Falk Knoch

Asymmetric Michael additions via SAMP-/RAMP-hydrazones anti-diastereo- and enantioselective synthesis of 3,4-disubstituted 5-oxo-alkanoates

Abstract An efficient and highly anti-diastereo-(de=90–≈100%) and enantioselective (ee=92–≈100%) synthesis of 3,4-disubstituted 5-oxo-alkanoates 3 in good overall chemical yields is described. The procedure involves the asymmetric Michael addition of aldehydes or ketones to enoates via their lithiated SAMP-/RAMP-hydrazones. Both enantiomers are accessible at will.

Niederkoordinierte phosphorverbindungen ☆: LIII. 1,3-Diphosphaallyl-nickelkomplexe

Abstract (R = 2,4,6-tri-t-butylphenyl) and (R = 2,4,6-tri-t-butylphenyl) are two new nickel complexes with a 1,3-diphosphaallyl ligand. Both structures have been determined by X-ray analysis.

Transition metal complexes with sulfur ligands Part LXXIX. Crown thioether complexes of iron, cobalt, nickel and copper with bzo2-18S6. X-ray structure analysis of [Ni(bzo2-18S6)][B(C6H5)4]2 (bzo2-18S6 = 2,3,11,12-dibenzo-1,4,7,10,13,16-hexathiacyclooctadeca-2,11-diene)

Abstract Reaction of bzo2-18S6 (2,3,11,12-dibenzo-1,4,7,10,13,16-hexathiacyclooctadeca-2,11-diene) with Fe, Co, Ni and Cu salts yields the corresponding metal complexes [M(bzo2-18S6)]n+. Their trifluoromethanesulfonate salts were characterized by spectroscopic and electrochemical methods and the structure of [Ni(bzo2-18S6)][B(C6H5)4]2 was elucidated by X-ray structure determination. It crystallizes in space group P21/n with a = 1497.8(4), b = 1096.5(4), c = 1772.5(5) pm, β = 104.26(2)°, Z = 2 and Dcalc = 1.36 g/cm3; R = 0.061, Rw = 0.041. The nickel centre is surrounded by the six sulfur atoms of the ligand in a slightly distorted octahedron. The NiS distances indicate a ligand compression effect of bzo2-18S6. The different electrochemical behaviour of the [M(bzo2-18S6)]n+ complexes is discussed.

Transition metal complexes with sulfur ligands CIV. Protonation and alkylation of thiolate donors of [Fe(CO)2(‘S4’)] and [Fe(CO)(‘S5’)]: syntheses and properties of Fe(II) complexes with open-chain thioether ligands (‘S4’2−=1,2-bis(2-mercaptophenylthio)ethane(2−); ‘S5’2−=2,2′-bis(2-mercapto-phenylthio)diethylsulfide(2−))

Abstract [Fe(CO) 2 (‘S 4 ’)] and [Fe(CO)(‘S 5 ’)] could be reversibly protonated in two steps by strong acids such as CF 3 SO 3 H yielding species whose ν(CO) bands are shifted to higher wavenumbers by ∼40 cm −1 per equivalent of acid. The ν(CO) shifts are explained by protonation of the thiolate donors leading to a decrease of electron density at the metal centers and consecutive weakening of FeCO π backbonds. While the protonated species could be detected in solution only, analogous isoelectronic complexes which are alkylated at the thiolate donors were isolated and fully characterized spectroscopically and by X-ray structure analyses. Upon reaction with one or two equivalents of oxonium salts R 3 OBF 4 (RMe, Et), [Fe(CO) 2 (‘S 4 ’)] yielded [Fe(CO) 2 (R‘S 4 ’)]BF 4 (RMe: [ 1a ]BF 4 , REt: [ 1b ]BF 4 ) and [Fe(CO) 2 (R 2 ‘S 4 ’)](BF 4 ) 2 (RMe: [ 3a ](BF 4 ) 2 , REt: [ 3b ](BF 4 ) 2 ). In an analogous way, [Fe(CO)(‘S 5 ’)] yielded [Fe(CO)(R-‘S 5 ’)]BF 4 (RMe: [ 2a ]BF 4 , REt: [ 2b ]BF 4 ) and [Fe(CO)(R 2 ‘S 5 ’)](BF 4 ) 2 (REt: [ 5 ](BF 4 ) 2 ). The ‘asymmetrically’ alkylated [Fe(CO) 2 (Me‘S 4 ’Et)](BF 4 ) 2 , [ 4 ](BF 4 ) 2 , was obtained by reacting [Fe(CO) 2 (‘S 4 ’)] first with Me 3 OBF 4 and subsequently with Et 3 OBF 4 . Further complexes obtained by alkylation were [Fe(CO)(Bz‘S 5 ’)]PF 6 ([ 2c ]PF 6 ), containing the benzylated ‘S 5 ’ ligand, [Fe(CO)(I)(Me 2 ‘S 4 ’)]FeI 4 ([ 6 ]FeI 4 ) and [Fe(I) 2 (Me 2 ‘S 4 ’)] ( 7 ). Except 7 , all Fe(II) complexes are diamagnetic containing low-spin Fe(II) centers. Per step of alkylation, the ν(CO) frequencies are raised by ∼40 cm −1 in the case of [Fe(CO) 2 (‘S 4 ’)] and by ∼32 cm −1 in case of [Fe(CO)(‘S 5 ’)]. These ν(CO) shifts are explained in the same way as for the protonated species and corroborate the assumption that protonation takes place at the thiolate donors. X-ray structure determinations were carried out for [ 1b ]BF 4 , [ 3a ](BF 4 ) 2 , [ 3b ](BF 4 ) 2 , [ 5 ](BF 4 ) 2 , [ 6 ]FeI 4 and 7 . Although the ν(CO) shifts indicate large differences of the electron densities at the iron centers, in a remarkable way the average FeS distances of ∼228 pm remain practically invariant in all low-spin Fe(II) complexes regardless of the charge or the degree of alkylation. This is traced back to the transformation of FeS(thiolate) σ-donor bonds into FeS(thioether) σ-donor-π-acceptor bonds upon alkylation. This lowers the electron densities at the iron centers but leaves FeS distances unchanged because weakening of the σ bonds is compensated by the formation of additional π-acceptor bonds. The mono- and dialkylated complexes hydrolyze much more rapidly than the neutral patent complexes and allow the facile synthesis of the corresponding sulfur ligands in the free state. The complexes further prove that 3d metals can form stable complexes not only with crown thioethers but also with open chain thioethers. Correlation of states of protonation of iron sulfur ligand complexes with electron densities at the metal center and expected redox potentials allows the hypothesis to be made that reducing the N 2 molecule at either FeS or MoS sites of the cofactor in nitrogenases requires previous protonation of the S donors.

