΤΥΠΟΥ D^6-ML5 ΚΑΙ D^8ML5. ΚΑΤ' ΑΡΧΗΝ ΜΕΛΕΤΩΝΤΑΙ ΔΥΟ ΒΑΣΙΚΑ ΜΟΝΤΕΛΑ ΣΥΜΠΛΟΚΩΝ ΚΑΙ ΣΥΓΚΕΚΡΙΜΕΝΑ ΤΟ N^2-(HP =PH)PD(PH3)2, ΟΠΟΥ ΤΟ ΔΙΦΩΣΦΕΝΙΟ ΣΥΝΑΡΜΟΖΕΤΑΙ ΩΣ Π-LIGAND ΜΕΣΩ ΤΟΥ ΔΙΠΛΟ Υ ΔΕΣΜΟΥ Ρ=Ρ ΚΑΙ ΤΟ N^1-(HP-PH)PD(PH3)2, ΟΠΟΥ ΤΟ ΔΙΦΩΣΦΕΝΙΟ ΔΡΑ ΩΣ ΚΛΑΣΣΙΚΟ LIGAND ΔΟΤΗΣ ΔΥΟ ΗΛΕΚΤΡΟΝΙΩΝ ΜΕΣΩ ΤΟΥ ΜΟΝΗΡΟΥΣ ΖΕΥΓΟΥΣ ΕΝΟΣ ΑΤΟΜΟΥ ΦΩΣΦΟΡΟΥ, ΜΕ ΒΑΣΗ ΤΑ ΑΠΟΤΕΛΕΣΜΑΤΑ AB INITIO ΥΠΟΛΟΓΙΣΜΩΝ ΤΟΥ ΤΥΠΟΥ HF, MP2 ΚΑΙ DFT, ΑΛΛΑ ΚΑΙ ΗΜΙΕΜΠΕΙΡΙΚΩΝ ΥΠΟΛΟΓΙΣΜΩΝ ΤΥΠΟΥ ΕΗΤ ΣΤΑ ΠΛΑΙΣΙΑ ΤΗΣ ΜΕΘΟΔΟΥ ΤΗΣ ΑΝΑΛΥΣΗΣ ΤΗΣ ΑΛΛΗΛΕΠΙΔΡΑΣΗΣ ΜΕΤΩΠΙΚΩΝ ΤΡΟΧΙΑΚΩΝ. ΣΤΗ ΣΥΝΕΧΕΙΑ ΜΕΛΕΤΑΤΑΙ Η ΜΟΡΙΑΚΗ ΚΑΙ ΗΛΕΚΤΡΟΝΙΚΗ ΔΟΜΗ ΣΥΜΠΛΟΚΩΝ ΕΝΩΣΕΩΝ ΜΕ ΑΡΙΘΜΟ ΣΥΝΑΡΜΟΓΗΣ ΠΕΝΤΕ, ΟΠΩΣ D^6-OSHCL(CO)(P(I-PR)3)2, D^6-OS(CH =CHPH)CL(CO)(P(I-PR)3)2, ΚΑΘΩΣ ΚΑΙ ΤΩΝ ΠΕΝΤΑΣΥΝΑΡΜΟΣΜΕΝΩΝ ΣΥΜΠΛΟΚΩΝ ΤΗΣ ΝΙΤΡΟΖΥΛΟ ΟΜΑΔΑΣ, NO, D ^8-OSCL(CO)(NO)(PR3)2 ΚΑΙ [D^8-IRCL(CO)(NO)(PR3)2] ^+, ΜΕ ΒΑΣΗ AB INITIO ΚΑΙ ΗΜΙΕΜΠΕΙΡΙΚΟΥΣ ΥΠΟΛΟΓΙΣΜΟΥΣ.