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Group 10 Metal Complexes of SPS-Based Pincer Ligands: Syntheses, X-ray Structures, and DFT Calculations
Doux, Marjolaine,Mezailles, Nicolas,Ricard, Louis,Le Floch, Pascal
, p. 3878 - 3894 (2007/10/03)
The 2,6-bis(diphenylphosphanylsulfide)phosphinine (1) reacts with water to afford a 1,2-dihydrophosphinine oxide 5 featuring a P-H bond. Reaction of 5 with one equivalent of [Pd(COD)Cl2] yields the SPS pincer-based complex 6 with a P(OH) λ5-phosphinine central ligand. Complex 6 has been structurally characterized. Two possible mechanisms account for the formation of 5: an intramolecular P-H to P-Pd metathesis or one based on the P= O to POH equilibrium. Methanol, ethanol or diethylamine also react with 1 to afford the corresponding P(H)(OMe) 7, P(H)(OEt) 8, and P(H)(NEt2) 9 λ5-phosphinines. No definitive mechanism for the formation of 7-9 can be proposed since no intermediates were detected in situ by 31P NMR spectroscopy. However, DFT calculations (at the B3LYP 6-311+G(d,p) level of theory) suggest that the conversion of 1,2-dihydrophosphinines into λ5-phosphinines is not viable because it involves a high activation energy. Like 5, λ5-phosphinines 7 and 8 react with [Pd(COD)Cl2] to afford the expected palladium complexes 10 and 11. An alternative method relies on the reactivity of nucleophiles with a SPS pincer-based complex 2 featuring a P-Cl bond. (-)-Menthol and lithium diethylamide react with 2 to yield the expected P-OMen 13 and P-NEt2 14 complexes. Both complexes have been structurally characterized. Bromonickel 18 and chloroplatinum 19 complexes of the SPS ligand, featuring a P-Br or P-Cl bond, have also been prepared by reacting 1 with [NiBr2(DME)] and [Pt(COD)Cl2], respectively. Like their palladium congener, both species react with ethanol to afford the corresponding P-OEt derivatives 20 [M = Ni] and 21 [M = Pt]. nButyl derivatives of these SPS ligands also bind to Ni-Br (complex 22) and Pt-Cl (complex 23) fragments. Both complexes were straightforwardly prepared by reacting anion 3, resulting from the reaction of nBuLi with 1, with the [NiBr2(DME)] and [Pt(COD)Cl2] precursors. The chloride ligand is readily substituted by acetonitrile in complexes 4, 11, 20, and 21 upon treatment with AgBF4 in dichloromethane. Reaction of AgOTf with the palladium complex 4 affords complex 28 via substitution of the chloride ligand by TfO-. The X-ray crystal structures of the dimethyl-λ5 derivative 29 of 1, and that of its P-OMe anion 30, have been recorded. Anion 30 can be regarded as a phosphanyl-substituted pentadienyl anion. DFT calculations and a charge decomposition analysis (CDA) show that the phosphorus atom in these SPS-pincer structures is a classical tertiary phosphane ligand in terms of donation and acceptance. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).
