Synthesis and Reactivity of N-Heterocycle-B(C₆F₅)₃ Complexes. 4. Competition between Pyridine- and Pyrrole-Type Substrates toward B(C₆F₅)₃:  Structure and Dynamics of 7-B(C₆F₅)₃-7-azaindole and [7-Azaindolium]⁺[HOB(C₆F₅)₃]^-

Abstract

Reaction between 7-azaindole and B(C6F5)3 quantitatively yields 7-(C6F5)3B-7-azaindole (4), in which B(C6F5)3 coordinates to the pyridine nitrogen of 7-azaindole, leaving the pyrrole ring unreacted even in the presence of a second equivalent of B(C6F5)3. Reaction of 7-azaindole with H2O-B(C6F5)3 initially produces [7-azaindolium]+[HOB(C6F5)3]- (5) which slowly converts to 4 releasing a H2O molecule. Pyridine removes the borane from the known complexes (C6F5)3B-pyrrole (1) and (C6F5)3B-indole (2), with formation of free pyrrole or indole, giving the more stable adduct (C6F5)3B-pyridine (3). The competition between pyridine and 7-azaindole for the coordination with B(C6F5)3 again yields 3. The molecular structures of compounds 4 and 5 have been determined both in the solid state and in solution and compared to the structures of other (C6F5)3B-N-heterocycle complexes. Two dynamic processes have been found in compound 4. Their activation parameters (DeltaH = 66 (3) kJ/mol, DeltaS = -18 (10) J/mol K and DeltaH = 76 (5) kJ/mol, DeltaS = -5 (18) J/mol K) are comparable with those of other (C6F5)3B-based adducts. The nature of the intramolecular interactions that result in such energetic barriers is discussed.

Stable Borane Adducts of Alcoholates and Carboxylates

“…On the other hand, complexes of the conjugate base anions, namely carboxylates and phosphinates with B(C 6 F 5 ) 3 are also stable as demonstrated by the isolation and full characterization of the complex anions [ R CO 2 · B(C 6 F 5 ) 3 ] – ( R = H; R = Me), [RCO 2 · 2B(C 6 F 5 ) 3 ] –[20] and [Ph 2 PO 2 · B(C 6 F 5 ) 3 ] – , respectively. This stability compliments a large number of stable adducts between inorganic anions and B(C 6 F 5 ) 3 including 1:1 complexes [ X · B(C 6 F 5 ) 3 ] – ( X = H, OH,, , F, Cl,, PhNH, PhS, CN, SCN, NO 3 , [HSO 3 ,, ) as well as 1:2 complexes [ X · 2 B(C 6 F 5 ) 3 ] – ( X = OH,, NH 2 , PH 2 , CN,, ) and [ X · 2 B(C 6 F 5 ) 3 ] 2– ( X = O, SO 4 ), respectively. In this context, the neutral donor‐acceptor complex (C 6 F 5 ) 3 B · N(H)SO needs to be also mentioned .…”

Investigation of the Reactivity of Hydroxyborate Salts with Group IV Metal Complexes: Synthesis and Structural Characterization of the Zirconium and Hafnium Ionic Complexes [PPN]+[Cp2MMe(OB(C6F5)3)]−

“…The B–O and O–H bond lengths were determined to be 1.475 and 0.799 Å, respectively. The length of the B–O bond is in the range of B–O bonds in tris(pentafluorophenyl)hydroxyborate that have been cited in the literature (1.500 Å in [7-azaindolium] + [HOB(C 6 F 5 ) 3 ] − , 1.470 Å in [ N -isoquinolinium] + [HOB(C 6 F 5 ) 3 ] − , 1.466 Å in [btmgbH] + [HOB(C 6 F 5 ) 3 ] − (btmgb = 1,2-bis( N,N,N′,N′ -tetramethylguanidino)benzene)). This B–O bond is longer than that observed in the borinic acid (Mes) 2 BOH, which exhibits an average B–O bond length of 1.368 Å .…”

Mono‐ and Diprotonation of the Superbasic Bisguanidine 1,2‐Bis(N,N,N′,N′‐tetramethylguanidino)benzene (btmgb) and PtII and PtIV Complexes of Chelating Bisguanidines and Guanidinates

“…[17] The free [btmgbH] + cation has been studied previously by using quantum chemical calculations, [18] which found an N À H bond length of 99.7 pm in the minimum-energy struc- Table 2 compares some of the structural elements. The nomenclature (which is similar to that used in ref.…”