439291-48-2Relevant academic research and scientific papers
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)
Landau, Shaun E.,Groh, Kai E.,Lough, Alan J.,Morris, Robert H.
, p. 2995 - 3007 (2008/10/08)
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 protonichydridic 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(Pi Pr3)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)][transIrH4(Pi Pr3)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 protonichydridic hydrogen bond while the other forms an inter-ion-pair NH···Hlr 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 PiP3 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(Pi-Pr3)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 H4(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.
