Michael Büchner

Chirale tripod-rhodium-komplexe: Ligandsynthese, komplexchemie, katalyse☆

The reaction of epichlrohydrine (fx45-1) with lithium-diphenylphosphide (LiP(Ph)2 yields the alcohol (HOCH(CH2P(Ph)2)2) 1 in a stereochemically controlled reaction. To prove the constitution and coordination ability of 1, the compound has been used to synthesise the homoleptic bisdiphosphine-rhodium complexes trans/cis-[(1)2Rh1]B(Ph)42a, b. The X-ray structure of 2b shows a significant tetrahedral distortion of the planar coordination geometry theoretically favoured for a tetracoordinate metal d8 coordination compound. The diphosphino alcohol 1 easily reacts with chiral phosphorchloridites X2PCI(X2 = 2 R, 4R-2,4-pentanedioxy-3a); (±)- and R-2,2′-bi-1-naphthoxy-(3b)) to yield chiral-racemic as well as enantiomerically pure mixed donor group tripodal ligands (X2POCH(CH2P(Ph)2)2) 5a, b containing both phosphite and phosphine donor groups. The identity of these compounds has been proven by 1H-, 31P- and 13C-NMR spectroscopy, mass-spectra and microanalysis. The coordination capabilities of these novel tripod ligands are demonstrated by the synthesis and characterisation of the chiral rhodium-cyclooctadiene complexes {[(5a,b)Rh1(COD)]PF6} 6a,b, which show the typical hetero-bicyclooctane tripod metal cage of this type of tripod metal template. The rhodium complexes 6a,b are catalysts for the hydrogenation of prochiral olefines. Their activity is not too high and the enantioselectivity is low. The trihapto-coordination of the tripodal ligands is more of an impediment for this type of catalytic transformation.

Heterometallic early–late π-tweezer complexes: their synthesis, electrochemical behaviour and the solid-state structures of (η5-C5H4SiMe3)2Ti(CCPh)2 and [(η5-C5H4SiMe3)2Ti(CCPh)2]Pd(PPh3)

The reaction of [Ti](CCPh)2 (1) {[Ti]=(η5-C5H4SiMe3)2Ti} with equimolar amounts of CuBr, Ni(PPh3)3 or Pd(PPh3)4 produces the heterobimetallic early–late transition metal complexes of general type {[Ti](CCPh)2}MX [2: MX=CuBr, 3: MX=Ni(PPh3), 4: MX=Pd(PPh3)} in which the respective transition metal atoms are linked by σ,π-bound alkynyl ligands. The solid-state structure of 1 and 4 is reported. In heterobimetallic 4 the Pd(0) centre possesses a trigonal–planar environment caused by the two η2-coordinated Me3SiCC ligands and the datively bonded PPh3 group. The PPh3 moiety is thereby located out of the best Ti(CCSi)2Pd plane. Comparative cyclic voltammetric studies on complexes 1–4 as well as {[Ti](CCPh)2}Ni(CO), for comparison, are presented. These studies reveal a strong influence of the η2-coordinated low-valent transition metal complex fragments MX on the reduction behaviour of the Ti(IV) centre.

Four-Coordinate Group-14 Elements in the Formal Oxidation State of Zero – Syntheses, Structures, and Dynamics of [{(CO)5Cr}2Sn(L2)] and Related Species

