Manuel Alcarazo has moved to the University of Göttingen as Professor for Organic Chemistry in December 2015. Information on his current research is available here. This web page documents the activities of his group at the Max-Planck-Institut für Kohlenforschung (until 2015).
Research in our group is primarily directed toward the coordination chemistry of main group element in unusual oxidation states, the design of novel “frustrated Lewis pairs” and applications thereof to homogeneous catalysis and organic synthesis.
Total Synthesis (I), TU Dortmund, WS 2009/2010
Principles in Organometallic Chemistry, TU Dortmund, SS 2010
Stereoselective Synthesis (I), TU Dortmund, WS 2010/2011
Stereoselective Synthesis (II), TU Dortmund, SS 2011
Total Synthesis (I), TU Dortmund, WS 2011/2012
Stereoselective Synthesis, Heinrich-Heine University Düsseldorf, SS 2012 (please find the slides here)
Organometallic Chemistry (II), TU Dortmund, WS 2013/2014
Organometallic Chemistry (I), TU Dortmund, SS 2013
Stereoselective Synthesis, Heinrich-Heine University Düsseldorf, SS 2012
Total Synthesis (I), TU Dortmund, WS 2011/2012
Stereoselective Synthesis (II), TU Dortmund, SS 2011
Stereoselective Synthesis (I), TU Dortmund, WS 2010/2011
Principles in Organometallic Chemistry, TU Dortmund, SS 2010
Total Synthesis (I), TU Dortmund, WS 2009/2010
The goal of this project is the synthesis of extreme π-acceptor phosphines through the introduction of positively charged homo- or heteroaromatic substituents directly attached to the phosphorus atom. By exploiting this property, new Au and Pt catalysts have been developed that display a dramatically enhanced capacity to activate π-systems.
Very recently, we reported the synthesis of the first ever isolated carbene-stabilized P1-centered trication [L3P]3+ (L = 2,3-dialkylaminocyclopropenium) 1 by reaction of the 1-chloro-2,3-(dimethylamino) cyclopropenium salt 2 and P(SiMe3)3 (Scheme 1). Despite the three positive charges on the groups directly attached to the P atom, this compound can still serve as a ligand for π-acidic metals such as Pt. Thus, when 1 is treated with K2PtCl4 in acetonitrile, the bench stable complex 3 is formed. More interestingly, charge decomposition analysis of the metal-ligand interaction in 3 gave the surprising result that the total L→M σ-donation (0.31 e) is lower than the L→M π-back donation (0.43 e) into the very low-lying LUMO of 1, which must hence be regarded as the main interaction in 3. This unconventional situation in which the P-ligand removes net electron density from the metal suggests that compound 1 increases the natural π-acidity of Pt(II) centers. It should thus accelerate known reactions, or even permit new ones, in which either the coordination of the substrate or the nucleophilic attack to the activated substrate are the rate-determining steps.
Accordingly, we chose for our studies on ligand effects a series of phosphanes such as PPh3, P(OPh)3, P(C6F5)3 and precatalyst 3 in combination with a silver salt. As expected, both P(OPh)3 and P(C6F5)3 performed better than PPh3 in terms of reactivity (Scheme 2).
In addition, our synthetic program has already benefitted from these novel tools and natural products such as Orchinol, Ochrolide, Bulbophyllantrin and Epimedoicarisoside A have been prepared using our Pt and Au catalysts for the key hydroarylation step (Scheme 3).
In this area, our research has been strongly inspired by the theoretical work of Frenking about the nature of carbodiphosphorane 1 (Scheme 1). His studies revealed that in compound 1 and analogues the central carbon atom retains its four valence electrons that are thus all available for coordination. In fact, carbodiphosphoranes are known to react with two Lewis acids such as AuCl affording diaurated derivatives. However, their ability to donate their four electrons to the same electrophile in a simultaneous σ- and π-donation had not been described.
In this regard, we envisaged that the use carbodiphosphoranes may provide sufficient stabilization to attenuate the reactivity and allow the isolation of dihydrido borenium cations [L→BH2]+ (L = carbodiphosphorane), a series of compounds that cannot be isolated when classical σ-donating ligands are employed.
Our strategy is already producing some positive results with other low valent cations. Up to now we have been able to synthesize compound 4 which already depicts a σ- and π-dative bond between the central carbon atom and the GeCl moiety. Reaction with dimethylamino pyridine affords adduct 5 where the π interaction is not existing anymore.