Ion-pair charge-transfer complexes of a dithiooxalate zinc donor component with viologens. Synthesis, structural and electronic characterization

Abstract Bipyridinium and phenanthrolinium acceptors of different reduction potentials form with zinc 1,2-dithiooxalates (dto) ion-pair charge-transfer complexes of the general formula {A 2+ [Zn(dto) 2 ] 2− }. The contact ion pairs exhibit absorptions in the range 390–490 nm which can be attributed to the ion-pair charge-transfer (IPCT) type. On the base of spectroscopic, electrochemical and quantum-chemical investigations the relation between optical and thermal electron transfer within the ion pair applying the Hush theory is discussed. The mean reorganization energy of 12 complexes is 180 U mol −1 and exceeds the values found for the dithiolene systems. Due to the diminished donor ability of the dithiooxalate unit, a hypsochromic shift of the position of the IPCT band, compared with the metal dithiolenes, results. The extent of electron delocalization from [Zn(dto) 2 ] 2− to pQ 2+ , as described by the parameter α 2 , is calculated as 4.1 × 10 −6 . X-ray analyses of BQ[Zn(dto) 2 ] and DP[Zn(dto) 2 ] reveal that the solid-state structure is largely determined by the geometry of the acceptor component.

Übergangsmetallkomplexe mit Schwefelliganden: XLIII. UV-Photolyse der Thilat-amin-Komplexe [Ru(CO)2(bmae)] und [Ru(CO)2(bubmae)] (bmae2 = 1,2-Bis(2-mercapto-anilino)ethan(−2); bubmae2− = 1,2-Bis(2-mercapto-3,5-di-tbutyl-anilino)ethan(−2))☆

Abstract UV-photolysis of the thermally stable thilate amine complexes [Ru(CO) 2 (bmae)] ( 1 ) and [Ru(CO) 2 ( bu bmae)] ( 2 ) leads to elimination of CO. In presence of L = PPh 3 , NH 3 , N 2 H 4 , and NO the monocarbonyl complexes [Ru(CO)(PPh 3 )( bu bmae)] ( 3 , [Ru(CO)(NH 3 )( bu bmae)] ( 7 ), [Ru(CO)(NH 3 )(bmae)] ( 8 ), [Ru(CO)(N 2 H 4 )(bmae)] ( 10 ) and the binuclear [Ru(NO)(bmae)] 2 ( 11 ) are obtained. In absence of L the binuclear complexes [Ru(CO)( bu bmae)] 2 ( 9 ) and [Ru(CO)(bmae)] 2 ( 6 having six coordinate Ru centers are formed. Complete CO elimination from 2 yields binuclear [Ru( bu bmae)] 2 ( 5 ) which was characterized by an X-ray diffraction study. 5 contains distorted planar [Ru( bu bmae)] units which are associated via two RuSRu bridges, such that the Ru centers each have a distorted square-pyramidal configuration and a vacant coordination site. In all the main, the coordinatively unsaturated [Ru(CO)(bmae)] fragment and [Ru(CO)( bu bmae)], which is stabilized by the π-donor properties of the thiolate atoms, appear in all reactions.

