Difluoroborenium Cation Stabilized by Hexaphenyl‐Carbodiphosphorane: A Concise Study on the Molecular and Electronic Structure of [(Ph₃P)₂C⇉BF₂][BF₄]

Abstract

The reaction of hexaphenyl‐carbodiphosphorane C(PPh3)2 (CDP, 1) with BF3·OEt2 provides the corresponding difluoroborenium cation [CDP–BF2]+ (2+) through fluoride abstraction. Advanced NMR spectroscopy methods, including 19F,31P HMQC; 31P,13C HMQC; 19F,1H HOESY; 19F NOESY; 31P,13C INEPT; and 1H, 31P, 19F, and 11B diffusion NMR measurements, were performed, and they revealed strong ion pairing of 2+ with the [BF4]– counterion in chloroform solution. Structural and computational studies showed strong donor–acceptor interactions, in which the σ and π lone pairs of electrons of C(PPh3)2 donate into the vacant orbitals of the [BF2]+ fragment. The C–B bond shows the highest interaction energy of 242.9 kcal mol–1 found for the corresponding carbodiphosphorane adducts.

An Easily Accessible Chiral Carbodiphosphorane and its Coinage Metal Complexes

“…The elongated PÀ C1 bond lengths in 4 Cu (173.2(2) and 175.0(5) pm) compared to 3 (166.7 pm) point to a four-electron-coordination-mode of the ligand 3 in complex 4 Cu . [42,43] The CÀ Cu bond lengths of 194.1(5) and 194.2 (5) pm are in agreement to other compounds of the form [(R 3 P) 2 C(CuX) 2 ] (X = Cl-I; 195.6(3)-207.5(1) pm). [9,21] The Cu • • • Cu distance of 255.05( 9) and the CuÀ CÀ Cu angle of 82.1(2) °also fits the reference compounds and hints at cuprophilic interactions between the copper centers (sum of van der Waals radii: 280 pm; distance in the Cu 2 dimer in the gas phase: 222 pm).…”

An Experimental and Theoretical Study of the Structures and Properties of [CDPMe‐Ni(CO)3] and [Ni2(CO)4(µ2‐CO)(µ2‐CDPMe)]

“…The former assumption is supported by the elongated P–C1 bond lengths in 2 (174.2(5) and 175.3(5) pm) which are about ten pm longer than those in non‐coordinating CDP Me (164.9 pm) . P–C1 bond lengths > 170 pm are observed for adducts and complexes in which CDP R ligands act as four electron donors (bonding mode ΙΙΙ, Scheme ) . This is due to the fact that the lone pair (in π symmetry) of the central carbon atom is no longer available for π back‐donation to the PPh 2 Me groups.…”

Comparison of Chemical and Interpretative Methods: the Carbon–Boron π‐Bond as a Test Case**

“…71 These boron species have been used in numerous catalytic processes. [72][73][74][75] They are stabilized through electronic -donation from the -cloud of the boron substituents, [76][77][78][79] and neutral divalent carbon-donor compounds, such as normal NHC, [80][81][82][83][84][85] mesoionic NHC 86 and carbones, 87 have been used for this purpose (Scheme 1). For dihydrido borenium (R = H), only their two-electrons -donor L ligand provide partial mitigation of their electron deficiency and their stabilization requires strong donor.…”

“…88,89 DFT studies on C-donor ligand-BR 2 + borenium reveal a short CB bond reflecting a partial double-bond character due to CB -electronic transfer. 82,84,[87][88][89][90][91] Beyond structural parameters, various theoretical indicators have been used to analyze the electronic structure of these and other related compounds, [92][93][94] among them the nature of the highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO), the atomic charges, the energy associated to the -and donation through energy decomposition analysis of the B-C bond, and the Wiberg bond index between these two atoms. Only few studies have used such indicators to compare the bonding situation in borenium complexes.…”

“…For dihydrido borenium (R=H), only their two‐electrons σ‐donor L ligand provide partial mitigation of their electron deficiency and their stabilization requires strong π‐donor [88, 89] . DFT studies on C‐donor ligand‐BR 2 + borenium reveal a short CB bond reflecting a partial double‐bond character due to C→B π‐electronic transfer [82, 84, 87–91] . Beyond structural parameters, various theoretical indicators have been used to analyze the electronic structure of these and other related compounds, [92–94] among them the nature of the highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO), the atomic charges, the energy associated to the σ‐ and π‐donation through energy decomposition analysis of the B−C bond, and the Wiberg bond index between these two atoms.…”