16971-01-0Relevant articles and documents
Metallaboratranes: Bis- and tris(methimazolyl)borane complexes of group 9 metal carbonyls and thiocarbonyls
Crossley, Ian R.,Hill, Anthony F.,Willis, Anthony C.
, p. 326 - 336 (2010/03/25)
The iridium poly(methimazolayl)borane complexes [IrH(CE)(PPh3) {κ3-B,S,S-B(mt)2R}](Ir→B) (mt = methimazolyl = 2-mercapto-3-methylimidazol-l-yl; E = O, S; R = mt, H) are described in detail. For R = mt, these materials are elucidated as paradigms for the final mechanistic intermediate in metallaboratrane formation, a role illustrated through hydride abstraction to afford the cationic salts [Ir(CE)(PPh 3){κ4-B(mt)3}]X(Ir→)8 (E = O, S; X = Cl, BF4). The rhodium poly(methimazolyl)borate complexes [Rh(CO)(PPh3){κ2-S,S'-HB(mt)2R}] (R = mt, H) are also reported. These compounds are obtained in preference to the respective borane complexes (analogous to iridium); however [Rh(CO)(PPh 3){κ2-S,S'-HB(mt)3}] is observed to undergo facile solution-phase conversion to [Rh(CO)(PPh3) {κ4-B,S,S ,S"-B(mt)3}]Cl(Rh→B)8 in chlorinated solvents. The ramifications of these results, with respect to metallaboratrane formation, are discussed, substantiating previous mechanistic conjecture. In an attempt to establish an alternative route to iridaboratranes, the first isolable tris(methimazolyl)borate complex of iridium, cis,cis-[IrHCl(PPh3)2{κ2-S,S'-HB(mt)3], is reported and shown not to evolve to the iridaboratrane [IrCl(PPh 3){κ4-B(mt)3}](Ir→B)8 under conditions that lead to the corresponding rhodaboratrane. Factors are discussed that may contribute to this fine balance between the formation of methimazolylborate and methimazolylborane complexes.
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.
Iridium(III) Complex Containing a Unique Bifurcated Hydrogen Bond Interaction Involving Ir-H?H(N)?F-B atoms. Crystal and Molecular Structure of [IrH(η1-SC5H4NH)(η2-SC 5H4N)(PPh3)2](BF 4)·0.5C6H6
Park, Sunghan,Lough, Alan J.,Morris, Robert H.
, p. 3001 - 3006 (2008/10/09)
A synthetic route to a new iridium(III) complex containing a novel proton hydride bonding interaction has been established. fac-IrH3(PPh3)3 reacts with 2-mercaptopyridine HSpy (Spy = 2-SC5H4N) to give the known dihydride Ir(H)2(η2-Spy)(PPh3)2 8. Ir(H)2(η2-Spy)(PPh3)2 reacts with HSpy· HBF4 to give [IrH(η1-SC5H4NH)(η2-SC 5H4N)-(PPh3)2](BF4) 9 which possesses a unique bifurcated hydrogen bonding interaction involving Ir-H?H(N)?F-B atoms with the distances of 2.0(1) A? for the H?H unit and of 2.0(1) A? for the F?H unit in the crystalline state. In solution the N-H?H-Ir interaction is maintained according to 1H T1(min) and nOe measurements. Isotope shifts in the chemical shifts of the hydride and one phosphorus of 9 have been observed in 1H and 31P{1H} NMR spectra of [IrH(η1-SC5H4ND)(η2-SC 5H4N)(PPh3)2](BF4), 9-d1, prepared by the reaction of 9 with MeOD or CF3-CO2D. The crystal and molecular structure of [IrH(η1-SC5H4NH)(η2-SC 5H4N)(PPh3)2](BF 4)·0.5C6H6 9 has been solved by X-ray analysis: monoclinic space group P21/c with a = 17.723(3) A?, b = 10.408(1) A?, c = 26.073(4) A?, β= 108.08(1)°, V = 4572.0(11) A?3, and Z = 4. The known complex fac-IrH3(PPh3)3, 7, is made by a new and improved method by reacting mer-IrHCl2(PPh3)3 with NaOEt and H2(g). VT-1H NMR spectra (+90 to -80 °C) of the hydrides of 7 reveal that the JAA and JAX couplings change in the AA'A''XX'X'' pattern (A = 1H, X = 31P) but that the complex is not fluxional. The T1(min) value of 0.144 s for the hydrides of 7 at -60 °C (300 MHz) indicates that the shortest H-H distances are about 1.8 A?.
