Marco Keijser - Academia.edu (original) (raw)

Papers by Marco Keijser

Research paper thumbnail of Reactivity of 1-aza-4-oxa-1,3-butadienes (.alpha.-imino ketones) toward triorganoaluminum reagents. 2. Syntheses of triorganoaluminum .alpha.-imino ketone coordination complexes, diorganoaluminum (.alpha.-imino)alkoxides, and diorganoaluminum (.alpha.-imino)enolates and study of their dynamic beh...

Organometallics, 1987

The reactions of triorganoaluminum reagents with a-imino ketones [R1N=C(R2)C(R3)=O] and 2oxopyrid... more The reactions of triorganoaluminum reagents with a-imino ketones [R1N=C(R2)C(R3)=O] and 2oxopyridyl derivatives [NC5H4-2-C(R3)=0] follow a distinct course in which product formation is almost quantitative. The first stage of these reactions involves formation of 1:l and 2:l coordination products of type 1, [ (A1R3) (u-N-or a-0-( RIN=C (R2)C (R3)=0) )] and [ (AlR&{ u,u-N,O-(R'N=C ( R2) C(R3)=0) )I, respectively. Intermolecular exchange processes between the compounds 1 and either free ligand or free (AlR3)2 occur and have been studied by NMR spectrometry. Addition products [Me2Al(R1)N=C(R2)-C(R3,R4)0A1Me3] (2) with an oxygen-coordinated trimethylaluminum unit were formed from the 2:l coordination complexes. At higher temperatures the methyl groups of the MezAl and the Me3A1 units undergo exchange involving dissociation of the dimethylaluminum-nitrogen bond followed by methyl exchange as in (A1MeJ2. The 1:l A1R3:a-imino ketone coordination complexes react further to dimeric addition complexes [R2A1(R1)N=C(Rz)C(R3,R4)O]z (3). If R3 # R4, two diastereoisomers are formed. In one case optically pure (R)-l-(2-pyridyl)ethanol was used to synthesize the dimeric aluminum complex 3d in order to identify (assign) the enantiomeric pairs of these diastereoisomers. For one isomer, the RRISS one, equilibria between a five-and a four-coordinate species could be established involving an AI-N bond dissociation-association process with retention of the dinuclear structure via the AlzOi bridge. Finally, oxygen-coordinated diorganoaluminum (a-imino)enolates, [&A1(R1)N=C(R2)C(=CH2)O], (4), have been synthesized, isolated, and characterized. An equilibrium between mononuclear and higher nuclearity species was established. , I , I , , (1) (a) van Koten, G.; Vrieze, K. Adu. Organornet. Chem. 1982,21,153. (b) van Koten, G.; Vrieze, K. RecE: J. R. Neth. Chem. SOC. 1981,100,129. (2) (a) van Koten, G.; Jastrzebski, J. T. B. H.; Vrieze, K. J. Organornet. Chem. 1983,250,49 and references therein. (b) Jastrzebski, J. T. B. H.; Klerks, J. M.; van Koten, G.; Vrieze, K. J. Organornet. Chem. 1981,210, C49. (c) Klerks, J. M.; Jastrzebski, J. T. B. H.; van Koten, G.; Vrieze, K. J. Organomet. Chem. 1982,224, 107. (d) Klerks, J. M.; Stufkens, D. J.; van Koten, G.; Vrieze, K. J. Organornet. Chem. 1979,181, 271. (e) van Wet, M. R. P.; Jastrzebski, J. T. B. H.; van Koten, G.; Vrieze, K.; Spek, A. L.

Research paper thumbnail of Coordination preferences of 3,3′-biisoxazolidines: A new kind of conformationally flexible chelating ligand

Polyhedron, 2005

ABSTRACT 3,3′-Bi{2-methyl-5-Ar}isoxazolidines (Ar=2-Py, L1; Ph, L2) were designed as new conforma... more ABSTRACT 3,3′-Bi{2-methyl-5-Ar}isoxazolidines (Ar=2-Py, L1; Ph, L2) were designed as new conformational flexible N-donor multidentates. They readily form complexes with metal ions and the coordination preferences of the ligands were characterized by means of 1H NMR spectroscopy and X-ray crystallography. In the [(Cp*IrCl2)2{L1}] complex the ligand bridges two iridium ions employing pyridyl-N functions, while in [Cp*Ir(L2)Cl]Cl and Cu{L2}Cl2·CHCl3 the ligand forms five-membered chelates via the isoxazolidine nitrogen atoms. Tridentate coordination in [Ni{L1}(H2O)(NO3)]NO3 supports formation of two chelates involving donors of two isoxazolidine and of pyridyl groups, with a facial arrangement of the binding sites around octahedral Ni ions. In associate [UO2(CH3OH)2(NO3)2]·L1 the non-coordinating biisoxazolidine is involved in hydrogen bonding with molecular bis-methanol uranyl nitrate moieties.

