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Krzysztof Radacki

Publications and source records attributed to Krzysztof Radacki.

16 recordsLinked to original sources
PubMed2006

Synthesis of ansa-[n]silacyclopentadienyl-cycloheptatrienyl-chromium complexes (n = 1, 2): novel precursors for polymers bearing chromium in the backbone.

Reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with a variety of dialkyl(dichloro)silanes in aliphatic solvents afforded the corresponding [1]silatrochrocenophanes. Structural characterization by X-ray diffraction analysis of the [1]silatrochrocenophanes bearing Me2Si, (iPr)2Si, and silacyclobutane bridges revealed tilt angles alpha of 15.56(12) degrees , 15.8(1) degrees , and 16.33(17) degrees , respectively. Analogously, a [2]silatrochrocenophane (6) was prepared in excellent yield by reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with 1,2-dichloro-1,1,2,2-tetramethyldisilane. This complex also was characterized structurally and exhibited a tilt angle alpha of 2.60(15) degrees. The [1]silatrochrocenophane bearing the Me2Si bridge underwent facile and regioselective carbon-silicon bond cleavage with [Pt(PEt3)4] to give a very high yield of an oxidative addition product. The ring-opening polymerization of these novel [1]silatrochrocenophanes afforded ring-opened chromium-based polymers.

Journal Article↗
PubMed2006

6H,13H-Pyrazino[1,2-a;4,5-a']diindole analogs: probing the pharmacophore for allosteric ligands of muscarinic M2 receptors.

A series of 6H,13H-pyrazino[1,2-a;4,5-a']diindole analogs was synthesized in order to probe the pharmacophore hypothesis for allosteric ligands of muscarinic M(2) receptors. The 3D structure of the novel ring system was determined by means of NMR spectroscopy and X-ray diffraction revealing a totally flat geometry. Low binding affinities for the [(3)H]N-methylscopolamine-occupied M(2) receptors (reflected by EC(50,diss)) indicated that the spatial arrangement of the pharmacophore elements (two aromatic rings flanked by two cationic centers) incorporated in the bisquaternary analogs 5 and 6 is unfavorable for strong ligand-receptor interactions. Due to the structural similarity of the novel compounds to neuromuscular-blocking agents, their affinities (reflected by K(i)) to the muscle type of nicotinic acetylcholine receptors were also determined. The dimethyl and diallyl analogs 5 and 6 exhibited rather high affinities to the muscle type of nicotinic acetylcholine receptors, suggesting a pronounced neuromuscular-blocking activity. Compound 5 showed a 34-fold higher affinity for the muscle type nAChR than for the allosteric site of M(2) receptors.

Allosteric Regulation↗
PubMed2005

Heterodinuclear bridged borylene complexes.

Heterodinuclear bridged borylene complexes are synthesized via oxidative addition of the B-Br bond of bromoboryl complex precursors to an electron-rich palladium species. The synthetic protocol grants access to the first compound featuring the reactive bromoborylene ligand.

Journal Article↗
PubMed2003

Formation, structure and reactivity of boryloxycarbyne complexes of group 6 metals.

Reaction of the diborane(4) B(2)(NMe(2))(2)I(2) with two equivalents of K[(eta(5)-C(5)H(5))M(CO)(3)] (M=Cr, Mo, W) yielded the dinuclear boryloxycarbyne complexes [[(eta(5)-C(5)H(5))(OC)(2)M(triple bond)CO](2)B(2)(NMe(2))(2)] (4 a, M=Mo; b, M=W; c, M=Cr), which were fully characterised in solution by multinuclear NMR methods. The Mo and W complexes 4 a, b proved to be kinetically favoured products of this reaction and underwent quantitative rearrangement in solution to afford the complexes [[(eta(5)-C(5)H(5))(OC)(2)M(triple bond)CO]B(NMe(2))B(NMe(2))[M(CO)(3)(eta(5)-C(5)H(5))]] (5 a, M=Mo; b, M=W); 5 a was characterised by X-ray crystallography in the solid state. Corresponding reactions of B(2)(NMe(2))(2)I(2) with only one equivalent of K[(eta(5)-C(5)H(5))M(CO)(3)] (M=Mo, W) initially afforded 1:1 mixtures of the boryloxycarbyne complexes 4 a, b and unconsumed B(2)(NMe(2))(2)I(2). This mixture, however, yielded finally the diborane(4)yl complexes [(eta(5)-C(5)H(5))(OC)(3)M[B(NMe(2))B(NMe(2))I]] (6 a, M=Mo; b, M=W) by [(eta(5)-C(5)H(5))(OC)(3)M] transfer and rearrangement. Density functional calculations were carried out for 4 c and 5 a, b.

Journal Article↗