Synthesis and Chemistry of [Hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borato]silver(I) Complexes

The syntheses, spectroscopy, and structures of silver(I) hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate complexes with tetrahydrofuran (THF), toluene, carbon monoxide, ethylene, acetylene, phenylacetylene, tert -butyl isocyanide, and tert -butyl cyanide ligands are presented. These complexes can be synthesized conveniently starting from the sodium salt of [HB(3,5-(CF 3 ) 2 Pz) 3 ] - ligand. The toluene ligand of [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(η 2 -toluene) exhibits fluxional behavior in solution and η 2 -coordination in the solid state. The Ag−C distances, however, are not equal. The toluene ligand can be displaced reversibly with CO. [HB(3,5-(CF 3 ) 2 Pz) 3 ]AgCO has mainly a σ-type Ag−CO bonding interaction. The Ag−C and C−O distances are 2.037(5) and 1.116(7) Å, respectively. [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(H 2 C CH 2 ) and [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(HC⋮CH) have similar solid state structures. The H 2 C CH 2 and HC⋮CH bind symmetrically to silver ion. The Ag−C distances of [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(H 2 C CH 2 ) are 2.294(7) and 2.307(7) Å. In [HB(3,5-(CF 3 ) 2 Pz) 3 ]Ag(HC⋮CPh), the alkyne unit coordinates to silver ion in an asymmetric fashion with Ag−C distances of 2.263(5) and 2.407(5) Å. The υ C ⋮ C is about 69 cm - 1 lower than that for free HC⋮CPh. The coordinated alkyne moiety shows only a small bending-back angle (6.7°). The C−C bond distances of H 2 C CH 2, HC⋮CH, and HC⋮CPh ligands remain virtually unchanged upon coordination to silver(I). [HB(3,5-(CF 3 ) 2 Pz) 3 ]AgCNBu t has a relatively strong Ag−C bond. The isocyanide carbon resonance appears at δ 137.4 in the 13 C NMR spectrum. The υ CN band appears at 2214 cm - 1, which is about 76 cm - 1 higher than that for free CNBu t . The Ag−C and C−N distances are 2.059(4) and 1.139(5) Å, respectively. The isocyanide group is slightly bent with a Ag−C−N angle of 173.7(4)° and a C−N−C angle of 176.2(4)°. Structural features of [HB(3,5-(CF 3 ) 2 Pz) 3 ]AgNCBu t are very similar to those of the CNBu t analogue. The υ NC band appears at 2277 cm - 1 . All these complexes show pseudo-tetrahedral silver centers with pyrazolyl N−Ag distances ranging from 2.297 to 2.447 Å. The stability of these silver adducts may be primarily attributed to the unique electronic properties of the [HB(3,5-(CF 3 ) 2 Pz) 3 ] - ligand.