Activation of Strong Boron–Fluorine and Silicon–Fluorine σ‐Bonds: Theoretical Understanding and Prediction

Abstract

The oxidative addition of BF3 to a platinum(0) bis(phosphine) complex [Pt(PMe3)2] (1) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF3 to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol(-1), respectively) and require large Gibbs activation energies (ΔG°(≠)=56.3 and 38.9 kcal mol(-1), respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF3 to 1 in the presence of a second BF3 molecule occurs with ΔG°(≠) and ΔG° values of 10.1 and -4.7 kcal mol(-1), respectively. ΔG°(≠) becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF3, occurs from the dissociating fluoride to the second non-coordinated BF3. This CT interaction stabilizes both the transition state and the product. The B-F σ-bond cleavage of BF2Ar(F) (Ar(F)=3,5-bis(trifluoromethyl)phenyl) and the B-Cl σ-bond cleavage of BCl3 by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF4 to 1 easily occurs in the presence of a second SiF4 molecule via the formation of a hypervalent Si species.

Formation of a Trifluorophosphane Platinum(II) Complex by P−F Bond Activation of Phosphorus Pentafluoride with a Pt0Complex

“…According to spectroscopic data, the formation of the Lewis pair [(Cy 3 P) 2 Pt→BF 2 Ar F ] constitutes the initial reaction step. This observation was supported by theoretical studies on trans ‐[(Cy 3 P) 2 Pt(BF 2 )(FBF 3 )] and [(Cy 3 P) 2 Pt(BFAr F )][BAr Cl 4 ], which are predicted to be formed by [(Cy 3 P) 2 Pt→BF 3 ] and [(Cy 3 P) 2 Pt→BF 2 Ar F ], respectively …”

“…Furthermore, there is a precedent for the abstraction of a fluoride anion from a [PF 4 ] − complex in the literature: The reaction of [(Et 3 P) 2 Ir(CO)Cl 2 (PF 4 )] with BF 3 to give [(Et 3 P) 2 Ir(CO)Cl 2 (PF 3 )][BF 4 ] . Mechanisms related to that suggested for the transformation of 4 a into 3 a in Scheme have been predicted for the reaction of [(Me 3 P) 2 Pt→BF 3 ] with BF 3 to give trans ‐[(Me 3 P) 2 Pt(BF 2 )(FBF 3 )], and the reaction of [(Me 3 P) 2 Pt→SiF 4 ] with SiF 4 to give trans ‐[(Me 3 P) 2 Pt(SiF 3 )(FSiF 4 )], on the basis of DFT calculations . In these studies, intramolecular reactions have also been found to be unlikely due to energetically high‐lying transition states.…”

“…This observation was supported by theoretical studies on trans-[(Cy 3 P) 2 Pt(BF 2 )(FBF 3 )] and [(Cy 3 P) 2 Pt(BFAr F )][BAr Cl 4 ], whicha re predicted to be formedb y[ (Cy 3 P) 2 Pt!BF 3 ]a nd [(Cy 3 P) 2 Pt!BF 2 Ar F ], respectively. [14,15] In the course of our ongoing studies on the coordination chemistry of the electron-rich metalb ase [(Cy 3 P) 2 Pt] (1)w ith main-group elementL ewis acids to prepare M!EL ewis pairs, [12a] the reaction of 1 with PF 5 (2)a nd relatedp erfluoroalkyl(fluoro)phosphoranes (C 2 F 5 ) x PF 5Àx (x = 1-3) [16] was investigated. Compound [(Cy 3 P) 2 (Scheme 1).…”

Activation of the B−F Bond by Diphenylcarbene: A Reversible 1,2‐Fluorine Migration between Boron and Carbon

“…Bertrand et al described af ormal 1,2-addition of as table (phosphanyl)(silyl)carbene with dimesitylfluoroborane,t hus resulting in ab orylated phosphorus ylide. [9] Thed iphenylcarbene 1 is ap rototypical transient carbene [10] with at riplet ground state and has been subject to alarge number of mechanistic studies using time-resolved or low-temperature spectroscopy. [8] According to recent DFT calculations by Kameo and Sakaki, this reaction is endergonic and has al arge activation barrier if only one BF 3 molecule is involved.…”

“…As econd molecule of BF 3 is necessary to reduce the activation barrier and to make the reaction thermodynamically feasible. [9] Thed iphenylcarbene 1 is ap rototypical transient carbene [10] with at riplet ground state and has been subject to alarge number of mechanistic studies using time-resolved or low-temperature spectroscopy. [11][12][13][14] Recently,w ef ound that the interaction of the triplet state of 1 (T-1)with either H 2 O [15] or CH 3 OH [16] results in as witching of the spin state of the carbene from triplet to singlet (S-1)u pon formation of the strongly hydrogen-bonded complexes S-1···H À OH and S-1···H À OCH 3 ,r espectively (Scheme 2).…”