Investigation of the Electronic and Geometric Effects of Trifluoromethyl Substituents on Tris(pyrazolyl)borate Ligands Using Manganese(I) and Copper(I) Complexes

Abstract

Manganese tricarbonyl complexes of fluorinated tris(pyrazolyl)borate ligands [HB(3,5-(CF3)2Pz)3]- and [HB(3-(CF3)Pz)3]- (where Pz = pyrazolyl) were synthesized by treating BrMn(CO)5 with [HB(3,5-(CF3)2Pz)3]Ag(THF) or [HB(3-(CF3)Pz)3]Na(THF). The reaction of [HB(3-(CF3)Pz)3]Na(THF) with copper(I) trifluoromethanesulfonate under CO afforded [HB(3-(CF3)Pz)3]CuCO. Compounds [HB(3,5-(CF3)2Pz)3]Mn(CO)3 (5), [HB(3-(CF3)Pz)3]Mn(CO)3 (6), and [HB(3-(CF3)Pz)3]CuCO (7) were characterized by 1H NMR, 19F NMR, and IR spectroscopy and by X-ray crystallography. They have relatively high C−O stretching frequencies. However, the νCO values are much lower than that in free CO and the relative lowering is higher for manganese adducts. The CF3 substitution on the 5-position has a significant effect on the metal center. This is readily apparent from the infrared spectroscopic data. Theoretical calculations of the geometries of [tris(pyrazolyl)borato]manganese(I) and -copper(I) carbonyls are in excellent agreement with the experimental results. Increasing the degree of fluorination lengthens the metal−C and metal−N bonds and shortens the C−O distance. The metal−Pz bonding is essentially a pure σ-interaction. Cyclic voltammetry data for the copper complexes show high oxidation potentials for the fluorinated analogs. IR spectroscopic data of the [tris(pyrazolyl)borato]manganese and -copper carbonyls have also been compared to those of cyclopentadienyl analogs.

Synthesis and Copper Coordination Chemistry of Hindered 1,4,7-Triazacyclononane Ligands with Amide Appendages

“…pairs of entries 8/14 and 9/15 in Table 3). 23 In addition, the lower ν CO for the complex of L MeAmMe compared to that for the L MeAmH case shows that amide N-alkylation, despite being at a relatively remote position, noticeably increases the amount of electron density at the metal. 21 Amide carbonyl coordination is retained in solution, as evidenced by FTIR data for [L MeAmH -CuCl]PF 6 ‚MeOH in CHCl 3 , which showed an amide I band at an energy identical to that observed in the KBr spectrum.…”

Nitrene Insertion into Aromatic and Benzylic C−H Bonds Catalyzed by Copper Complexes of Fluorinated Bis‐ and Tris(pyrazolyl)borates

“…Details of the synthesis of [HB(3,5-(CF 3 ) 2 Pz) 3 ]Cu(NCMe) (2) [43] and [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(NCMe) (3) [42] catalysts utilized in this work have been reported elsewhere ( Figure 1). The related fluorinated bis(pyrazolyl)borate copper complex [H 2 B(3,5-(CF 3 ) 2 -4-(NO 2 )Pz) 2 ]Cu(NCMe) (4) possessing NO 2 groups at the pyrazolyl ring 4-positions was prepared in an analogous manner to that of 3 using 3,5-(CF 3 ) 2 -4-(NO 2 )PzH [44] and KBH 4 and CuOTf.…”

“…The tris-and bis(pyrazolyl)borate ligand supported catalysts 2 and 3 show remarkable difference in, and opposite selectivity towards benzylic vs aromatic CÀ H aminations with mesitylene. The 4nitro-3,5-bis(trifluoromethyl)pyrazole, [44] [HB(3,5-(CF 3 ) 2 Pz) 3 ]Cu(NCMe) (2) [43] and [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(NCMe) (3) [42] were prepared by published methods. This work also highlights the value of less explored bis(pyrazolyl)borate ligand support in the scorpionate family.…”

Copper(I) Complexes of Naphthyl‐Substituted Fluorinated Trispyrazolylborate Ligands with Ethene and Carbon Monoxide

“…free CO 2143 [18] [Cu(Ttz CF3,CF3 )(CO)] 2138 [19] [Cu(Tp CF3,CF3 )(CO)] 2137 [6] [Cu(Tp CF3,1Nt )(CO)] 2109 this work [Cu(Tp CF3,CH3 )(CO)] 2109 [20] [Cu(Tp CF3,2Nt )(CO)] 2103 this work [Cu(Tp CF3,Ph )(CO)] 2102 [2] [Cu(Tp CF3 )(CO)] 2100 [4] [Cu(Tp)(CO)] 2083 [7] [Cu(Tp Ph,Ph )(CO)] 2080 [21] [Cu(Tp Ms )(CO)] 2079 [20] [Cu(Tpt Bu )(CO)] 2069 [22] [Cu(Tp Me,Me )(CO)] 2066 [7] [Cu(Tp iPr,iPr )(CO)] 2056 [23] …”

“…A great variety of scorpionate ligands has been reported to date, most of which retain the hydridotrispyrazolylborate backbone. [2][3][4] The presence of electron-withdrawing groups like trifluoromethyl groups results in comparatively electron-deficient copper(I) centers that are capable of only limited π-backbonding interaction with π-acceptor ligands such as ethene and carbon monoxide. The substituent on the 5-position of the pyrazole ring is not in proximity to the metal center but does play an important role in the chemistry of the complex by providing steric bulk, thus forcing the substituents on the 3-position inwards and decreasing the size of the coordination pocket, or by electronically modifying the nitrogen atoms which tunes the Lewis basicity of the ligand.…”