Intramolecular coordination systems at platinum and palladium
Creators: name: Patel, Jim
Publisher: name: University Of Tasmania
Year: 2023

description: This thesis describes studies into the synthesis, characterisation and reactivity of organometallic complexes of the nickel triad elements containing intramolecular coordination systems based on N-heterocyclic donor groups. Oxidative addition of the bromoarene 2,6-bis{(3,5-dimethylpyrazol-1 yl)methyl}bromobenzene to [PtMez(SEt)2 ]2 gives the platinum(IV) complex PtBrMe2{2,6 (3,5-Me2pzCH2)2C6H3} in which the NCN ligand coordinates in a facial manner. The reagent reacts differently with [Pt(p-tolyl)z(SEt)2 ]2 to give the platinum(II) complex PtBr{2,6-(3,5 Me2pzCH2)2C6H3} and 4,4'-bitolyl. The method used to obtain the platinum(II) complex represents a new synthetic route to the platinum(II) NCN kernel and is shown to be applicable to other NCN ligand systems. Activation of both C(sp2)-H and C(sp3)-H bonds by palladium(II) acetate is used to generate aryl- and alkylpalladium(II) NCN complexes. Arylpalladium complexes are prepared with pyrazol-1-yl based donor groups and alkylpalladium complexes with pyrazol-1-yl, pyridin-2-yl and N-methylimidazol-2-yl donor groups. A hexametallic complex bearing six palladated NCN units at its periphery is obtained on palladation of the ligand hexakis{3,5 bis[(pyrazol-1-yl)methyl]phenyl} benzene. Oxidative addition of the bromoarene reagents 2,6-bis{ (pyrazol-1 yl)methyl} bromobenzene and 2,6-bis{ (3,5-dimethylpyrazol-1-yl)methyl} bromobenzene to the nickel(O) reagents affords nickel(II) NCN complexes. Cationic platinum, palladium and nickel NCN aqua complexes of the type [M(OH2){2,6 (3,5-Me2pzCH2)2C6H3} ][BF4], are found to catalyse the Michael addition of ˜í¬±-cyano carboxylates to methyl vinyl ketone. The palladium and nickel complexes are found to be more active catalysts than the platinum complex. Platinum(IV) and palladium(IV) complexes containing CN intramolecular coordination systems have been prepared. Ionic complexes of the type [PdR1R2{(pz)2BH2} ]K {(R1, R2) = (Me, Me), (Me, Ph), (Me, p-tolyl), (CH2CMe3, p-tolyl)} react with 8-(bromomethyl)quinoline to give the first isolable palladium(IV) complexes containing an intramolecular coordination system, Pd(CH2C9H6N-C,N)R1Rz{(pz)2BH2}. Structural studies of the complexes Pd(CH2C9H6N-C,N)Me2{(pz)2BH2} and Pd(CH2C9H6N-C,N)MePh{(pz)2BH2} reveal C-N intramolecular coordination of the 8-methylquinolinyl groups and include the first structural analysis of an arylpalladium(IV) complex. The palladium(IV) complexes show high thermal stability in solution but decompose in refluxing acetone by reductive elimination, with low selectivity in C-C coupling. The platinum complex Pt(CH2C9H6N-C,N)Me2{(pz)2BH2} has been prepared and found to be isostructural with Pd(CH2C9H6N-C,N)Me2{(pz)2BH2}, with the M-N bonds significantly longer for the palladium complex but the M-C bonds slightly shorter. Complexes containing bis(pyrazol-1-yl)borate in the absence of an intramolecular coordination system have also been studied, and include the structural characterisation of PtMe3 { (pz)2BH2} (py) and the detection of PdMe3 { (pz)2BH2} (PMePh2), the first example of a neutral palladium(IV) complex containing a phosphorus donor ligand.