Influence of Charge and Coordination Number on Bond Dissociation Energies, Distances, and Vibrational Frequencies for the Phosphorus鈥揚hosphorus Bond

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• 作者：Saurabh S. Chitnis ; J. Marc Whalen ; Neil Burford
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：September 3, 2014
• 年：2014
• 卷：136
• 期：35
• 页码：12498-12506
• 全文大小：465K
• ISSN：1520-5126

文摘

We report a comprehensive and systematic experimental and computational assessment of the P鈥揚 bond in prototypical molecules that represent a rare series of known compounds. The data presented complement the existing solid-state structural data and previous computational studies to provide a thorough thermodynamic and electronic understanding of the P鈥揚 bond. Comparison of homolytic and heterolytic bond dissociation for tricoordinate-tricoordinate, tricoordinate-tetracoordinate, and tetracoordinate-tetracoordinate P鈥揚 bonds in frameworks 1鈥?b>6 provides fundamental insights into covalent bonding. For all types of P鈥揚 bond discussed, homolytic dissociation is favored over heterolytic dissociation, although the distinction is small for 2¹⁺ and 6¹⁺. The presence of a single cationic charge in a molecule substantially strengthens the P鈥揚 bond (relative to analogous neutral frameworks) such that it is comparable with the C鈥揅 bond in alkanes. Nevertheless, P鈥揚 distances are remarkably independent of molecular charge or coordination number, and trends in values of d(PC) and 谓_symm(PC) imply that a molecular cationic charge is distributed over the alkyl substituents. In the gas phase, the diphosphonium dication 3²⁺ has similar energy to two [PMe₃]⁺ radical cations, so that it is the lattice enthalpy of 3[OTf]₂ in the solid-state that enables isolation, highlighting that values from gas-phase calculations are poor guides for synthetic planning for ionic compounds. There are no relationships or correlations between bond lengths, strengths, and vibrational frequencies.