Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Abstract

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HCºCSiMe3 are also reported. They are three-coordinate copper complexes featuring η2-bound alkynes. Raman data show significant red-shifts in CºC stretch of [H2B(3,5-(CF3)2Pz)2]Cu(HCºCH) and [H2B(3,5-(CF3)2Pz)2]Cu(HCºCSiMe3) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu2(μ-[3,5-(CF3)2Pz])2(HCºCH)2 display similar Cu-alkyne bonding features. The mononuclear [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) complex catalyzes [3+2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF3)2Pz]Cu}3 involving bridging pyrazolates.

Isolable acetylene complexes of copper and silver

“…Note however that the copper complex [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(C 2 H 2 ) (4) is isolable. 18 Neutral bis(pyrazolyl)methane donors are close relatives of the anionic, bis(pyrazolyl)borates. 22b,23a We discovered that even the non-uorinated and easily accessible H 2 C(3,5-(CH 3 ) 2 Pz) 2 can be employed to stabilize copper and silver acetylene complexes successfully.…”

“…(2[ClO 4 ]), 17 Cu 2 (m-[4-Br-3,5-(CF 3 ) 2 -Pz]) 2 (C 2 H 2 ) 2 (3), 10a and [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(C 2 H 2 ) (4), 18 and four silver complexes [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(C 2 H 2 ) (5), 19 [Ag(C 2 H 2 ) 3 ][Al(OC(CF 3 ) 3 ) 4 ] (6[Al(OC(CF 3 ) 3 ) 4 ]), 20 [Ag(C 2 H 2 ) 4 ] [Al(OC(CF 3 ) 3 ) 4 ] (7[Al(OC(CF 3 ) 3 ) 4 ]), 20 and [Al(OC(CH 3 )(CF 3 ) 2 ) 4 ] Ag(C 2 H 2 ) (8) 20 containing terminal M(h 2 -HC^CH) bonds (Fig. 1, M ¼ Cu, Ag).…”

“…1 However, despite over a 100 year history of coinage metal (Cu, Ag, Au) chemistry of acetylene, 3 b ,14 and the current importance, 1 a ,4 well-characterized molecules featuring terminal Cu(η 2 -HCCH) and Ag(η 2 -HCCH) bonds are still very limited. For example, a search of the Cambridge Structural Database 15 revealed only four copper complexes, [Cu{NH(Py) 2 }(C 2 H 2 )][BF 4 ] ( 1 [BF 4 ]), 16 [Cu(phen)(C 2 H 2 )][ClO 4 ] ( 2 [ClO 4 ]), 17 Cu 2 (μ-[4-Br-3,5-(CF 3 ) 2 Pz]) 2 (C 2 H 2 ) 2 ( 3 ), 10 a and [H 2 B(3,5-(CF 3 ) 2 Pz) 2 ]Cu(C 2 H 2 ) ( 4 ), 18 and four silver complexes [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(C 2 H 2 ) ( 5 ), 19 [Ag(C 2 H 2 ) 3 ][Al(OC(CF 3 ) 3 ) 4 ] ( 6 [Al(OC(CF 3 ) 3 ) 4 ]), 20 [Ag(C 2 H 2 ) 4 ][Al(OC(CF 3 ) 3 ) 4 ] ( 7 [Al(OC(CF 3 ) 3 ) 4 ]), 20 and [Al(OC(CH 3 )(CF 3 ) 2 ) 4 ]Ag(C 2 H 2 ) ( 8 ) 20 containing terminal M(η 2 -HCCH) bonds (Fig. 1, M = Cu, Ag).…”

Coinage metal-ethylene complexes of sterically demanding 1,10-phenanthroline ligands

“…We have been utilizing nitrogen-based chelators such as bis(pyrazolyl)borates, 26–36 bis(pyrazolyl)methanes, 30,34,37 and bis(pyridyl)borates 38,39 in coinage metal (Cu, Ag, Au) chemistry, in particular, to develop homogeneous catalysts, 27,29,40 achieve olefin-paraffin separations, 35,36 and to stabilize molecules with CO, ethylene and acetylene, and larger alkenes and alkynes on these metal ions 26,28–30,36,37,40–42 for bonding investigations and to serve as models for reaction intermediates in catalytic processes involving these metal-gas combinations. In this work, we report the use of two sterically demanding phen ligands, 2,9-bis(2,4,6-triisopropylphenyl)-1,10-phenanthroline ( L1 ) and 2,9-bis(2,4,6-trifluoromethylphenyl)-1,10-phenanthroline ( L2 ) in a systematic study of coinage metal ethylene chemistry (Fig.…”

“…3,4 1,10-Phenanthroline ( phen) decorated with several different backbone substituents are known, and they as well as the parent phen have been utilized in a variety of applications including the development of luminescent materials, 1,5-10 mechanochromic indicators, 11 homogeneous catalysts, 8,[12][13][14][15][16][17][18] molecular chemo-sensors for anions and metal cations, 19,20 and DNA intercalating and antibacterial and anticancer agents. [21][22][23][24][25] We have been utilizing nitrogen-based chelators such as bis ( pyrazolyl)borates, [26][27][28][29][30][31][32][33][34][35][36] bis( pyrazolyl)methanes, 30,34,37 and bis ( pyridyl)borates 38,39 in coinage metal (Cu, Ag, Au) chemistry, in particular, to develop homogeneous catalysts, 27,29,40 achieve olefin-paraffin separations, 35,36 and to stabilize molecules with CO, ethylene and acetylene, and larger alkenes and alkynes on these metal ions 26,[28][29][30]36,<...…”