Ab initio /GIAO-MP2-calculated structures and ¹¹ B- ¹³ C NMR chemical shift relationship in hypercoordinate onium-carbonium dications and isoelectronic onium-boronium cations

Abstract

The boronium-carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-boronium cation analogs. Structures and 13 [1]In Eq. 1, the ␦ 13 C is the chemical shift of the cationic carbon of the carbenium ion with respect to tetramethylsilane, and the ␦ 11 B is the chemical shift of the corresponding boron atoms with respect to the BF 3 :OEt 2 . The empirical Eq. 1 is in good agreement with most of the available data. Later, G.K.S.P. et al. (3) reported an extension of the relationship to cage compounds containing trivalent carbon and boron atoms. Williams et al. (4) derived a similar empirical Eq. 2 for hypercoordinate (5) carbocations (carbonium ions) and their corresponding hypercoordinate boron compounds (e.g., square pyramidal structure of C 5 H 5 ϩ i and square pyramidal structure of pentaborane ii).Recently, we have been able to show (6) a good boroniumcarbonium ion relationship for the hypercoordinated hydriodo carbocations and their isoelectronic and isostructural boron compounds (e.g., parent five coordinated carbonium ion CH 5 ϩ iii and five coordinated boronium ion BH 5 iv) based on ab initio͞GIAO-MP2 calculations. These relationships show that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei. Based on the ab initio͞GIAO-MP2 calculations we now extend this boronium-carbonium continuum to hypercoordinate onium-carbonium dications (v) and the *To whom reprint requests should be addressed.

Quantum Mechanical Design and Structure of the Li@B10H14Basket with a Remarkably Enhanced Electro-Optical Response

“…The magnetic shieldings were calculated on optimized geometries by employing gauge-including atomic orbitals (GIAOs) with the MP2/6-31+G* level of theory. Several reports of Rasul et al have demonstrated that the GIAO-MP2 method can give reliable results for 11 B NMR chemical shift calculations. The 11 B NMR chemical shifts were first computed with B 2 H 6 [the calculated absolute shift, i.e., σ(B), is 103.9] as a reference, which is in accordance with previous (GIAO-MP2) calculations .…”

Ab Initio/GIAO-CCSD(T) Calculated 13C–11B NMR Chemical Shift Relationships in Isoelectronic Hypercoordinate Carbonium and Boronium As Well As Carbenium and Borenium Ions

“…Similarly hypervalent boronium cation (BH 6 + ) is isoelectronic with the corresponding carbonium dication (CH 6 2+ ). Previously we have been able to show a good boronium–carbonium NMR chemical shift relationship for the carbonium dications H 4 CX 2+ and boronium cations H 4 BX + (X = NH 3 , PH 3 , H 2 O, H 2 S, CO, N 2 , HF, HCl, CO 2 , and CS 2 ), based on ab initio/GIAO-MP2 calculations. The general correlation equation is shown below (eq ).…”

GIAO-MP2/SCF/DFT Calculated NMR Chemical Shift Relationships in Isostructural Onium Ions Containing Hypercoordinate Boron, Carbon, Aluminum, and Silicon Atoms

“…As boron and carbon are consecutive first-row elements, onium−boronium cations 1 are isoelectronic with the corresponding onium−carbonium dications 2 (Scheme ). Recently we have been able to show a good boronium−carbonium NMR chemical shift relationship for the carbonium dications H 4 CX 2+ 2 and boronium cations H 4 BX + 1 (X = NH 3 , PH 3 , H 2 O, H 2 S, CO, N 2 , HF, HCl, CO 2 , and CS 2 ), based on ab initio/GIAO-MP2 calculations. The general correlation equation is shown below (equation 1).…”