12125-87-0Relevant articles and documents
Bimetallic activation in homogeneous catalysis. 3. Mechanistic study of the methoxycarbonylation of tricarbonyl(chlorobenzene)chromium: Isolation and reactivity of possible reaction intermediates
Dufaud, Véronique,Thivolle-Cazat, Jean,Basset, Jean-Marie,Mathieu, René,Jaud, Jo?l,Waissermann, Jacqueline
, p. 4005 - 4015 (2008/10/08)
The coordination of the Cr(CO)3 moiety to the aromatic ring allows the carbonylation of chlorobenzene, catalyzed by palladium complexes, to esters, aldehydes, amides or α-oxo-amides. The mechanism of methoxycarbonylation of tricarbonyl(chlorobenzene)chromium, (η6-C6H5Cl)Cr(CO)3, and the role of the Cr(CO)3 moiety are now investigated. Tricarbonyl(chlorobenzene)chromium reacts at room temperature with Pd(PPh3)4 or Pd(dba)2 and PR3 via an oxidative addition to give aryl-palladium complexes of the type {Pd[(η6-C6H5)Cr(CO)3](Cl)L y}2/y, which are monomers (L = PPh3 (1), PEt2Ph (4), PPh2Et (5)) or dimers (L = PPh3 (2), PCy3 (3)). By comparison, the oxidative addition of PhCl to Pd(PPh3)4 is known to proceed at 140 °C, indicating that the coordination of Cr(CO)3 to PhCl greatly enhances the rate of this reaction. However, this reaction does not proceed with L2 = dppe or dpph, but the same complexes can be prepared by Cl-bridge cleavage and/or phosphine exchange with PR3 on Pd2[(η6-C6H5)Cr(CO) 3]2(μ-Cl)2(PPh3)2 to give the monomers (L = PEt2Ph (4), PPh2Et (5); L2 = dppe (6), dpph (7)) and the dimer (L = PCy3 (3)). The X-ray structures of complexes trans-Pd2[(η6-C6H5)Cr(CO) 3]2(μ-Cl)2(PCy3)2 (3) and cis-Pd[(η6-C6H5)Cr(CO)3]Cl (dppe) (6) have been determined. Crystal data for 3: orthorhombic with the space group Pccm; a = 18.486 (8) A?, b = 20.401 (7) A?, c = 17.255 (6) A?, V = 6508 A?3, Z = 8. Crystal data for 6: monoclinic with the space group P21/n, a = 9.841 (2) A?, b = 12.783 (5) A?, c = 28.377 (2) A?, β = 92.23 (1)°, V = 3567 A?3, Z = 4. These aryl-palladium complexes react at room temperature with CO under atmospheric pressure (L = PPh3, PEt2Ph; L2 = dpph) or 5 bar (L = PCy3) to give the corresponding monomeric or dimeric acyl-palladium complexes of the type {Pd[(η6-C6H5CO)Cr(CO) 3](Cl)Ly}2/y (y = 2: L = PPh3 (8), PEt2Ph (9), L2 = dpph (10); y = 1: L = PPh3 (11), PCy3 (12)). The reaction does not proceed with L2 = dppe even under 30 bar of CO; Cl-bridge cleavage and phosphine exchange with dppe on Pd2[(η6-C6H5CO)-Cr(CO) 3]2(μ-Cl)2(PPh3)2 enable the formation of cis-Pd[(η6-C6H5CO)Cr(CO) 3]Cl(dppe) (13). Methanolysis of complexes Pd[(η6-C6H5CO)Cr(CO) 3]Cl(PPh3)2 (8) and Pd2[(η6-C6H5CO)Cr(CO) 3]2(μ-Cl)2(PPh3)2 (11) in the presence of triethylamine at room temperature proceeds rapidly and leads to the formation of (η6-C6H5COOMe)Cr(CO)3, which is the product of methoxycarbonylation of (η6-C6H5Cl)Cr(CO)3. Complexes {Pd[(η6-C6H5)Cr(CO)3]Cl(PPh 3)y}2/y (1, 2) and {Pd[(η6-C6H5CO)Cr(CO) 3]Cl(PPh3)y}2/y (8, 11) then appear to be reasonable intermediates in the catalytic cycle of methoxycarbonylation of (η6-C6H5Cl)Cr(CO)3. A possible mechanism for this reaction is discussed.
DERIVES HYDROSILYLES DES COMPLEXES (Η-ARENE) TRICARBONYLCHROME, DE TYPE (ΗC6R6)(CO)2Cr(H)SiHPh2; LIAISON A 2 ELECTRONS/3 CENTRES, Cr-H-Si
Matarasso-Tchiroukhine, Elisabeth,Jaouen, Gerard
, p. 2157 - 2160 (2007/10/02)
Diphenylsilane reacts photocemically, at low temperature, on the η(tricarbonylchromium)arenes, to give unstables hydrosilylcomplexes, (η-C6R6)(CO)2Cr(H)SiHPh2 with a three-center two electron bond, Cr-H-Si; according to 29Si NMR data, the degree of this bond is higher than both the degree of the Mn-H-Si bond in isoelectronic manganese compounds, (η-C5R5)L2Mn(H)SiHPh2, and the degree of the three-center Cr-H-Si bond in the permethylated complex, (η-C6Me6)(CO)2Cr(H)SiHPh2, of chromium.The variation of /2J(Si-Cr-H)/ depending on the electron density of the metal is discussed.