Transition metal complexes with sulfur ligands CXI. Skeletal rearrangement of 2,3-dibromo-1-propanol in the template alkylation of [Ni(‘S2C6H4’)]2− (‘S2C6H4’2−=1,2-benzeneditiotale(2−)). Syntheses of [M(‘S4-C3OH’)] complexes (M=NiII,PtII; ‘S4-C3OH’2− = 1,3-bis(2-mecaptophenylthio)-2-propanol(2–))

Abstract Template alkylation of Na2[Ni(‘S2C6H4’)2] with 2,3-dibromo-1-propanol yielded [Ni(‘S4-C3OH’)] (1) from which the free thiol ‘S4-C3OH’-H2 (2) was obtained by hydrolysis with aqueus HCl. 2 contains a symmetrical C3 bridge carrying the OH function at the central C atom, because the C skeleton of 2,3-dibromo-1-propanol rearranges in the course of the alkylation reaction. This was proved by independent synthesis of 2 from Na2[Ni(‘S2C6H4’)2] and 1,3-dibromo-2-propanol followed by hydrolysis of the resulting nickel complex, and the X-ray structure determination of [Pt(‘S4-C3OH’)]·THF (3·THF) which is homologous to 1. (Crystal data of 3·THF: monoclinic, P2 1 c , a=10.173(3), b=12.585(4), c=15.536(4) A , β=93.07(2)°, R/R w =0.071/.0063.) The Pt centre of 3·THF exhibits approximately square planar coordination with nearly equidistant bond lengths to the thioether and thiolate sulfur donors. The rearrangement of the C skeleton of 2,3-dibromo-1-propanol is traced back to the neighbouring-group effect of the OH function.

Transition metal complexes with sulfur ligands Part XCIII. Synthesis, structure and reactivity of [MoIV(μ-S)(‘buS4’)]2 (‘buS4’2−=1.2-bis(di(t-butyl)-2-mercaptophenylthio)ethane(2−))

Abstract In search for model compounds of the active centers of enzymes containing Mo we obtained in DMF the binuclear complexes [MoS(‘S4’)]2 (1) (‘S4’2−=1.2-bis(2-mercaptophenylthio)ethane(2−)) and [Mo(μ-S)(‘buS4’)]2 (2) (‘buS4’2−=1.2-bis(3.5-di(t-butyl)-2-mercaptophenylthio)ethane(2−)) from either (a) H2S and [MoCl2(L)] or (b) H2S, [MoCl4(MeCN)2] and L-H2 (L‘S4’, ‘buS4’). According to method (b) [MoS(‘N2H2S2’)]2 (3) (‘N2H2S2’2−=1.2- bis(2-mercaptophenylthio)ethane(2−)) could also be prepared, being isolated as the solvate 3·2DMF. [Mo(μ- S)(‘buS4’)]2·6CD2Cl2 (2·6CD2Cl2) was obtained as single crystals and characterized by X-ray structure analysis (monoclinic space group P21/c, Z=2, a=1607.4(16), b=1540.3(14), c=1836.6(14) pm, β=111.43(6)°, R (Rw)=0.065 (0.056)). 2 contains two enantiochiral [Mo(‘buS4’)] fragments which are connected via two sulfido bridges and one MoMo bond such that the Mo centers become seven-coordinate. 2 is electrochemically redox active, showing two oxidation and reduction waves each in the cyclic voltammogram (CH2Cl2), but does not react with either N2H4 and O2 or CO and PMe3. Attempts to prepare anionic [Mo(‘N2H2S2’)] complexes with sulfido ligands led to NBu4Cl·(NBu4)2[Mo3(μ3-S)(μ2-S2)3S6] (4) as the minor by-product. 4 was characterized by X-ray structure analysis (monoclinic space group P21/c, Z=4, a=1274.4(7), b=1322.6(6), c=4143.8(15) pm, β=97.30(4)°, R (Rw)=0.098 (0.078)).

Valence Isomerization Of Phosphaalkenes

Abstract The main topic of this lecture is valence isomerization with participation of the PC-double bond. This is a matter of intramolecular structure conversion which takes place under shifting of α- and π-bonds. This phenomenon was at first observed in the reactions of disilylphosphanes with phosgene and isocyanide dichlorides.

DYNAMIC STEREOCHEMISTRY OF SYMMETRICALLY BUT DIFFERENTLY SUBSTITUTED DIPHOSPHANES

Abstract The main interest of our work in Bonn during the last years was in the field of phosphorus-carbon compounds with multiple bonds. Beside the synthesis of new classes of compounds we were particularly interested in the amazing analogy between the PC- and the CC-double bond, which could be proved by evidence of E/Z isomers and a clear indication of pericyclic reactions.