Ernesto Colomer

On the behaviour of an optically active cobalt—silicon bond. Evidence for the formation of analogues of silyl-grignard reagents☆

Abstract We describe the behaviour of (S)(+)-(CO) 4 CoSiMePh(1-Np), the absolute configuration of which is determined by reference to (S)(+)-(CO) 4 CoGeMePh(1-Np). Electrophiles(Cl 2 , Br 2 ) cleave the silicon—cobalt bond with retention of configuration at silicon, while nucleophiles(LiAlH 4 , H 2 O, MeOH, KOAc, Hg(OAc) 2 ) cleave the bond with inversion. Organolithium and Grignard reagents attack at carbonyl ligands to displace silicon as an anion, yielding R 3 SiLi and R 3 SiMgX. Reactions of R 3 SiLi proceed with predominant retention of configuration. The formation of the silyl-Grignard reagent is confirmed by its reaction.

Synthesis, chemical behaviour and crystal structure of cobalt-stabilized carbenes, (Ph3Ge)(CO)3CoC(OEt)R

Abstract Cobalt stabilized carbenes are readily synthesized by reaction of organolithium compounds with (CO) 4 CoGePh 3 . The neutral carbenes are formed from the anion thus obtained by treatment with an ethylating reagent. Anions α to the carbene atom can be generated by treatment with a strong base (NaH, RLi) and trapped with Et 3 OBF 4 . However attempts to trap both types of anions with chlorosilanes failed, and instead the compound (CO) 4 CoGePh 3 was recovered in good yield. An X-ray structural determination of one of these complexes, (Ph 3 Ge)(CO) 3 Co(OEt)Et, shows unusually short bond lengths in the carbene moiety and the linkage trans to the triphenylgermyl group. The unusual chemical behaviour can be related to special features of the structure of the complex.

The chemical behaviour of cobalt-stabilized carbenes having a trisubstituted silyl or germyl ligand. Stereospecific formation of benzoylsilanes from the reaction of organosilyl-cobalt tetracarbonyl derivatives with phenyllithium

Abstract We report the chemical behavior of cobalt-stabilized carbenes, R 3 M(CO) 3 CoC(OEt)R′, and their parent anions, R 3 M(CO) 3 CoC(O − )R′, where M = Si or Ge. The anions where M = Si, R′ = Ph decompose thermally into the corresponding benzoylsilanes; when the silicon atom is chiral (R 3 = MePh-1-Np) optically active R 3 SiCOPh is obtained with complete retention of configuration.

Preparation et reactivite de composes chiraux et non chiraux derives de (η5-cyclopentadienyl) dicarbonylfer. stereochimie de la coupure de la liaison fer—silicium

Abstract The preparation and some properties of compounds of the type (η5-C5H5)Fe(CO)(L)SiR3 (L = CO, PPh3, PCy3 (Cy = cyclohexyl), P(OEt)3 and R3 = Ph3, Ph2Me, PhMe2, Ph2(CH=CH2) or optically active MePh-1-Np) are described. When the environments of the silicon and iron atoms are asymmetric, it is possible to isolate the diastereoisomers. The iron—silicon bond is particularly stable; it is cleaved with retention of configuration by some nucleophiles (H2O, LiAlH4); electrophilic cleavages (Cl2, Br2, Cl2/AlCl3, Cl2/PPh3) are more complex and lead both to retention and inversion depending on the nature of the reagent and the substrate.

Introduction of optically active triorganogermyl ligands into transition metal complexes. Synthesis of carbene complexes, crystal structure and absolute configuration of cis-S(-)(methylphenyl-1-naphthylgermyl)-(methylethoxycarbene) tetracarbonylmanganese

The attachment of triorganogermyl ligands to transition metals by displacement of a CO ligand is described. The optical stability of the germyl anions has been used to prepare a nickel-germanium complex by displacement of chloride (this reaction representing a limiting case) and more generally in the synthesis of germanium-transition metal bonds by displacement of CO (the transition metal being Cr, Mo, W, Mn, Fe, or Co). Optically active germyl anions are used in the synthesis of carbene complexes by insertion of CO ligands into a carbon-transition metal sigma bond. A crystallographic study of the complex MePh-(1-Np)Ge(CO)4MnC(OEt)Me reveals that the carbene unit is cis to the germanium and that the germyllithium has reacted with retention of configuration.

