Group 10 Metal Complexes of SPS‐Based Pincer Ligands: Syntheses, X‐ray Structures, and DFT Calculations

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)Cl 2 ] yields the SPS pincer‐based complex 6 with a P(OH) λ 5 ‐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)(NEt 2 ) 9 λ 5 ‐phosphinines. No definitive mechanism for the formation of 7 − 9 can be proposed since no intermediates were detected in situ by 31 P 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 λ 5 ‐phosphinines is not viable because it involves a high activation energy. Like 5 , λ 5 ‐phosphinines 7 and 8 react with [Pd(COD)Cl 2 ] 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‐NEt 2 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 [NiBr 2 (DME)] and [Pt(COD)Cl 2 ], respectively. Like their palladium congener, both species react with ethanol to afford the corresponding P−OEt derivatives 20 [M = Ni] and 21 [M = Pt]. n Butyl 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 n BuLi with 1 , with the [NiBr 2 (DME)] and [Pt(COD)Cl 2 ] precursors. The chloride ligand is readily substituted by acetonitrile in complexes 4 , 11 , 20 , and 21 upon treatment with AgBF 4 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‐λ 5 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)