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Bulky 4-phosphacyclohexanones: diastereoselective complexations, orthometallations and unprecedented [3.1.1]metallabicycles

Doherty, Ruth, Haddow, Mairi F., Harrison, Zoë A., Orpen, A. Guy, Pringle, Paul G., Turner, Alex and Wingad, Richard L. 2006. Bulky 4-phosphacyclohexanones: diastereoselective complexations, orthometallations and unprecedented [3.1.1]metallabicycles. Dalton Transactions 2006 (36) , pp. 4310-4320. 10.1039/b607490a

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The 4-phosphacyclohexanones, 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone (La), 1,2,6-triphenyl-4-phosphorinanone (PhLb), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone (CyLb) and 1-tert-butyl-2,6-diphenyl-4-phosphorinanone (BuLb) have been made by modifications of literature methods. Phosphines RLb are each formed as mixtures of meso- and rac-diastereoisomers. Isomerically pure rac-PhLb, rac-CyLb and meso-BuLb can be isolated by recrystallisation from MeCN. Heating mixtures of isomers of RLb with TsOH leads to isomerisations to give predominantly the meso-RLb. The complex trans-[PdCl2(La)2] (1) is readily made from [PdCl2(NCPh)2] but the analogous platinum complex 2 has not been detected and instead, cyclometallation at the 3-position (α to the ketone) in the phosphacycle occurs to give trans-[PtCl(La)(La–3H)] (3) (where La–3H = La deprotonated at the 3-position) featuring a [3.1.1]metallabicycle as confirmed by X-ray crystallography. The analogous palladabicycle 4 has been detected upon treatment of 1 with Et3N in refluxing toluene. The type of complex formed by RLb depends on which diastereoisomer (meso or rac) is involved. rac-PhLb (a mixture of R,R- and S,S-enantiomers, labelled α and β) forms trans-[MCl2(rac-PhLb)2], M = Pd (5) or Pt (6), as mixtures of diastereoisomers (αα/ββ and αβ forms). The structure of αα-6 has been determined by X-ray crystallography. Ligand competition experiments monitored by 31P NMR showed that Pd(II) and Pt(II) have a significant preference to bind rac-PhLb over meso-PhLb. meso-BuLb reacts with [PtCl2(NCBut)2] under ambient conditions to give the binuclear complex [Pt2Cl2(meso-BuLb-2′H)2] (7) where orthometallation has occurred on one of the exocyclic phenyl substituents as confirmed by X-ray crystallography. rac-BuLb reacts with [PtCl2(NCBut)2] to give a mononuclear cyclometallated species assigned the structure trans-[PtCl(rac-BuLb-2′H)(BuLb)] (8) on the basis of its 31P NMR spectrum. rac-CyLb reacts with [PtCl2(NCBut)2] in refluxing toluene to give trans-[PtCl2(rac-CyLb)2] (9) and the crystal structure of αβ-9 has been determined.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Publisher: Royal Society of Chemistry
ISSN: 1477-9226
Date of Acceptance: 27 June 2006
Last Modified: 21 Jan 2020 10:30

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