The sodium salts Na2[{(CO)5M}2EX2] (M = Cr, Mo, W; E = Ge, Sn, Pb; X = Cl, I, OOCCH3) react with 2,2′-bipyridine (bipy) to form neutral compounds [{(CO)5M}2E(bipy)] (E = Sn: 1a–1c; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds 1a–1c and 3a [{(CO)5M}2E(phen)] (E = Sn: 1d–1f, E = Ge: 3b) are as well accessible. The 2,2′-bipyridine ligand in 1 may be formally replaced by two pyridine (py) ligands resulting in [{(CO)5M}2Sn(py)2] (1g: M = Cr, 1h: M = W). The bis-bidentate ligand 2,2′-bipyrimidine (bpmd) is found to coordinate just one [{(CO)5M}2Sn] entity in [{(CO)5M}2Sn(bpmd)] (2b: M = Cr, 2c: M = W). The biimidazolato (biim) ligand binds two [{(CO)5Cr}2Sn] moieties in [{(CO)5Cr}2Sn(biim)Sn{Cr(CO)5}2]2–, 2a. It is shown by 1H-NMR that the pyrimidine entities in these compounds (2b, 2c) are able to rotate by a full 180° turn-around with respect to one another. This process must involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, the activation energy for this process being around 60 kJ/mol. By 119Sn-NMR spectroscopy of almost all of the tin compounds described it is shown that equilibria between [{(CO)5M}2Sn(L2)] and [{(CO)5M}2Sn(L)] + L exist in all cases. From the temperature dependence of the δ values it is concluded that the activation barriers for this association/dissociation process is below 10 kJ/mol. The structures of all new compounds are documented by X-ray analyses and all compounds are characterized by the usual analytical and spectroscopical techniques.

Coordination Compounds of tripodCoII and tripodCoI − Selective Substitution and Redox Behaviour

The five-coordinate tripodCobalt(II) compound [tripodCoIICl2] (2) [tripod = CH3C(CH2PPh2)3] undergoes selective substitution of its chlorine groups on activation with KPF6 in the first substitution step and by TlPF6 in the second. Compounds of the type [tripodCoIILL′]2+ with two nitrile (32+) or isonitrile (52+) ligands are obtained by this route. Compounds [tripodCoIIL2] containing two equal ligands L are also accessible from CoIIaq as the starting material. The syntheses of [tripodCoII(CNR)2]2+ (52+) and [tripodCoIIX2] (X = CN, NCO, NCS) (6) are reported. Different routes to tripodCoI derivatives are described. Depending on the nature of the co-ligands, four-coordinate − [tripodCoINCO] (7) − or five-coordinate − [tripodCoI(CNR)2]+ (5+) − compounds are obtained. Several high-yield syntheses of [tripodCoI-alkyne]+ (8+) compounds are reported. The compounds are characterised by the usual analytical and spectroscopic techniques including X-ray analysis of selected examples.

NOVEL INTER- AND INTRA-MOLECULAR DONOR-STABILIZED 1-METALLA-2-SILA-1,3-DIENES

The synthesis of the inter- and intra-molecular donor-stabilized 1-metalla-2-sila-1,3-dienes Cl(H2CCH)SiMLn·OP(NMe2)3[MLn= Fe(CO)4 3a, Cr(CO)5 3b], Ph(PhHCCH)SiFe(CO)4·OP(NMe2)3 3c and (C6H4CH2NMe2-2)(H2CCH)Si MLn[MLn= Fe(CO)4 6a, Cr(CO)5 6b] is described; the X-ray structures of compounds 3c and 6b are reported.

Neue Silicium- und Phosphor-haltige Käfigverbindungen mit Bicyclo[2.2.2]octan-Gerüst

The tripodal triphosphide H3CC[CH2P(Ph)(Li)]3 reacts with MeSiCl3 to yield the triphosphinosilane H3CC[CH2P(Ph)]3SiMe, 2a. The analogous reaction with PBr3 produces the triphosphinophosphine H3CC[CH2P(Ph)]3P, 2b. The bicyclo[2.2.2]octane-type cage structure of 2 is revealed by NMR data as well as X-ray analyses. 2b is one of the rare examples of a compound with mere C3-symmetry.

Fünffach koordinierte Komplexe vom Typ [tripodM-(ortho-(X)(Y)C6H4)]n (X, Y = O, S) bei d5-, d6- und d7-systemen. synthese, struktur, elektrochemie und esr-spektren / Five-coordinate complexes [tripodM-(ortho-(X)(Y)C6H4)]n (X, Y = O, S) with d5-,d6- and d7-Systems. Synthesis, Structure, Electrochemistry and ESR-Spectra

