Carsten Strohmann

Enantiomerically enriched ‘carbanions’:: Studies on the stereochemical course of selective transformations of metal alkyls

Abstract Two (aminomethyl)(lithiomethyl)silanes Ph 2 Si(CH 2 Li)(CH 2 NC 5 H 10 ) (NC 5 H 10 =1-piperidinyl) ( 2 ) and Me 2 Si{[ R ]-[CHLiPh]}(CH 2 SMP) {SMP=1-[( S )-2-(methoxymethyl)pyrrolidinyl]} [( R , S )- 17 ] are presented including their solid state structures, the first one non-chiral, the latter highly diastereomerically enriched. By metathesis reactions with metal(II) halides (metal=Mg, Ga, Pd, Cd and Hg), the corresponding bis{[(aminomethyl)silyl]methyl}metal(II) compounds or the [(aminomethyl)silyl]methylmetal(II) halides were obtained. In the case of highly diastereomerically enriched (aminomethyl)(lithiomethyl)silane ( R , S )- 17 , the ‘carbanionic’ fragment could be transferred with high stereoselectivities on the metals Hg and Pd. For all of the compounds, the solid state molecular structures were determined.

Synthesis and reactivity of dinuclear iron–platinum, chromium–platinum, molybdenum–platinum and tungsten–platinum complexes with bridging carbonyl, isocyanide and aminocarbyne ligands. An empirical study on the parameters decisive for the bonding mode of the isocyanide ligand

The dppm-bridged heterobimetallic μ-carbonyl complexes [(OC) 4 M(μ-CO)(μ-dppm)Pt(PPh 3 )] ( 1a , M=Cr; 1b , M=Mo; 1c , M=W) have been prepared by the reaction of [M(CO) 5 (η 1 -dppm)] (M=Cr, Mo, W) with [Pt(CH 2 CH 2 )(PPh 3 ) 2 ]. The outcome of stoichiometric isocyanide addition to 1 is electronically controlled by the π-accepting propensity of CNR. Addition of isocyanide ligands with strongly electron withdrawing substituents R affords the isonitrile-bridged complexes [(OC) 4 M(μ-CN–R)(μ-dppm)Pt(PPh 3 )] 2 (M=W; R=CF 3 ), 3 ( 3a , M=Cr; 3b M=Mo, 3c M=W; R=CH 2 SO 2 p -tolyl), and 4 (M=W; R=[CH 2 PPh 3 ][PF 6 ]. With less π-accepting isocyanides (R=CH 2 Ph, C 6 H 11 , CH 2 PO(OEt) 2 ,) the labile complexes [(RNC)(OC) 3 W(μ-CO)(μ-dppm)Pt(PPh 3 )] ( 5–7 ) ligated by a terminal isonitrile ligand are formed. In contrast, treatment of [(OC) 3 Fe(μ-CO)(μ-dppm)Pt(PPh 3 )] with CNCH 2 PO(OEt) 2 yields exclusively [(OC) 3 Fe{μ-CNCH 2 PO(OEt) 2 }(μ-dppm)Pt(PPh 3 )] ( 9 ) with the isocyanide ligand in a bridging bonding mode. Upon protonation of 2 and 3b with HBF 4 , the stable μ-aminocarbyne complexes [(OC) 4 M(μ-CN(H)R′)(μ-dppm)Pt(PPh 3 )][BF 4 ] ( 10–11 ) are formed by electrophilic addition of H + on the basic isonitrile nitrogen atom. The molecular structures of 1a , c , 2 and 3c have been determined by X-ray diffraction methods. The μ-CO and the μ-CNR ligands bridge the metal centres in an asymmetric manner, the Pt–μ-C distances being significantly shorter than the corresponding M–μ-C distances. In contrast, the μ-CNCH 2 PO(OEt) 2 ligand of [(OC) 3 Fe{μ-CN–CH 2 PO(OEt) 2 }(μ-dppm)Pt(PPh 3 )] ( 9 ) bridges symmetrically the two metal centres. Furthermore, the molecular structure of cis -[(benzylNC)(OC) 4 W(η 1 -dppm)] ( 8a ) resulting from degradation of 5 has been determined.

