Hartmut Schenkluhn

Organometallic complex compounds, part 51. Ligand property controlled CO-insertion in nickel complexes: Separation of electronic and steric effects

SummaryThe influence of twenty phosphorus-containing ligands on the CO insertion with four-coordinated Ni11 complexes as starting reagents is reported. Quantitative separation of the electronic and steric effects by a multilinear regression analysis (55% electronic and 45% steric influence) is presented together with a three dimensional representation. An increase in donor-capacity favours CO insertion and an increase in steric hindrance leads to a decrease in the fraction of the corresponding ketone.

Thermodynamische steuerung metallorganischer elementarschritte am beispiel der nickelkatalysierten cyclotrimerisation von butadien

Zusammenfassung Die Steuerung der Isomerenverteilung in der pyridinmodifizierten, nickelkatalysierten Cyclotrimerisation von Butadien ist, ein ausgezeichnetes Modell zum Studium eines thermodynamischen Steuerungsprozesses. Die hier im experimentellen Detail vorgestellte Analyse uber Ligandkonzentrations-Steuerungskarten in halblogarithmischer Auftragung liefert fur die thermodynamische Selektivitat typische “Titrationskurven”. Um Assoziationsphanomene in einem Elementarschritt oder beim katalytischen Prozess in mehreren Elementarschritten zu erkennen, muss die Konzentration des assoziierenden Partners logarithmisch variiert werden. Das Erfullen der Stochiometrie bei der Assoziation erfordert also die Konzentrationsanderung in Zehnerpotenzen. Bereits die Zugabe von einem Molprozent Pyridin pro g-Atom Ni fuhrt im System Ni/Butadien praktisch zum Abschalten der trans,cis,cis-Cyclododecatrien-Bildung.

Organometallic complex compounds, part 6(1). Property-specific ligand control of stability and reactivity of (1,3-dimethyl-?3-allyl)methylnickel-ligand complexes. Separation of electronic and steric effects

SummaryThe property-specific ligand control of 28 ligands on the decomposition temperatures in solution, measured by d.t.a. of a four-coordinate nickel(II)-complex is reported. A quantitative separation of electronic and steric effects by a multilinear regression analysis (75% electronic and 25% steric influence for the chosen ligands) is presented. The controlling effect of the selectivity on the decomposition (fraction of the C-C-linked product) (25 P-ligands) leads to an electronic: steric ratio of the property-specific ligand control of 55∶45 for the chosen ligands. An increase in the relative acceptor character of the P-ligands relatively destabilizes the complexes and thereby favours formation of a C-C-bond. An increase in steric hindrance also favours C-C-bond formation. A method for revising the steric parameter of P-ligands is presented and is used to correct the Θ-value of (PhCH2)3P is corrected to 135°. SCCC-MO-calculations for testing the chemical reasoning of the separated electronic and steric ligand property control are shown.

Basic Parameters in Metal-Catalysed Processes: The “Method of Inverse Titration”

The formalisms of Ni-catalysed organic syntheses using alkenes, alkynes, 1, 3-dienes and 1, 3, 5-trienes or their heteroanalogous substrates are compared with those of enzyme chemistry. For the unevolved metalorganic systems we developed the “method of inverse titration” to get evidence for relevant actual “metal-fractions” in the catalytic cycles. Depending on the real steady-state-concentrations of the active metal-complexes the amount of steering ligands has to be added. The concentration-control-maps give an insight into the relevant intermediates, their concentrations, correlations and coupling; this enables us to look at FMO-control in these catalytic processes leading to Metala-logy-Principle and its rules.