Cyclometalation of phosphorus ligands by UV irradiation of complexes having transition metalsilicon bonds

UV irradiation of complexes of the type (η5-C5H5)(CO)nMSiR3 (n = 2, M  Fe; n = 3, M  Mo) in the presence of phosphorus ligands such as P(XC6H5)3 (X  O, S, CH2) and phosphines containing allyl, 1-naphthyl or tolyl groups gives cyclometalated complexes, R3SiH being eliminated with retention of configuration at Si. In the cyclometalation five-membered rings are formed in preference to six-membered rings, and metalation occurs more easily at sp2 than at sp3 carbon atoms. Methylphenyl-1-naphthylphosphine undergoes rapid racemization upon UV irradiation at room temperature.

Transition metal complexes corresponding to the insertion into a group IVB element-carbon bond: II. Preparation of manganese complexes. Mechanism of the deinsertion reaction

Abstract The anions [(η5-CH3C5H4)(CO)2(R3M)Mn]− (M = Si, Ge; R3 = Ph3, (1- C10H7)PhMe) react with alkyl, alkenyl or benzyl halides affording the neutral complexes (η5-CH3C3H4)(CO)2(R′)(R3M)Mn. These new compounds possess a piano stool geometry with the CO ligands in a diagonal (trans) arrangement. Their thermal reaction with PPh3 leads to the formation of R3MR′ (corresponding formally to the deinsertion reaction) and R3MH (corresponding to the migration of the R′ group to the cyclopentadienyl ring). A mechanism for these competitive reactions is proposed.

The reaction between organosilyl derivatives of (η5-C5H5)Fe(CO)2 and triphenyl phosphite. New evidence for ortho-metalated phosphite ligands

Abstract UV irradiation of (η5-C5H5)Fe(CO)2SiR3 in the presence of triphenyl phosphite gives the ortho-metalation product (η5-C5H5) Fe- o -C 6 H 4 OP (OC6H5)2-[P(OC6H5)3] with elimination of R3SiH. Triethyl phosphite leads with substitution of one carbonyl group to (η5-C5H5)Fe(CO)[P(OC2H5)3]SiR3. The optically active R(+)-(η5-C5H5)Fe(CO)2Si(CH3)(C6H5)(1-C10H7) yields (—)-CH3C6H5-(1-C10H7)SiH with complete retention of configuration. Mechanisms are suggested for these reactions.

Synthesis of optically active silicon–iron compounds. Stereochemistry of silicon–iron bond breaking

U.v. irradiation of the optically active compound (+)-[(π-Cp)Fe(CO)2SiMePh(1-Np)](I) in the presence of PPh3 gives the diastereoisomers (–)- and (+)-[(π-Cp)Fe(CO)(PPh3)SiMePh(1-Np)](II); cleavage by chlorine of the Si–Fe bond occurs with predominant retention at silicon in the case of (I) and (II), and with predominant inversion for the diastereoisomers (II) in the presence of PPh3.

The crystal structure of tetracarbonyl[η4-(1,1,3,4-tetramethylsilole)]chromium

An X-ray diffraction study has shown that tetracarbonyl[η4-(1,1,3,4-tetramethyl- silole)]chromium has a conjugated 1,3-diene bonded to a distorted piano stool Cr(CO)4 fragment. The intra-ring CC bond lengths (139.2, 145.8 and 139.0 pm) indicate predominant diene-to-metal donor bonding. The bending angle of the silole ligand is 37.7°, and the Cr(CO)2 trans angles are 105.87 and 149.12°.