Research paper thumbnail of Reactivity of 1-aza-4-oxa-1,3-butadienes (.alpha.-imino ketones) toward triorganoaluminum reagents. 2. Syntheses of triorganoaluminum .alpha.-imino ketone coordination complexes, diorganoaluminum (.alpha.-imino)alkoxides, and diorganoaluminum (.alpha.-imino)enolates and study of their dynamic beh...

Organometallics, 1987

The reactions of triorganoaluminum reagents with a-imino ketones [R1N=C(R2)C(R3)=O] and 2oxopyrid... more The reactions of triorganoaluminum reagents with a-imino ketones [R1N=C(R2)C(R3)=O] and 2oxopyridyl derivatives [NC5H4-2-C(R3)=0] follow a distinct course in which product formation is almost quantitative. The first stage of these reactions involves formation of 1:l and 2:l coordination products of type 1, [ (A1R3) (u-N-or a-0-( RIN=C (R2)C (R3)=0) )] and [ (AlR&{ u,u-N,O-(R'N=C ( R2) C(R3)=0) )I, respectively. Intermolecular exchange processes between the compounds 1 and either free ligand or free (AlR3)2 occur and have been studied by NMR spectrometry. Addition products [Me2Al(R1)N=C(R2)-C(R3,R4)0A1Me3] (2) with an oxygen-coordinated trimethylaluminum unit were formed from the 2:l coordination complexes. At higher temperatures the methyl groups of the MezAl and the Me3A1 units undergo exchange involving dissociation of the dimethylaluminum-nitrogen bond followed by methyl exchange as in (A1MeJ2. The 1:l A1R3:a-imino ketone coordination complexes react further to dimeric addition complexes [R2A1(R1)N=C(Rz)C(R3,R4)O]z (3). If R3 # R4, two diastereoisomers are formed. In one case optically pure (R)-l-(2-pyridyl)ethanol was used to synthesize the dimeric aluminum complex 3d in order to identify (assign) the enantiomeric pairs of these diastereoisomers. For one isomer, the RRISS one, equilibria between a five-and a four-coordinate species could be established involving an AI-N bond dissociation-association process with retention of the dinuclear structure via the AlzOi bridge. Finally, oxygen-coordinated diorganoaluminum (a-imino)enolates, [&A1(R1)N=C(R2)C(=CH2)O], (4), have been synthesized, isolated, and characterized. An equilibrium between mononuclear and higher nuclearity species was established. , I , I , , (1) (a) van Koten, G.; Vrieze, K. Adu. Organornet. Chem. 1982,21,153. (b) van Koten, G.; Vrieze, K. RecE: J. R. Neth. Chem. SOC. 1981,100,129. (2) (a) van Koten, G.; Jastrzebski, J. T. B. H.; Vrieze, K. J. Organornet. Chem. 1983,250,49 and references therein. (b) Jastrzebski, J. T. B. H.; Klerks, J. M.; van Koten, G.; Vrieze, K. J. Organornet. Chem. 1981,210, C49. (c) Klerks, J. M.; Jastrzebski, J. T. B. H.; van Koten, G.; Vrieze, K. J. Organomet. Chem. 1982,224, 107. (d) Klerks, J. M.; Stufkens, D. J.; van Koten, G.; Vrieze, K. J. Organornet. Chem. 1979,181, 271. (e) van Wet, M. R. P.; Jastrzebski, J. T. B. H.; van Koten, G.; Vrieze, K.; Spek, A. L.

Research paper thumbnail of Coordination preferences of 3,3′-biisoxazolidines: A new kind of conformationally flexible chelating ligand

Polyhedron, 2005

ABSTRACT 3,3′-Bi{2-methyl-5-Ar}isoxazolidines (Ar=2-Py, L1; Ph, L2) were designed as new conforma... more ABSTRACT 3,3′-Bi{2-methyl-5-Ar}isoxazolidines (Ar=2-Py, L1; Ph, L2) were designed as new conformational flexible N-donor multidentates. They readily form complexes with metal ions and the coordination preferences of the ligands were characterized by means of 1H NMR spectroscopy and X-ray crystallography. In the [(Cp*IrCl2)2{L1}] complex the ligand bridges two iridium ions employing pyridyl-N functions, while in [Cp*Ir(L2)Cl]Cl and Cu{L2}Cl2·CHCl3 the ligand forms five-membered chelates via the isoxazolidine nitrogen atoms. Tridentate coordination in [Ni{L1}(H2O)(NO3)]NO3 supports formation of two chelates involving donors of two isoxazolidine and of pyridyl groups, with a facial arrangement of the binding sites around octahedral Ni ions. In associate [UO2(CH3OH)2(NO3)2]·L1 the non-coordinating biisoxazolidine is involved in hydrogen bonding with molecular bis-methanol uranyl nitrate moieties.