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Karlheinz Sünkel

Publications and source records attributed to Karlheinz Sünkel.

2 recordsLinked to original sources
PubMed2002

Alpha-amino acids with metallocenyl side chains.

A straightforward method for the synthesis of enantiomerically pure bis(valine)metallocenes is presented. Derivatives of lithium cyclopentadienylvaline 1a, b were obtained by addition of the (R)- or (S)-Schöllkopf reagents to 6,6-dimethylfulvene as single enantiomers and gave with FeCl2 or [RuCl2(dmso)4] the chiral metallocenes [Fe[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2] (2a, b) and [Ru[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2] (3a, b). Complex 2b was hydrolyzed to the ferrocenylene-bis(valine-methylester) [[Fe[C5H4-CMe2-CH(NH3+)COOMe]2]2+(Cl-)2] (7) without racemization. Complex 7 could be used as ligand and was treated with [[Cp*IrCl2]2] to afford [Fe[C5H4-CMe2-CH(COOMe)(NH2-IrCp*Cl2)]2] (10). The reactions of 1 with CoCl2, [Re(CO)5Br], [[(cod)RhCl2]2] (cod= 1,5-cyclooctadiene) or [Cp*MCl3] (M= Ti, Zr) gave the cyclopentadienyl complexes [[Co[C5H4-CMe2-[C4H2N2(OMe)2iPr]]2]+ I-] (11) and [Re[C5H4-CMe2-[C4H2N2(OMe)2iPr]](CO)3] (13), [(C8H12)Rh[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (14). [[Rh[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]I]2(mu-I)2] (15), [Cp*Cl2Ti-[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (16), and [Cp*Cl2Zr[C5H4-CMe2-[C4H2N2(OMe)2(iPr)]]] (17), with chiral valine derivatives as substituents on the cyclopentadienyl ring and with excellent diastereoselectivities. Also the Seebach reagent (Boc-BMI) or O'Donnell reagent could be added to 6,6-dimethylfulvene to give the lithium cyclopentadienides Li[C5H4-CMe2-[C3H2(tBu)(N-Boc)(NMe)O]] (18) and Li[C5H4-CMe2-CH(NCPh2)(COOEt)] (21), which formed the ferrocene derivatives [Fe[C5H4-CMe2-[C3H2(tBu)(N-Boc)(NMe)O]]2] (19) and [Fe[C5H4-CMe2-CH(NCPh2)(COOEt)]2] (22). The stable cobaltocinium cation in 11 and the complex 19 could be hydrolyzed to the metallocenes 12 and [Fe(C5H4-CMe2-CH(NH3+)(COO-)]2] (20) with two valines in the 1,1'-position. The structures of 2a, b, 11, 15, and 16 were determined by X-ray diffraction and confirm the diastereomeric purity of the compounds.

Amino Acids↗
PubMed1996

Synthesis, Structure, and Magnetic Properties of Transition Metal Complexes of the Nitroxide 2,5-Dihydro-4,5,5-trimethyl-2,2-bis(2-pyridyl)imidazole-1-oxyl.

With the radical 2,5-dihydro-4,5,5-trimethyl-2,2-bis(2-pyridyl)imidazole-1-oxyl (L) a series of transition metal complexes have been prepared: [ML(2)](SbF(6))(2) with M(2+) = Mn(2+) (1), Fe(2+) (2), Co(2+) (3), Ni(2+) (4), Cu(2+) (5), and Zn(2+) (6), Cu(L)(Cl)(2)(MeOH) (7), and Cu(L)SO(4).H(2)O (8). The structures of 1, 3, and 6 were determined by X-ray structural analyses. In these compounds the tridendate L is coordinated to the metal ion by the two pyridine nitrogen donors and by the oxygen atom of the nitroxide group. The N-O bond distances are 1.25(2) Å (1), 1.267(13) Å (3), and 1.260(11) Å (6). The M-O-N angles are 117.0(10) degrees (1), 114.5(8) degrees (3), and 114.2(7) degrees (6). Crystal data: space group P2(1)/n, for 1, 3, and 6; compound 1, a = 10.806(3) Å, b = 14.101(6) Å, c = 14.253(4) Å, beta = 108.82(2) degrees, V = 2055.7(12) Å(3), Z = 2, R(1) = 0.0677, wR(2) = 0.1512. Compound 3, a = 10.761(4) Å, b = 14.253(6) Å, c = 14.108(5) Å, beta = 111.16(3) degrees, V = 2017.9(13) Å(3), Z = 2, R(1) = 0.0702, wR(2) = 0.1460; compound 6, a = 10.788(2) Å, b = 14.147(3) Å, c = 14.196(3) Å, beta = 109.93(3) degrees, V = 2036.8(7) Å(3), Z = 2, R(1) = 0.0573, wR(2) = 0.1194. Magnetic measurements of 1, 2, 5, and 8 show strong antiferromagnetic interaction between the spin of the metal ion and the spin of the radical which increases at lower temperatures. For 6 the magnetic moment corresponds to two noninteracting spins in the temperature range 60-300 K.

Journal Article↗