Silver(I) and Copper(I) Adducts of a Tris(pyrazolyl)borate Decorated with Nine Trifluoromethyl Groups Naleen B. Jayaratna, † Igor I. Gerus,* ,‡ Roman V. Mironets, ‡ Pavel K. Mykhailiuk,* ,§ Muhammed Yousufuddin, † and H. V. Rasika Dias* ,† † Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019, United States ‡ Department of Fine Organic Synthesis, Institute of Bioorganic Chemistry and Petrochemistry NUAS, Murmanskaya Strasse 1, Kiev 02094, Ukraine § Chemistry Department, Kyiv National Taras Shevchenko University, Volodymyrska 64, 01033 Kiev, Ukraine * S Supporting Information ABSTRACT: Silver and copper ethylene adducts and the silver carbonyl complex of the tris(pyrazolyl)borate [HB(3,4,5-(CF 3 ) 3 Pz) 3 ] - (which is based on one of the most acidic pyrazoles known) have been synthesized. 13 C NMR resonance signals of metal-bound ethylene carbon atoms of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Ag(C 2 H 4 ) and [HB(3,4,5- (CF 3 ) 3 Pz) 3 ]Cu(C 2 H 4 ) appear at δ 111.6 and 94.9, respectively. The CO stretching frequency of the silver adduct [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Ag(CO) is significantly higher than that of free CO, but it appears at a region less sensitive to the ligand electronic effects of tris(azolyl)- borate silver adducts. T ris(pyrazolyl)borates are very popular auxiliary ligands in inorganic and organometallic chemistry. 1-3 It is possible to vary the steric and electronic properties of these ligands quite easily by changing the substituents on the boron atom or pyrazolyl moiety. In fact, a large number of tris(pyrazolyl)- borate ligand varieties are now known. An area of research focus on in one of our laboratories concerns the development of fluorinated versions of these ligands and their use in various applications. 2 For example, we have reported the synthesis of several polyfluorinated tris(pyrazolyl)borates including [HB(3- (CF 3 )Pz) 3 ] - and [HB(3,5-(CF 3 ) 2 Pz) 3 ] - (Figure 1) and boron- substituted varieties such as [MeB(3-(CF 3 )Pz) 3 ] - . 2 Metal adducts of fluorinated tris(pyrazolyl)borates feature more electrophilic metal sites and display interesting properties and reactivity compared to the nonfluorinated electron-rich tris- (pyrazolyl)borate analogues. 4-6 Recently, a practical route to 3,4,5-tris(trifluoromethyl)- pyrazole [3,4,5-(CF 3 ) 3 PzH] was reported. 7 It is one of the most acidic pyrazoles known with a pK a value of 4.5 (which is more acidic than acetic acid, with pK a = 4.7)! Considering the importance of weakly coordinating ligands like [HB(3,5- (CF 3 ) 2 Pz) 3 ] - (which is based on 3,5-(CF 3 ) 2 PzH with a pK a of 7.1) 8 in metal coordination chemistry and catalysis, 2 we set out to develop poly(pyrazolyl)borates based on 3,4,5- (CF 3 ) 3 PzH. In this Communication, we describe the synthesis of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ] - , which has nine trifluoromethyl groups on the periphery (Figure 1) and some of its copper and silver complexes. The sodium salt [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Na was readily synthesized by the reaction of NaBH 4 with 3,4,5-(CF 3 ) 3 PzH at ca. 190 °C in a solventless process. It was isolated as its tetrahydrofuran (THF) adduct after a workup involving THF. The 19 F NMR spectrum of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Na(THF) displays three peaks centered at δ -55.1, -57.0, and -62.3 corresponding to the fluorine atoms of CF 3 groups on pyrazolyl moieties. For comparison, fluorine atoms of the starting material, 3,4,5-(CF 3 ) 2 PzH, in CDCl 3 give rise to two peaks at δ -56.1 and -61.3 (1:2 ratio). The treatment of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Na(THF) with AgOTf in THF under an atmosphere of ethylene affords the silver(I) ethylene complex [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Ag(C 2 H 4 ). It is a white powder and stable to loss of ethylene in a nitrogen atmosphere. The X-ray structure of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Ag- (C 2 H 4 ) is illustrated in Figure 2. Such structurally characterized silver(I) ethylene complexes are of interest because of their relevance in various industrial and biological processes. 2,9 The silver atom of [HB(3,4,5-(CF 3 ) 3 Pz) 3 ]Ag(C 2 H 4 ) adopts a pseudotetrahedral geometry. Interestingly, the ethylene moiety coordinates to the metal center in η 2 fashion but somewhat asymmetrically having one short bond and one long Ag-C bond, 2.294(4) and 2.337(4) Å. This asymmetric arrangement is atypical for ethylene even though that is common in arene silver complexes. 10,11 The [HB(3,4,5-(CF 3 ) 3 Pz) 3 ] - moiety shows κ 3 coordination but with three different Ag-N distances [2.369(3), 2.399(3), and 2.444(3) Å]. Such variations in the metal-N distance are not unusual, and there are even κ 2 -ligated Received: December 11, 2012 Published: January 31, 2013 Figure 1. [HB(3,5-(CF 3 ) 2 Pz) 3 ] - and [HB(3,4,5-(CF 3 ) 3 Pz) 3 ] - . Communication pubs.acs.org/IC © 2013 American Chemical Society 1691 dx.doi.org/10.1021/ic302715d | Inorg. Chem. 2013, 52, 1691-1693