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-(CF3)2Pz)3]-
ligand. The toluene ligand of
[HB(3,5-(CF3)2Pz)3]Ag(η2-toluene)
exhibits
fluxional behavior in solution and η2-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-(CF3)2Pz)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-(CF3)2Pz)3]Ag(H2CCH2)
and
[HB(3,5-(CF3)2Pz)3]Ag(HC⋮CH)
have similar solid state structures. The
H2CCH2 and HC⋮CH bind symmetrically to
silver ion. The Ag−C distances of
[HB(3,5-(CF3)2Pz)3]Ag(H2CCH2) are 2.294(7) and 2.307(7) Å.
In
[HB(3,5-(CF3)2Pz)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
υC⋮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
H2CCH2, HC⋮CH, and HC⋮CPh ligands remain
virtually unchanged
upon coordination to silver(I).
[HB(3,5-(CF3)2Pz)3]AgCNBut
has a relatively strong Ag−C bond. The isocyanide
carbon resonance appears at δ 137.4 in the 13C NMR
spectrum. The υCN band appears at 2214
cm-1, which is
about 76 cm-1 higher than that for free
CNBut. 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-(CF3)2Pz)3]AgNCBut
are very similar to those of the CNBut
analogue.
The υNC 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-(CF3)2Pz)3]-
ligand.