The d6-Co(III)-species [tripodCo-(ortho-(X)(Y)C6H4)]+ (X, Y = O, S, tripod = CH3C(CH2PPh2)3) 1 are reversibly reduced to the neutral d7-Co(II)-compounds [tripodCo-(ortho-(X)(Y)C6H4)] (X, Y = O, S) 2. Both species show fivefold coordination of cobalt with coordination polyhedra in between the limits of the square pyramid and the trigonal bipyramid respectively. The low-spin d7-species 2 give clearly resolved ESR-spectra revealing the coexistence of two geometric isomers above -80 °C, with only one isomer persistent at temperatures around 100 K. As an analogous d5-system [benzyltripodFe-(ortho-(S)(S)C6H4)]+ 3 (benzyltripod = C6H5CH2C(CH2PPh2)3) has been obtained from [benzyltripodFe(NCCH3)3]2+ and C6H6S2. Alternatively complexes of this type, e.g. [tripodFe-(ortho-(S)(S)C6H4)]+ 4, may be prepared from Fe(H2O)6(BF4)2/tripod/C6H6S2 when the reaction mixture is activated by acidification with HBF4. The geometry of the d5-species 3 and 4 is close to a trigonal bipyramid

REAKTIONSVERHALTEN METALLKOORDINIERTER 1-MOLYBDA-2-PHOSPHA-1,3-DIENE GEGENUBER ALKINEN UND DIINEN

Abstract Treatment of η 2 -{(R 1 )[(Ph)(H)CCH]P[Mo]}Fe(CO) 4 ( 1 ) or η 4 -{(R 1 )[(Ph)(H)CCH]P[Mo]}Fe(CO) 3 ( 2 ) {[Mo] = Mo(η 5 -C 5 H 5 )(CO) 2 ; R 1 = 2,4,6- t Bu 3 C 6 H 2 O} with HCCR 2 [ 3a : R 2 = (CH 2 ) 2 CH 3 ; 3b : R 2 = Ph] or HCCC 6 H 4 CCH ( 5 ) produces complexes [ 4a : R 2 = (CH 2 ) 2 CH 3 ; 4b : R 2 = Ph] or {ν 3 -{(R 1 )− ( 6 ) respectively. Each of these molecules contains a 1-ferraallyl moiety, which is η 3 -coordinated to an [Mo] building block. A possible reaction sequence for the formation of compounds 4 and 6 is described. The presented mechanism is corroborated by systematic studies of the reaction behaviour of 2 with different Lewis bases L [L = CO, PPh 3 , PPh 2 (CCPh)]. As an initial step, the formation of η 2 -{(R 1 )[(Ph)(H)CCH]P[Mo]}Fe(CO) 3 (L) [ 1 : L = CO; 8a : L = PPh 3 ; 8b : L = PPh 2 (CCPh)] is discussed. The result of the X-ray structure analysis of compound ν 3 -{(R 1 )[(Ph)(H)C= CH]- ( 4b ) is reported. 4b crystallizes in the triclinic space group P 1 with the cell parameters a = 1064.7(2), b = 1411.0(3), c = 1617.3(4)pm, α = 81.74(2), β = 80.89(2), γ = 73.05(2)°, V = 2282.5(9) × 10 6 pm 3 and Z = 2.

Darstellung und Struktur von tripod-Cobalt-Aminocarboxylato-Komplexen / Syntheses and Structure of tripod Cobalt Aminocarboxylate Complexes

Reaction of triphos (CH3C(CH2P(Ph)2)3) with Co(II)aq(BF4)2 followed by reaction with aminoacids leads to the cationic complexes 1-6 ([triphosCoNH2CH(R)COO]+ (R = H; Gly (1), R = methyl: L-Ala (S-2), D-Ala (R-2), R = isopropyl: L-Val (3), R = N -propyl: L - Pro (4), R = phenyl: D-phenylglycine (5), R = benzyl: L - Phe (6 )), which can be isolated in good yields by crystallization as their B(Ph)4- salts. The analogous reaction of the modified tripod ligand PhCH2C(CH2P(Ph)2)3 with L-alanine leads to the complex [PhCH2C(CH2P(Ph)2)3Co(L-Ala)]+, 7. The cations 1-7 have been characterized by spectroscopic methods and their structures determined by X -ray analyses which unequivocally demonstrate pentacoordinated Co(II) centers.