Coordination chemistry and hydroformylation activity of platinum complexescontaining 1-aryl-phospholes

The reaction of the sterically crowded 1-aryl-phospholes (1-(2',4',6'-tri-i sopropylphenyl)-3-methylphosphole (1), 1-(2',4',6'-tri-tert-butylphenyl)-3- methyl-phosphole (2) and 1-(2',4'-di-tert-butyl-6'-methylphenyl)-3-methylph osphole (3)) with PtCl2(PhCN)(2) was investigated by NMR spectroscopy. Sign ificant differences in their reactivity towards PtCl2(PhCN)(2) have been ob served. Both cis-PtCl2(phosphole)(PhCN) and trans-PtCl2(phosphole), complex es were formed under normal reaction conditions. The corresponding reaction with the more basic 1-phenyl-3,4-dimethyl-phosphole (4) resulted in the im mediate formation of cis-PtCl2(4), as the major product accompanied by appr oximate to 3% trans-PtCl2(4)(2). The structure of the two types of platinum complexes in solution has been confirmed by (1)J(Pt-195,P-31) coupling con stants in P-31-NMR and several shielding effects in H-1-NMR spectrometry. T he reduced aromatic character of the coordinated phosphole ligands has been confirmed by the pyramidalization of the phosphorus and the loss of the pe rpendicular arrangement of the phosphole and aryl rings. While the reaction of the sterically congested phospholes (1, 2) with [Rh(nbd)Cl](2) resulted in the formation of Rh(nbd)(phosphole)Cl complexes, the most basic 4 broug ht about the [Rh(nbd)(4)(2)](+) cation. Both the conversion and the regiose lectivity of platinum- and rhodium-catalysed hydroformylation of styrene sh ow strong dependence on the basicity of the phosphole ligand. (C) 1999 Else vier Science S.A. All rights reserved.