Large Effects of Ion Pairing and Protonic−Hydridic Bonding on the Stereochemistry and Basicity of Crown-, Azacrown-, and Cryptand-222-potassium Salts of Anionic Tetrahydride Complexes of Iridium(III)

The compounds [K(Q)][IrH4(PR3)2] (Q = 18-crown-6, R = Ph, iPr, Cy; Q = aza-18-crown-6, R = iPr; Q =
1,10-diaza-18-crown-6, R = Ph, iPr, Cy; Q = cryptand-222, R = iPr, Cy) were formed in the reactions of IrH5(PR3)2 with KH and Q. In solution, the stereochemistry of the salts of [IrH4(PR3)2]- is surprisingly sensitive to the
countercation:  either trans as the potassium cryptand-222 salts (R = Cy, iPr) or exclusively cis (R = Cy, Ph) as
the crown- and azacrown-potassium salts or a mixture of cis and trans (R = iPr). There is IR evidence for protonic−hydridic bonding between the NH of the aza salts and the iridium hydride in solution. In single crystals of [K(18-crown-6)][cis-IrH4(PR3)2] (R = Ph, iPr) and [K(aza-18-crown-6)][cis-IrH4(PiPr3)2], the potassium bonds to three hydrides
on a face of the iridium octahedron according to X-ray diffraction studies. Significantly, [K(1,10-diaza-18-crown-6)][trans-IrH4(PiPr3)2] crystallizes in a chain structure held together by protonic−hydridic bonds. In [K(1,10-diaza-18-crown-6)][cis-IrH4(PPh3)2], the potassium bonds to two hydrides so that one NH can form an intra-ion-pair protonic−hydridic hydrogen bond while the other forms an inter-ion-pair NH···HIr hydrogen bond to form chains through the
lattice. Thus, there is a competition between the potassium and NH groups in forming bonds with the hydrides on
iridium. The more basic PiR3 complex has the lower N−H stretch in the IR spectrum because of stronger
N−H···HIr hydrogen bonding. The trans complexes have very low Ir−H wavenumbers (1670−1680) due to the
trans hydride ligands. The [K(cryptand)]+ salt of [trans-IrH4(PiPr3)2]- reacts with WH6(PMe2Ph)3 (pKαTHF 42) to give
an equilibrium (Keq = 1.6) with IrH5(PiPr3)2 and [WH5(PMe2Ph)3]- while the same reaction of WH6(PMe2Ph)3 with
the [K(18-crown-6)]+ salt of [cis-IrH4(PiPr3)2]- has a much larger equilibrium constant (Keq = 150) to give IrH5(PiPr3)2 and [WH5(PMe2Ph)3]-; therefore, the tetrahydride anion displays an unprecedented increase (about 100-fold)
in basicity with a change from [K(crypt)]+ to [K(crown)]+ countercation and a change from trans to cis stereochemistry.
The acidity of the pentahydrides decrease in THF as IrH5(PiPr3)2/[K(crypt)][trans-IrH4(PiPr3)2] (pKαTHF = 42) > IrH5(PCy3)2/[K(crypt)][trans-IrH4(PCy3)2] (pKαTHF = 43) > IrH5(PiPr3)2/[K(crown)][cis-IrH4(PiPr3)2] (pKαTHF = 44) > IrH5(PCy3)2/[K(crown)][cis-IrH4(PCy3)2]. The loss of PCy3 from IrH5(PCy3)2 can result in mixed ligand complexes and
H/D exchange with deuterated solvents. Reductive cleavage of P−Ph bonds is observed in some preparations of
the PPh3 complexes.