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Title: Cyclopalladation of the prochiral (di-tert-butyl)(diphenylmethyl)phosphine: Kinetic lability of the corresponding (+)-phosphapalladacyclic Pd-C bond and the reluctance of the phosphine to bind in a monodentate fashion
Authors: Ng, J.K.-P.
Chen, S.
Li, Y.
Tan, G.-K.
Koh, L.-L. 
Leung, P.-H.
Issue Date: 11-Jun-2007
Citation: Ng, J.K.-P., Chen, S., Li, Y., Tan, G.-K., Koh, L.-L., Leung, P.-H. (2007-06-11). Cyclopalladation of the prochiral (di-tert-butyl)(diphenylmethyl)phosphine: Kinetic lability of the corresponding (+)-phosphapalladacyclic Pd-C bond and the reluctance of the phosphine to bind in a monodentate fashion. Inorganic Chemistry 46 (12) : 5100-5109. ScholarBank@NUS Repository.
Abstract: The ortho palladation of prochiral (di-tert-butyl)(diphenylmethyl)phosphine proceeded readily to give rise to the dimeric complex, di-μ- chlorobis{[(phenyl)(di-tert-butylphosphino)methyl]phenyl-C2, P}dipalladium(II). The (S,S)-(+)-dimer was subsequently obtained by optical resolution with sodium (S)-prolinate. The absolute configuration of the optically resolved (+)-dimer was concluded from the X-ray diffraction studies of the derivatized O,O-acetylacetonate complex. The availability of the (+)-dimer is crucial to the study of the properties of the Pd-C bond. The phosphapalladacycle Pd-C bond exhibited a remarkable thermodynamic stability. It could not be permanently ruptured to give rise to the η1-P monodentate even in a refluxing acetone solution containing concentrated hydrochloric acid. Instead, the phosphine was noted to fluctuate between the ring closed and opened states via the reversible Pd-C bond cleavage/formation under this condition. Inevitably, this resulted in the racemization of the five-membered organopalladium ring structure. In contrast, such bond cleavage was not observed at room temperature in the absence of HCl. In fact, the phosphine was observed to readily ortho palladate even under conditions not favorable to cyclopalladation. Indeed, the difficulty of isolating the phosphine as a simple η1-P monodentate coordination complex was further noted by its lack of reactivity toward the N,N-dimethyl-1-(1′naphthyl) ethylaminate palladacycle μ-chloro dimer. Only by enhancing the Lewis acidity of the palladacycle in the form of the positively charged bis(acetonitrile) complex could the phosphine be encouraged to participate in monodentate η1-P bonding. Even then, this form of coordination was weak and was only observed by NMR spectroscopy. © 2007 American Chemical Society.
Source Title: Inorganic Chemistry
ISSN: 00201669
DOI: 10.1021/ic0702320
Appears in Collections:Staff Publications

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