29477-07-4Relevant academic research and scientific papers
Tri- and tetranuclear palladium-cobalt clusters containing bridging Ph2PCH2PPh2 (dppm) ligands. Crystal structures of [Pd2Co2(μ3-CO)2(CO) 5(μ-dppm)2] and [Pd2Co(μ3-CO)2(CO) 2(μ-dppm)2][PF6]
Braunstein, Pierre,De Méric De Bellefon, Claude,Ries, Michel,Fischer, Jean,Bouaoud, Salah-Eddine,Grandjean, Daniel
, p. 1327 - 1337 (2008/10/08)
The heterotetranuclear cluster [Pd2Co2(CO)7(dppm)2] (1) was synthesized in high yield by the reaction of [Co(CO)4]- with [Pd2Cl2(dppm)2] (dppm = μ-Ph2PCH2PPh2), whereas the A-frame complexes [Pd2Cl2(μ-Y)(dppm)2] (Y = CO, CH2) are much less reactive. The molecular structure of 1·2.5THF has been determined by X-ray diffraction. Crystal data: triclinic, space group P1 with Z = 2, a = 18.417 (8) A?, b = 14.798 (6) A?, c = 13.855 (6) A?, α = 113.61 (2)°, β = 107.50 (2)°, γ = 82.20 (2)°, V = 3299 A?3, R = 0.055, Rw = 0.076. This cluster contains a metalloligated triangular core of which two edges are bridged by the dppm ligands in such a way that the four P atoms and the four metal atoms are almost coplanar. The lability of the P→Pd bond of the precursor complex accounts for the easy formal insertion of the Co(CO)3 fragment into this bond. A metal-exchange reaction can be thermally induced that transforms 1 into the triangular cluster [PdCo2(CO)5(dppm)2]. The reaction of 1 with anionic nucleophiles X- was found to regioselectively break the exocyclic Pd-Co bond, and it afforded the clusters [Pd2CoX-(CO)3(dppm)2] (X = Cl, Br, I, OH, SCN). The reversibility of this reaction was investigated, and the reaction leading to the halogeno clusters was best carried out in acetone, proceeding faster depending upon the nature of X- (I- ≈ Br- ? Cl-) and of the corresponding cation (PPN+ ? K+, Na+). Re-formation of the exocyclic Pd-Co bond was observed in Et2O. The cationic cluster [Pd2Co(CO)4(dppm)2]+ was prepared by carbonylation of the halide-substituted Pd2Co clusters in the presence of a halide abstractor. Its unique Pd-bound terminal CO ligand is very labile and can be reversibly and selectively replaced by a solvent molecule (acetone, THF, MeCN) depending upon CO partial pressure. The molecular structure of [Pd2Co(CO)4(dppm)2]-[PF 6]·C3H6O (7·acetone) has been determined by X-ray diffraction. Crystal data: monoclinic, space group Cc with Z = 4, a = 22.87 (2) A?, b = 14.198 (4) A?, c = 22.27 (2) A?, β = 122.35 (5)°, V = 6109 A?3, R = 0.053, Rw = 0.069. The structure of the cation may be considered as derived from that of 1 by the replacement of the terminally bound Co(CO)4 unit by a carbonyl group. Spectroscopic IR and 1H and 31P{1H} NMR data are discussed in relation with the structure and reactivity of these new clusters. The synthesis and chemistry of 1 are characterized by reactions formally taking place within the Pd2P4 plane. The bonding description of the clusters with a Pd2Co(dppm)2 core emphasizes their belonging to a new class of clusters where an anionic 18-electron metal carbonyl fragment is part of a closo structure.
