Modular Phosphole-Methano-Bridged-Phosphine(Borane) Ligands. Application to Rhodium-Catalyzed Reactions

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• 作者：Duc Hanh Nguyen ; J茅r么me Bayardon ; Christine Salomon-Bertrand ; Sylvain Jug茅 ; Philippe Kalck ; Jean-Claude Daran ; Martine Urrutigoity ; Maryse Gouygou
• 刊名：Organometallics
• 出版年：2012
• 出版时间：February 13, 2012
• 年：2012
• 卷：31
• 期：3
• 页码：857-869
• 全文大小：529K
• 年卷期：v.31,no.3(February 13, 2012)
• ISSN：1520-6041

文摘

The synthesis of the phospholyl(phosphinoborane)methane air- and moisture-stable hybrid ligands 4a鈥?b>f, starting from 1-phenylphospholes 1a鈥?b>d, was performed via P鈥揅 bond coupling on the methano bridge. Two strategies were investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the phospholyl anions react with the easily available (chloromethyl)diphenylphosphine鈥揵orane 3 to afford ligands 4a鈥?b>d in 29鈥?7% isolated yields. In the second pathway, the phospholyl(dicyclohexylphosphinoborane)methane ligands 4e,f were synthesized in 18鈥?3% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH₃ moiety on 4a鈥?b>c assisted by DABCO leads to the hybrid phospholyl(diphenylphosphino)methanes 5a鈥?b>c. Compounds 4 and 5 were fully characterized by multinuclear NMR spectroscopy (¹H, ³¹P, ¹³C, ¹¹B), mass spectrometry, and elemental analysis, and the X-ray crystal structures of 4a,c and 5a,b have been established. Ligands 5a,b were used to prepare the cationic rhodium complexes [Rh(畏⁴-COD)(5a)]⁺ (8a鈥?/b>), [Rh(畏⁴-COD)(5b)]⁺ (8b), [Rh(5a)₂]⁺ (9a鈥?/b>), and [Rh(5b)₂]⁺ (9b), containing four-membered chelate rings with BF₄^{鈥?/sup> or CF₃SO₃鈥?/sup> as counterions. Ligands 4a鈥?b>f} were also used to synthesize the [Rh(畏⁴-COD)(4)]⁺ chelate complexes 10a鈥?b>f, resulting from coordination of the phospholyl part and the BH₃ group via a 畏² mode with two bridging B鈥揌鈥揜h 3c鈥?e bonds, as shown by the X-ray crystal structures of the complexes 10b,c. Rhodium complexes 8 and 10 isolated or formed in situ with ligands 4 and 5 were studied for catalytic hydrogenation of methyl 2-(acetamidomethyl)acrylate (11) and hydroboration of styrene (13) with catecholborane. In both reactions, the catalytic systems prepared either from the phospholyl(phosphinoborane)methane ligands 4 or the corresponding free ligands 5, gave good to excellent conversions. In addition, the regioselectivity of the catalyzed hydroboration is slightly influenced using these ligands. Finally, the use of hybrid phospholyl(phosphinoborane)methanes as ligands offers a new, efficient way to improve catalytic processes, for designing both the structure and the electronic properties of the catalyst, or still to implement it without removing the borane protecting group.