Synthesis, Reactivity and Molecular Structures of Bis(diphenylphosphanyl)methane‐Bridged Heterobimetallic Iron−Platinum Isocyanide Complexes: Breaking and Formation of Metal−Metal Bonds

When [(OC)3Fe(μ-CO)(μ-dppm)PtCl2] (1) is allowed to react with stoichiometric amounts of various isocyanides, cleavage of the metal−metal bond occurs, yielding the heterodinuclear isocyanide complexes [(OC)4Fe{μ-dppm}Pt(Cl)2(CNR)] (2a: R = 2,6-xylyl; 2b: R = o-anisyl; 2c: R = benzyl; 2d: R = cyclohexyl; 2e: R = tosylmethyl). Reduction of 2a−2e by NaBH4 in the presence of PPh3 affords the isocyanide-bridged complexes [(OC)3Fe(μ-C=N−R)(μ-dppm)Pt(PPh3)] (3a: R = 2,6-xylyl; 3b: R = o-anisyl; 3c: R = benzyl; 3d: R = cyclohexyl; 3e: R = tosylmethyl). Metathesis of 2a−2d with NaI rapidly results in the formation of [(OC)4Fe{μ-dppm}PtI2(CNR)] (4a−4d), which is slowly transformed under extrusion of CO giving [(OC)2IFe{μ-dppm}(μ-CO)PtI(CNR)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = benzyl; 6d: R = cyclohexyl), bearing an iodine ligand at the iron center. Due to this intramolecular iodide migration from Pt to Fe, an FeI d7 fragment interacts with a PtI d9 fragment through a covalent bond. Alternatively, 6a−6d are obtained by stoichiometric treatment of [(CO)3Fe(μ-I)(μ-dppm)PtI] (5) with CNR. Single-crystal X-ray diffraction studies are performed on 2d, 2e and 3c as well as on 6d. In the solid state, the two metal centers of 2e remain in close contact (3.862 A), whereas in the case of 2d they are separated by 6.573 A after cleavage of the metal−metal bond by CNR. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Heterobimetallic intermediates in alkene insertion reactions into a Pd–acetyl bond

The reactivity of diphosphine-bridged heterobimetallic Fe–Pd alkyl complexes was evaluated for the insertion of CO, isonitriles, ethylene, methyl acrylate and norbornadienes and the crystal structures of the precursor alkyl complex, the iminoacyl derivative and the five-membered ring complex resulting from ethylene insertion into the palladium–acyl bond are reported.

Synthesis of a highly enantiomerically enriched silyllithium compound

The highly enantiomerically enriched silyllithium compound lithiomethylphenyl(1-piperidinylmethyl)silane (4) reacts stereospecifically with chlorosilanes, but over a period of several hours slow racemization in solution at room temperature occurs, which can be suppressed by a transmetalation reaction with MgBr2(thf)4.

Bis{[diphenyl(piperidinomethyl)silyl]-methyl}cadmium and -magnesium

The homoleptic and monomeric metal alkyls bis[[diphenyl(piperidinomethyl)silyl]methyl]cadmium, [Cd(C(19)H(24)NSi)(2)] or [Cd[CH(2)SiPh(2)(CH(2)NC(5)H(10))](2)], (I), and bis[[diphenyl(piperidinomethyl)silyl]methyl]magnesium, [Mg(C(19)H(24)NSi)(2)] or [Mg[CH(2)SiPh(2)(CH(2)NC(5)H(10))](2)], (II), (CH(2)NC(5)H(10) is piperidinomethyl) are isostructural, and the molecules exhibit crystallographically imposed C(2) symmetry. The metal centres are located on special positions and, for each structure, half of the molecule is located in the asymmetric unit. The metal centres are intramolecularly coordinated and stabilized by two piperidinomethyl groups (side-arm donation). The Si-C and M-C bonds (M is Cd or Mg) are shortened compared with the corresponding non-metallated compounds, indicating stabilization by the diffuse polarizable Si centres (alpha effect). The C-M-C angle is 140.53 (12) degrees in (I) and 123.39 (11) degrees in (II).

Bis-, Tris- and Tetrakis(lithiomethyl)germanes: New Building Blocks for Organogermanium Compounds

Bis(lithiomethyl)germanes, R2Ge(CH2Li)2, tris(lithiomethyl)germanes, RGe(CH2Li)3, and tetrakis( lithiomethyl)germane, Ge(CH2Li)4, were prepared by the reductive C-S bond cleavage with lithium naphthalenide (LiC10H8) or lithium p,p’-di-tert-butylbiphenylide (LiDBB) and characterized by trapping with Bu3SnCl. The bis(lithiomethyl)germanes were used for the synthesis of 1,1-dimethyl-3,3-diphenyl-1-germa-3-silacyclobutane, 1,1-diethyl-3,3-diphenyl-1-germa-3-silacyclobutane, 1,1,3,3-tetraphenyl-1-germa-3-silacyclobutane and 1,1,3,3-tetraphenyl-1,3-digermacyclobutane. The single-crystal X-ray diffraction studies of methyltris(phenylthiomethyl)germane and tetrakis(phenylthiomethyl)germane, starting materials for the corresponding poly(lithiomethyl) germanes, indicate tetrahedrally arranged substituents at the germanium atoms.