128138-42-1Relevant 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.
Steric Modification of Metal-Phosphorus Bond Lengths: the Preparation, Characterization and Crystal Structures of mer-trans-(PPri3)2(PMe2Ph)Cl-cis-H2IrIII and mer-trans-(PPri3)2(PMe2Ph)H3IrIII
Ditzel, Evert J.,Robertson, Glen B.
, p. 1183 - 1192 (2007/10/02)
The syntheses and subsequent characterization of the complexes mer-trans-(PPri3)2(PMe2Ph)-Cl-cis-H2IrIII (1) and mer-trans-(PPri3)2(PMe2Ph)H3IrIII (2) by n.m.r. and by low temperature (153+/-5 K) X-ray diffraction analyses are reported.Crystals of (1) are monoclinic, space group P21/c with a 19.277(2), b 9.020(1), c 17.657(2) Angstroem, β 101.40(1) deg and Z 4.Crystals of (2) are orthorhombic, space group P212121, with a 19.373(3), b 18.724(2), c 8.113(1) Angstroem and Z 4.Full-matrix least-squares analyses converged with R = 0.027 and wR = 0.031 for (1) (3243 reflections), and R = 0.030 and wR = 0.038 for (2) (2892 reflections).Consistent with previous observation, the unit increase in chloride content (in place of hydride) in (1) is accompanied by a global lengthening of 0.036 Angstroem (av.) in the Ir-P bond lenghts cf. those in (2).Also, because of increased steric crowding (two PPri3 ligands in place of two PMe2Ph), the Ir-PMe2Ph bond in (1) is 0.019(2) Angstroem longer than the chemically equivalent bond in mer-(PMe2Ph)3Cl-cis-H2IrIII.In previously reported complexes in this series metrically similar increases in Ir-PMe2Ph distances result from the replacement of just one PMe2Ph ligand by PPri3.
